JP2005159693A - Image processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing apparatus provided with a dynamic gamma correction section activated accurately at a high speed by obtaining luminance distribution information in parallel with the writing of main exposure image data to a frame memory. <P>SOLUTION: The image processing apparatus is configured of: the frame memory 5 for storing image data from an imaging element 1 via a system bus 6; a histogram arithmetic section 2 for receiving the image data in parallel with the storage of the image data to the frame memory and obtaining a histogram of the lightness information of at least one chrominance signal data in the image data to set a gamma characteristic; and an image processing section 3 for using the gamma characteristic obtained by the histogram arithmetic section to apply gamma correction to the image data stored in the frame memory. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image processing apparatus, and more particularly to an image processing apparatus that performs gamma correction of an image.

  In an image processing apparatus such as a digital camera intended to obtain an image of a desired image quality by digital image processing from an image signal obtained from an image pickup device such as a CCD, there is gamma correction processing as one function of image processing. The gamma correction process corrects the brightness and contrast of the image so that the brightness is displayed optimally when the image is displayed on an output device such as a display or printer. Usually, these output devices are nonlinear. Since it has display characteristics, gamma correction performs non-linear conversion opposite to the display characteristics of the output device. For this reason, in gamma correction processing, conversion using a LUT (Look Up Table) using a memory, conversion using a broken line approximation formula combining a plurality of linear expressions, and the like are often used. In digital cameras, when changing the characteristics of these LUTs and polygonal line approximation formulas, manual setting is generally performed before shooting.

  On the other hand, there is a method of correcting the brightness and contrast of an image more finely by dynamically changing the gamma characteristic according to the state of the subject. For example, Japanese Patent Laid-Open No. 8-23460 proposes a method of obtaining a histogram of an input image and selecting one from a plurality of gamma correction characteristics based on the result.

In addition, the digital camera proposed in Japanese Patent Laid-Open Nos. 11-196292 and 2000-138862 obtains a histogram and a luminance distribution using pre-image data exposed by the image sensor immediately before photographing, and uses this information. It controls the gamma correction processing of the image actually taken (hereinafter referred to as the main exposure image).
JP-A-8-23460 JP 11-196292 A JP 2000-138862 A

  However, when the technique disclosed in Japanese Patent Laid-Open No. 8-23460 is used for a digital camera, there is no disclosure as to when the histogram is created in the camera shooting sequence. If the histogram is created after the image data is once stored in the frame memory, and then gamma conversion is performed using the gamma characteristics generated from the histogram, there is a problem that the processing time becomes long. (A) and (B) of FIG. 15 are diagrams showing this processing sequence. FIG. 15A shows a processing sequence when the histogram is not obtained (dynamic gamma correction is not performed), and FIG. 15B obtains the histogram and dynamically selects the gamma correction characteristic. Sequence of cases. In the processing sequence shown in FIG. 15A, imaging data for one frame from the start of imaging is written in a frame memory such as a DRAM. Thereafter, images are sequentially read from the frame memory, subjected to image processing including gamma correction processing, and then written back to the frame memory. Here, in FIG. 15A, imaging data reading, gamma correction processing, and post-processing data writing are illustrated as being processed at the same time, but in actuality, a delay in units of clocks occurs in each processing. It is omitted in the figure.

  On the other hand, in the processing sequence shown in FIG. 15B, image data for one frame is written in a frame memory such as a DRAM from the shooting start time. Next, images are sequentially read from the frame memory, a histogram is created, and gamma characteristics are set in the gamma correction LUT. Thereafter, images are sequentially read from the frame memory again, and after being subjected to gamma correction processing based on the set characteristics, the image is written back to the frame memory. Therefore, it takes an extra time to read the imaging data for one frame with respect to the processing sequence shown in FIG.

  In the methods disclosed in JP-A-11-196292 and JP-A-2000-138862, since the histogram and the luminance distribution are not obtained using the main exposure image, a subject moving particularly fast is photographed. In some cases, an accurate histogram or luminance distribution cannot be obtained. Furthermore, when subject light is split into a viewfinder and an image sensor using a mirror, such as a single-lens reflex digital camera, pre-imaging data acquisition is not possible because the subject light hits the image sensor only during main exposure. This is possible, so the gamma correction cannot be changed dynamically.

  The present invention has been made in view of the above problems, and includes a dynamic gamma correction unit that operates accurately and at high speed by obtaining luminance distribution information in parallel with writing the main exposure image data into the frame memory. An object of the present invention is to provide an image processing apparatus.

