JP2008219117A - Image processor and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately perform correction, thereby allowing a digital image signal relative to the change of a light amount to have prescribed linearity without increasing a storage capacity for storing correction values even if ISO sensitivity and a gain to be set are stepless. <P>SOLUTION: An image processor includes: a digital signal correcting unit 13 for correcting a digital image signal C according to the gain of a variable gain amplifier 8. The digital signal correcting part 13 includes: a look-up table 17 for storing correction values of the digital image signal C by association with the prescribed gain; and an interpolation processing part 16 for generating the correction values of the digital image signal C based on the correction value P<SB>1</SB>on the look-up table 17 and a noncoincidence gain when the gain is the noncoincidence gain which is not coincident with the prescribed gain. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image processing apparatus and an image processing method for digitally converting and outputting photographing light obtained by photographing a subject, and more particularly to a correction method for photoelectrically converting incident light to output a digital image signal. .

  2. Description of the Related Art Conventionally, in a digital image processing apparatus such as a digital camera, an image sensor (for example, a CCD: Charge Coupled Devices) in which a plurality of photoelectric conversion elements are arranged and photoelectrically converts incident light to output an electric signal, and the electric A variable gain amplifier for amplifying the signal; and an A / D converter for A / D converting the image signal output from the variable gain amplifier to output a digital image signal. Some are configured to output an image signal.

  At this time, the photoelectric conversion characteristics and A / D conversion characteristics with respect to the amount of incident light are measured in advance, and the digital image signal is corrected so that the digital image signal with respect to the change in the amount of light has a predetermined linearity. Some have a correction table storing values (for example, see Patent Documents 1 and 2).

Some digital cameras change the gain of a variable gain amplifier according to ISO sensitivity (gain). For example, in the case of ISO sensitivity 100, 0.1 lux · sec. In the case where the signal obtained from the light quantity of 1 is an amplified signal of 1 time and ISO sensitivity is 200, 0.05 lux · sec. In the case of a double amplified signal with an ISO sensitivity of 400, the signal obtained from the light quantity of 0.025 lux · sec. The signal obtained from the amount of light is output as an amplified signal of 4 times.
Japanese Patent Laid-Open No. 2005-205211 JP 2006-180500 A

  However, since the linearity of the electric signal input from the variable gain amplifier to the A / D converter with respect to the amount of light changes according to the gain of the variable gain amplifier, there is room for further improvement in order to accurately correct the digital signal. was there. Further, if a correction value is provided for each of a plurality of ISO sensitivities (gains), there is a risk that the storage capacity for storing the correction value may increase and the productivity may be impaired, and further, the gain setting may be performed. However, it is difficult to store the correction value, and further, it is difficult to accurately correct the linearity.

  Therefore, according to the present invention, the digital image signal can be accurately corrected so as to have a predetermined linearity with respect to a change in the amount of light in accordance with a plurality of ISO sensitivities and gain settings. Provided is an image processing apparatus and an image processing method that can correct even if the gain is stepless without increasing the storage capacity for storing the correction value, and thus can reduce the circuit scale and have excellent productivity. For the purpose.

  The invention according to claim 1, which has been made to achieve such an object, is an image processing device in which a plurality of photoelectric conversion elements are arranged, photoelectric conversion of incident light is performed, and an analog image signal is output. A variable gain amplifier for amplifying the analog image signal, an A / D converter for A / D converting the image signal output from the variable gain amplifier and outputting a digital image signal, and a gain of the variable gain amplifier And a photoelectric conversion characteristic correcting means for correcting the digital image signal.

  According to the image processing apparatus of the first aspect, since the photoelectric conversion characteristic correcting unit that corrects the digital image signal according to the gain of the variable gain amplifier is provided, the light amount of each of the plurality of ISO sensitivities is determined. The digital image signal with respect to the change can be accurately corrected so as to have a predetermined linearity, and the gradation corresponding to the light amount can be generated with high accuracy.

