JP2008301341A - Image signal processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image signal processing apparatus capable of reducing memory capacitance and computational complexity and performing gradation correction processing while preventing color saturation and hue change. <P>SOLUTION: An image signal processing apparatus comprises a maximum signal value selecting section 2 for selecting a maximum signal value from among signal values of a plurality of color signals constituting an image signal; a conversion magnification determining section which determines a conversion magnification for converting a gradation level of a color signal having the maximum signal value based on a conversion property specifying the conversion magnification in gradation correction processing for the image signal; and a correction section 5 which performs gradation correction processing on the plurality of color signals on the basis of the conversion magnification operated by the conversion magnification determining section. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image signal processing apparatus that performs gradation correction processing.

  As shown in FIG. 8, the conventional image signal processing apparatus includes a correction value calculation circuit 60 and a gradation correction circuit 61 (see, for example, Patent Document 1).

The correction value calculation circuit 60 calculates a correction value k based on the input luminance signal Y and the input color difference signals Cr and Cb, and outputs the correction value k to the gradation correction circuit 61. The gradation correction circuit 61 is obtained by multiplying the input luminance signal Y and the input color difference signals Cr and Cb by the correction value k output from the correction value calculation circuit 60, as shown in the following equation (1). The corrected values are output as corrected luminance signal Yo and color difference signals CrO, CbO.
Yo = k · Y
CrO = k · Cr
CbO = k · Cb (1)

  Thus, by multiplying the luminance signal Y and the color difference signals Cr and Cb by the same correction value k, the ratio between the color signals is prevented from changing, and when the signal levels of the color difference signals Cr and Cb are large, The correction error of the luminance signal Y can be reduced.

  FIG. 9 shows a detailed configuration example of the correction value calculation circuit 60 of the conventional image signal processing apparatus. The histogram generation circuit 71 of the correction value calculation circuit 60 generates a histogram of the input luminance signal Y (frequency distribution with respect to each signal level of the luminance signal Y) for each image and outputs it to the correction value LUT generation circuit 72.

  The correction value LUT generation circuit 72 of the correction value calculation circuit 60 is based on the histogram of the luminance signal Y input from the histogram generation circuit 71, and the signal levels of the luminance signal Y and the color difference signal C (the color difference signal Cr and the color difference signal Cb are large). The correction value LUT indicating the correction value k for the combination of the two color difference signals) is generated, and the correction value LUT is stored in the correction value LUT memory 74.

Specifically, the correction value LUT generation circuit 72 accumulates the histogram of the luminance signal Y input from the histogram generation circuit 71, accumulates the frequency for each signal level of the histogram, and represents the curve A shown in FIG. Generate a cumulative histogram. Further, in consideration of Weber-Fechina's law regarding human visual characteristics (the law that the amount of human sense is proportional to the logarithm of the stimulus intensity), the correction value LUT generation circuit 72 approximates the curve A to a predetermined logarithmic curve. A curved curve B is obtained. In FIG. 10, the horizontal axis represents the input luminance level Y, and the vertical axis represents the luminance signal level Ye in which the dynamic range of the corrected luminance signal is adapted to the cumulative frequency. The logarithmic curve B is given by the following equation (2). Here, a and b are predetermined coefficients.
Ye = a · log (Y) + b (2)

Next, the correction value LUT generation circuit 72 indicates a correction value k corresponding to the combination of the luminance signal Y and the color difference signal C expressed by the following equation (3) based on Ye calculated by the equation (2). A correction value LUT is generated and stored in the correction value LUT memory 74.
k = f (Y, C) = (Ye / Y) ^ {(Cmax−C) / Cmax} (3)
Here, Cmax is the maximum value of the signal level that can be taken by the color difference signal C, and x ^ y represents x to the power of y.

  The comparator 73 of the correction value calculation circuit 60 compares the signal levels of the input color difference signals Cr and Cb and outputs the higher signal level to the correction value LUT memory 74 as the color difference signal C. The correction value LUT memory 74 stores the correction value LUT from the correction value LUT generation circuit 72. Further, the correction value LUT memory 74 compares the combination of the input luminance signal Y and the color difference signal C with the correction value LUT, acquires the corresponding correction value k, and outputs it to the gradation correction circuit 61.

