JP2009118052A - Image signal processing method and apparatus - Google Patents

Abstract

An image signal processing method and apparatus capable of obtaining a high-quality image while suppressing the occurrence of false colors.
When color correction is performed by applying a predetermined color correction gain to color signals of R, G, and B colors for each pixel and outputting as an N-bit signal, a predetermined color correction gain is applied to each color signal. Color correction is performed to generate a color signal having the number of bits (M) with a margin above the desired number of bits (N). Then, when the color signal that is the maximum among the color signals after the color correction is selected and the selected color signal is set to N bits, a saturated signal level is detected. A color signal exceeding the detected signal level is subjected to false color correction by applying a false color correction gain larger than the same magnification, and is output with a limit to be N bits.
[Selection] Figure 10

Description

  The present invention relates to an image signal processing method and apparatus, and more particularly to an image signal processing method and apparatus for performing color correction by applying a predetermined color correction gain to each color signal constituting the image signal.

  One of the signal processing performed by a digital camera is white balance correction. White balance correction is a process for correcting white so that white is accurately projected even under light source conditions with different color temperatures, and the R, G, and B color signals obtained when a white subject is imaged are all equal. So that gain is applied.

  However, when white balance correction is performed by applying gain in this way, as shown in FIG. 18, there is a problem that false color occurs in a high luminance portion because the saturation level differs for each color.

Therefore, in Patent Document 1, it is determined whether or not each color signal after gain processing is in a saturated state, and if it is in a saturated state, generation of a false color due to color saturation is performed by replacing it with the level of another color signal. Methods for preventing it have been proposed.
JP 2004-328564 A

  However, the method of Patent Document 1 has a drawback in that colors are switched depending on the result of threshold discrimination.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an image signal processing method and apparatus capable of obtaining a high-quality image while suppressing generation of false colors.

  The invention according to claim 1 is an image signal processing method for generating an N-bit color signal by performing color correction by applying a predetermined color correction gain to each color signal constituting the image signal in order to achieve the object. Thus, each color signal constituting the image signal is subjected to color correction by applying a predetermined color correction gain to generate a color signal of M (N <M) bits, and the maximum among the color signals after color correction. A step of selecting a color signal, a step of detecting a signal level that saturates when the selected color signal is N bits, and a predetermined false color for a color signal that exceeds the signal level for each color signal after color correction An image signal processing method comprising: a step of performing false color correction by applying a correction gain and generating an N-bit color signal.

  According to the first aspect of the present invention, first, color correction is performed by applying a predetermined color correction gain to each color signal, and the color signal having the number of bits (M) with a margin above the desired number of bits (N). Is generated. Then, when the color signal that is the maximum among the color signals after the color correction is selected and the selected color signal is set to N bits, a saturated signal level is detected. Here, if the color signal exceeding the detected signal level is set to N bits, the ratio of each color is not accurately maintained and a false color is generated. Therefore, for each color signal, a predetermined false color correction gain is applied to the color signal exceeding the detected signal level, and the color signal is corrected so as to be kept at the original color ratio as much as possible, thereby generating an N-bit color signal. To do. By processing in this manner, the saturation is reduced in the region where the false color is generated, so that the color change becomes difficult to understand, and a high-quality image without a sense of incongruity can be obtained.

  The invention according to claim 2 is characterized in that, in order to achieve the object, information on a shooting mode when the image signal is acquired is acquired, and the false color correction gain is switched according to the shooting mode. An image signal processing method according to claim 1 is provided.

  According to the second aspect of the present invention, the false color correction gain is switched according to the shooting mode when the image signal is acquired. Thereby, false color correction can be performed using a more appropriate false color correction gain. For example, in the case of the manual mode, the false color correction gain is set so as to be always the same magnification in consideration of the photographer's intention (no false color correction is performed). In the underwater mode, since there are many B components and the B signal is likely to be saturated, the false color correction gain is set so as to positively correct the saturation of the B signal. In the sunset mode, since there are many R components and the R signal is likely to be saturated, the false color correction gain is set so as to positively correct the saturation of the R signal. In this way, by using information on the shooting mode set according to the shooting scene, false color correction can be performed more appropriately, and a higher quality image can be obtained.

  The invention according to claim 3 is characterized in that, in order to achieve the object, information on a color temperature when the image signal is acquired is acquired, and the false color correction gain is switched according to the color temperature. An image signal processing method according to claim 1 is provided.

  According to the invention of claim 3, the false color correction gain is switched in accordance with the color temperature when the image signal is acquired. Thereby, false color correction can be performed using a more appropriate false color correction gain. For example, when the color temperature is low, redness is strong as a whole and saturation of the R signal is likely to occur in a wide range. Therefore, the false color correction gain is set so as to positively correct the saturation of the R signal. On the other hand, in the case of a high color temperature, since the entire image is bluish and the B signal saturation is likely to occur in a wide range, the false color correction gain is set so as to positively correct the B signal saturation. As described above, by using the information on the color temperature of the shooting scene, false color correction can be performed more appropriately, and a higher quality image can be obtained.

  According to a fourth aspect of the present invention, in order to achieve the above object, the false color correction is performed when the dynamic range to be set is less than a threshold when performing processing for expanding the dynamic range for the image signal. The image signal processing according to any one of claims 1 to 3, wherein each color signal constituting the image signal is subjected to a color correction by applying a predetermined color correction gain to generate an N-bit color signal. Provide a method.

  When processing to expand the dynamic range is performed, even if the subject is a white-out subject (a subject in which all color signals are saturated) in the normal dynamic range, only some of the color signals are saturated There is. On the other hand, if the false color correction is further performed on the color signal subjected to the color correction as in the first to third aspects of the invention, the color signal is likely to be saturated with white and the dynamic range becomes narrow. Therefore, in the invention according to claim 4, the presence or absence of false color correction is switched depending on whether the dynamic range to be set is wide or narrow, and the false color correction process is performed only when the dynamic range to be set is equal to or greater than a threshold value. Thereby, a mutual fault can be compensated and a higher quality image can be obtained.

  The invention according to claim 5 is an image signal processing apparatus for generating an N-bit color signal by performing color correction by applying a predetermined color correction gain to each color signal constituting the image signal in order to achieve the object. Then, each color signal constituting the image signal is subjected to a color correction by applying a predetermined color correction gain to generate a color signal of M (N <M) bits, and each color color corrected by the color correction unit Color selecting means for selecting the maximum color signal among the signals, detecting means for detecting a signal level that saturates when the color signal selected by the selecting means is set to N bits, and color correction by the color correcting means False color correction means for generating a N-bit color signal by performing false color correction on each color signal by applying a predetermined false color correction gain to the color signal exceeding the signal level. An image signal processing apparatus is provided.

  According to the fifth aspect of the invention, similarly to the first aspect, it is possible to obtain a high-quality image that does not seem strange to the eye by reducing the saturation in the area where the false color is generated.

