JP2010263267A - Image correction apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image correction apparatus that effectively corrects gray scale according to captured images. <P>SOLUTION: A scene analysis processing section detects a shooting condition of captured images from luminance distribution of the captured image and information on an imaging device for imaging the captured image. A tone curve selection section sets a tone curve for correcting input/output correspondence of luminance in the captured image according to the detected shooting condition of the captured image. Gray scale can be effectively corrected according to the captured image. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image correction apparatus that corrects a captured image by an imaging apparatus.

  2. Description of the Related Art Conventionally, there has been known an image correction device for making an image shot by a shooting device such as a digital still camera or a digital video camera clearer or correcting according to the purpose. As such an image correction apparatus, for example, a configuration for performing gradation correction by selecting a luminance input / output characteristic, that is, a tone curve, based on a histogram of luminance levels of a photographed image (see, for example, Patent Document 1), In addition, a configuration is known in which the type of light source at the time of photographing is identified and gradation correction such as color correction and γ correction is performed according to the type of the light source (see, for example, Patent Document 2).

Japanese Patent No. 3714657 (page 3-6, Fig. 4-6) Japanese Patent No. 4217494 (page 3-8, Fig. 5-6)

  In general, the optimum gradation characteristics vary depending on the shooting situation (scene) of the subject. For example, if an image obtained by photographing a night view is corrected brightly, the night view quality is impaired. The above-described configuration has a problem that the correction according to the shooting situation of the subject is not taken into consideration.

  Further, in normal exposure correction in the photographing apparatus, when the exposure is adjusted to the main subject, the sky and background other than the main subject may be saturated, so-called whiteout. In such a case, although the overexposure can be suppressed by photographing the exposure correction in the minus direction, in that case, the entire photographed image including the main subject is darkly developed. In such a case, with the above-described configuration, it is not possible to select a tone curve for realizing optimum gradation characteristics in consideration of exposure correction.

  SUMMARY An advantage of some aspects of the invention is that it provides an image correction apparatus capable of effective gradation correction corresponding to a photographed image.

  The image correction apparatus according to claim 1, wherein a detection unit that detects a shooting state of the photographed image from information on a luminance distribution of the photographed image and a photographing device that photographed the photographed image; And setting means for setting a tone curve for correcting the correspondence between the luminance input and output of the photographed image in accordance with the photographing situation.

  The image correction apparatus according to claim 2 is the image correction apparatus according to claim 1, wherein the detection unit detects the photographing state of the photographed image from the luminance distribution of the photographed image and the exposure information of the photographing apparatus that photographed the photographed image. To do.

  According to a third aspect of the present invention, in the image correction apparatus according to the first or second aspect, the setting means is one of a plurality of predetermined photographing situations in which the photographing situation of the photographed image detected by the detecting means is preset. When it is determined that the image is selected from a plurality of predetermined tone curves corresponding to each of the predetermined imaging conditions set in advance according to the information of the imaging device, A tone curve for correcting a captured image is set.

  According to a fourth aspect of the present invention, in the image correction device according to the third aspect, the setting means is such that the photographing situation of the photographed image detected by the detecting means is not any of a plurality of predetermined photographing situations set in advance. When it is determined, a tone curve for correcting the photographed image is set based on the brightness values at at least two different points in the cumulative histogram of the brightness of the photographed image.

  The image correction apparatus according to claim 5 is the image correction apparatus according to any one of claims 1 to 4, wherein the correction is set by the setting means in accordance with a ratio of pixels having a predetermined luminance value or less in the photographed image. Adjusting means for shifting the tone curve to the high luminance input side.

  The image correction apparatus according to claim 6 is the image correction apparatus according to claim 5, wherein the adjustment means uses the correction tone curve set by the setting means as a ratio of pixels equal to or lower than a predetermined luminance value in the photographed image. The gain is corrected with a gain value corresponding to.

  According to the image correction apparatus of the first aspect, the photographing state of the photographed image is detected from the luminance distribution of the photographed image and the information of the photographing apparatus that photographed the photographed image, and the photographing state of the photographed image is detected. Accordingly, by setting the tone curve for correcting the correspondence between the luminance input and output of the photographed image by the setting means, effective gradation correction corresponding to the photographed image can be performed.