  Since the combination of the luminance signal Y and the color difference signal C and the correction value k have the relationship shown in the above equation (3), for example, when the signal level of the color difference signal C is the maximum value Cmax, the correction value k = 1. Therefore, the input luminance signal Y and the color difference signals Cr and Cb are multiplied by k = 1, and the input luminance signal Y and the color difference signals Cr and Cb are directly used as the luminance signal Yo and the color difference signals CrO and CbO. Is output as Therefore, it is possible to prevent the hue from changing due to an overflow in the corrected color difference signals CrO and CbO.

For example, when the signal levels of the color difference signals Cr and Cb are both 0 and the color difference signal C is the minimum value (= 0) (when the pixel is an achromatic color), the expression (3) is Equation (4) is obtained, and the corrected luminance signal Yo = Ye.
k = Ye / Y (4)
In other words, the gradation correction (curve B in FIG. 10) in consideration of human visual characteristics is applied to the achromatic pixel as it is.
Japanese Patent Laid-Open No. 2002-135584

  However, in the conventional image signal processing apparatus, although the hue change and the color saturation are prevented by the configuration using the correction value LUT, the correction value LUT memory 74 is a combination of the input luminance signal Y and the color difference signal C. The dimension correction value LUT is stored. This two-dimensional correction value LUT has a problem that a very large memory capacity is required.

  Further, in the conventional image signal processing apparatus, since it is necessary to obtain the correction value k corresponding to the combination of the luminance signal Y and the color difference signal C in order to generate the correction value LUT, the correction value LUT generation circuit 72 generates the luminance signal. By calculating the number of combinations of Y and the color difference signal C, there is a problem that the amount of calculation becomes very large.

  The present invention has been made in order to solve the conventional problems, and has a configuration capable of reducing the memory capacity and the calculation amount, and performs gradation correction processing that suppresses hue change and does not cause color saturation. An object of the present invention is to provide an image signal processing apparatus capable of

  An image signal processing apparatus according to the present invention includes a maximum signal value selection unit that selects a maximum signal value from signal values of a plurality of color signals constituting an image signal, and a conversion characteristic that defines a conversion magnification in gradation correction processing for the image signal. A conversion magnification determining unit that determines a conversion field rate for converting the gradation level of the color signal having the maximum signal value, and a plurality of color signals based on the conversion magnification determined by the conversion magnification determining unit And a correction unit that performs the tone correction process.

  According to this configuration, the gradation level conversion magnification of the color signal having the maximum signal value is determined, and the gradation levels of the plurality of color signals are corrected based on the determined conversion magnification. The gradation correction process can be performed while preventing the change. Since the gradation level is adjusted with respect to the color signal, a two-dimensional correction value LUT based on a combination of the luminance signal and the color difference signal becomes unnecessary, and the memory capacity and the calculation amount can be reduced.

  An image signal processing apparatus of the present invention includes a histogram generation unit that generates a histogram of maximum signal values selected for each pixel by a maximum signal value selection unit, and a conversion characteristic generation unit that generates conversion characteristics based on the histogram. The conversion magnification determination unit determines the conversion magnification based on the conversion characteristic generated by the conversion characteristic generation unit.

  According to this configuration, a histogram is generated using the maximum signal value selected for each pixel, and the gradation level is adjusted based on the histogram. Appropriate gradation correction processing can be performed by suppressing the bias toward the low luminance side and preventing generation of conversion characteristics that excessively emphasize the gradation level on the low luminance side.

  In the image signal processing apparatus of the present invention, the conversion magnification determining unit performs nonlinear conversion on the gradation level of the color signal having the maximum signal value. According to this configuration, it is possible to perform gradation conversion using conversion characteristics suitable for adjusting image contrast or image brightness.

  In the image signal processing apparatus of the present invention, the plurality of color signals are three color signals in the RGB format. According to this configuration, in the gradation level correction for RGB color signals, the application of the present invention eliminates the need for a two-dimensional correction value LUT based on a combination of a luminance signal and a color difference signal, thereby reducing the memory capacity and calculation amount. be able to. Then, the saturation of the color signal and the hue change are corrected by correcting the gradation level of the three color signals in the RGB format based on the conversion magnification of the gradation level of the color signal having the maximum signal value among the RGB signals. It is possible to perform gradation correction processing while preventing it.