  In order to achieve the above object, the invention according to claim 6 further includes photographing mode information acquisition means for acquiring information about a photographing mode when the image signal is acquired, and the false color correction means includes the photographing color information. The image signal processing apparatus according to claim 5, wherein the false color correction gain is switched in accordance with a shooting mode acquired by a mode information acquisition unit.

  According to the invention of claim 6, as in the invention of claim 2, false color correction is performed using a more appropriate false color correction gain by switching the false color correction gain according to the shooting mode. be able to.

  In order to achieve the above object, the invention according to claim 7 includes color temperature information acquisition means for acquiring color temperature information when the image signal is acquired, and the false color correction means includes the color 6. The image signal processing apparatus according to claim 5, wherein the false color correction gain is switched in accordance with the color temperature acquired by the temperature information acquisition means.

  According to the invention of claim 7, as in the invention of claim 3, false color correction is performed using a more appropriate false color correction gain by switching the false color correction gain according to the color temperature. be able to.

  According to an eighth aspect of the present invention, in order to achieve the above object, when performing a process of expanding a dynamic range for the image signal, a color correction gain is applied to each color signal constituting the image signal. A second color signal correcting unit that corrects and generates an N-bit color signal; a dynamic range information acquiring unit that acquires information on a dynamic range to be set; and the N bit generated by the second color signal correcting unit When the dynamic range acquired by the dynamic range information acquisition unit is less than a threshold value, the second color signal correction unit Output switching means for outputting the N-bit color signal generated by the false color signal correcting means when the N-bit color signal generated by the false color signal is equal to or greater than a threshold value; To provide an image signal processing apparatus according to any one of claims 5-7, characterized in that there was e.

  According to the eighth aspect of the invention, similarly to the fourth aspect of the invention, the occurrence of false color can be effectively suppressed by switching the presence or absence of false color correction depending on the dynamic range to be set. High quality images can be obtained.

  With the image signal processing method and apparatus according to the present invention, it is possible to obtain a high-quality image while suppressing the occurrence of false colors.

  The best mode for carrying out an image signal processing method and apparatus according to the present invention will be described below with reference to the accompanying drawings.

  1 and 2 are a front perspective view and a rear perspective view, respectively, showing the external configuration of the digital camera 10 to which the present invention is applied.

  As shown in FIG. 1, a photographing lens 14, a strobe 16 and the like are provided on the front surface of a camera body 12 formed in a rectangular box shape, and a shutter button 18, a power button 20 and the like are provided on an upper surface. Is provided.

  As shown in FIG. 2, various operation buttons such as a zoom button 22, a menu button 24, a cancel button 26, a determination button 28, a cross button 30, and a play button 32, and various displays are displayed on the back of the camera body 12. A monitor 34 and the like are provided.

  Although not shown, the bottom surface of the camera body 12 is provided with a memory card slot for loading a memory card, a battery loading chamber for loading a battery, and the like through a cover that can be freely opened and closed.

  The taking lens 14 is constituted by a retractable zoom lens, and is extended from the front surface of the camera body 12 when the camera is turned on.

  The strobe 16 is composed of a xenon tube, and emits strobe light toward a subject as necessary.

  The shutter button 18 is constituted by a two-stage stroke type push button that can be pressed halfway and fully. When the shutter button 18 is half-pressed, the digital camera 10 performs AE (automatic exposure), AWB (automatic white balance), and AF (automatic focusing) processes to prepare for shooting. When the button is fully pressed, the actual shooting process is executed, and an image obtained by shooting is recorded on the memory card.

  The power button 20 is a push button and is used to turn on / off the power of the camera. When the power button 20 is pressed while the power is off, the digital camera 10 is activated in the shooting mode. Then, when the playback button 32 is pressed in the state of the photographing mode, the mode is switched to the playback mode. When the playback button 32 is pressed while the power is off, the playback mode is activated. Then, when the shutter button 18 is pressed in the state of the reproduction mode, the mode is changed to the photographing mode.

  The zoom button 22 is constituted by a seesaw type switch, and when operated to one side, zooming to the tele side is instructed, and when operated to the other side, zooming to the wide side is instructed.

  The menu button 24 is used as a button for instructing display of a menu screen on the monitor 34. In the digital camera 10 of the present embodiment, various settings are performed using a menu screen displayed on the monitor 34. For example, image size, shooting sensitivity, shooting mode (auto mode, manual mode, aperture priority AE mode, shutter speed priority AE mode, program AE mode, scene program mode (person, underwater, evening scene, night scene, sport, landscape, etc.)) , Flash mode (auto flash, forced flash, red-eye reduction flash, slow sync, flash off), macro mode (ON / OFF), white balance setting (auto, preset (fluorescent lamp, light bulb, clear, cloudy, shade, etc.), Manual), metering method (division metering, spot, center weight, etc.), focus (auto area AF, center fixed AF, area selection AF, manual), AF method (single, continuous), dynamic range (normal, wide dynamic) Range) and the like are set. The user makes various settings using the cancel button 26, the determination button 28, the cross button 30 and the like according to the display on the monitor 34.

  Note that “Auto mode” in the shooting mode settings above is a mode in which the camera automatically performs all settings except image size and shooting sensitivity, and “Manual mode” allows the aperture and shutter speed to be set freely. “Aperture priority AE mode” is an auto mode in which the aperture can be set freely. “Shutter speed priority AE mode” is an auto mode in which the shutter speed can be freely set. “Program AE mode” "Is an auto mode in which settings other than the aperture and shutter speed can be freely set.

  The “scene program mode” is a mode in which an exposure setting suitable for the scene is automatically performed and image processing suitable for the scene is automatically performed. Here, “person” is a mode in which processing suitable for portrait shooting is performed, “underwater” is a mode in which processing suitable for underwater shooting is performed, and “evening” is a mode in which processing suitable for sunset shooting is performed. “Night scene” is a mode in which processing suitable for night scene photography is performed, “Sport” is a mode in which processing suitable for sports photography is performed, and “Landscape” is a mode in which processing suitable for landscape photography is performed. .

  The “wide dynamic range” in the setting of the dynamic range is a mode for photographing a subject having a high luminance portion and a low luminance portion, and processing for expanding the dynamic range is performed.

  The monitor 34 is composed of a color liquid crystal display, and is used as an operation screen at the time of various settings described above. In addition, a captured image is displayed in the playback mode and used as a playback monitor. Further, at the time of photographing, an image captured by the image sensor is displayed as a through display and used as an electronic viewfinder.

  FIG. 3 is a block diagram showing an electrical configuration of the digital camera 10.

  The entire operation of the digital camera 10 is comprehensively controlled by the CPU 50. The CPU 50 executes various control programs such as the operation unit (shutter button 18, power button 20, zoom button 22, menu button 24, cancel button 26, enter button 28, cross button 30, play button 32, etc. Each part of the digital camera 10 is controlled in accordance with an operation signal input from the operation member 52.

  The ROM 54 stores a control program executed by the CPU 50 and various data necessary for control. The CPU 50 controls each part of the digital camera 10 by reading out the control program recorded in the ROM 54 to the SDRAM 56 and sequentially executing the program.

  The SDRAM 56 is used as a program execution processing area, a temporary storage area for image data, and various work areas for arithmetic processing.