  In order to solve the above problem, the invention according to claim 1 is directed to a frame memory for storing image data from an image sensor, and image data is input in parallel with the storage in the frame memory, and the luminance distribution of the image data A luminance distribution information calculation unit that obtains information and a gamma correction unit that performs gamma correction on image data stored in the frame memory based on the obtained luminance distribution information constitute an image processing apparatus. .

  According to a second aspect of the present invention, in the image processing apparatus according to the first aspect, the luminance distribution information calculation unit generates the luminance distribution information from a histogram of at least one color signal data in the image data. It is what.

  According to a third aspect of the present invention, in the image processing apparatus according to the first aspect, the luminance distribution information calculation unit includes a first threshold value for the brightness of at least one color signal data of the image data, and a first threshold value. A second threshold different from the first threshold is set, and at least one of the number of image data equal to or greater than the first threshold or the number of image data equal to or smaller than the second threshold is counted, and the first threshold At least one of the above image data count number or the image data count number equal to or less than the second threshold is used as the luminance distribution information.

  According to a fourth aspect of the present invention, in the image processing apparatus according to the third aspect, the gamma correction unit includes a memory that stores a plurality of lookup tables including gamma correction data corresponding to input image data, and the count number. And a selector for selecting one look-up table in the memory.

  According to a fifth aspect of the present invention, in the image processing apparatus according to the third aspect, the gamma correction unit is configured to look from gamma correction data corresponding to input image data loaded from the outside in accordance with the count number. It has a selector for selecting and loading an up table, and a memory for storing the loaded look-up table.

  According to a sixth aspect of the present invention, in the image processing apparatus according to the third aspect, the gamma correction unit stores a lookup table including gamma correction data corresponding to input image data, and a memory from the memory. An arithmetic unit that performs a product-sum operation on a coefficient calculated from the count number with respect to the gamma correction data.

  According to a seventh aspect of the present invention, in the image processing apparatus according to the first aspect, the luminance distribution information calculation unit sets a weight according to the position of the region of the image data, and uses the weight to determine the luminance distribution information. Is calculated.

  An embodiment corresponding to the invention according to each claim will be described as follows. That is, Example 1 corresponds to the invention according to claims 1, 2, and 7. Embodiments 2, 3, and 4 correspond to the invention according to claim 3. Example 2 corresponds to the invention according to claim 4. Example 3 corresponds to the invention according to claim 5. Example 4 corresponds to the invention according to claim 6.

  In the present invention, it is possible to obtain accurate and high-speed luminance distribution information by using the main exposure image data and creating luminance distribution information in parallel with writing the image data into the memory. Even in a digital camera such as a camera that cannot perform pre-imaging, the gamma conversion characteristics can be dynamically changed according to the luminance distribution of the subject.

  Next, the best mode for carrying out the invention will be described.

(Example 1)
First, a first embodiment of the image processing apparatus according to the present invention will be described. In the first embodiment, a case where the image processing apparatus according to the present invention is applied to a digital camera will be described. FIG. 1 is a block diagram illustrating the configuration of the digital camera according to the first embodiment. In FIG. 1, 1 is an image sensor, 2 is a histogram calculation unit that obtains a histogram of image brightness information as image luminance distribution information, and 3 is an image processing unit that performs various image processing including gamma correction. The gamma correction unit in the processing unit 3 is composed of an LUT using a memory. Reference numeral 4 denotes a CPU for controlling each component block, 5 denotes a frame memory for storing an image for one screen, and 6 denotes a system bus through which image data and control signals flow. Note that control blocks such as a memory controller necessary for the actual hardware configuration are omitted because they are not related to the essence of the present invention.

  Next, the operation of the digital camera shown in FIG. 1 will be described using the processing sequence diagram of FIG. First, when a shutter (not shown) of the digital camera is pressed, the image data photoelectrically converted by the image sensor 1 is AD converted (not shown) to become digital image data via the system bus 6 and the frame memory 5. Is written to. In parallel with this, the digital image data is also input to the histogram calculation unit 2. The histogram calculation unit 2 creates histogram data from the input image data with the horizontal axis representing brightness and the vertical axis representing frequency. At this time, as the image data used for creating the histogram, only the color signal including a lot of luminance information among all the digital image data is used. For example, when a CCD having an RGB color filter is used as the image sensor 1, only the G signal is used among the RGB signals. As a result, a histogram can be efficiently obtained from a small amount of data, and a memory for storing the histogram data can be reduced.