  The image signal processing method of the present invention selects the maximum signal value from the signal values of a plurality of color signals constituting the image signal, and determines the maximum signal based on the conversion characteristic that defines the conversion magnification in the gradation correction processing for the image signal. A conversion magnification for converting a gradation level of a color signal having a value is determined, and gradation correction processing of a plurality of color signals is performed based on the determined conversion magnification.

  According to this configuration, the gradation level conversion magnification of the color signal having the maximum signal value is determined, and the gradation levels of the plurality of color signals are corrected based on the determined conversion magnification. The gradation correction process can be performed while preventing the change. Since the gradation level is adjusted with respect to the color signal, the two-dimensional correction value LUT based on the combination of the luminance signal and the color difference signal becomes unnecessary, and the memory capacity and the calculation amount can be reduced.

  The present invention provides an image signal processing device that can reduce the memory capacity and the amount of calculation, and that can perform tone correction processing that suppresses hue change and does not cause color saturation.

(First embodiment)
Hereinafter, an image signal processing apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  An image signal processing apparatus 1 according to a first embodiment of the present invention is shown in FIG. The image signal processing apparatus 1 includes a maximum value selection unit 2, a gradation level conversion unit 3, a conversion magnification calculation unit 4, and a correction unit 5. The image processing device 1 is provided in an imaging device such as a digital camera, for example, and receives an image signal generated by the imaging unit.

  The maximum value selection unit 2 selects the maximum signal value from the signal values of a plurality of color signals constituting the image signal. Specifically, the plurality of color signals are RGB format signals as shown in FIG. The maximum value selection unit 2 inputs RGB color signals for each pixel, and selects a signal having the maximum signal value among the R signal, the G signal, and the B signal.

  As shown in FIG. 1, the gradation level conversion unit 3 and the conversion magnification calculation unit 4 constitute a conversion magnification determination unit of the present invention. The conversion magnification determination unit is configured to calculate a conversion magnification for converting the gradation level of the color signal having the maximum value signal selected by the maximum value selection unit 2, and is thus applied to the gradation correction of the RGB signal. Determine the conversion magnification to be done.

  The gradation level conversion unit 3 converts the gradation level of the color signal input from the maximum value selection unit 2 based on predetermined conversion characteristics. The conversion characteristics are stored in a conversion characteristic storage unit configured by a memory (not shown). For example, the gradation level conversion unit 3 performs nonlinear conversion on the color signal input from the maximum value selection unit 2 with reference to the LUT in order to adjust the contrast of the image or the brightness of the image. This LUT may be a one-dimensional table for color signal values.

  The conversion magnification calculation unit 4 inputs a signal value before gradation level conversion from the maximum value selection unit 2 and inputs a signal value after gradation level conversion from the gradation level conversion unit 3. Then, the conversion magnification calculator 4 calculates the conversion magnification in gradation level conversion by dividing the signal value after gradation level conversion by the signal value before gradation level conversion.

  The correction unit 5 performs gradation correction processing for a plurality of color signals based on the conversion magnification in gradation level conversion. Specifically, as illustrated in FIG. 1, the correction unit 5 includes multipliers 11, 12, and 13, and the multipliers 11, 12, and 13 respectively receive R signal, G signal, and B signal, A conversion magnification is input from the conversion magnification calculator 4. The multipliers 11, 12, and 13 multiply the R signal, the G signal, and the B signal by the conversion magnification, respectively, perform gradation correction processing, and output the output signals Rout, Gout, and Bout, respectively.

  Next, the operation of the image signal processing apparatus 1 according to the present embodiment shown in FIG. 1 will be described using a specific example.

  First, as shown in FIG. 1, an image signal in RGB format is input to the image signal processing apparatus 1. This RGB format image signal is composed of an R signal, a G signal, and a B signal for each pixel. For example, each of the R signal, the G signal, and the B signal is an 8-bit digital signal.

  The maximum value selection unit 2 selects the maximum signal value for each pixel from the input RGB signals. For example, as shown in FIG. 2, in a certain pixel, the signal value of the R signal is 180 (R = 180), the signal value of the G signal is 150 (R = 150), and the signal value of the B signal is 30 (B = 30). ), Since the signal value of the R signal is the maximum, in this pixel, the maximum value selection unit 2 selects the maximum signal value R = 180.

