JP6543786B2 - Image processing apparatus and image processing method - Google Patents

Description

  The present invention relates to an image processing apparatus and an image processing method.

  In recent years, imaging functions such as WDR (wide dynamic range) or HDR (high dynamic range) to obtain an image (hereinafter, also referred to as "WDR signal") capturing a dynamic range beyond the dynamic range that the sensor can image are increasing. ing. Such a photographing function is particularly effective in a scene with very high contrast, such as a composition of backlight.

  As means for obtaining the WDR signal, an image of short exposure (hereinafter, also referred to simply as “short exposure image”) and an image of long exposure (hereinafter, referred to simply as “long exposure image”) are continuous one by one. Means for capturing and combining images, means for capturing and combining short-exposure images and long-exposure images for each area, means for using a sensor capable of obtaining a wide dynamic range by single-image shooting, etc. There is. The dynamic range obtained by such means may be in the range of 16 bits to 20 bits or more.

  However, even if a WDR signal having such a dynamic range is obtained, there may be a situation that the display capability of the display to be finally displayed is limited to about 10 bits. Performing various signal processing causes a problem that the amount of processing becomes enormous. Therefore, for example, the WDR signal needs to be greatly range-compressed such as compressing each pixel value from 20 bits to 10 bits.

  Here, even when the WDR system capable of capturing a 20-bit range is used, if the subject range reaches the upper limit of 20 bits, it may reach only about 16 bits depending on the scene. Sometimes there is not. Therefore, when the ratio of the output upper limit range to the input upper limit range is fixedly used as the compression ratio, a dark image may be output using only the low luminance side of the output range, and the compression ratio is small. If it is, compression will be insufficient and the output image will be saturated.

  Therefore, in order to prevent saturation of the output image while effectively utilizing the dynamic range of the output image, it is necessary to perform adaptive compression in accordance with the dynamic range of the input image. As a technique for achieving such an object, techniques as disclosed in the following Patent Documents 1 to 4 are disclosed.

  For example, in Patent Document 1, the maximum value of the input RGB signal is detected, the level ratio of the maximum value that the signal after compression of the input RGB signal can take to the input RGB signal is taken as the compression ratio, and the compression ratio is the input RGB signal Discloses a technique for multiplying by. According to this arithmetic processing, it is possible to prevent the signal after compression from being saturated beyond the output range.

  Patent Document 2 discloses a technique of defining a correction value according to the level of an input signal, and adding or subtracting the correction value to the input signal. By such calculation, color saturation can be reduced, in particular, by lowering the level of the highlight portion of the input signal.

  Further, in Patent Document 3, a luminance signal is calculated from an input RGB signal, this luminance signal is subtracted from the input RGB signal to generate a color difference signal, a luminance process is performed on the luminance signal, and the luminance signal is calculated. A technique is disclosed for re-adding to a color difference signal.

  Further, Patent Document 4 performs gain operation on an input RGB signal, detects a maximum value from the calculated RGB signal, obtains a suppression coefficient based on the detected maximum value, and uses the suppression coefficient to near the saturation level. A technique is disclosed for compressing pixel values of.

JP 2000-115796 A JP, 2005-109871, A JP, 2009-111894, A Unexamined-Japanese-Patent No. 2004-180090

  However, in the technique described in Patent Document 1, the color reproducibility of the object using the range near the saturation is not sufficient.

  Further, in the technology described in Patent Document 2, the object is to keep the range of the output signal within the range that does not saturate, and the color reproducibility of the object using the range near the saturation is not sufficient.

  Further, in the technique described in Patent Document 3, the color reproducibility of the object using the range near the saturation of the output signal is not sufficient. Further, in the technology described in Patent Document 3, knee processing is performed to perform range compression only on high luminance portions above a certain level, and it seems difficult to apply the technology to large range compression. Be

  Further, in the technology described in Patent Document 4, the application of amplifying the number of bits of each pixel value to about 8 to 9 bits and keeping the saturated pixel value within 8 bits is assumed, and a strong range is expected. No compression is assumed. Further, in the technique described in Patent Document 4, the color reproducibility of an object using a range near the saturation is not sufficient.

  Therefore, the present invention provides a technology capable of obtaining a range-compressed image in which the color reproducibility of an object using a range near the saturation is improved.