  According to the image correction apparatus of the second aspect, in addition to the effect of the image correction apparatus according to the first aspect, the detection means takes a photographed image from the luminance distribution of the photographed image and the exposure information of the photographing apparatus that photographed the photographed image. By detecting this shooting situation, it is possible to more effectively correct the gradation of the shot image according to the exposure situation at the time of shooting.

  According to the image correction apparatus of the third aspect, in addition to the effect of the image correction apparatus of the first or second aspect, a plurality of predetermined photographing situations in which the photographing situation of the photographed image detected by the detecting unit is preset. When it is determined that either one of them is set, the setting unit selects one of the predetermined tone curves set in advance corresponding to each of the predetermined shooting situations set in accordance with information of the shooting apparatus. Thus, by setting the tone curve for correcting the photographed image, the tone curve for correcting the photographed image can be finely adjusted in accordance with the photographing situation and information of the photographing apparatus.

  According to the image correction apparatus of the fourth aspect, in addition to the effect of the image correction apparatus according to the third aspect, any one of a plurality of predetermined photographing situations in which the photographing situation of the photographed image detected by the detecting unit is set in advance. If it is determined that there is no image, the setting means sets a tone curve for correcting the captured image based on the brightness values at at least two different points in the accumulated histogram of the brightness of the captured image. Even when it is determined that the situation is not a predetermined shooting situation set in advance, it is possible to set a tone curve for efficient correction.

  According to the image correction apparatus of the fifth aspect, in addition to the effect of the image correction apparatus according to any one of the first to fourth aspects, the adjustment unit is configured according to a ratio of pixels having a predetermined luminance value or less in the photographed image. However, by shifting the correction tone curve set by the setting means to the high luminance input side, the contrast of the photographed image can be improved and so-called black float can be suppressed.

  According to the image correction apparatus of the sixth aspect, in addition to the effect of the image correction apparatus of the fifth aspect, the correction means sets the correction tone curve set by the setting means to the predetermined luminance value in the photographed image. By correcting with a gain value corresponding to the ratio of the following pixels, it is possible to prevent the entire captured image from becoming dark even when the correction tone curve is shifted to the high luminance input side.

It is a flowchart which shows each control of determination of the imaging condition of the image correction apparatus of one embodiment of this invention, selection of a tone curve, and adjustment. It is a block diagram which shows the principal part of an image correction apparatus same as the above. It is a block diagram which shows the imaging device provided with the image correction apparatus same as the above. It is explanatory drawing shown in (a) thru | or (e) of the example of the tone curve corresponding to each imaging | photography condition of an image correction apparatus same as the above. It is explanatory drawing which shows an example of the accumulation histogram for the determination of the flare scene of an image correction apparatus same as the above. It is explanatory drawing which shows an example of the table for the determination of the flare scene of an image correction apparatus same as the above. It is explanatory drawing which shows an example of the accumulation histogram for adjustment of the tone curve by the adjustment means of an image correction apparatus same as the above. (a) is explanatory drawing which shows the state which shifted the tone curve to the high-intensity input side by the adjustment means same as the above, (b) is explanatory drawing which shows correction | amendment of the tone curve by the adjustment means same as the above. (a) is explanatory drawing which shows an example of the histogram for determination of the 2 hump scene of an image correction apparatus same as the above, (b) is explanatory drawing which shows the cumulative histogram of the histogram of (a). It is explanatory drawing which shows the other example of the histogram for the determination of the 2 hump scene of an image correction apparatus same as the above. It is explanatory drawing which shows selection of the tone curve in the auto scene of an image correction apparatus same as the above.

  The configuration of an embodiment of the present invention will be described below with reference to the drawings.

  In FIG. 3, reference numeral 10 denotes a camera as a photographing apparatus. This camera 10 is a so-called digital still camera, and records image data photographed by the image pickup means 12 on a recording medium 14 as digital data. The camera 10 includes a case 20, which includes an aperture device 21, a lens 22, a flash device 23, an image pickup means 12 that is a charge coupled device (CCD), a double correlation sampling circuit (CDS) 24, Amplifier circuit (AMP) 25, analog-digital converter (A / D) 26, first image data memory 27, image data processing unit 28, second image data memory 29, compression / decompression circuit 31, timing generator (TG) 32, a memory controller 33, a control means 34 having a function of an image correction apparatus including a CPU, a power supply circuit (not shown), and the like are housed. The control means 34 is connected to a working RAM and a memory 35 such as a ROM storing preset values or programs. Further, the case 20 is provided with a display device 36 that is a liquid crystal panel (LCD), an operation unit 37, and the like. In this camera 10, the control means 34 controls the amplification circuit 25, the compression / decompression circuit 31, and the memory controller 33, respectively. In the camera 10, the control unit 34 controls the first image data memory 27 and the second image data memory 29 via the memory controller 33. Further, in the camera 10, the control means 34 controls the diaphragm device 21, the lens 22, the flash device 23, and the timing generator 32, respectively. In the camera 10, the control unit 34 controls the imaging unit 12, the double correlation sampling device circuit 24, and the analog / digital converter 26 via the timing generator 32.