  The histogram calculation unit 2 also has a function of varying the weight of the histogram frequency depending on the location of the image when creating the histogram. For example, as shown in FIG. 3, for example, the weight of the peripheral part = 1 and the weight of the central part = 2 are set so that the weight value of the central part of the image is larger than that of the peripheral part. Doubles the frequency of the histogram. Fig. 3 shows an example of weighting assuming that there is an important subject in the center of the image. By doing this, gamma correction is performed so that the brightness and contrast of the more important subject are appropriate. Is possible.

  Next, the histogram calculation unit 2 creates a cumulative histogram obtained by accumulating the histogram created from the image data for one frame from the lower luminance, and loads it into the gamma correction LUT in the image processing unit 3. In this case, it goes without saying that the maximum value of the cumulative histogram must be normalized according to the number of output bits of the LUT. Here, the obtained cumulative histogram will be described with reference to FIGS. 4A to 4C are diagrams showing a histogram (solid line) and a cumulative histogram (dotted line) for two images each having a different brightness distribution. However, the frequency is adjusted so that the histogram and the cumulative histogram have the same scale. FIG. 4A is a diagram when there are many bright portions in the image, and the cumulative histogram has a large slope in the bright portions. Therefore, when gamma correction is performed using this characteristic, a large number of gradations are assigned to the bright part, resulting in good gradation characteristics. On the other hand, FIG. 4B is a diagram in the case where there are many dark portions in the image, and the cumulative histogram has a large inclination in the dark portions. Therefore, when gamma correction is performed using this characteristic, a large number of gradations are assigned to dark portions, resulting in good gradation characteristics.

  However, if the cumulative histogram obtained by this method is used as it is for gamma correction, the following problems occur. For example, in the cumulative histogram described with reference to FIG. 4A, the gradation of the dark part is hardly expressed, and only the contrast of the bright part changes greatly. Such an image is greatly different from the contrast of the original subject, resulting in an uncomfortable image. For example, when the image before gamma correction has a uniform luminance distribution, the cumulative histogram is a straight line with a slope of 1. If this is used as a characteristic of gamma correction as it is, gamma correction will not be performed as a result, and it will not be possible to express good brightness and contrast on the output device that was the original purpose of gamma correction. End up. In order to solve these problems, a gamma characteristic that cancels the gradation display characteristic of the output device is held in advance, and the cumulative histogram is set so that the difference between this and the obtained cumulative histogram does not exceed a certain range. It is necessary to take a method of correcting. This mode is shown in FIG. If the obtained cumulative histogram is a dotted line, and the preset gamma characteristic is a solid line, the corrected gamma correction characteristic is a one-dot chain line.

  After obtaining the cumulative histogram by the above method, the image processing unit 3 sequentially reads out the image data from the frame memory 5 via the system bus 6, performs gamma correction processing using the gamma characteristic set by the histogram calculation unit 2, and other various types The processed image data is written back to the frame memory 5 via the system bus 6. Since each process of reading out the image data, image processing, and post-processing data writing back is pipelined for each pixel, as shown in FIG. 2, it starts and ends at substantially the same timing. The processing sequence described so far is controlled by the CPU 4.

  By performing the gamma correction process with the above configuration, it is possible to dynamically change the gamma correction characteristic without increasing the processing time. In addition, since a histogram is created from the exposure image data, accurate luminance distribution information can be obtained, and gamma correction characteristics can be dynamically changed even in a single-lens reflex digital camera having a mechanism for mirror spectroscopy. Is feasible.

(Example 2)
Next, a second embodiment of the present invention will be described. In the first embodiment, the histogram is used as the luminance distribution information of the image. However, in this embodiment, the luminance distribution information of the image is obtained by a simpler method, and the gamma characteristic is dynamically calculated from the luminance distribution information. The form which changes is demonstrated. FIG. 5A is a block diagram showing a configuration of a digital camera according to Embodiment 2 of the present invention. In FIG. 5A, reference numeral 7 denotes a bright part counter for counting pixels having a brightness equal to or higher than a first threshold in the image, and a dark part counter for counting pixels having a brightness lower than the second threshold, and 8 denotes a gamma. The image processing unit performs various image processing including correction. The gamma correction unit in the image processing unit 8 includes a plurality of LUTs 9 using a memory as shown in FIG. And a selector 10 for selecting one. The other constituent blocks are the same as the constituent blocks of the first embodiment shown in FIG. 1, and therefore, the same constituent blocks are denoted by the same reference numerals and description thereof is omitted. The image processing unit 8 may include image processing blocks other than the gamma correction unit, but illustration and description thereof are omitted because they do not affect the present invention.