  According to an embodiment of the present invention, in an image processing apparatus which performs range compression on the number of bits of each pixel value constituting an input image from A bits to B bits (where A> B), the pixels constituting the input image A maximum value detection unit that detects a maximum value of the values, a margin determination unit that determines a margin value based on the maximum value, and a coefficient calculation unit that calculates a coefficient based on an addition value of the maximum value and the margin value And a compression unit for performing range compression on the input image using the coefficients.

  According to such a configuration, it is possible to obtain a range-compressed image with improved color reproducibility of a high-brightness / high-saturation object by performing control to discontinue use of the range of a certain area from the upper limit of the output range. .

  The margin determination unit may determine the margin value based on a comparison result of a saturation value of pixel values constituting the input image and the maximum value, or a comparison result of a predetermined threshold and the maximum value. The margin value may be determined based on

  For example, the margin determining unit may determine zero as the margin value when the maximum value is equal to or more than the saturation value. When the input image is saturated, it is natural that the compressed image is also saturated.

  Also, for example, when the maximum value is less than the threshold, the margin determining unit may determine a specified value as the margin value. Also, for example, when the maximum value is between the saturation value and the threshold value, the margin determining unit may determine a value calculated by linear interpolation as the margin value.

  The saturation value may be set in any way. For example, the input image is a composite image of a short exposure image and a long exposure image, and the saturation value is the number of bits of each pixel value output from a sensor, the short exposure image photographed by the sensor, and the saturation image It may be a multiplication value with the exposure ratio of the long exposure image.

  Alternatively, the input image is a composite image of a short exposure image and a long exposure image, and the margin determination unit is configured to use a saturation value of pixel values constituting the short exposure image and a pixel value constituting the short exposure image. The margin value may be determined based on the comparison result with the maximum value.

Further, according to another embodiment of the present invention, in the image processing method for range-compressing the number of bits of each pixel value constituting the input image from A bits to B bits (where A> B), the input image Detecting a maximum value of the pixel values to be configured; determining a margin value based on the maximum value; calculating a coefficient based on an addition value of the maximum value and the margin value; Range-compressing the input image using
An image processing method is provided, including:

  According to such a method, it is possible to obtain a range-compressed image with improved color reproducibility of a high-brightness / high-saturation object by performing control so as not to use the range of a certain area from the upper limit of the output range. .

  As described above, according to the present invention, it is possible to obtain a range-compressed image in which the color reproducibility of an object using a range near the saturation is improved.

It is a figure for demonstrating the color reproducibility at the time of using the range of saturation vicinity. It is a figure showing an example of functional composition of an image processing device concerning an embodiment of the present invention. It is a block diagram which shows the detailed function structural example of a range compression part. It is a figure for demonstrating the example of determination of a margin value. WDR composite image whose maximum pixel value has not reached the saturation value, WDR composite image after compression to a 12-bit range using the maximum value, and compression to a 12-bit range using the sum of the maximum value and the margin value It is a figure which shows the histogram of each WDR synthetic | combination image after being carried out. WDR composite image with maximum pixel value reaching saturation value, WDR composite image after compression into 12-bit range using maximum value and margin value, and compression into 12-bit range using maximum value It is a figure which shows the histogram of each WDR synthetic | combination image after being carried out.

  The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. In the present specification and the drawings, components having substantially the same functional configuration will be assigned the same reference numerals and redundant description will be omitted.

  Further, in the present specification and the drawings, a plurality of components having substantially the same functional configuration may be distinguished by attaching different alphabets after the same reference numerals. However, when it is not necessary to distinguish each of a plurality of components having substantially the same functional configuration, only the same reference numerals will be given.

  First, color reproducibility when using a range near saturation will be described with reference to FIG. FIG. 1 is a diagram for explaining color reproducibility when using a range near the saturation. In FIG. 1, each RGB pixel value representing a blue object is shown as an 8-bit value for simplicity. As shown in FIG. 1, when the “short exposure image” has a value of (R, G, B) = (96, 144, 192), the photographed object is a blue object having a very high lightness. is there. Specifically, the clear blue sky on a clear day is a typical example of a blue object.

  After WDR combining is performed on the short exposure image and the long exposure image, when the range compression matched to the output range is performed on the WDR combined image using the conventional technique, the "output image" shown in FIG. Is output. If “short exposure image” and “output image” in FIG. 1 are expressed in HSV color system and compared, only “V (brightness)” is different between “short exposure image” and “output image”. Since the H (hue) and the S (saturation) are not different and the saturation is not, the "output image" has no problem at first glance.