  The camera 10 converts the field light captured via the aperture device 21 and the lens 22 into an electrical signal by the imaging means 12. The timing of conversion of the electric signal is controlled by the timing generator 32. The electrical signal output from the imaging means 12 is subjected to signal processing by the double correlation sampling circuit 24, amplified by the amplifier circuit 25, and then converted into digital data by the analog-digital converter 26. This digital data is temporarily recorded in the first image data memory 27 as image data. The image data temporarily recorded in the first image data memory 27 is subjected to predetermined image processing by the image data processing unit 28. The image data subjected to the image processing in this way is displayed on the display device 36 and recorded in the second image data memory 29. Further, the image data recorded in the second image data memory 29 is compressed by the compression / decompression circuit 31 and recorded as image data on the recording medium 14. The image data recorded on the recording medium 14 can be displayed on the display device 36 after being decompressed by the compression / decompression circuit 31 in accordance with an instruction from the operator.

  In the camera 10, the state is switched by the user operating the operation unit 37. For example, in the preview mode before the main photographing, the imaging unit 12 continuously outputs an electrical signal at a constant interval, The image data output from the data processing unit 28 is displayed on the display device 36. Then, the control means 34 controls the aperture of the aperture device 21 so as to obtain an appropriate exposure as the automatic exposure control (AE), sets the exposure time of the image pickup means 12, and performs automatic focus control (AF). As described above, the lens 22 is controlled so that the image of the target subject is focused by the imaging means 12.

  Here, the control means 34 uses the image data recorded in the first image data memory 27, and performs automatic exposure control and automatic focus control automatically or according to the operation of the operation unit 37 by the operator. Do. That is, the control means 34 divides the image data composed of the luminance data of a large number of pixels into a predetermined number of vertical and horizontal blocks, calculates the RGB luminance data and the average value of the color data for each block, and the luminance data for each block. And block characteristics such as color data are calculated. Then, the control means 34, the appropriate exposure amount calculated based on the shooting situation (scene) and the position (distance) of the subject determined using the calculated block characteristics, the lens driving amount, the timing of flash irradiation and Appropriate automatic exposure control and automatic focus control according to the subject are performed according to the amount of irradiation. That is, the control unit 34 controls the timing control of the timing generator 32 based on the obtained exposure amount and the like, and controls the driving of the lens 22 according to the obtained lens driving amount, and the obtained flash irradiation timing. The flash unit 23 is controlled based on the irradiation amount.

  Then, when the user half-presses the shutter button (release switch) of the operation unit 37, the user is ready for shooting, determines the exposure and focus, and the user fully presses the shutter button of the operation unit 37. By operating, it becomes the state of actual shooting, and the flash device 23 irradiates the flash light toward the subject at the timing and irradiation amount set by the control means 34 as necessary to compensate for the insufficient light amount of the object field. The image pickup means 12 performs exposure for a predetermined exposure time controlled by the control means 34, outputs an electric signal based on the accumulated charges, and the image processed by the image data processing unit 28 via the first image data memory 27. Data is recorded on the recording medium 14 via the second image data memory 29.

  Here, the control means 34 analyzes the image data recorded in the first image data memory 27 or the second image data memory 29 based on the input from the image data processing unit 28, etc., and determines the status of the image data. Appropriate image data such as white balance correction, γ correction, color correction, brightness correction, and color correction is controlled by controlling the image data processing unit 28 in accordance with the operation of the operation unit 37 by the operator. Processing is performed to provide preferred image data.