  According to a first aspect of the present invention, in the image processing apparatus according to the second aspect, the photoelectric conversion characteristic correction unit associates the correction value of the digital image signal with the predetermined gain. The digital image signal is corrected based on the correction value and the mismatch gain on the lookup table when the gain is a mismatch gain that does not match the predetermined gain. Since the interpolation means for generating the value is provided, even if a plurality of ISO sensitivities and gains set via the variable gain amplifier are provided, the storage capacity for storing the correction value does not increase. Even if the ISO sensitivity and gain that are set are stepless, it can be corrected without increasing the storage capacity for storing the correction value, and the circuit scale can be reduced and the productivity can be reduced. Can be obtained.

  According to a second aspect of the present invention, as in the third aspect of the present invention, the look-up table includes an integer part bit string and a data string representing the digital image signal before correction, A bit string of a decimal part representing a gain is stored, and the correction value is thinned out and stored by the number of bits of the decimal part, so that the data storage capacity in the lookup table can be reduced. That is, if a bit string representing a gain is added to the data string, the data storage capacity in the lookup table increases, and therefore the data storage capacity in the lookup table can be reduced by thinning out the correction value by the number of bits representing the gain.

  Further, the thinned correction value may be obtained by performing interpolation processing using a correction value stored in the lookup table and close to the thinned correction value.

  The image processing apparatus according to any one of claims 1 to 3, wherein, as in the invention according to claim 4, the image sensor includes a color filter that passes each color of a plurality of colors, and the photoelectric conversion Since the characteristic correction means is provided for each color that has passed through the color filter, it is possible to satisfactorily obtain linearity for each color in color color generation. That is, in general, since a photoelectric conversion characteristic shifts for each color (wavelength) in the photoelectric conversion element, it is preferable to provide a photoelectric conversion characteristic correction unit for each color.

  The image processing apparatus according to any one of claims 1 to 4 is output from the image sensor between the image sensor and the correction unit, as in the invention according to claim 5. Dark current offset means for offsetting dark current is provided, and the photoelectric conversion characteristic correction means corrects a digital image signal when the black level signal output through the dark current offset means is zero. By being configured to do so, the digital image signal can be accurately corrected according to the amount of light without being affected by dark current.

  Next, according to a sixth aspect of the present invention, in the image processing method, a plurality of photoelectric conversion elements are arranged, an image pickup element that photoelectrically converts incident light and outputs an analog image signal, and the analog image signal is amplified. A variable gain amplifier, an A / D converter that A / D converts an analog image signal output from the variable gain amplifier and outputs a digital image signal, and the digital image according to a gain of the variable gain amplifier A digital image processing method using a photoelectric conversion characteristic correction unit for correcting a signal, wherein the photoelectric conversion characteristic correction unit stores a correction value of the digital image signal in association with a predetermined gain When the gain is a mismatch gain that does not match the predetermined gain, based on the correction value and the mismatch gain on the lookup table And generating a correction value of the digital image signal.

  According to the image processing method of claim 6, the photoelectric conversion characteristic correction unit uses a look-up table storing a correction value of the digital image signal in association with the predetermined gain, and the gain is By generating a correction value of the digital image signal based on the correction value and the mismatch gain on the lookup table when the mismatch gain does not match a predetermined gain, via a variable gain amplifier For each of a plurality of ISO sensitivities and gains to be set, the digital image signal with respect to the change in the light amount can be accurately corrected so as to have a predetermined linearity, and a gradation corresponding to the light amount can be generated with high accuracy.

  According to the image processing method of claim 6, even when the set ISO sensitivity (gain) is plural or stepless, the correction is performed accurately without increasing the storage capacity for storing the correction value. And an image processing apparatus with excellent productivity can be obtained.

  According to a sixth aspect of the present invention, as in the seventh aspect of the present invention, the lookup table includes an integer part bit string and a data string representing the digital image signal before correction, By storing a fractional bit string representing a gain and arranging the correction values by thinning out the number of bits corresponding to the fractional part, the data storage capacity in the lookup table can be reduced. In other words, if a data string is provided with a bit string representing a gain and a correction value is stored according to a change in gain, the data storage capacity in the lookup table increases, so the correction value is thinned out by the number of bits representing the gain. As a result, the data storage capacity in the lookup table can be reduced, and the circuit scale can be reduced, thereby improving productivity.

  Further, the thinned correction value may be obtained by performing interpolation processing using a correction value stored in the lookup table and close to the thinned correction value.