  However, when observing the color of the "output image", the sky appearing in the "output image" does not look perfect blue but looks bright blue, and the impression of the real thing is different. Taking this as an example, even if a WDR composite image is generated after capturing a high-brightness / high-saturation object as a “short-exposure image”, deep color can not be reproduced in the “output image” unless the range compression is properly performed. There is a problem that is different from the real thing.

  Therefore, in the present specification, when performing range compression on an input image, not only the output image is not saturated beyond the output range, but also the color reproducibility near the saturation level is insufficient. Focus on Specifically, in the present specification, a range-compressed image with improved color reproducibility of a high-brightness / high-saturation object is obtained by performing control not to use the range of a certain area from the upper limit of the output range. We propose the technology that can be done. The case of using an input RGB signal will be described as an example of an input image.

  Subsequently, embodiments of the present invention will be described in detail. First, the functional configuration of the image processing apparatus 1 according to the embodiment of the present invention will be described. FIG. 2 is a diagram showing an example of a functional configuration of the image processing apparatus 1 according to the embodiment of the present invention. As shown in FIG. 2, the image processing apparatus 1 includes a sensor 10, a frame memory 20, a combining unit 30, and a range compression unit 40. The functions of the functional blocks included in the image processing apparatus 1 will be sequentially described in detail below.

  The image processing apparatus 1 changes the exposure setting of the sensor 10 and continuously captures two images. Here, short exposure shooting is performed first, and then long exposure shooting is performed. However, long exposure shooting may be performed first, and then short exposure shooting may be performed. The short exposure image and the long exposure image captured in this manner are written to the frame memory 20 as a pair. The photographing of the long exposure image and the short exposure image and the writing of the photographed long exposure image and the short exposure image into the frame memory 20 are continuously performed.

  Here, in the present specification, at least the current long exposure image and the current short exposure image may be left in the frame memory 20. Therefore, the intervals at which the long exposure image and the short exposure image are captured are not particularly limited. Further, the long exposure image and the short exposure image may be written in the frame memory 20 for each frame, or may be written in the frame memory 20 once in a plurality of frames.

  For example, as in the example illustrated in FIG. 2, when the frame memory 20 has an area in which a pair of a long exposure image and a short exposure image is to be written, the image processing apparatus 1 includes a pair of a long exposure image and a short exposure image. Can be written continuously to the area. For example, the previous short exposure image and the previous long exposure image written in the frame memory 20 may be overwritten by the current short exposure image and the current long exposure image.

  In the example shown in FIG. 2, the image processing apparatus 1 has one common system for outputting a long exposure image and a short exposure image, and the sensor 10 has a long exposure image and a short exposure image. Although output is made by division, a long exposure image and a short exposure image may be simultaneously output. In such a case, the image processing apparatus 1 may have two systems of a system for outputting a long exposure image from the sensor 10 and a system for outputting a short exposure image. Each shutter time is determined by, for example, a dynamic range of an object to be photographed, a sensor specification, and the like.

  In the embodiments of the present invention, the terms short exposure image and long exposure image are used, but these terms do not limit the absolute exposure time of each of the two captured images. Therefore, when two images having different exposure times are taken, of the two images, an image with a relatively short exposure time corresponds to a short exposure image, and an image with a relatively long exposure time is a long exposure It corresponds to an image. For example, the time of long exposure (hereinafter, also simply referred to as “exposure ratio”) may be set to several to ten times the time of short exposure.

  The combining unit 30 combines the long exposure image and the short exposure image to generate a WDR combined image. Specifically, referring to the use image selection information, the combining unit 30 uses the short exposure image for the short exposure image use area and uses the long exposure image for the long exposure image use area. Generate For example, even if the number of bits of each of the short exposure image and the long exposure image output from the sensor 10 is 12 bits, the number of bits of the WDR combined image generated by the combining unit 30 may be about 16 bits.

  The use image selection information may be generated in any way, but for example, since the area saturated in the long exposure image is highly likely not saturated in the short exposure image, A short exposure image may be selected as a use image. On the other hand, for example, in a long exposure image, a long exposure image may be selected as a use image of the area that is not saturated.