  Next, the operation of the second embodiment shown in FIG. 5 will be described using the processing sequence diagram of FIG. First, when a shutter (not shown) of the digital camera is pressed, the image data photoelectrically converted by the image sensor 1 is AD converted (not shown) to become digital image data via the system bus 6 and the frame memory 5. Is written to. In parallel with this, the digital image data is also input to the bright / dark counter 7. The bright and dark area counter 7 has two counters, and counts pixels that are equal to or higher than a certain first threshold level and pixels that are equal to or lower than a second threshold level in the input image data. At this time, as the image data to be counted, only the color signal containing a lot of luminance information among all the digital image data is used as in the first embodiment. Also, the weighting of the count value according to the location of the image is the same as in the first embodiment.

  Next, the bright / dark counter unit 7 generates a select signal based on the count result. This select signal is a signal for switching a plurality of gamma correction LUTs 9 in the image processing unit 8. For example, when the bright part counter value and the dark part counter value are each equal to or greater than a preset third threshold value, 1 or less. When 0 is set to 0, a 2-bit select signal as shown in Table 1 is generated.

  Next, the image processing unit 8 sequentially reads out image data from the frame memory 5 via the system bus 6, and performs gamma correction using the LUT 9 selected via the selector 10 by the select signal and other various image processing. And write back to the frame memory 5 via the system bus 6. Here, the relationship between the select signal and the gamma characteristic in the selected LUT 9 will be described with reference to FIG. FIG. 7 is a diagram showing gamma characteristic curves set in the four LUTs 9. When the select signal is 00, it means that the ratio of the bright part and the dark part is small in the image. Therefore, the characteristic shown by a in FIG. 7 is set so that many gradations are assigned to the intermediate brightness range. The selected LUT 9 is selected. When the select signal is 01, it means that there are many dark parts. Therefore, the LUT 9 having the characteristics shown in FIG. 7b is selected so that many gradations are assigned to the dark area of the image, and the select signal is selected. When the signal is 10, it means that there are many bright parts. Therefore, the LUT 9 having the characteristics shown by c in FIG. 7 is selected so that many gradations are assigned to the bright area of the image, and the select signal is selected. 11 indicates that there are a lot of bright and dark areas. Therefore, the LUT 9 having the characteristics shown by d in FIG. 7 is set so that many gradations are assigned to the bright and dark areas of the image. select.

  In the second embodiment, since the bright and dark portions of the image are counted, the number of LUTs 9 is 4. However, when the brightness range to be counted is further subdivided, it can be handled by increasing the number of LUTs 9. On the contrary, when only one of the bright part and the dark part is counted, the number of LUTs 9 can be reduced. Further, the memory constituting the LUT 9 may be either ROM or RAM.

  With the configuration as described above, the luminance distribution information of the image can be obtained more easily, and the gamma correction characteristics can be dynamically switched without increasing the processing time.

(Example 3)
Next, Embodiment 3 of the present invention will be described. In the second embodiment, the number of bright and dark portions of the image is counted as the luminance distribution information of the image, and the gamma correction LUT is switched according to the count value. However, in this embodiment, the count value is shown. A mode in which the gamma characteristic is dynamically changed by another method will be described. FIGS. 8A and 8B are block configuration diagrams showing the configuration of a digital camera according to Embodiment 3 of the present invention. In FIG. 8A, reference numeral 11 denotes an image processing unit that performs various image processing including gamma correction. The gamma correction unit in the image processing unit 11 includes a selector as shown in FIG. 12, the data input to the address port of the LUT 13 can be switched. In this embodiment, the LUT 13 is constituted by a RAM, and FIG. 8B shows a configuration in the case of using a single port RAM. The other constituent blocks are the same as the constituent blocks of the second embodiment shown in FIG. 2, and therefore the same constituent blocks are denoted by the same reference numerals and the description thereof is omitted. However, the output signal line of the bright / dark counter 7 is connected to the system bus 8.