  Specifically, as shown in FIG. 2, the control unit 34 includes a scene analysis processing unit 41 as a detection unit, a tone curve selection unit 42 as a setting unit, a parameter setting unit 43 as an adjustment unit, and a cumulative histogram creation Part 44. Then, based on the histogram (brightness distribution) output from the image data processing unit 28, the cumulative histogram creation unit 44 creates a cumulative histogram (histogram increase rate), and this cumulative histogram and the image data processing unit 28 output it. The scene analysis processing unit 41 determines the shooting situation (scene) of the shot image based on the brightness data and information of the camera 10, for example, an exposure correction value that is exposure information at the time of shooting the image. In addition, according to the shooting situation determination in the scene analysis processing unit 41, the tone curve selection unit 42 selects a plurality of tone curves (intensity input / output correspondences) recorded in the memory 35 for each of these shooting situations. From the input / output characteristics graph for correction, one of them is selected and set according to the information of the camera 10. Further, the parameter setting unit 43 adjusts the tone curve selected and set by the tone curve selection unit 42 as necessary, and outputs it to the image data processing unit 28.

  The image data processing unit 28 includes an RGB separation unit 51, a white balance (WB) processing unit 52, a γ correction unit 53, a color correction unit 54, a first conversion unit 55, a histogram creation unit 56, a luminance correction unit 57, A color difference processing unit 58 and a second conversion unit 59 are provided. Then, the RGB separation unit 51 separates the image data recorded in the first image data memory 27 (FIG. 3) into a plurality of luminance data of R (red), G (green), and B (blue). The white balance processing unit 52 performs white balance processing on the separated image data by multiplying the corresponding color component data by white balance gain, that is, R gain, G gain, and B gain. Further, the RGB image data subjected to the white balance processing by the white balance processing unit 52 is subjected to γ correction and color correction by the γ correction unit 53 and the color correction unit 54 in accordance with the characteristics of the imaging unit 12, respectively. Further, the RGB image data corrected through the γ correction unit 53 and the color correction unit 54 is converted into Y (luminance), Cr (red difference), and Cb (blue difference) data by the first conversion unit 55. To do. Further, the histogram creation unit 56 creates a histogram based on the Y (luminance) data and outputs it to the cumulative histogram creation unit 44. Further, the luminance correction unit 57 applies the tone curve output via the parameter setting unit 43 to the Y (luminance) data to correct the Y (luminance) data, and according to the correction of the Y (luminance) data. Thus, the color difference correction unit 58 corrects the Cr (red difference) data and the Cb (blue difference) data, respectively. Then, each of the corrected Y (luminance), Cr (red difference), and Cb (blue difference) data is converted into RGB data that can be displayed on the display device 36 shown in FIG. The data is output to the second image data memory 29 and the display device 36.

  Each part of the image data processing unit 28 and the control unit 34 is separated as a block for convenience, and either of them may be integrated with each other, or the control unit 34 and the image data processing unit 28 One of the blocks may be appropriately incorporated into the other.

  Next, the shooting situation analysis process and tone curve setting process of the above-described embodiment will be described. In the following description, it is assumed that the luminance value corresponds to, for example, 1024 gradations (scale), but the present invention is not limited to this gradation.

  As shown in FIG. 1, first, the scene analysis processing unit 41 stores the cumulative histogram created by the cumulative histogram creation unit 44, Y (luminance) data, the subject distance, the type of light source, exposure information, etc. Information is input (step 1).

  Next, the scene analysis processing unit 41 determines the shooting state of the shot image based on the input information. For example, first, the scene analysis processing unit 41 determines whether or not the shooting situation is a flare scene, that is, whether or not the reflected light from the lens 22 or the like is included in the shot image (step 2).

  For this determination, as shown in FIG. 5, a cumulative histogram is used. The scene analysis processing unit 41 calculates the luminance value until the accumulated histogram reaches a predetermined value empirically set in advance, for example, 1%, as a black floating value (Black offset) BO, and maximizes the luminance value. Let the ratio of the pixels that are present be the whiteout (saturation) ratio SR. Here, the black float value BO indicates the ratio of low-luminance pixels below a predetermined luminance value in the captured image, that is, the degree of so-called black float. Specifically, the larger the black float value BO, the more the image is captured. There are few black pixels in the image, and the black color in the captured image is whitish (close to gray). Further, the whiteout ratio SR indicates the ratio of saturated pixels in the captured image, that is, the degree of so-called whiteout, and specifically, the larger the whiteout ratio SR, the more saturated pixels in the captured image, The shot image is whitish. Then, in this scene analysis processing unit 41, a plurality of threshold values are provided for each of the black float value BO and the whiteout ratio SR, and whether or not the shooting situation is a flare scene by comparing with the threshold value, Then, the degree of reflected light in the captured image (here, for example, weak, medium, strong) is determined. Specifically, for example, a table as shown in FIG. 6 is recorded in advance in the memory 35 or the like, and this table is compared with the black float value BO and the whiteout ratio SR. Note that the threshold values of the black float value BO and the whiteout ratio SR can be arbitrarily set in addition to the numerical values in the table shown in FIG.