  The flash memory 58 is used as a recording area for various setting information such as user setting information, and the VRAM 60 is used as a recording area dedicated for image data to be displayed on the monitor 34.

  The photographic lens 14 includes a zoom lens, a focus lens, and a diaphragm (not shown), and is operated by being driven by a driving device (not shown). The CPU 50 controls the operation of the zoom lens, the focus lens, and the diaphragm by controlling the driving of the driving device via a lens control unit (not shown).

  A color CCD image sensor (CCD) 62 is disposed as an image pickup element at the rear stage of the photographing lens 14. As is well known, the CCD 62 has a light receiving surface on which a large number of light receiving elements are arranged in a matrix. The subject light that has passed through the photographing lens 14 forms an image on the light receiving surface of the CCD 62 and is converted into an electric signal by each light receiving element.

  The CCD 62 outputs the charges accumulated in each pixel as a serial image signal line by line in synchronization with the vertical transfer clock and horizontal transfer clock supplied from the CCD driver 64. The CPU 50 controls the drive of the CCD 62 by controlling the CCD driver 64.

  The charge accumulation time (exposure time) of each pixel is determined by an electronic shutter drive signal given from the CCD driver 64. The CPU 50 instructs the CCD driver 64 about the charge accumulation time.

  The output of the image signal is started when the mode of the digital camera 10 is set to the shooting mode. That is, when the mode of the digital camera 10 is set to the shooting mode, output of an image signal is started in order to display a through image on the monitor 34.

  The image signal output from the CCD 62 is an analog signal, and this analog image signal is taken into the analog signal processing unit 66.

  The analog signal processing unit 66 includes a correlated double sampling circuit (CDS), an automatic gain control circuit (AGC), and the like. The CDS removes noise contained in the image signal, and the AGC amplifies the noise-removed image signal with a predetermined gain.

  The analog image signal that has been subjected to the required signal processing by the analog signal processing unit 66 is taken into the A / D converter 68. The A / D converter 68 converts the captured analog image signal into a digital image signal having a gradation width of N bits (14 bits in this example). This image signal is so-called RAW data, and has a gradation value indicating the density of R, G, and B for each pixel.

  The image signal for one frame converted into a digital signal by the A / D converter 68 is stored in the SDRAM 56 via the bus 70.

  The bus 70 includes the CPU 50, ROM 54, SDRAM 56, flash memory 58, VRAM 60, A / D converter 68, digital signal processing unit 100, AF detection unit 74, AE / AWB detection unit 76, compression / decompression processing unit. 78, a recording control unit 80, a display control unit 84, and the like are connected, and these can exchange information with each other via a bus 70.

  The image signal for one frame stored in the SDRAM 56 is taken into the digital signal processing unit 100 dot-sequentially (pixel order).

  The digital signal processing unit 100 performs predetermined signal processing on image signals (color signals) of R, G, and B colors that are captured in a dot-sequential manner, and an image signal that includes a luminance signal Y and color difference signals Cr and Cb. (YC signal) is generated.

  FIG. 4 is a block diagram illustrating a schematic configuration of the digital signal processing unit 100. As shown in the figure, the digital signal processing unit 100 includes a white balance gain calculation circuit 102, an offset correction circuit 104, an RGB interpolation calculation circuit 106, a gain correction circuit 108, a gradation correction circuit 110, an RGB / YC conversion circuit 112, The image forming apparatus includes an outline correction circuit 114, a color difference matrix circuit 116, a color temperature evaluation value calculation circuit 118, and the like.

  In order to perform white balance correction, the white balance gain calculation circuit 102 takes in the integrated value calculated by the AE / AWB detection unit 76 and calculates a white balance correction gain value (color correction gain).

  The offset correction circuit 104 has a predetermined offset with respect to the R, G, and B color image signals (N bits) captured in a dot-sequential manner from the SDRAM 56 so that black is expressed when a black subject is photographed. Apply processing. That is, a preset offset value is subtracted from the R, G, and B image signals and output.

  The RGB interpolation arithmetic circuit 106 interpolates the offset R, G, B color signals (N bits) to obtain R, G, B3 color signals at each pixel position. That is, in the case of a single-plate image sensor, each pixel outputs only a signal of any one color of R, G, and B. Therefore, a color that is not output is obtained from the color signals of surrounding pixels by a complementary operation. For example, in a pixel that outputs R, the level of the G and B color signals at this pixel position is determined by interpolation from the G and B signals of surrounding pixels.

  Note that the RGB complementary calculation is specific to the single-plate image sensor, and thus is not necessary when a three-plate image sensor is used as the image sensor 134.

  The gain correction circuit 108 uses the gain value (color correction gain) calculated by the white balance gain calculation circuit 102 to perform white balance correction (color correction) on the synchronized color signal (N bits) of each pixel. And false color correction using a predetermined false color correction gain. Then, it is output to the gradation correction circuit 110 as a signal of N bits (14 bits in this example). The processing in the gain correction circuit 108 will be described in detail later.

  The gradation correction circuit 110 performs gradation conversion processing on the gain-corrected image signal. That is, when the image data is output to the monitor, a deviation occurs between the gradation value input to the monitor and the gradation value output from the monitor. In order to correct this deviation, the image signal after gain correction is performed. Is subjected to predetermined gradation conversion processing (so-called gamma correction).

  As shown in FIG. 5, the gradation correction circuit 110 is provided with a gamma conversion table for correcting the above-described deviation. The gradation correction circuit 110 converts the input gradation value of the image signal based on this gamma conversion table.

  Note that when the digital camera 10 is set to the wide dynamic range shooting mode, gradation conversion processing using the gamma conversion table is performed after predetermined preprocessing. Hereinafter, this preprocessing will be described.

  As shown in FIG. 6, the gradation correction circuit 110 is provided with three gradation conversion tables of 100% mode, 200% mode, and 400% mode. The gradation correction circuit 110 selects one of the three gradation conversion tables according to the dynamic range of the input image, and for each pixel included in the image signal based on the selected gradation conversion table. The tone values are converted and pre-processed.

  Here, the gradation conversion table used in this preprocessing is determined by the following procedure.

  First, an input image is divided into 16 and an average value of luminance (luminance average value) in each region is calculated. Then, the maximum luminance average value is detected by comparing the average luminance values in all 16 regions.

  The gradation correction circuit 110 selects the 100% mode when the maximum luminance average value is 0 to 255, that is, when it is determined that the subject luminance is low. When the maximum luminance average value is 256 to 511, the 200% mode is selected, and when it is 512 to 1023, the 400% mode is selected.

  As shown in FIG. 7, in the 100% mode, gradation conversion processing is performed so that the output gradation value is four times the input gradation value (when the input gradation value is 255, the output gradation value is (Tone conversion processing is performed with input / output characteristics that draw a straight line with a tone value of 1023).

  In the 200% mode, tone conversion is performed with input / output characteristics that draw a gentle curve as the input tone value increases (the output tone value is 1023 when the input tone value is 511). Tone conversion processing is performed with input / output characteristics that draw a non-linear curve.)