  Further, in the image processing method according to claim 6 or 7, as in the invention according to claim 8, the image sensor is provided with a color filter that passes each color of a plurality of colors, and the color filter By correcting the digital image signal for each color that has passed through, linearity for each color can be satisfactorily obtained in the generation of color colors, as in the case of the invention described in claim 4. That is, in general, the photoelectric conversion element has a deviation in the photoelectric conversion characteristics for each color (wavelength), and therefore it is preferable to provide a photoelectric conversion characteristic correction unit for each color.

  The image processing apparatus and the image processing method of the present invention use a look-up table storing a correction value of a digital image signal in association with a predetermined gain, and when the gain is a mismatch gain that does not match the predetermined gain, By generating a correction value of the digital image signal based on the correction value on the lookup table and the mismatch gain, the digital image signal with respect to the change in light amount has a predetermined linearity for each of a plurality of ISO sensitivities. Thus, it is possible to correct with high accuracy and to generate a gradation according to the amount of light with high accuracy.

  In addition, the image processing apparatus and the image processing method of the present invention can accurately correct without increasing the storage capacity for storing the correction value even if the gain set by the variable gain amplifier is plural or stepless. An image processing apparatus with excellent productivity can be obtained.

In the image processing apparatus and the image processing method of the present invention, the look-up table includes a bit string of an integer part and a bit string of a decimal part representing the gain as a data string representing the digital image signal before correction. Since the correction values are arranged by being thinned out by the number of bits of the decimal part, the data storage capacity in the lookup table can be reduced, and thus productivity can be improved. In other words, if a data string is provided with a bit string representing a gain and a correction value is stored according to a change in gain, the data storage capacity in the lookup table increases, so the correction value is thinned out by the number of bits representing the gain. Thus, the data storage capacity in the lookup table can be reduced. Further, the thinned correction value may be obtained by performing interpolation processing using a correction value stored in the lookup table and close to the thinned correction value.

  Next, an embodiment of the image processing apparatus 1 and the image processing method of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the image processing apparatus 1 of the embodiment, FIG. 2 is an explanatory diagram of exposure adjustment in the image processing apparatus 1 of the embodiment, and FIG. 3 shows a digital image signal correction method in the embodiment. FIG. 2A is a photoelectric conversion characteristic diagram, where FIG. 2A is a photoelectric conversion characteristic diagram before correction, FIG. 2B is a graph illustrating a correction value of a digital image signal, and FIG. 2C is a photoelectric conversion characteristic diagram after correction; It is.

  FIG. 4 is a diagram illustrating the configuration of the lookup table 17 in the embodiment, and FIG. 5 is a diagram illustrating photoelectric conversion characteristics that are expressed when an electric signal output from the image sensor 5 is amplified. ) Is a diagram showing photoelectric conversion characteristics before amplification, and (b) is a diagram showing photoelectric conversion characteristics when amplified with a gain twice that of (a).

FIG. 6 shows the correction value stored in the lookup table 17 when the gain set by the variable gain amplifier 8 is a mismatch gain that does not match the gain of the correction value stored in the lookup table 17 in the same embodiment. 7 is a flowchart showing a procedure for generating the correction value P ₂ based on P ₁ and the mismatch gain, FIG. 7 is a flowchart showing a procedure for correcting the pixel value in the flowchart of FIG. 6, and FIG. 8 shows the correction value P ₂ . It is explanatory drawing at the time of acquisition.

  As shown in FIG. 1, the image processing apparatus 1 is a digital camera that communicates an imaged image signal S (so-called incident light) to an external host. The image signal S is photoelectrically converted to a digital image signal. The camera module 10 that outputs as C and the image processing apparatus main body 11 that outputs the digital image signal C after converting the digital image signal C into image data D in a predetermined format in accordance with human vision.

  The camera module 10 is a lens 3, a filter (which is an infrared filter or an optical filter) 4 that removes harmful infrared rays and unnecessary spatial frequency components, etc., and an analog image signal of RGB color by photoelectrically converting the imaging signal S An image pickup device (CCD: Charge Coupled Devices) 5, an analog image signal output from the image pickup device 5, an AFE (Analog Front End) 6 that converts the image signal to a digital image signal C, and outputs the image pickup device 5, the AFE 6, and the like. A timing generator (TG: Timing Generator) 26 that is controlled by a cycle is used.