  The gradation level conversion unit 3 performs nonlinear conversion on the maximum signal value selected by the maximum value selection unit 2. In this case, the gradation level conversion unit 3 may perform nonlinear conversion using a conversion table such as an LUT, a broken line approximation, or an arithmetic circuit for a nonlinear function. Further, the conversion characteristics of the non-linear conversion may be defined in advance, or may be defined based on characteristics such as a histogram corresponding to the input image signal. For example, when the conversion characteristics as shown in FIG. 3 are used as the conversion table, the maximum signal value R = 180 input from the maximum value selection unit 2 to the gradation level conversion unit 3 is nonlinear by the gradation level conversion unit 3. After the conversion, the gradation level conversion unit 3 outputs the signal value 220 after the gradation level conversion to the conversion magnification calculation unit 4.

  The conversion magnification calculator 4 calculates the conversion magnification in gradation level conversion by dividing the signal value after gradation level conversion by the signal value before gradation level conversion. For example, as shown in FIG. 2, when the signal value after gradation level conversion is 220 and the signal value before gradation level conversion is 180, the conversion magnification is calculated as 220/180 = 1.22 times. .

In the multipliers 11, 12, and 13, the correction unit 5 receives the conversion magnification calculated by the conversion magnification calculation unit 4 and multiplies the R signal, the G signal, and the B signal by the conversion magnification. For example, as shown in FIG. 2, when the conversion magnification is 1.22, the correction unit 5 multiplies R = 180, G = 150, and B = 30 by the conversion magnification 1.22, respectively, Output signals Rout, Gout, and Bout shown in 5) are output.
Rout = R × conversion magnification = 180 × 1.22 = 220
Gout = G × conversion magnification = 150 × 1.22 = 183
Bout = B × conversion magnification = 30 × 1.22 = 37 (5)

  As described above, the image signal processing apparatus 1 according to the present embodiment inputs a color signal in RGB format, the maximum signal value is selected by the maximum value selecting unit 2, and the selected maximum value signal is The gradation level conversion unit 3 performs nonlinear conversion, and the conversion magnification calculation unit 4 calculates the conversion magnification. Then, the correction unit 5 performs gradation correction processing by multiplying the calculated conversion magnification by the R signal, G signal, and B signal, respectively.

  According to the present embodiment, since the gradation level is adjusted with respect to the color signal, the two-dimensional correction value LUT based on the combination of the luminance signal and the color difference signal becomes unnecessary, and the memory capacity and the calculation amount can be reduced. .

  Further, according to the present embodiment, the gradation levels of a plurality of color signals are corrected based on the conversion magnification of the gradation level of the color signal having the maximum signal value, thereby preventing color saturation and hue change. A gradation correction process can be performed. That is, by selecting the maximum signal value that is most likely to be saturated among RGB signals, performing nonlinear conversion so that the maximum signal value is not saturated, and multiplying all color signals by the conversion magnification of the maximum signal value, All color signals after conversion can be kept within a predetermined dynamic range without being saturated. Further, by multiplying all the color signals by the calculated conversion ratio, the ratio of R: G: B can be maintained, and gradation correction processing can be performed while preventing the hue change of the image signal. .

  Further, according to the present embodiment, the gradation level conversion unit 3 performs nonlinear conversion on the gradation level of the color signal having the maximum signal value, which is suitable for adjusting the contrast of the image or the brightness of the image. Conversion characteristics can be obtained.

(Second Embodiment)
FIG. 4 shows an image signal processing apparatus 10 according to the second embodiment of the present invention. In addition, about the structure similar to 1st Embodiment, since it attaches | subjects the same code | symbol and bears the same function and operation | movement, description is abbreviate | omitted.

  The image signal processing device 10 is different from the image signal processing device 1 according to the first embodiment in that it includes a histogram generation unit 6 and a conversion characteristic generation unit 7. The histogram generation unit 6 generates a histogram of the maximum signal value selected for each pixel by the maximum signal value selection unit 2. Specifically, as shown in FIG. 4, the maximum signal value of each pixel is input from the maximum signal value selection unit 2 to the histogram generation unit 6, and the histogram generation unit 6 inputs the maximum signal value of each pixel. Is measured for each gradation level, and a histogram of the maximum value signal is generated.