  In the 400% mode, gradation conversion is performed with input / output characteristics that draw a gentler curve as the input gradation value increases (the output gradation value becomes 1023 when the input gradation value is 1023). Tone conversion processing is performed with input / output characteristics that draw a non-linear curve.)

  As described above, when the wide dynamic range shooting mode is set, the image signal input to the gradation correction circuit 110 is first subjected to gradation conversion processing (preprocessing) by a predetermined gradation conversion table, The preprocessed image signal is further subjected to gradation conversion processing (gamma conversion processing) using a gamma conversion table. As a result, the image signal that has been subjected to the gradation conversion processing by the gradation conversion tables in the 100% mode, the 200% mode, and the 400% mode is finally output after the gradation value is converted as shown in FIG. .

  In this way, the gradation correction circuit 110 performs a predetermined gradation correction process on the image signal that has been subjected to white balance correction.

  The RGB / YC conversion circuit 112 generates a luminance signal Y and color difference signals Cr and Cb from the tone-corrected image signal. The generated luminance signal Y and color difference signals Cr and Cb are output to the contour correction circuit 114 and the color difference matrix circuit 116, respectively.

  The contour correction circuit 114 performs a predetermined contour correction process on the acquired luminance signal Y.

  On the other hand, the color difference matrix circuit 116 performs color correction by multiplying the color difference signals Cr and Cb after the level conversion processing by a predetermined color difference matrix (C-MTX). That is, the color difference matrix circuit 116 is provided with a plurality of types of color difference matrices corresponding to the color temperature evaluation values, and the color difference matrix to be used is switched according to the color temperature evaluation values obtained by the color temperature evaluation value calculation circuit 118. Then, the color difference matrix Cr after switching is multiplied by the input color difference signals Cr and Cb to correct the color tone of the color difference signals Cr and Cb.

  The color temperature evaluation value calculation circuit 118 takes in the integrated value calculated by the AE / AWB detection unit 76, performs a predetermined calculation process, and calculates a color temperature evaluation value (determines the light source type). Then, the calculated color temperature evaluation value information is output to the color difference matrix circuit 116.

  As described above, the digital signal processing unit 100 generates an image signal (YC signal) including the luminance signal Y and the color difference signals Cr and Cb from the R, G, and B color image signals captured in a dot-sequential manner.

  The AF detection unit 74 takes in R, G, and B color image signals taken into the SDRAM 56 according to a command from the CPU 50 and calculates a focus evaluation value necessary for AF control. The AF detection unit 74 includes a high-pass filter that passes only high-frequency components of the G signal, an absolute value processing unit, a focus area extraction unit that extracts a signal within a predetermined focus area set on the screen, and a focus area An integration unit for integrating the absolute value data is included, and the absolute value data in the focus area integrated by the integration unit is output to the CPU 50 as a focus evaluation value. During the AF control, the CPU 50 searches for a position where the focus evaluation value output from the AF detection unit 74 is maximized, and moves the focus lens of the photographing lens 14 to that position, thereby focusing on the main subject. Do.

  The AE / AWB detection unit 76 takes in the image signals of R, G, and B colors taken into the SDRAM 56 in accordance with a command from the CPU 50 and calculates an integrated value necessary for AE control and AWB control. That is, the AE / AWB detection unit 76 divides one screen into a plurality of areas (for example, 8 × 8 = 64 areas), and calculates an integrated value of R, G, and B signals for each divided area. At the time of AE control, the CPU 50 acquires an integrated value of R, G, B signals for each area calculated by the AE / AWB detection unit 76, obtains the brightness (photometric value) of the subject, and obtains an appropriate exposure amount. Set the exposure to obtain

  In addition, during the AWB control, the CPU 50 calculates the integrated value of the R, G, and B signals for each area calculated by the AE / AWB detection unit 76, calculates the white balance gain calculation circuit 102 of the digital signal processing unit 100, and the color temperature evaluation value. Add to circuit 118. The white balance gain calculation circuit 102 calculates a white balance correction gain value (color correction gain) based on the integrated value calculated by the AE / AWB detection unit 76. The color temperature evaluation value calculation circuit 118 calculates a color temperature evaluation value based on the integrated value calculated by the AE / AWB detection unit 76.

  The compression / decompression processing unit 78 applies compression processing in a predetermined format (for example, JPEG) to the image signal (YC signal) composed of the input luminance signal Y and the color difference signals Cr and Cb in accordance with a command from the CPU 50 to compress the image signal. Generate image data. Further, in accordance with a command from the CPU 50, the input compressed image data is subjected to a decompression process in a predetermined format to generate non-compressed image data.

  The recording control unit 80 controls reading / writing of data with respect to the memory card 82 loaded in the memory card slot in accordance with a command from the CPU 50.

  The display control unit 84 controls display on the monitor 34 in accordance with a command from the CPU 50. That is, in accordance with a command from the CPU 50, the input image signal is converted into a video signal (for example, an NTSC signal, a PAL signal, or a SCAM signal) for display on the monitor 34 and output to the monitor 34.

  Next, a basic photographing processing operation by the digital camera 10 of the present embodiment will be described.

  As described above, when the power switch 20 is pressed while the power is off, the digital camera 10 is activated in the shooting mode.

  When the camera is activated in the photographing mode, output of an image signal is first started from the CCD 62 and is displayed on the monitor 34 as a through display. The photographer determines the composition by looking at the display on the monitor 34 and presses the shutter button 18 halfway.

  When the shutter button 18 is half-pressed, an S1 ON signal is input to the CPU 50. In response to the input of the S1 ON signal, the CPU 50 executes shooting preparation processing, that is, AE, AF, and AWB processing.

  First, the image signal output from the CCD 50 is added to the AE / AWB detection unit 76 and the AF detection unit 74 via the analog signal processing unit 66 and the A / D converter 68.

  The AE / AWB detection unit 76 calculates an integrated value necessary for AE control and AWB control from the input image signal, and outputs the integrated value to the CPU 50. The CPU 50 calculates subject brightness based on the integrated value obtained from the AE / AWB detector 76, and determines an aperture value, shutter speed, and the like for obtaining proper exposure. Further, the integrated value obtained from the AE / AWB detector 76 is added to the digital signal processor 100 for white balance correction.

  The AF detection unit 74 calculates an integrated value necessary for AF control from the input image signal and outputs it to the CPU 50. The CPU 50 controls the photographing lens 14 based on the output from the AF detection unit 74 and focuses on the main subject.

  The photographer looks at the display on the monitor 34, confirms the angle of view, the focus state, and the like, and instructs the execution of photographing. That is, the shutter button 18 is fully pressed.

  When the shutter button 18 is fully pressed, an S2 ON signal is input to the CPU 50. The CPU 50 executes the actual photographing process in response to the S2ON signal.

  First, the CCD 62 is exposed with the aperture value and shutter speed obtained as a result of the AE control, and a recording image is taken.