  As shown in FIG. 1, when the scene analysis processing unit 41 determines that there is reflected light (flare), the tone curve selection unit 42 selects a plurality of tone curves for the flare scene recorded in the memory 35. One of them is selected according to the information of the camera 10 (step 3). For example, as shown in FIG. 4 (a), these flare scene tone curves are such that the output for the saturated (high luminance) portion of the photographed image is lowered and the change from the low luminance to the middle portion is not changed so much. And In addition, when using an exposure correction value as information of the camera 10, a tone curve having a smaller ratio of increasing the output luminance with respect to the input luminance is selected as the exposure correction value increases in the positive direction, and the exposure correction value is negative. A tone curve having a larger ratio of increasing output luminance with respect to input luminance as the direction is larger is selected.

  Thereafter, the parameter setting unit 43 sets the parameter of the selected tone curve in the luminance correction unit 57 (FIG. 2) according to the degree of reflected light in the captured image (step 4). Specifically, as shown in FIG. 4 (a), the parameter setting unit 43 increases the tone curve to increase the black pixels as the degree of reflected light in the captured image increases, so that so-called black is drawn. A large shift to the input side (right side in the figure).

  Returning to FIG. 1, when the scene analysis processing unit 41 determines that there is no reflected light (flare) in step 2, the scene analysis processing unit 41 further determines that the shooting state of the captured image is a night flash scene. That is, it is determined whether or not the photographed image was photographed with the flash device 23 on a dark background (step 5). For this determination, a well-known technique can be applied as appropriate. Briefly, a captured image is divided into a plurality of blocks, and whether or not a block with low luminance among these blocks is larger than a predetermined threshold value set in advance. (Whether it is greater than or equal to a threshold value) and at the same time, it is determined whether or not the contrast of the captured image is greater than a predetermined threshold value (whether it is greater than or equal to the threshold value). It is determined whether or not the degree to which the flash light from the lens contributes to the captured image is greater than a predetermined threshold value (whether or not it is greater than or equal to the threshold value).

  When the scene analysis processing unit 41 determines that the scene is a night flash scene, the tone curve selection unit 42 uses the plurality of tone curves for the night flash scene recorded in the memory 35 according to the information of the camera 10. Either one is selected (step 6). For example, as shown in FIG. 4B, the tone curve for the night flash scene does not change so much from the low luminance to the middle portion of the photographed image, and does not change much according to the photographed image in the high luminance portion. Or, the output luminance is lowered with respect to the input luminance. That is, as shown in FIG. 1, the parameter setting unit 43 sets the reduction amount of the output luminance with respect to the input luminance of the high luminance part of the selected tone curve in the luminance correction unit 57 (FIG. 2) according to the histogram. (Step 7).

  On the other hand, when the scene analysis processing unit 41 determines in step 5 that the scene is not a night flash scene, the scene analysis processing unit 41 determines whether the shooting state of the shot image is a sky blue scene, that is, the shot image has a blue sky. It is determined whether or not the image is included (step 8). For this determination, a well-known technique can be applied as appropriate. Therefore, for example, the color characteristic and luminance characteristic of a blue sky that is a subject assumed in an image photographed in a sky blue scene are stored in advance in the memory 35 or the like. Record and divide the captured image into a plurality of blocks, and determine whether the number of blocks having the recorded color characteristics and luminance characteristics is greater than a predetermined threshold value (whether it is greater than or equal to the threshold value) .

  When the scene analysis processing unit 41 determines that the scene is a sky blue scene, the tone curve selection unit 42 uses a plurality of tone curves similar to those for the night flash scene recorded in the memory 35 (FIG. 4B). Then, one of them is selected according to the information of the camera 10 (step 9), and the parameter setting unit 43 displays the output reduction amount of the high-intensity part of the selected tone curve in the histogram as in step 7. Set according to (step 10). Further, the parameter setting unit 43 performs tone curve correction (adaptive offset correction) based on the cumulative histogram of the photographed image (step 11).