  The range compression unit 40 performs range compression on the number of bits of each pixel value constituting the WDR composite image from A bits to B bits (where A> B). As such compression processing, tone mapping in accordance with a look-up table (LUT) may be used, but any particular method may be used. For example, even if the number of bits of the WDR combined image generated by the combining unit 30 is about 16 bits, the range compression unit 40 performs compression so that the number of bits of the WDR combined image is 12 bits.

  The subsequent stage of the range compression unit 40 is connected to an image processing engine including, for example, a demosaicing unit that generates an RGB plane from Bayer data, an edge enhancement unit, and color management. Therefore, it is preferable that the amount of data of the output signal from the range compression unit 40 be adjusted (for example, to about 12 bits) so as to conform to the size of the input data to the image processing engine, for example. Since the image is converted to a dark image simply by reducing the data size, it is preferable that the high luminance side be strongly compressed so as to approach human visual characteristics.

  In the example described above, the example of photographing and combining two types of images (short-exposure image and long-exposure image) having different exposure amounts has been described. However, the type of image used for composition is not particularly limited. For example, the present embodiment can be applied to an example in which three or more types of images having different exposure amounts are captured and combined. When three or more types of images are taken and synthesized, it is expected that the dynamic range of the obtained WDR synthesized image can be extended to 20 bits or more. However, it is preferable that the range after compression by the range compression unit 40 be constant.

  Subsequently, a detailed functional configuration example of the range compression unit 40 will be described with reference to FIG. FIG. 3 is a block diagram showing a detailed functional configuration example of the range compression unit 40. As shown in FIG. As shown in FIG. 3, the image processing apparatus 1 includes a maximum value detection unit 41, a margin determination unit 42, an addition unit 43, a coefficient calculation unit 44, and a compression unit 45. In the following, the case where the input RGB signal to the range compression unit 40 is the WDR composite image generated by the combination unit 30 will be mainly described, but the input RGB signal to the range compression unit 40 is a WDR composite image It is not limited.

  The maximum value detection unit 41 detects the maximum value hmax of pixel values constituting the input image. For example, as shown in FIG. 3, when the input RGB signal whose dynamic range is expanded is input, the maximum value detection unit 41 detects the maximum value hmax from all pixel values constituting the input RGB signal. You may

  Here, it is desirable that the maximum value detection unit 41 take a histogram of all pixel values constituting the input RGB signal, and detect the largest value of the pixel values as the maximum value among the pixel values existing in a predetermined number or more. If even one pixel is detected as the maximum value, there is a possibility that a defective pixel is detected, or a very small object with high brightness which is less important from the whole image may be detected. It is because that possibility can be reduced.

  Further, when taking a histogram of the input RGB signal, it is more desirable to quantize the gradation and then take the histogram. When the input RGB signal is a WDR synthesized image, the memory used for the histogram becomes very large if the histogram of all gradations is taken. The maximum value hmax detected by the maximum value detection unit 41 is output to the margin determination unit 42 and the addition unit 43.

  The margin determination unit 42 determines a margin value margin based on the maximum value hmax detected by the maximum value detection unit 41. Details of the determination of the margin value margin by the margin determination unit 42 will be described later. Further, the addition unit 43 calculates an addition value hmax ′ of the maximum value hmax detected by the maximum value detection unit 41 and the margin value margin determined by the margin determination unit 42.

  The coefficient calculation unit 44 calculates the coefficient coeff based on the addition value hmax '. For example, the coefficient calculation unit 44 calculates the coefficient coeff by dividing the upper limit value of the output range by the addition value hmax '. Then, it is possible to calculate a coefficient coeff for making the addition value hmax 'coincide with the upper limit value of the output range.

  The compression unit 45 performs range compression on the input RGB signal using the coefficient coeff. The compression unit 45 can compress the input RGB signal by multiplying each pixel value of the input RGB signal by the coefficient coeff.

  In this way, by performing control so as not to use the range of a certain area from the upper limit of the output range, it is possible to obtain a range-compressed image in which the color reproducibility of an object with high brightness and high saturation is improved. The details of the determination of the margin value margin by the margin determination unit 42 will be described below. FIG. 4 is a diagram for explaining an example of determining the margin value margin. FIG. 4 shows an example of the correspondence between the maximum value hmax and the margin value margin.

  For example, the margin determination unit 42 may determine the margin value margin based on the comparison result of the saturation value VALu of the pixel values constituting the input RGB signal and the maximum value hmax. For example, as shown in FIG. 4, the margin determination unit 42 may determine zero as the margin value margin when the maximum value hmax is equal to or greater than the saturation value VALu.