  The imaging element 5 is configured such that a plurality of photoelectric conversion elements are arranged in a matrix, and the imaging signal S is photoelectrically converted for each photoelectric conversion element to output an analog image signal. The image pickup device 5 is provided with a primary color filter composed of a Bayer array of R (red), G (green), and B (blue) in each of the plurality of photoelectric conversion elements. The amount of light that has passed is converted into an analog image signal and output. Then, an analog image signal (pixel data) associated with the photoelectric conversion element is output from the imaging element 5 to the AFE 6.

  The AFE 6 is a correlated double sampling circuit (CDS: Correlated Double Sampling) 7 that removes noise from an analog image signal output via the image sensor 5, and an analog that has been correlated double sampled by the correlated double sampling circuit 7. A digital gain signal (AGC) 8 that amplifies an image signal, an A / D converter 9 that converts an analog image signal output from the variable gain amplifier 8 into a digital image signal C, and the like. C is output to the image processing apparatus main body 11.

  At this time, the camera module 10 may be configured by using a CMOS (Complementary Metal Oxide Semiconductor) sensor instead of the imaging device 5, the correlated double sampling circuit 7, the variable gain amplifier 8, the A / D converter 9, and the like. Good.

Next, the image processing apparatus main body 11 includes a dark current subtracter (so-called dark current offset in the present invention) that subtracts the dark current that appears in the image sensor 5 from the digital image signal C output from the A / D converter 9. a means) 12 corrects the digital image signal P ₀ which is input through the dark current subtractor 12, to a digital image signal P ₂ so as to have a predetermined linearity in association with the light amount change of the image signal S digital signal correction unit (so-called, is a photoelectric conversion characteristic correcting means in the present invention) 13, an image processing unit 14, CPU (Central processing unit) 24 for converting a digital image signal _{P 2} to the image data D having a predetermined hue, A ROM (Red Only Memory) 25 and the like, and the CPU 24 follows a control program stored in the ROM 25. Each process of the image processing apparatus 1 is controlled.

  The dark current subtracter 12 offsets the dark current for each of the plurality of photoelectric conversion elements in the image sensor 5 based on the dark current adjustment result value measured in advance. Specifically, the digital image signal C output from the A / D converter 9 is stored in the ROM 25 in advance at a timing at which the amount of light is not incident on the image sensor 5, and this stored value is used as the dark current offset value.

The image processing unit 14, the exposure adjustment unit 19 for setting an exposure amount, a digital image signal a white balance (AWB) adjustment portion 20 for white adjustment of P _2, the color reproducing unit 21 to adjust the digital image signal P ₂ to a predetermined color tone The digital image signal P is correlated with the color display characteristics of the display on which the image data D is displayed, and the image quality correction unit 22 for suppressing noise and false colors contained in the digital image signal P ₂ and correcting the contour of the image. _And a gamma conversion unit 23 that performs ₂ gradation conversion.

  The exposure adjustment unit 19 sets exposure conditions such as exposure sensitivity, aperture, and shutter based on the operator's operation, and sets the gain of the variable gain amplifier 8.

Specifically, as shown in FIGS. 2A and 2B, a saturation output of a signal output from the image sensor 5 (when a predetermined amount of light is received and saturation occurs over time, In accordance with the number of bits of data processing when the A / D converter 9 performs digital conversion on the output voltage output from the image pickup device 5), the Min. G is set by an arithmetic expression of G = 20 × Log ₁₀ (Vadc / Vccd).

Also, Min. ISO sensitivity I at the time of using the gain (gain) G is obtained by an arithmetic expression of I = 120 × A ² / (Lsat × T), and the Min. Of exposure sensitivity SV is associated with the ISO sensitivity I. S is obtained by an arithmetic expression of S = Log ₂ (ISO / 3.125). Lsat is the exposure amount when the output of the image sensor 5 is saturated, A is the F number, and T is the shutter speed.

  That is, in the image processing apparatus 1, the gain set by the variable gain amplifier 8 is set according to the ISO sensitivity. Based on the ISO sensitivity, shutter speed, aperture, etc. selected by the operator, the CPU 24 cooperates with the exposure adjustment unit 26 to control the gain of the variable gain amplifier 8 and the like.