  The tone curve correction is preferably performed first when the above-described black float value BO (FIG. 7) calculated by the scene analysis processing unit 41 is larger than a predetermined threshold (for example, more than a predetermined threshold) (for example, FIG. In the case of 18 ≦ BO shown in FIG. The parameter setting unit 43 generates a black pixel by setting a parameter in the luminance correction unit 57 (FIG. 2) so as to shift the tone curve to the high luminance input side with a shift amount corresponding to the black floating value BO. As a result, the contrast of the appearance of the photographed image is improved, and the black float of the photographed image is improved (FIG. 8A). Further, the parameter setting unit 43 corrects the shifted tone curve with a gain value corresponding to the black float value BO, thereby preventing the entire captured image from being darkened (FIG. 8B). Specifically, the parameter setting unit 43 corrects the output luminance corresponding to each input luminance of the shifted tone curve so as to approach the output luminance corresponding to those input luminances in the tone curve before the shift.

  If it is determined in step 8 that the scene analysis processing unit 41 is not a sky blue scene, the scene analysis processing unit 41 determines whether the shooting state of the shot image is a text scene, that is, a document shot. It is determined whether or not (step 12). For this determination, a well-known technique can be applied as appropriate.In short, for example, subject distance, environmental brightness, presence / absence of a person (face) in a captured image, type of light source, relationship between a light source and a main subject, etc. In addition, whether or not the color change in the entire captured image is small, specifically, the captured image is divided into a plurality of blocks, the average value of each representative color value is calculated, and the average value is constant. It is determined whether or not the number of blocks in which the representative color value falls within the range is greater than a predetermined threshold (whether or not it is equal to or greater than the threshold).

  When the scene analysis processing unit 41 determines that the text scene is included, the tone curve selection unit 42 selects one of the plurality of tone curves for the text scene recorded in the memory 35 according to the information of the camera 10. One is selected (step 13). For example, as shown in FIG. 4C, the tone curves for the text scene lower the output luminance with respect to the input luminance at the intermediate portion from the low luminance of the photographed image, and output the high luminance portion with respect to the input luminance. The brightness is slightly increased. Thereafter, the parameter setting unit 43 sets parameters according to the selected tone curve (step 14), and performs tone curve correction similar to step 11 (step 15).

  If it is determined in step 12 that the scene analysis processing unit 41 is not a text scene, the scene analysis processing unit 41 determines whether the shooting state of the shot image is a double-humped scene, that is, FIG. As shown in FIG. 6, it is determined whether or not the captured image has two different luminance value peaks on the low luminance input side and the high luminance input side in the histogram (step 16).

For this determination, as shown in FIG. 9A and FIG. 9B, a histogram and a cumulative histogram are used. First, the scene analysis processing unit 41 calculates a cumulative histogram width from 0 to a predetermined value, for example, 15 as a black ratio BR, and the cumulative histogram is empirically stored in advance. A luminance range that is set to a predetermined value, for example, 2.5% to 97.5% is calculated as an effective range ER, and a predetermined value, for example, luminance, is calculated from the luminance value for which the cumulative histogram is 97.5%. The ratio of the cumulative histogram up to a luminance value that is 64 less than the value is calculated as a white ratio WR. Further, the scene analysis processing unit 41 calculates the luminance width of the portion where the cumulative histogram is flat at the luminance value of the intermediate portion as the flat length FL. Further, in the scene analysis processing unit 41, in the histogram, the difference between the ratio of the luminance value of the peak part on the low luminance side and the ratio of the luminance value one smaller than the luminance value, and the luminance value one larger than the luminance value. The maximum value of the sum of the difference and the ratio is calculated as an edge value EV. That is, the edge value EV is HIST [i] where the histogram value of the luminance value i is
EV = MAX {(HIST [i] −HIST [i-1]) + (HIST [i] −HIST [i + 1])}
= MAX (2 ・ HIST [i] −HIST [i-1] −HIST [i + 1])
Is required.

  When calculating the edge value EV, it may be preferable to reduce the gradation (resolution) of the histogram as shown in FIG.