  Here, when the input RGB signal is a WDR composite image of a short exposure image and a long exposure image, the saturation value VALu may be any value that can be taken in the saturation state of the short exposure image. Specifically, the saturation value VALu may be a theoretical upper limit of pixel values of the WDR composite image. For example, as the saturation value VALu is expressed by the following equation (1), the bit number n of each pixel value output from the sensor 10 and the exposure ratio Exp of the long exposure image to the short exposure image photographed by the sensor 10 It may be theoretically calculated by the multiplication value of.

VALu = 2 ⁿ × Exp (1)

When the bit number n of each pixel value output from the sensor 10 is 12 and the exposure ratio of the long exposure image to the short exposure image is 10 times, the theoretical upper limit value of the pixel value of the WDR composite image is It is considered that basically 2 ¹² × 10 = 40960 that a pixel value larger than this upper limit value is not present in the WDR composite image.

  Alternatively, the saturation value VALu may be a saturation value of pixel values constituting the short exposure image. For example, in such a case, the margin determination unit 42 may determine the margin value margin based on the comparison result of the saturation value of the pixel values constituting the short exposure image and the maximum value of the pixel values constituting the short exposure image. The comparison between the saturation value of the pixel values constituting the short exposure image and the maximum value of the pixel values constituting the short exposure image may be performed by a comparison unit (not shown).

  Also, for example, the margin determination unit 42 may determine the margin value margin based on the comparison result between the predetermined threshold TH and the maximum value hmax. For example, as shown in FIG. 4, the margin determination unit 42 may determine the specified value as the margin value margin when the maximum value hmax is smaller than the threshold value TH.

  Further, as shown in FIG. 4, if the maximum value hmax is between the saturation value VALu and the threshold value TH, the margin determining unit 42 may determine the value calculated by linear interpolation as the margin value margin. Good.

  Here, the description is made using the exposure ratio of the long exposure image to the short exposure image, but when using three or more types of images photographed with different exposure amounts, the longest exposure image to the shortest exposure image VALu may be calculated using the exposure ratio of

  Subsequently, an example of an effect exerted by the embodiment of the present invention will be described. First, the case where the maximum value hmax of the pixel values has not reached the saturation value VALu will be described. FIG. 5 shows a WDR composite image (upper row) in which the maximum value hmax of pixel values has not reached the saturation value VALu, a WDR composite image (middle row) after compression into a 12-bit range using the maximum value hmax, and the maximum value hmax It is a figure which shows the histogram of each WDR synthetic | combination image (lower stage) after compressing to 12 bit range using addition value hmax 'with margin value margin.

  Referring to the WDR composite image (the middle part of FIG. 5) after compression using the maximum value hmax, the output range is fully used, but as described in the background art section, the high brightness and high saturation portion The color reproducibility of the image becomes insufficient.

  On the other hand, referring to the WDR composite image (the lower part of FIG. 5) after compression into a 12-bit range using the addition value of the maximum value hmax and the margin value margin, high saturation The color reproducibility of high saturation objects is improved. However, if the margin value margin is made too large, the number of unused tones on the highlight side of the output range may be increased to lower the contrast of the output image, or the image may appear dark. Therefore, it is preferable to set a margin value that balances the color reproducibility of an object with high brightness and high saturation with the contrast of the image.

  Subsequently, the case where the maximum value hmax of the pixel values reaches the saturation value VALu will be described. FIG. 7 shows a WDR composite image (upper part) in which the maximum value of the pixel values has reached the saturation value, and the WDR composite image after compression into a 12-bit range using the sum hmax ′ of the maximum value hmax and the margin value margin. FIG. 16 is a diagram showing histograms of respective WDR composite images (lower) after compression to a 12-bit range using (middle) and the maximum value hmax.

  Referring to the WDR composite image (upper part of FIG. 6) in which the maximum value of the pixel value has reached the saturation value, the histogram of the highlight portion has reached the saturation value VALu of the WDR composite image, and hmax = VALu. . The fact that the WDR composite image is saturated means that an object of very high brightness is taken that is saturated even in a short exposure image.

  Referring to the WDR composite image (middle part of FIG. 6) after compression to a 12-bit range using the added value hmax ′ of the maximum value hmax and the margin value margin, the added value hmax ′ of the maximum value hmax and the margin value margin Range compression is performed, and the highlight portion is output using saturation and a slightly smaller gradation. As a result, although only a short exposure image looks saturated and looks white or nearly white, it does not look saturated when it is seen in a composite image but looks light gray and looks unnatural.