  Next, the operation of the third embodiment shown in FIGS. 8A and 8B will be described with reference to the processing sequence diagram of FIG. First, after the shutter (not shown) of the digital camera is pressed, the first threshold level of the image data input by the bright / dark counter 7 is written in parallel with the writing of the image data into the frame memory 5. The steps up to counting the above pixels and pixels below the second threshold level and generating a select signal are the same as those in the second embodiment shown in FIG. The generated select signal is input to the CPU 4 via the system bus 6. Based on the select signal, the CPU 4 selects one from a memory (not shown) in which a plurality of gamma characteristics shown in FIG. 7 are stored, for example, and selects it in the gamma correction LUT 13 in the image processing unit 11. The gamma characteristic data (LUT data) and the LUT memory address are output. At this time, the CPU 4 switches the selector 12 so that the LUT 13 can input the LUT data and the LUT address from the CPU 4 by the table load / gamma correction select signal. After loading the LUT data into the LUT 13, the CPU 4 switches the selector 12 so that image data can be input. Next, the image processing unit 11 sequentially reads out the image data from the frame memory 5 via the system bus 6 and performs gamma correction using the LUT 13 loaded with the LUT data by the CPU 4 and other various image processings. Write back to the frame memory 5 via the bus 6.

  With the configuration as described above, the luminance distribution information of the image can be obtained more easily, and the gamma correction characteristics can be dynamically switched with a small circuit scale.

Example 4
Next, a fourth embodiment of the present invention will be described. In the present embodiment, the count value is used as the luminance distribution information as in the second and third embodiments, but the gamma characteristic is dynamically changed by a method different from the second and third embodiments. FIGS. 10A and 10B are block configuration diagrams showing the configuration of a digital camera according to Embodiment 4 of the present invention. In FIG. 10A, reference numeral 14 denotes an image processing unit that performs various image processing including gamma correction. The gamma correction unit in the image processing unit 14 includes an LUT 15 as shown in FIG. A product-sum operation is performed using the multiplier 16 and the adder 17 on the output signal and the signal from the product-sum coefficient generation unit 19. Reference numeral 18 denotes a clip portion. The other constituent blocks are the same as the constituent blocks of the second embodiment shown in FIG. 2, and therefore the same constituent blocks are denoted by the same reference numerals and the description thereof is omitted.

  Next, the operation of the fourth embodiment shown in FIGS. 10A and 10B will be described with reference to the processing sequence diagram of FIG. The image data is the same as that in the second embodiment until the bright portion / dark portion counter 7 counts the pixels having the first threshold level or higher and the pixels having the second threshold level or lower. The two count values are output to the image processing unit 14, and a product-sum coefficient generation unit 19 in the image processing unit 14 calculates a product-sum coefficient value for changing the gamma correction characteristic from the two count values. Here, the function of the product-sum coefficient will be described with reference to FIGS. First, a basic gamma correction characteristic is set in the LUT 15. The basic gamma characteristic is a gamma characteristic that is the reverse characteristic of the display characteristic of the output device, and is, for example, a characteristic such as a thin solid line in FIGS. 12A and 12B.

  For this basic gamma characteristic, the multiplier 16 first adjusts the inclination. When the multiplication coefficient is 1 or more, the larger the LUT output value, the larger the increase after multiplication, that is, a characteristic in which a large number of gradations are assigned to a bright region such as the dotted line in FIG. . By adding a negative coefficient value to the adder 17 to this, the characteristic as shown by the thick line in FIG. The value after addition is clipped to 0 in the clip unit 18. On the other hand, when the multiplication coefficient is 1 or less, the larger the LUT output value, the larger the decrease in the slope, that is, the characteristic that many gradations are assigned to a dark region such as the dotted line in FIG. Become. By adding a plus coefficient to the adder 17, the characteristic is adjusted to the characteristic shown by the thick line in FIG. The value after the addition is clipped to a desired output data width by the clip unit 18.

In order to obtain the above gamma characteristics, the product-sum coefficient generator 19 calculates the product-sum coefficient based on the two count values as follows, for example.
When the bright part count value> dark part count value and the bright part count value exceeds a certain threshold, the multiplication coefficient K1 is
K1 = 1 + (bright part count value / total number of pixels) × α
And the addition coefficient K2 is
K2 = −K1 × Y
And

  Here, α is a set value for adjusting the change width of K1, and here, 0 <α <10. For example, when α = 0.5, K1 takes a value in the range of 1 to 1.5, so that the multiplier for the basic gamma characteristic can be limited to 1.5 at the maximum. Y is a value that determines the amount by which the multiplied gamma characteristic value is offset, and the offset amount with respect to the basic characteristic can be adjusted by interlocking with the magnitude of K1. For example, in FIG. 12A, since Y is the maximum output value of the basic characteristic, offset is performed so that the maximum value of the basic characteristic matches the output maximum value after the product-sum operation.