  The recording image signal output from the CCD 62 is subjected to necessary signal processing by the analog signal processing unit 66, converted to a digital signal by the A / D converter 68, and stored in the SDRAM 56. Then, it is added from the SDRAM 56 to the digital signal processing unit 100.

  The image signal captured by the digital signal processing unit 100 is first subjected to a predetermined offset process by the offset correction circuit 104, and then added to the RGB interpolation calculation circuit 106 to perform a predetermined interpolation calculation. R, G, and B3 color signals at the position are obtained. Then, after being subjected to white balance correction and false color correction in addition to the gain correction circuit 108, the gradation correction circuit 110 performs a predetermined gradation conversion process according to the setting mode. The tone-corrected image signal is then converted into a luminance signal Y and color difference signals Cr and Cb by the RGB / YC conversion circuit 112. The color difference signals Cr and Cb are subjected to predetermined color correction by the color difference matrix circuit 116, and the luminance signal Y is output after being subjected to predetermined contour correction processing by the contour correction circuit 114.

  The image signal (YC signal) generated in this way is once added to the SDRAM 56 and then added to the compression / decompression processing unit 78. Then, after a predetermined compression process is performed by the compression / decompression processing unit 78, it is stored again in the SDRAM 56.

  The CPU 50 adds a predetermined shooting information (information on shooting such as shutter speed, aperture value, shooting sensitivity, shooting mode, etc. at the time of shooting) to the compressed image data stored in the SDRAM 56 (an image file of a predetermined format). For example, an Exif format image file) is generated and recorded in the memory card 82 via the recording control unit 80.

  Thus, the photographing and recording processes are completed. The image recorded in the memory card 82 in this manner can be reproduced and displayed on the monitor 34 by setting the mode of the digital camera 10 to the reproduction mode. That is, when the playback button 32 is pressed to change the mode of the digital camera 10 to the playback mode, the compressed image data of the image file recorded last on the memory card 82 is read and added to the compression / expansion processing unit 78. The compressed / decompressed processing unit 78 generates an uncompressed image signal, adds it to the VRAM 60, and outputs it from the VRAM 60 to the monitor 34 via the display control unit 84. As a result, the image recorded on the memory card 82 is reproduced and displayed on the monitor 34.

  The frame advance of the image is performed by the left and right keys of the cross button 30, and when the right key is pressed, the next image is read from the memory card 82 and reproduced and displayed on the monitor 34. When the left key is pressed, the previous image is read from the memory card 82 and reproduced and displayed on the monitor 34.

  As described above, in the digital camera 10 of the present embodiment, when the gain correction circuit 108 performs gain correction of the image signal, the captured R, G, and B color image signals (color signals) White balance correction (color correction) is performed using a predetermined color correction gain, and false color correction is performed using a predetermined false color correction gain, and gradation correction is performed as an N-bit (14 bits in this example) signal. Output to the circuit 110.

  FIG. 8 is a block diagram showing the configuration of the gain correction circuit 108. As shown in the figure, the gain correction circuit 108 includes a color correction unit 120, a false color correction unit 122, and a false color correction gain calculation unit 124.

  The color correction unit 120 performs white balance correction (color correction) by applying the gain value (color correction gain) calculated by the white balance gain calculation circuit 102 to the color signals of R, G, and B for each pixel. At this time, the color correction unit 120 outputs the color signals of the R, G, and B colors that have been color corrected as signals of M (M> N) bits. That is, the higher bits are output with a margin than the N bits that are the final output from the gain correction circuit 108.

  In this example, since the image signal after gain correction is output with N = 14 bits, for example, it is output with M = 16 bits. This is based on the setting of the color correction gain. In other words, since the gain of white balance correction is generally up to 4 times, it is 16 bits with a margin of 2 bits. Therefore, the number of bits output by the color correction unit 120 is preferably output with a margin corresponding to the color correction gain applied to the color signal by the color correction unit 120.

  The false color correction unit 122 takes in the color signals of the R, G, and B colors that have been color corrected by the color correction unit 120 for each pixel, applies a predetermined false color correction gain to each pixel, and outputs the signal as an N-bit signal. To do.

  The false color correction gain calculation unit 124 calculates, for each pixel, a false color correction gain used by the false color correction unit 122 based on the color signal for each pixel that has been color corrected by the color correction unit 120. Hereinafter, the calculation procedure of the false color correction gain in the false color correction gain calculation unit 124 will be described.

  Assume that the output after color correction in the color correction unit 120 is as shown in FIG. This figure shows an output example of an image signal when a subject with a monochrome gradation pattern is imaged. Therefore, the pixel position can also be regarded as luminance.

  As shown in the figure, in this case, when N bits are set, the R signal (the maximum color signal among the color signals of R, G, and B) is saturated after point A. As a result, the color balance is lost after point A.

  Therefore, as shown in FIG. 9B, the false color correction gain is set so that the magnification is equal to the point A and is larger than the magnification after the point A. Here, the false color correction gain is set so as to change linearly after point A.

  As described above, the false color correction gain calculation unit 124 selects the maximum color signal among the color signals after color correction, and saturates the signal level (point A) when the selected color signal is set to N bits. And a false color correction gain is set so that a gain larger than the same magnification is applied to a signal exceeding the detected signal level.

  Note that the false color correction gain amount applied to a signal exceeding the saturated signal level (point A) is calculated using a function prepared in advance, for example.

  The false color correction unit 122 corrects each color signal after color correction using the false color correction gain set in this way, and outputs the color signal as an N-bit signal.

  FIG. 9C shows an output example (N bits) of the color signal after the false color correction by the false color correction unit 122. As shown in the figure, since the equal gain is applied up to the point A, there is no change in the output of each signal. However, after point A at which the R signal reaches the saturation level, each color signal is multiplied by a gain larger than the same magnification, so the values of the B signal and the G signal approach the R signal. As a result, the saturation of the pixels in which the false color occurs is reduced, and the color change is difficult to understand. In addition, the number of color areas that are visually uncomfortable is reduced (the white areas are increased), and a high-quality image can be obtained.

  FIG. 10 is a flowchart illustrating a procedure of gain correction processing by the gain correction circuit 108.

  The R, G, and B color signals input to the gain correction circuit 108 are first multiplied by the gain value (color correction gain) calculated by the white balance gain calculation circuit 102 in the color correction unit 120 to obtain white. Balance correction (color correction) is performed (step S10).

  The color signal of each color subjected to color correction is output to the false color correction unit 122 and the false color correction gain calculation unit 124. At this time, each color signal is output to the false color correction unit 122 and the false color correction gain calculation unit 124 as an M-bit signal having a margin higher than N bits (step S11).

  Once the color correction is performed by the color correction unit 120, the false color correction gain calculation unit 124 calculates a false color correction gain for each pixel from each color signal after color correction (step S12). That is, first, the color signal that is the maximum among the color signals after color correction is selected. When the selected color signal is set to N bits, a saturated signal level (point A) is detected. The signal below the detected signal level is multiplied by the same magnification, and the signal exceeding the detected signal level is multiplied by a gain greater than the equal magnification so that the false color correction gain is applied. Is set.