  On the other hand, referring to the WDR composite image (lower part of FIG. 6) after compression to the 12-bit range using the maximum value hmax, the case where the WDR composite image is saturated is shown. In such a case, it is natural that the WDR composite image after compression is also saturated. That is, it is preferable to compress the WDR composite image using the maximum value hmax without using the addition value hmax '.

  As in the example of the effects described above, in the embodiment of the present invention, the maximum value hmax and the saturation value VALu are compared, and when the maximum value hmax reaches the saturation value VALu, the margin value margin is set. Introduce control such as zeroing. By this, it is considered that a natural result is obtained even when the WDR composite image is saturated.

  The embodiments of the present invention have been described above. According to the embodiment of the present invention, in the image processing apparatus 1 for performing range compression on the number of bits of each pixel value constituting the input image to A bits to B bits (where A> B), the pixel values constituting the input image A maximum value detection unit 41 that detects the maximum value of the above, a margin determination unit 42 that determines a margin value based on the maximum value, and a coefficient calculation unit 44 that calculates a coefficient based on the sum of the maximum value and the margin value , And a compression unit 45 which performs range compression on an input image using coefficients.

  According to such a configuration, it is possible to obtain a range-compressed image with improved color reproducibility of a high-brightness / high-saturation object by performing control to discontinue use of the range of a certain area from the upper limit of the output range. .

  Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to such examples. It is obvious that those skilled in the art to which the present invention belongs can conceive of various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also fall within the technical scope of the present invention.

  Wide dynamic range technology is regarded as particularly important as a network camera differentiation technology. The embodiment of the present invention enables high brightness and high saturation objects, whose color reproducibility is insufficient in the prior art, to be reproduced with colors closer to real colors, and side effects are suppressed by adaptive control of the margin value. There is. Therefore, it is superior in that the image quality can be stably improved, the processing is not complicated and can be realized with a realistic circuit scale, and the number of parts requiring control is small.

Reference Signs List 1 image processing apparatus 10 sensor 20 frame memory 30 combination unit 40 range compression unit 41 maximum value detection unit 42 margin determination unit 44 addition unit 44 coefficient calculation unit 45 compression unit coeff coefficient Exp exposure ratio hmax maximum value hmax 'addition value margin margin value TH threshold VALu saturation value

Claims (7)

In an image processing apparatus which performs range compression on the number of bits of each pixel value constituting an input image from A bits to B bits (where A> B),
A maximum value detection unit that detects the maximum value of pixel values constituting the input image;
A margin determination unit configured to determine zero as a margin value when the maximum value is equal to or more than a saturation value of pixel values constituting the input image ;
A coefficient calculation unit that calculates a coefficient based on an addition value of the maximum value and the margin value;
A compression unit that performs range compression on the input image using the coefficients;
An image processing apparatus comprising: The margin determination unit determines the margin value based on a comparison result of a predetermined threshold smaller than the saturation value and the maximum value.
The image processing apparatus according to claim 1 . The margin determination unit determines a specified value as the margin value when the maximum value is less than the threshold.
The image processing apparatus according to claim 2 . The margin determination unit determines a value calculated by linear interpolation as the margin value, when the maximum value is between the saturation value and the threshold value.
The image processing apparatus according to claim 3 . The input image is a composite image of a short exposure image and a long exposure image,
The saturation value is a product of the number of bits of each pixel value output from a sensor and the exposure ratio of the short exposure image and the long exposure image captured by the sensor.
The image processing apparatus according to claim 1 . The input image is a composite image of a short exposure image and a long exposure image,
The margin determining unit determines the margin value based on a comparison result of a saturation value of pixel values constituting the short exposure image and a maximum value of pixel values constituting the short exposure image.
The image processing apparatus according to claim 1 . In an image processing method for range-compressing the number of bits of each pixel value constituting an input image from A bits to B bits (where A> B),
Detecting a maximum value of pixel values constituting the input image;
If the maximum value is greater than or equal to a saturation value of pixel values constituting the input image, determining zero as a margin value ;
Calculating a coefficient based on an addition value of the maximum value and the margin value;
Range compressing the input image using the coefficients;
Image processing methods, including:

Images