  In the scene analysis processing unit 41, a threshold is provided for each of the black rate BR, the effective range ER, the white rate WR, the flat length FL, and the edge value EV, and at least one of the black rate BR and the edge value EV. Depending on whether each is greater than the respective threshold (whether it is greater than or equal to the threshold), and whether each of the effective range ER, white ratio WR, and flat length FL is greater than each threshold (whether greater than each threshold) Then, it is determined whether or not the shooting situation is a two-hump scene.

  As shown in FIG. 1, when the scene analysis processing unit 41 determines that the scene is a two-hump scene, the tone curve selection unit 42 uses a plurality of tone curves for the two-hump scene recorded in the memory 35 to correct the exposure. Any one is selected according to the information of the camera 10 such as a value (step 17). For example, as shown in FIG. 4 (d), the tone curve for these two-hump scenes increases the output luminance relatively large with respect to the input luminance from the low luminance to the middle portion of the photographed image, and the high luminance portion shows the photographed image. The output brightness is raised or lowered with respect to the input brightness according to the above. That is, as shown in FIG. 1, the parameter setting unit 43 sets the parameter of the high-intensity part of the selected tone curve according to the captured image (step 18).

  Furthermore, when the scene analysis processing unit 41 determines in step 16 that the scene is not a two-hump scene, the scene analysis processing unit 41 determines whether the shooting state of the shot image is a small range scene, that is, the contrast of the shot image. It is determined whether or not the histogram is biased within a narrow range (step 19). This determination is performed based on, for example, whether the effective range ER is narrower than a predetermined range set in advance.

  When the scene analysis processing unit 41 determines that the scene is a small range scene, the tone curve selection unit 42 selects one of a plurality of tone curves for the small range scene recorded in the memory 35 according to the information of the camera 10. One is selected (step 20). For example, as shown in FIG. 4E, these tone curves for small range scenes increase the output luminance relatively large with respect to the input luminance in the entire luminance range. Next, the parameter setting unit 43 sets parameters in the luminance correction unit 57 (FIG. 3) according to the selected tone curve (step 21).

  In step 19, when the scene analysis processing unit 41 determines that the scene is not a small range scene, the tone curve selection unit 42 does not depend on the type of the captured image, but is recorded in the memory 35 (for auto scene). Select a tone curve (step 22).

  When selecting the normal tone curve, the scene analysis processing unit 41, as shown in FIG. 11, in the histogram of the photographed image, one point on the low luminance side, for example, a point on the cumulative histogram 50%, and the high luminance side Distance values D1 and D2, which are differences from a reference cumulative histogram serving as a reference recorded in advance in the memory 35 or the like at each of the points, for example, 99% of the cumulative histogram, are calculated. Specifically, the tone curve selection unit 42 compares the distance values D1 and D2 with a table previously recorded in the memory 35 or the like corresponding to the distance values D1 and D2, respectively. Select the tone curve. That is, in step 22, a tone curve for operating the degree of lifting of one point on the low luminance side and the degree of suppression of one point on the high luminance side is set.

  Then, the parameter setting unit 43 sets parameters in the luminance correction unit 57 (FIG. 3) according to the selected tone curve (step 23), and further performs tone curve correction similar to step 11 (step 24). ).

  The tone curve set in each of the above steps is applied to Y (luminance) data by the luminance correction unit 57, and by correction of the Y (luminance) data, the color difference correction unit 58 sets Cr (red difference) and Cb (blue difference) is corrected.

  As described above, according to the above-described embodiment, the scene analysis processing unit 41 detects the shooting state of the shot image from the luminance distribution (histogram) of the shot image and the information of the camera 10 that shot the shot image. The tone curve selection unit 42 sets a tone curve for correcting the correspondence between the input and output of the brightness of the captured image according to the captured state of the captured image, so that the captured state is also taken into account for the captured image. Effective gradation correction becomes possible.

  Further, by using the luminance distribution (histogram) of the captured image, it is possible to efficiently perform both the analysis of the captured state of the captured image and the setting of the tone curve to be applied.

  Specifically, the scene analysis processing unit 41 detects the shooting status of the shot image by detecting the luminance distribution of the shot image and the exposure information of the camera 10 that shot the shot image, for example, the exposure correction value. Accordingly, the gradation of the captured image can be corrected more effectively. That is, for example, when exposure compensation is taken in the minus direction to suppress overexposure in the photographed image, the entire photographed image including the main subject is darkly developed, but gradation correction is performed as described above. By doing so, even in such a case, it is possible to select a tone curve for realizing optimum gradation characteristics in consideration of exposure correction.