  The false color correction unit 122 corrects each color signal after color correction for each pixel using the false color correction gain set for each pixel in this way (step S13). Then, the color signal after the false color correction is limited and output as an N-bit signal (step S14).

  As described above, the gain correction circuit 108 first performs color correction on the input image signal as an M-bit signal, and then performs false color correction and outputs it as an N-bit signal. Then, when performing false color correction, false color correction is performed by setting a false color correction gain so that a gain larger than the same magnification is applied only to a color signal exceeding a saturated signal level.

  As a result, the saturation of the pixel in which the false color occurs is lowered, and the color change is difficult to understand. In addition, the number of color areas that are visually uncomfortable is reduced (the white areas are increased), and a high-quality image can be obtained. In addition, since correction is performed with reference to the number of bits (M bits) larger than the finally required number of bits (N bits), the color changes smoothly when a gradation image is taken. Since it becomes white, it is possible to obtain an excellent output visually. Further, unlike color adjustment based on luminance, correction can be performed only on pixels in which the color signal is saturated, so that the overall color tone balance is not lost (the color is guaranteed for pixels that are not saturated). .)

  In the above embodiment, as an example of setting the false color correction gain, the false color correction gain is set so that the signal level (point A) is saturated up to the same magnification and linearly changes after the saturation signal level. However, the setting example of the false color correction gain is not limited to this. For example, as shown in FIG. 11, the signal level up to a saturated signal level (point A) can be set to the same magnification, and can be set so as to change in a curve after the saturated signal level (set so as to change gently). . Further, the rate of change is not particularly limited, and can be set to an optimal value as appropriate based on the correlation with the output image.

  FIG. 12 is a block diagram showing the configuration of the second embodiment of the gain correction circuit.

  As shown in the figure, the gain correction circuit 108A of the present embodiment is configured to switch the presence or absence of false color correction according to the setting of the dynamic range. That is, the selector 126 can switch and output a color signal that has been subjected to false color correction and a color signal that has not been subjected to false color correction.

  The selector 126 receives an N-bit color signal that has been subjected to false color correction via the false color correction unit 122 and a color signal that has been output as an N-bit color signal without being subjected to false color correction. Is done.

  For this reason, the color correction unit 122A of the present embodiment is configured to output each color signal subjected to color correction as an N-bit signal and an M-bit signal. Then, the color signal that is limited to N bits is output to the selector 126 as it is, and the color signal that is limited to M bits is output to the false color correction unit 122 and the false color correction gain calculation unit 124. It is configured as follows.

  The configurations of the false color correction unit 122 and the false color correction gain calculation unit 124 are the same as those of the false color correction unit 122 and the false color correction gain calculation unit 124 in the gain correction circuit 108 according to the first embodiment described above. .

  The selector 126 switches the output of the color signal based on the dynamic range setting acquired by the dynamic range setting acquisition unit 128. That is, switching is performed between outputting a color signal with false color correction or outputting a color signal without false color correction.

  Here, this switching is performed based on whether or not the set dynamic range is wider than the threshold value. If the set dynamic range is wider than the threshold value, a false color corrected color signal is output. If it is narrow, a color signal not subjected to false color correction is set to be output.

  In the digital camera of the present embodiment, there are two dynamic range settings: “wide dynamic range” and “normal dynamic range”. Therefore, when the dynamic range setting is “wide dynamic range”, false color is set. The corrected color signal is set to be output, and in the case of “normal dynamic range”, the color signal not subjected to false color correction is set to be output.

  The dynamic range setting acquisition unit 128 acquires from the CPU 50 dynamic range setting information that was set when the image data was captured.

  FIG. 13 is a flowchart showing the procedure of gain correction by the gain correction circuit 108A of the present embodiment.

  The R, G, and B color signals input to the gain correction circuit 108A are first multiplied by the gain value (color correction gain) calculated by the white balance gain calculation circuit 102 in the color correction unit 120A to obtain white. Balance correction (color correction) is performed. At this time, the color correction unit 120A outputs two types of color signals, an N-bit color signal and an M-bit color signal (step S20).

  The N-bit color signal is output to the selector 126, and the M-bit color signal is output to the false color correction unit 122 and the false color correction gain calculation unit 124.

  If color correction is performed by the color correction unit 120, then the false color correction gain calculation unit 124 calculates a false color correction gain for each pixel from each color signal after color correction (step S21). The false color correction unit 122 performs false color correction on the M-bit color signal after color correction using the false color correction gain calculated by the false color correction gain calculation unit 124 (step S22). Then, the color signal after the false color correction is limited and output to the selector 126 as an N-bit signal (step S23).

  In this manner, the selector 126 receives the N-bit color signal that has been subjected to false color correction and the N-bit color signal that has not been subjected to false color correction.

  Based on the dynamic range setting information acquired by the dynamic range setting acquisition unit 128, the selector 126 determines whether or not the dynamic range set at the time of shooting is wider than a threshold (step S24). In this example, as described above, the wide dynamic range or the normal dynamic range is determined.

  Here, when the dynamic range set at the time of shooting is wider than the threshold (in the case of a wide dynamic range), the selector 126 is set so as to output a color signal corrected for false color (step S25).

  On the other hand, when the dynamic range set at the time of shooting is narrower than the threshold (in the case of the normal dynamic range), the selector 126 sets so that a color signal not subjected to false color correction is output (step S26).

  As a result, if the dynamic range set at the time of shooting is wider than the threshold value (in the case of a wide dynamic range), a false color corrected color signal is output, and if it is narrow (in the case of a normal dynamic range), false color correction is performed. A signal that has not been processed is output.

  As described above, the gain correction circuit 108A according to the present embodiment can switch the presence / absence of the false color correction according to the setting of the dynamic range, and outputs the color signal corrected with the false color only when the dynamic range is wider than the threshold. The Thereby, a higher quality image can be obtained.

  In other words, when the process for expanding the dynamic range is performed, even in the normal dynamic range, even if the subject is whiteout (the subject in which all color signals are saturated), only a part of the color signals is saturated. May end up.

  On the other hand, if false color correction processing is performed, it is likely to be saturated with white and the dynamic range becomes narrow.

  Therefore, it is possible to effectively compensate for each other's defects by switching the presence or absence of false color correction depending on the dynamic range to be set and executing the false color correction process only when the set dynamic range is greater than or equal to the threshold value. Higher quality images can be obtained.

  In this example, there are only two dynamic ranges, normal and wide dynamic range, but more detailed settings may be made.

  FIG. 14 is a block diagram showing the configuration of the third embodiment of the gain correction circuit.

  As shown in the figure, the gain correction circuit 108B of the present embodiment is provided with a mode setting acquisition unit 130, and information on the shooting mode when the image signal to be processed is shot is acquired from the CPU 50. The The false color correction gain calculation unit 124A calculates a false color correction gain based on the shooting mode information acquired by the mode setting acquisition unit 130.

  In other words, since the subject (shooting scene) can be estimated by acquiring information on the shooting mode when the image signal to be processed is shot, it is more appropriate to set the false color correction gain according to the subject. The false color can be corrected.