  The white balance adjustment unit 20 corrects the digital image signal C so that the white color is viewed as white. That is, the white balance adjustment unit 20 corrects the RGB signal levels so that R = G = B when an achromatic subject is imaged.

  The color reproduction unit 21 determines RGB three-color components for each pixel and generates image data. That is, as described above, the image sensor 5 includes a color filter composed of a Bayer array of three colors R (red), G (green), and B (blue) in association with pixels, and a signal output from each pixel corresponds to each color. Since there is only information for one color that has passed through the filter, the color reproduction unit 21 determines the RGB three-color components for each pixel by interpolating the signal of each pixel, and generates image data. At this time, the spectral characteristics of the color filter are measured in advance, and a color interpolation table for generating three color components for each pixel to be interpolated in association with the measurement result and pixel signals around the pixel to be interpolated is a ROM 25. Is remembered.

  Further, the color reproduction unit 21 corrects the image data subjected to white balance by multiplying the coefficient stored in advance in the ROM 25 according to the light source irradiated to the subject, and has an optimum color tone. Generate image data.

  The image quality correction unit 22 performs image quality correction based on the lens aberration correction value stored in the ROM 25. Specifically, the lens aberration is obtained as a function of the image height and the aberration at the image plane where the distortion aberration and the chromatic aberration are obtained. The aberration characteristic value is obtained for each pixel, and a correction value for canceling this aberration is stored in the ROM 25. ing.

  Further, the image quality correction unit 22 performs correction such as noise reduction, false color reduction, and image edge enhancement included in each pixel.

  The γ conversion unit 23 performs γ conversion by associating the digital image signal output from the image quality correction unit 22 with the color display characteristics of the display on which the image data D is displayed. At this time, the γ conversion coefficient is stored in the ROM 25 in advance.

Next, the digital signal correction unit 13 acquires the correction value P ₁ stored in the lookup table (correction table) 17 for each image data P ₀ input via the camera module 10 and the dark current subtracter 12. The correction value acquisition unit 15 to perform, the look-up table 17 storing the correction value P ₁ of the digital image signal P ₀ in association with the predetermined gain, and the gain set by the variable gain amplifier 9 do not match the predetermined gain In the case of the mismatch gain, the interpolation processing unit 16 and the like that generate the correction value P ₂ of the digital image signal P ₀ based on the correction value P ₁ and the mismatch gain on the lookup table 17 are configured.

  Then, as shown in FIG. 3, the digital signal correction unit 13 obtains a correction value (b) and corrects the photoelectric conversion characteristic (a) of the digital image signal before correction to obtain a predetermined linearity. The photoelectric conversion characteristic (c) is obtained.

As shown in FIG. 4, the look-up table 17 represents a 12-bit integer part bit string and the gain of the variable gain amplifier 8 as a data string representing a pixel value (digital image signal P ₀ ) before correction. A decimal bit string is provided, and correction values (Data [0] to Data [4095]) corresponding to the digital image signal P ₀ before correction are stored. Further, a fractional bit number setting unit 18 for setting the number of fractional bits in the data string is provided in the digital signal correction unit 13, and a decimal part is supplied from the fractional bit number setting unit 18 to the correction value acquisition unit 15 and the interpolation processing unit 16. A signal representing the number of bits SB is input.

Look-up table 17, the data is represented by binary numbers, the gain set by the variable gain amplifier 8 is corrected value P ₁ at the time is a predetermined value are stored in association with the predetermined gain.

  Further, the image processing apparatus 1 according to the present embodiment can switch the ISO sensitivity to 100, 200, 400, 800, 1600, and the lookup table 17 sets the ISO sensitivity 100 as a predetermined gain, and sets each ISO sensitivity. The decimal bit number to be expressed is stored, and the decimal bit number is 0 bit when the ISO sensitivity is 100, 1 bit when the ISO sensitivity is 200, 2 bits when the ISO sensitivity is 400, and 3 when the ISO sensitivity is 800. When the bit and ISO sensitivity is 1600, it is represented by 4 bits. In this embodiment, in order to switch from ISO sensitivity 100 to 1600, the number of decimal bits is 4 bits.

The correction value P _1, depending on the number of bits of the fractional part is stored is thinned. That is, when the ISO sensitivity is 200, the number of bits in the decimal part is 1, and at this time, the correction value is thinned out by 2/1 and stored.