  The conversion characteristic generation unit 7 generates a conversion characteristic based on the histogram generated by the histogram generation unit 6. Specifically, as shown in FIG. 4, the histogram of the maximum value signal generated by the histogram generation unit 6 is input to the conversion characteristic generation unit 7, and the conversion characteristic generation unit 7 converts the input histogram into gradations. A cumulative histogram is generated for each level, a conversion characteristic is generated from the cumulative histogram, and the generated conversion characteristic is output to the gradation level conversion unit 3 of the conversion magnification determination unit. This conversion characteristic is stored in a conversion characteristic storage unit including a memory (not shown), and used for determination of conversion magnification, more specifically, processing in the gradation level conversion unit 3.

  Next, the operation of the image signal processing apparatus 10 according to the present embodiment shown in FIG. 4 will be described using a specific example. First, the histogram generation unit 6 aggregates the frequency of the maximum signal value selected for each pixel by the maximum value selection unit 2 to generate a histogram of the maximum signal value. For example, as illustrated in FIG. 5, the histogram generation unit 6 aggregates the frequencies of the maximum signal values in the sections 1 to 16 for the pixels for one image and creates a histogram. Note that the pixels for one image may be all pixels in one image, or pixels thinned out in one image. In the histogram of FIG. 5, the input signal is 8 bits (256 gradations), and the signal level is divided into 16 sections of sections 1 to 16 as sections of the histogram, and section 1 is a signal level of 0 to 15 The section 2 has a signal level of 16 to 31 and the section 16 has a signal level of 240 to 255. Further, in the histogram of FIG. 5, the frequencies N in the sections 1, 2, 3,... 16 are N1, N2, N3,.

Next, the conversion characteristic generation unit 7 generates a cumulative histogram from the histogram generated by the histogram generation unit 6. For example, the conversion characteristic generation unit 7 generates a cumulative histogram as shown in FIG. 6 from the histogram shown in FIG. In this case, in the cumulative histogram of FIG. 6, the cumulative frequencies S of sections 1, 2, 3... 16 are S1, S2, S3. Since the cumulative frequency S of the cumulative histogram of FIG. 6 is obtained by accumulating the frequency N of the histogram of FIG. 5 for each section, the cumulative frequency S is expressed by the following equation (6).
S1 = N1
S2 = S1 + N2 = N1 + N2
S3 = S2 + N3 = N1 + N2 + N3
...
S16 = S15 + N16 = N1 + N2 + N3... + N16 (6)

  The conversion characteristic generation unit 7 divides the cumulative histogram of 16 sections as shown in FIG. 6 by the total number of histograms (equal to the cumulative histogram of section 16) and normalizes them, so that P1, P2, P3 shown in FIG. ... 16 conversion characteristics composed of P16 are obtained. Then, the conversion characteristic generation unit 7 generates conversion characteristics of all signal levels by linearly interpolating between the representative points with these 16 points as representative points.

  As described above, the cumulative histogram shown in FIG. 6 is generated from the histogram shown in FIG. 5, and the conversion characteristics shown in FIG. 7 are generated based on the cumulative histogram. In the histogram of FIG. 5, when the frequency of each section is extremely small or extremely large, the slope of the obtained conversion characteristic is too small or too large. Therefore, in order to suppress an excessive or excessive slope of the conversion characteristic, the conversion characteristic generation unit 7 generates an appropriate cumulative histogram by setting an upper limit or a lower limit on the histogram of each section as shown in FIG. Good.

  Then, as shown in FIG. 4, the conversion characteristic generation unit 7 outputs the generated conversion characteristic to the gradation level conversion unit 3, and the gradation level conversion unit 3 converts the conversion generated by the conversion characteristic generation unit 7. Based on the characteristics, the maximum signal value selected by the maximum value selector 2 is nonlinearly transformed. The conversion magnification calculation unit 4 calculates the conversion magnification in the gradation level conversion unit 3 from the signal values before and after nonlinear conversion based on the conversion characteristics generated by the conversion characteristic generation unit 7. The correction unit 5 performs nonlinear conversion on the R signal, the G signal, and the B signal, respectively, using the conversion magnification calculated based on the conversion characteristic generated by the conversion characteristic generation unit 7.