  For example, in the case of shooting underwater, the obtained image has many B components, and the B signal is likely to be saturated. Therefore, in the underwater mode, the false color correction gain is set so as to positively correct the saturation of the B signal (for example, the rate of change (slope) is increased).

  Further, when shooting a sunset scene, the obtained image has many R components, and the R signal is likely to be saturated. Therefore, in the evening scene mode, the false color correction gain is set so as to positively correct the saturation of the R signal.

  In the case of the manual mode, the false color correction gain is set so as to always be the same magnification in consideration of the photographer's intention.

  Thus, the false color correction gain calculation unit 124A calculates the false color correction gain according to the shooting mode when the image signal to be processed is acquired. Specifically, a function for R signal, a function for G signal, and a function for B signal are prepared for each photographing mode. At this time, the rate of change (slope) of each function is set according to the characteristics of each shooting mode. For example, in the underwater mode, the change rate of the B signal is set large (in this case, for example, the function for the R signal and the function for the G signal are set so as not to be corrected). In the evening scene mode, the rate of change of the R signal is set large (in this case, for example, the function for the B signal and the function for the G signal are set not to be corrected). In the manual mode, settings are made so that each color signal is not corrected. Then, the functions prepared for each shooting mode are switched and used according to the set shooting mode.

  FIG. 15 is a flowchart showing a procedure of gain correction processing by the gain correction circuit 108B of the present embodiment.

  The R, G, and B color signals input to the gain correction circuit 108B are first multiplied by the gain value (color correction gain) calculated by the white balance gain calculation circuit 102 in the color correction unit 120 to obtain white. Balance correction (color correction) is performed (step S30).

  The color signal of each color subjected to color correction is output to the false color correction unit 122 and the false color correction gain calculation unit 124. At this time, each color signal is output to the false color correction unit 122 and the false color correction gain calculation unit 124A as an M-bit signal having a margin higher than N bits (step S31).

  When color correction is performed by the color correction unit 120, the mode setting acquisition unit 130 acquires shooting mode setting information from the CPU 50 (step S32). The acquired shooting mode setting information is added to the false color correction gain calculation unit 124A.

  The false color correction gain calculation unit 124A calculates a false color correction gain for each pixel based on the acquired shooting mode setting information and each color signal after color correction (step S33). In this example, for example, when the maximum color signal is selected from each color signal after color correction, and the selected color signal is set to N bits, a saturated signal level (point A) is detected. The signal below the detected signal level is multiplied by the same magnification, and the signal exceeding the detected signal level is multiplied by a false color correction gain so that a gain larger than the equal magnification is applied. Set. At this time, a gain value to be applied to a signal exceeding a saturated signal level is set from a function prepared according to the photographing mode.

  The false color correction unit 122 corrects each color signal after color correction for each pixel using the false color correction gain set for each pixel in this way (step S34). Then, the color signal after the false color correction is limited and output as an N-bit signal (step S35).

  Thus, by setting the false color correction gain according to the shooting mode, it is possible to more appropriately suppress the false color and obtain a higher quality image.

  In the case of this example as well, the presence / absence of false color correction may be switched according to the setting of the dynamic range, as in the gain correction circuit 108A of the second embodiment.

  FIG. 16 is a block diagram showing the configuration of the fourth embodiment of the gain correction circuit.

  As shown in the figure, the gain correction circuit 108C of the present embodiment includes a color temperature evaluation value acquisition unit 132, and information on the color temperature evaluation value of the image signal to be processed is calculated as a color temperature evaluation value. Obtained from circuit 118. The false color correction gain calculation unit 124B calculates a false color correction gain based on the information on the color temperature evaluation value acquired by the color temperature evaluation value acquisition unit 132.

  In other words, since the color tone of the subject (shooting scene) can be estimated by acquiring information on the color temperature of the image signal to be processed, false false correction can be more appropriately set by setting the false color correction gain according to the subject. Color correction can be performed.

  For example, when the color temperature is low, the obtained image as a whole is strongly reddish, and the R signal is likely to be saturated. Therefore, when the color temperature is low, the false color correction gain is set so as to positively correct the saturation of the R signal (for example, the rate of change (gradient) is increased).

  On the other hand, when the color temperature is high, the resulting image is strong blue as a whole, and the B signal is likely to be saturated. Therefore, when the color temperature is high, the false color correction gain is set so as to positively correct the saturation of the B signal.

  Thus, the false color correction gain calculation unit 124B calculates the false color correction gain according to the color temperature of the image signal to be processed. Specifically, a function for R signal, a function for G signal, and a function for B signal are prepared for each color temperature evaluation value. At this time, the change rate (slope) of each function is set according to the characteristics of the color temperature. For example, when the color temperature is high, the rate of change of the R signal is set large (in this case, for example, the function for the B signal and the function for the G signal are set so as not to be corrected). When the color temperature is high, the B signal change rate is set to be large (in this case, for example, the function for the R signal and the function for the G signal are set so as not to be corrected). The function prepared for each color temperature evaluation value in this way is switched and used according to the color temperature evaluation value acquired by the color temperature evaluation value acquisition unit 132.

  FIG. 17 is a flowchart showing a procedure of gain correction processing by the gain correction circuit 108C of the present embodiment.

  The R, G, and B color signals input to the gain correction circuit 108C are first multiplied by the gain value (color correction gain) calculated by the white balance gain calculation circuit 102 in the color correction unit 120 to obtain white. Balance correction (color correction) is performed (step S40).

  The color signal of each color subjected to color correction is output to the false color correction unit 122 and the false color correction gain calculation unit 124. At this time, each color signal is output to the false color correction unit 122 and the false color correction gain calculation unit 124B as an M-bit signal having a margin higher than N bits (step S41).

  When color correction is performed by the color correction unit 120, the color temperature evaluation value acquisition unit 132 acquires information on the color temperature evaluation value from the color temperature evaluation value calculation circuit 118 (step S42). The acquired color temperature evaluation value information is added to the false color correction gain calculation unit 124B.

  The false color correction gain calculation unit 124B calculates a false color correction gain for each pixel based on the acquired color temperature evaluation value information and each color signal after color correction (step S43). In this example, for example, when the color signal that is the maximum among the color signals after color correction is selected and the selected color signal is set to N bits, a saturated signal level (point A) is detected. The signal below the detected signal level is multiplied by the same magnification, and the signal exceeding the detected signal level is multiplied by the false color correction gain so that a gain larger than the equal magnification is applied. Set. At this time, a gain value to be applied to a signal exceeding a saturated signal level is set from a function prepared for each color temperature evaluation value within a certain range.

  The false color correction unit 122 performs false color correction on each color signal after color correction for each pixel using the false color correction gain set for each pixel in this way (step S44). Then, the color signal after the false color correction is limited and output as an N-bit signal (step S45).

  In this way, by setting the false color correction gain according to the color temperature evaluation value, it is possible to more appropriately suppress the false color and obtain a higher quality image.

  In this example, the false color correction gain is set according to the color temperature evaluation value. However, since the color temperature evaluation value is synonymous with the light source type, the false color correction gain is set according to the light source type. You may do it.