Since the linearity of the digital image signal P ₀ changes with respect to the amount of light according to the gain of the variable gain amplifier 8, the digital signal correction unit 13 performs correction via the interpolation processing unit 16 when there is a mismatch gain. to generate a value _{P 2.} That is, when the photoelectric conversion characteristic at the predetermined gain (ISO is 100) shown in FIG. 5A is set to a double gain (ISO is 200), it changes as shown in FIG. 5B. To do. Therefore, when the gain (gain) set by the variable gain amplifier 8 is a mismatch gain, the interpolation processing unit 16 corrects the correction value P ₂ based on the correction value P ₁ stored in the lookup table 17 and the mismatch gain. Is generated.

  Further, as described above, since the image sensor 5 outputs RGB three-color image signals, the lookup table 17 shown in FIG. 4 is provided for each of the RGB colors.

Next, a procedure for correcting the digital image signal P ₀ and generating the correction value P ₂ will be described with reference to FIGS. 6, 7, and 8. This procedure is executed by giving a command signal to each functional unit based on a program stored in the ROM 25 by the CPU 24. Moreover, S in FIG.6 and FIG.7 represents the step.

  First, this procedure starts when an activation signal is input to the image processing apparatus 1 by the operator.

Next, to obtain the address of a pixel of the digital image signal _{P 0} which is input to the digital signal correction unit 13 via the AFE6 moved to S110, then it proceeds to S120. The address is associated with each pixel in the Bayer array, and includes any color information of RGB together with the position information of the input pixel.

  Next, the process proceeds to S120, the lookup table 17 associated with each color of RGB is acquired, and then the process proceeds to S130. The lookup table 17 is provided for each color of RGB.

Next, the process proceeds to S130, the gain set by the variable gain amplifier 8 is acquired, and the process proceeds to S140. Next, in S140, the digital image signal P ₀ (pixel value) is acquired, and then the process proceeds to S150.

Then, in S150, based on the acquired in S130 the digital image signals _{P 1} (pixel value) obtained in (gain) and S140, and generates a correction value _{P 2} of the digital image signal _{P 0.}

Correction of the digital image signal _{P 0} of S150 is performed by the procedure of FIG. First, in S151, an index value (Index) on the lookup table 17 is calculated using an arithmetic expression of Index = rounddown (P * 1 / Gain) -1. Gain in this equation is a multiplication factor of the gain set by the variable gain amplifier 8 with respect to a predetermined gain (gain) associated with the correction value of the lookup table, and Index is the input pixel value P It is obtained by reducing the gain by ₀ by the multiplication factor of the gain.

Next, the process proceeds to S152, and the four correction values D0, D1, D2, D3, and D4 in the lookup table 17 are obtained using the Index and the decimal bit number SB of the lookup table 17. At this time, D0 is (Index + 0) * 2 ^(-SB) , D1 is (Index + 1) * 2 ^(-SB) , D2 is (Index + 2) * 2 ^(-SB) , D3 is (Index + 3) * 2 ^(-SB) (Index + 1) represents the correction value stored next to Index in the lookup table 17, (Index + 2) represents the correction value stored next to (Index + 1), and (Index + 3) represents (Index + 2). Next, the stored correction value is represented.

Then, in S153, the interpolation coefficients for the correction value _{P 2} is calculated in the digital image signal _{P 0} inputted fx0, fx1, calculates the fx2, fx3 like. At that time, first, a coefficient A and a maximum integer [A] not exceeding A are obtained using an arithmetic expression of A = (P ₀ * 1 / Gain), and [A] is subtracted from A to obtain a difference dx. calculate.

Then, using the calculated dx, fx0 = 4-8 * (1 + dx) + 5 * (1 + dx) ² − (1 + dx) ³ , fx1 = 1−2 * (0 + dx) ² + (0 + dx) ³ , fx2 = 1 ^{-2 * (1-dx) 2} + (1-dx) 3, fx3 = 4-8 * (2-dx) + 5 * (2-dx) 2 - (2-dx) 3, using a calculation formula Interpolation coefficients fx0 to fx3 are obtained.