  As described above, the image signal processing apparatus 10 according to the present embodiment inputs a color signal in RGB format, the maximum signal value is selected by the maximum value selector 2, and the histogram of the maximum value signal is selected by the histogram generator 6. A conversion characteristic is generated from the image data, a non-linear conversion is performed by the gradation level conversion unit 3 based on the conversion characteristic, and a conversion magnification is calculated by the conversion magnification calculation unit 4. Then, the correction unit 5 performs gradation correction processing by multiplying the calculated conversion magnification by the R signal, G signal, and B signal, respectively.

  In the present embodiment, as shown in FIG. 5, the example in which the histogram generation unit 6 divides the histogram into 16 sections has been described. However, the present invention can be similarly implemented by applying other division numbers.

  Further, in the present embodiment, as illustrated in FIG. 7, the example in which the conversion characteristic generation unit 7 performs linear interpolation between the 16 representative points and the representative points is described. Or a function approximating a plurality of representative points may be used as the conversion characteristic. Further, the conversion characteristics may be generated by a conversion table.

  According to the present embodiment, a histogram is generated using the maximum signal value selected for each pixel, and the gradation level is adjusted based on the histogram, so that even if the subject is a monochrome color signal, Appropriate gradation correction processing can be performed by preventing the histogram from being biased toward the low luminance side and preventing generation of conversion characteristics that excessively emphasize the gradation level on the low luminance side. . For example, even if the subject is a single object of red or blue, since the histogram is not biased toward the low luminance side, it is suppressed that the signal level on the low luminance side is excessively emphasized.

  The image signal processing apparatus according to the present invention has the effects that the memory capacity and the calculation amount can be reduced, and the gradation correction processing can be performed while preventing color saturation and hue change. It is useful as an image signal processing apparatus that performs processing.

1 is a block diagram showing a configuration example of an image signal processing device according to a first embodiment of the present invention; The figure explaining the signal processing of the image signal processing apparatus concerning the 1st Embodiment of this invention The figure which shows the example of the conversion characteristic in the image signal processing apparatus concerning the 1st Embodiment of this invention The block diagram which shows the structural example of the image signal processing apparatus concerning the 2nd Embodiment of this invention. The figure which shows the example of the histogram of the maximum signal value in the image signal processing apparatus concerning the 2nd Embodiment of this invention. The figure which shows the example of the cumulative histogram of the maximum value in the image signal processing apparatus concerning the 2nd Embodiment of this invention. The figure which shows the example of the conversion characteristic in the image signal processing apparatus concerning the 2nd Embodiment of this invention. The block diagram which shows the structural example of the conventional image signal processing apparatus. The block diagram which shows the detail of the correction value calculating circuit of the conventional image signal processing apparatus The figure which shows the example of the conversion characteristic in the conventional image signal processing apparatus

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,10 Image signal processing apparatus 2 Maximum value selection part 3 Gradation level conversion part 4 Conversion magnification calculation part 5 Correction part 6 Histogram generation part 7 Conversion characteristic generation part

Claims (5)

A maximum signal value selection unit that selects a maximum signal value from signal values of a plurality of color signals constituting the image signal;
A conversion magnification determining unit for determining a conversion magnification for converting a gradation level of the color signal having the maximum signal value, based on a conversion characteristic defining a conversion magnification in gradation correction processing for the image signal;
An image signal processing apparatus comprising: a correction unit that performs the gradation correction processing of the plurality of color signals based on the conversion magnification determined by the conversion magnification determination unit. A histogram generator that generates a histogram of the maximum signal value selected for each pixel by the maximum signal value selector;
A conversion characteristic generation unit that generates the conversion characteristic based on the histogram;
The image signal processing apparatus according to claim 1, wherein the conversion magnification determination unit determines the conversion magnification based on the conversion characteristic generated by the conversion characteristic generation unit.   The image signal processing apparatus according to claim 1, wherein the conversion magnification determination unit performs non-linear conversion on a gradation level of the color signal having the maximum signal value.   The image signal processing apparatus according to claim 1, wherein the plurality of color signals are three color signals in RGB format. Select the maximum signal value from the signal values of multiple color signals that make up the image signal,
Determining a conversion magnification for converting a gradation level of the color signal having the maximum signal value based on a conversion characteristic defining a conversion magnification in a gradation correction process for the image signal;
An image signal processing method, wherein the gradation correction processing of the plurality of color signals is performed based on the determined conversion magnification.

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