  Also in the case of this example, the presence or absence of false color correction may be switched according to the setting of the dynamic range, as in the gain correction circuit 108A of the second embodiment.

  In the above series of embodiments, the case where the present invention is applied to white balance correction has been described as an example. However, the application of the present invention is not limited to this, and a predetermined gain is applied to a plurality of color signals. And can be applied to all processes that output with a desired number of bits. For example, the present invention can be applied to color difference matrix processing in addition to the above white balance correction processing.

  In the series of embodiments described above, the case where the present invention is applied to a digital camera has been described as an example. However, the application of the present invention is not limited to this. It can be applied to devices having an imaging function, such as a mobile phone with a camera and a digital video camera, as well as so-called RAW image data (image data obtained by digitizing an image signal output from an image sensor). The present invention can be similarly applied to an apparatus that generates a luminance signal and a color difference signal from RAW image data. An apparatus for developing RAW image data can be configured, for example, by causing a computer to realize the above-described image processing function using a predetermined control program.

  In the digital camera of the above embodiment, the digital signal processing unit having the image processing function according to the present invention is configured by a hardware circuit. However, the same function as the hardware circuit can be configured by software. .

  In the digital camera of the above embodiment, a CCD is used as an image sensor. However, the image sensor is not limited to this, and an image sensor such as a CMOS sensor may be used.

The front perspective view which shows the external appearance structure of the digital camera to which this invention was applied The rear perspective view showing the appearance composition of the digital camera to which the present invention is applied Block diagram showing the electrical configuration of the digital camera Block diagram showing schematic configuration of digital signal processor A graph showing the relationship between the input tone value and the output tone value in the gamma conversion processing of the tone correction circuit A graph showing the relationship between the input tone value and the output tone value in the preprocessing of the tone correction circuit A graph showing the relationship between the input gradation value and the output gradation value in the gradation conversion processing of the gradation correction circuit Block diagram showing the configuration of the gain correction circuit Illustration of false color correction method Flow chart showing the procedure of gain correction processing by the gain correction circuit Graph showing another setting example of false color correction gain The block diagram which shows the structure of 2nd Embodiment of a gain correction circuit. The flowchart which shows the procedure of the gain correction by the gain correction circuit of 2nd Embodiment The block diagram which shows the structure of 3rd Embodiment of a gain correction circuit. The flowchart which shows the procedure of the gain correction by the gain correction circuit of 3rd Embodiment The block diagram which shows the structure of 4th Embodiment of a gain correction circuit. The flowchart which shows the procedure of the gain correction by the gain correction circuit of 4th Embodiment Explanatory drawing of conventional gain correction (white balance correction)

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Digital camera, 12 ... Camera body, 14 ... Shooting lens, 18 ... Shutter button, 34 ... Monitor, 50 ... CPU, 52 ... Operation part, 54 ... ROM, 56 ... SDRAM, 58 ... Flash memory, 60 ... VRAM, 62 ... CCD, 64 ... CCD driver, 66 ... analog signal processing unit, 68 ... A / D converter, 70 ... bus, 74 ... AF detection unit, 76 ... AE / AWB detection unit, 78 ... compression / decompression processing unit, 80 ... Recording control unit, 82 ... Memory card, 84 ... Display control unit, 100 ... Digital signal processing unit, 102 ... White balance gain calculation circuit, 104 ... Offset correction circuit, 108, 108A, 108B, 108C ... Gain correction circuit, DESCRIPTION OF SYMBOLS 110 ... Tone correction circuit, 106 ... RGB interpolation calculation circuit, 112 ... RGB / YC conversion circuit, 114 ... Contour correction circuit, 1 6 ... Color difference matrix circuit, 118 ... Color temperature evaluation value calculation circuit, 120 ... Color correction unit, 122 ... False color correction unit, 124, 124A, 124B ... False color correction gain calculation unit, 126 ... Selector, 128 ... Dynamic range setting Acquisition unit, 130 ... mode setting acquisition unit, 132 ... color temperature evaluation value acquisition unit

Claims (8)

An image signal processing method for performing color correction by applying a predetermined color correction gain to each color signal constituting an image signal and generating an N-bit color signal,
Performing color correction by applying a predetermined color correction gain to each color signal constituting the image signal to generate a color signal of M (N <M) bits;
Selecting the maximum color signal among the color signals after color correction;
When the selected color signal is N bits, detecting a saturated signal level;
For each color signal after color correction, a color signal exceeding the signal level is subjected to false color correction by applying a predetermined false color correction gain to generate an N-bit color signal;
An image signal processing method comprising:   The image signal processing method according to claim 1, wherein information on a shooting mode when the image signal is acquired is acquired, and the false color correction gain is switched according to the shooting mode.   2. The image signal processing method according to claim 1, wherein information on a color temperature when the image signal is acquired is acquired, and the false color correction gain is switched according to the color temperature.   When performing a process for expanding the dynamic range for the image signal, if the dynamic range to be set is less than a threshold value, the false color correction is not performed, and a predetermined color correction gain is applied to each color signal constituting the image signal. The image signal processing method according to claim 1, wherein color correction is performed to generate an N-bit color signal. An image signal processing apparatus that performs color correction by applying a predetermined color correction gain to each color signal constituting an image signal, and generates an N-bit color signal,
Color correction means for performing color correction by applying a predetermined color correction gain to each color signal constituting the image signal, and generating a color signal of M (N <M) bits;
Selecting means for selecting the maximum color signal among the color signals color-corrected by the color correcting means;
Detecting means for detecting a saturated signal level when the color signal selected by the selecting means is set to N bits;
False color correction means for generating a N-bit color signal by performing false color correction on each color signal color-corrected by the color correction means by applying a predetermined false color correction gain to a color signal exceeding the signal level; ,
An image signal processing apparatus comprising:   The image capturing mode information acquisition means for acquiring the information of the shooting mode when the image signal is acquired, and the false color correction means, the false color according to the shooting mode acquired by the shooting mode information acquisition means 6. The image signal processing apparatus according to claim 5, wherein the correction gain is switched.   A color temperature information acquisition unit configured to acquire color temperature information when the image signal is acquired; and the false color correction unit includes the false color according to the color temperature acquired by the color temperature information acquisition unit. 6. The image signal processing apparatus according to claim 5, wherein the correction gain is switched. In performing the process of expanding the dynamic range for the image signal,
Second color signal correction means for performing color correction by applying a predetermined color correction gain to each color signal constituting the image signal, and generating an N-bit color signal;
Dynamic range information acquisition means for acquiring dynamic range information to be set;
The N-bit color signal generated by the second color signal correction unit and the N-bit color signal generated by the false color signal correction unit are fetched, and the dynamic range acquired by the dynamic range information acquisition unit is If it is less than the threshold value, the N-bit color signal generated by the second color signal correction means is output, and if it is equal to or greater than the threshold value, the N-bit color signal generated by the false color signal correction means is output. Output switching means for
The image signal processing apparatus according to claim 5, further comprising:

Images