  In addition, the shooting status of the shot image detected by the scene analysis processing unit 41 may be a plurality of preset predetermined values such as a flare scene, a night flash scene, a sky blue scene, a text scene, a two-hump scene, or a small range scene. When it is determined that any one of the shooting conditions is selected, the tone curve selection unit 42 changes the information of the camera 10 from a predetermined tone curve set in advance corresponding to each of the predetermined shooting conditions set in advance. Depending on the shooting situation and the information of the camera 10, the tone curve for correcting the shot image can be fine-tuned and finely adjusted by setting the tone curve for correcting the shot image by selecting one of them. Compared with the case of calculating the adjustment parameters, the processing can be speeded up.

  In addition, the shooting status of the shot image detected by the scene analysis processing unit 41 may be a plurality of preset predetermined values such as a flare scene, a night flash scene, a sky blue scene, a text scene, a two hump scene, or a small range scene. When it is determined that none of the shooting conditions is selected, the tone curve selection unit 42 generates a tone curve for correcting the shot image based on the brightness values at at least two points different from each other in the cumulative histogram of the brightness of the shot image. By setting, it is possible to efficiently set a tone curve for correction even when it is determined that the shooting situation of the shot image is not a predetermined shooting situation set in advance. Specifically, an efficient tone curve can be created by operating at least two points, that is, the degree of lifting of one point on the low luminance side and the degree of suppression of one point on the high luminance side.

  In addition, the parameter setting unit 43 inputs the tone curve for correction set by the tone curve selection unit 42 according to the ratio of the pixels below the predetermined luminance value in the photographed image, that is, the black floating value BO. By shifting to the side, the contrast of the captured image can be improved and so-called black float can be suppressed.

  Further, the tone curve for correction set by the tone curve selection unit 42 is corrected by the parameter setting unit 43 with a ratio of pixels equal to or lower than a predetermined luminance value in the photographed image, that is, a gain value corresponding to the above-described black float value BO. By doing this, it is possible to prevent the entire captured image from becoming dark even if the correction tone curve is shifted to the high luminance input side.

  In addition, the shift amount of the tone curve and the gain value can be calculated efficiently by using the black float value BO calculated when the flare scene is determined.

  Note that the image correction apparatus according to the above-described embodiment may be incorporated in a photographing apparatus, or may be incorporated in an image processing apparatus for an image photographed by the photographing apparatus.

  Further, the processing flow may be programmed and automatically executed by a computer or the like.

  The present invention can be suitably used for, for example, a photographing apparatus such as a digital still camera or a digital video camera, and an image processing apparatus.

34 Control means having function of image correction device
41 Scene analysis processing section as detection means
42 Tone curve selection section as setting means
43 Parameter setting section as adjustment means

Claims (6)

Detecting means for detecting a photographing state of the photographed image from luminance distribution of the photographed image and information of a photographing device that photographed the photographed image;
An image correction apparatus comprising: setting means for setting a tone curve for correcting a correspondence relationship between input and output of luminance of the photographed image according to a photographing situation of the photographed image detected by the detection means. The image correction apparatus according to claim 1, wherein the detection unit detects a photographing state of the photographed image from a luminance distribution of the photographed image and exposure information of the photographing apparatus that photographed the photographed image. The setting means responds to each of the preset predetermined shooting situations when it is determined that the shooting situation of the shot image detected by the detection means is one of a plurality of preset predetermined shooting situations. 3. The tone curve for correcting the photographed image is set by selecting any one of a plurality of predetermined tone curves set in advance according to information of the photographing apparatus. Image correction device. The setting means, when it is determined that the shooting situation of the shot image detected by the detection means is not any of a plurality of predetermined shooting situations set in advance, at least two points different from each other in the cumulative histogram of luminance of the shot image The image correction apparatus according to claim 3, wherein a tone curve for correcting the photographed image is set based on a luminance value at. 2. An adjusting means for shifting the correction tone curve set by the setting means to the high-luminance input side in accordance with the ratio of pixels having a predetermined luminance value or less in the photographed image. 5. The image correction apparatus according to any one of 4 to 4. 6. The image correction according to claim 5, wherein the adjustment unit corrects the correction tone curve set by the setting unit with a gain value corresponding to a ratio of pixels equal to or less than a predetermined luminance value in the captured image. apparatus.

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