Then, the flow proceeds to S154, the correction value _{P 2} of the digital image signals _{P 0, P 2 = round (} ((fx0 * D0) + (fx1 * D1) + (fx2 * D2) + (fx3 * D3)) * Gain ).

That is, in this embodiment, the pixel value P ₀ at the time of mismatch gain is obtained by scaling down to an index at a predetermined gain in S151, and then the correction value of the pixel value in the predetermined gain table is obtained through S152 and S153. Then, in S154, a correction value at a predetermined gain is calculated by cubic interpolation, and thereafter, the correction value calculated by the cubic interpolation by the amount reduced from the mismatch gain to the predetermined gain is calculated. increasing multiplied seeking pixel value P _2.

Then, move to S160 of the flowchart of FIG. 6, it is judged whether there is input of the next digital image signals P _0, when the next input is not (No), the process is terminated, the next If there is an input (Yes), the process proceeds to S110, and S110 to S160 are repeated until there is no next input (No) in S160.

  As described above, according to the image processing apparatus 1 described in the embodiment, the digital signal correction unit 13 that corrects the digital image signal C according to the gain of the variable gain amplifier 8 is provided. Thus, the digital image signal corresponding to the change in the light amount can be accurately corrected so as to have a predetermined linearity for each of a plurality of ISO sensitivities, and the gradation of the digital image signal can be accurately generated according to the light amount.

Further, according to the image processing apparatus 1 described in the embodiment, the digital signal correction unit 13 stores a correction value P ₁ of the digital image signal P ₀ in association with a predetermined gain (ISO is 100). A correction value P of the digital image signal pixel value P ₀ based on the correction value P ₁ and the mismatch gain of the lookup table 17 when the gain is a mismatch gain that is configured by the up table 17 and the gain does not match the predetermined gain. ₂ is generated, the storage capacity for storing the correction value P ₁ is increased even if a plurality of ISO sensitivities and gains set via the variable gain amplifier 8 are provided. it no further, even the ISO sensitivity and the gain set is a stepless, digital image signal pixel values P ₀ without increasing the storage capacity for storing the correction value P ₁ Positive can, by extension may improve productivity to shrink the circuit size.

Further, according to the image processing apparatus 1 described in the embodiment, the look-up table 17 includes an integer part bit string and a decimal part bit string representing gain as data strings representing the digital image signal P ₀ before correction. is, the correction value P ₁ is, by being arranged are thinned by the number of bits of the decimal part, it is possible to reduce the data storage capacity of the look-up table 17. That is, since the addition of the bit string representing the gain data string data storage capacity in the look-up table 17 is large, the look-up table 17 by storing in only decimating the correction value P ₁ min of the number of bits representing the gain The storage capacity can be reduced.

  Further, according to the image processing apparatus 1 described in the embodiment, the image sensor 5 is provided with a color filter that passes for each color of RGB, and the digital signal correction unit 13 is provided for each color that has passed through the color filter. Thus, the linearity of each color can be favorably obtained in the generation of the color color.

  In addition, the image processing apparatus 1 described in the embodiment includes a dark current subtracter 12 that offsets the dark current output from the image sensor 5 between the image sensor 5 and the digital signal correction unit 13, so that the digital signal Since the correction unit 13 is configured to perform correction on the digital image signal C output when the black level signal output from the dark current subtractor 12 is zero, the influence of the dark current is obtained. The digital image signal C can be corrected with high accuracy according to the amount of light.

The image processing apparatus 1 of the present invention, also the gain set by the variable gain amplifier 8 is a multiple or steplessly, be accurately corrected without increasing the storage capacity for storing the correction value P ₁ , Improve productivity.

As mentioned above, although one Example of this invention was described, this invention is not limited to the said Example, It can take various aspects. For example, the present invention is the correction value P ₂ as shown in S151~S154 of this example was calculated by cubic interpolation, is not limited to cubic interpolation. In the present invention, the predetermined gain is not limited to the ISO sensitivity, but may be a predetermined gain set by the variable gain amplifier 8. Further, the present invention is not limited to the case where the pixel signal output from the image sensor 5 is output via the primary color filter of the RGB Bayer array, but is output via the complementary color filter. There may be.

It is a block diagram showing the structure of the image processing apparatus of the Example. It is explanatory drawing of exposure adjustment of the image processing apparatus in the Example. FIG. 3 is a photoelectric conversion characteristic diagram showing a digital image signal correction method in the embodiment, where (a) is a photoelectric conversion characteristic diagram before correction, and (b) is a correction value of a pixel value in (a). (C) is a photoelectric conversion characteristic diagram after correction. It is a figure showing the structure of the look-up table in the Example. In the same Example, it is a figure showing the photoelectric conversion characteristic which appears when the electric signal output from the image pick-up element is amplified, Comprising: (a) is a figure showing the photoelectric conversion characteristic before amplification, (b) is (a) It is a figure showing the photoelectric conversion characteristic at the time of amplifying with a gain of 2 times with respect to. It is a flowchart showing the procedure which produces | generates a correction value based on the correction value and mismatch gain on a lookup table. 7 is a flowchart illustrating a procedure for correcting a pixel value in the flowchart of FIG. 6. FIG. 8 is an explanatory diagram for obtaining a correction value.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image processing apparatus, 3 ... Lens, 4 ... Filter, 5 ... Image pick-up device, 6 ... AFE (Analog Front End), 7 ... Correlated double sampling circuit, 8 ... Variable gain amplifier (AGC: Automatic Gain Control), 9 A / D converter, 10 Camera module, 11 Image processing device main body, 12 Dark current subtractor, 13 Digital signal correction unit, 14 Image processing unit, 15 Correction value acquisition unit, 16 Interpolation process , 17 ... Correction table (lookup table), 18 ... Decimal bit number setting unit, 19 ... Exposure adjustment unit, 20 ... White balance adjustment unit, 21 ... Color reproduction unit, 22 ... Image quality correction unit, 23 ... γ conversion unit , 24 ... CPU, 25 ... ROM, 26 ... timing generator.

Claims (8)

An image sensor in which a plurality of photoelectric conversion elements are arranged and photoelectrically converts incident light to output an analog image signal;
A variable gain amplifier for amplifying the analog image signal;
An A / D converter for A / D converting an analog image signal output from the variable gain amplifier to output a digital image signal;
Photoelectric conversion characteristic correction means for correcting the digital image signal according to the gain of the variable gain amplifier;
An image processing apparatus comprising: The photoelectric conversion characteristic correcting means is
It is constituted by a look-up table that stores the correction value of the digital image signal in association with the predetermined gain.
Interpolation means for generating a correction value for the digital image signal based on the correction value and the mismatch gain on the lookup table when the gain is a mismatch gain that does not match the predetermined gain. Yes,
An image processing apparatus. The lookup table includes
As a data string representing the digital image signal before correction, a bit string of an integer part and a bit string of a decimal part representing the gain are stored,
The correction value is stored by being thinned by the number of bits of the decimal part,
The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus. The image sensor is provided with a color filter that passes each color of a plurality of colors, and the photoelectric conversion characteristic correction means is provided for each color that has passed through the color filter.
The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus. Between the image sensor and the correction unit, a dark current offset unit for offsetting a dark current output from the image sensor is provided,
The photoelectric conversion characteristic correction unit is configured to perform correction on a digital image signal that is output through the dark current offset unit and a black level signal is zero.
The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus. An image sensor in which a plurality of photoelectric conversion elements are arranged and photoelectrically converts incident light to output an analog image signal;
A variable gain amplifier for amplifying the analog image signal;
An A / D converter for A / D converting an analog image signal output from the variable gain amplifier to output a digital image signal;
Photoelectric conversion characteristic correction means for correcting the digital image signal according to the gain of the variable gain amplifier;
A digital image processing method using
The photoelectric conversion characteristic correcting means is
Using a lookup table storing correction values of the digital image signal in association with the predetermined gain,
When the gain is a mismatch gain that does not match the predetermined gain, a correction value of the digital image signal is generated based on the correction value and the mismatch gain on the lookup table. Image processing method. The lookup table includes
As a data string representing the digital image signal before correction, a bit string of an integer part and a bit string of a decimal part representing the gain are stored,
The correction value is thinned out by the number of bits of the decimal part and stored.
The image processing method according to claim 6. Using a color filter that allows each color of each of the plurality of colors to pass through the imaging device, and correcting the digital image signal for each color that has passed through the color filter;
The image processing method according to claim 6 or 7, wherein:

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