On the other hand, when the bright part count value <dark part count value and the dark part count value exceeds the threshold value,
K1 = 1− (dark area count value / total number of pixels) × α
K2 = K1 × Y
And
If the above two conditions are not met,
K1 = 1
K2 = 0
And This is a coefficient that uses the basic characteristics as they are.

  After calculating the product-sum coefficient value, the image processing unit 14 sequentially reads out the image data from the frame memory 5 via the system bus 6, and performs gamma correction using the LUT and the product-sum operation unit and other various image processing. And write back to the frame memory via the system bus.

  With the above configuration, the luminance distribution information of the image can be obtained more easily, and the gamma correction characteristics can be switched dynamically without increasing the processing time with a simple configuration.

(Example 5)
Next, a fifth embodiment of the present invention will be described. In this embodiment, the luminance distribution information calculation unit is configured to be shared with other processes. In the present invention, as the luminance distribution information of the image, the histogram of the entire image or the count value of the bright and dark portions is calculated. In a digital camera, one of the processes that require information from the entire image is, for example, an auto white balance process. The simplest auto white balance processing is to obtain an average value of each color of the entire photographed image and adjust each color signal so that the average value becomes the same value. In the image processing apparatus according to the present invention, As used in the gamma correction unit, if the average value can be calculated in parallel with the writing of the image sensor data to the frame memory, the white balance processing can be performed without extending the processing time.

  Therefore, as shown in FIG. 13, in the digital camera, the luminance distribution information is obtained, and the luminance distribution information / each color average value calculation unit 20 that obtains the average value or the cumulative addition value of each color signal is provided, whereby the processing of FIG. As shown in the sequence, the luminance distribution information and each color average value calculation unit 20 can calculate the luminance distribution information and each color average value at the same time as the imaging data is written to the frame memory, and the parameters for gamma correction and auto white balance Parameters are calculated at the same time, and the image processing unit 21 can perform the gamma correction process and the white balance correction process without increasing the processing time.

1 is a block configuration diagram showing a configuration of Embodiment 1 of an image processing apparatus according to the present invention. It is a figure which shows the process sequence for demonstrating operation | movement of Example 1 shown in FIG. It is a figure which shows the example of weighting with respect to an image. It is a figure which shows the relationship between the histogram regarding brightness, and a cumulative histogram, and the correction | amendment aspect of a cumulative histogram. It is a block block diagram which shows the structure of Example 2 of this invention. It is a figure which shows the process sequence for demonstrating operation | movement of Example 2 shown in FIG. FIG. 6 is a diagram illustrating gamma characteristic curves set in four LUTs in the second embodiment illustrated in FIG. 5. It is a block block diagram which shows the structure of Example 3 of this invention. It is a figure which shows the process sequence for demonstrating operation | movement of Example 3 shown in FIG. It is a block block diagram which shows the structure of Example 4 of this invention. FIG. 11 is a diagram showing a processing sequence for explaining an operation of the fourth embodiment shown in FIG. FIG. 11 is an explanatory diagram illustrating an operation of a product-sum operation unit in the fourth embodiment illustrated in FIG. 10. It is a block block diagram which shows the structure of Example 5 of this invention. FIG. 14 is a diagram showing a processing sequence for explaining the operation of the fifth embodiment shown in FIG. It is a figure which shows the processing sequence for demonstrating the conventional gamma correction method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image pick-up element 2 Histogram calculation part 3 Image processing part 4 CPU
5 Frame memory 6 System bus 7 Bright / dark counter 8 Image processor 9 LUT
10 Selector
11 Image processing section
12 Selector
13 LUT
14 Image processing section
15 LUT
16 multiplier
17 Adder
18 Clip section
19 Product-sum coefficient generator
20 Luminance distribution information / average value calculation unit for each color
21 Image processing section

Claims (7)

  A frame memory that stores image data from the image sensor, a luminance distribution information calculation unit that receives the image data in parallel with the storage in the frame memory, and obtains luminance distribution information of the image data, and the obtained luminance distribution information And a gamma correction unit that performs gamma correction on the image data stored in the frame memory.   The image processing apparatus according to claim 1, wherein the luminance distribution information calculation unit generates the luminance distribution information from a histogram of at least one color signal data in the image data.   The luminance distribution information calculation unit sets a first threshold value and a second threshold value different from the first threshold value for the brightness of at least one color signal data in the image data, At least one of the number of image data equal to or greater than the threshold or the number of image data equal to or less than the second threshold is counted, and the count of image data equal to or greater than the first threshold or image data equal to or less than the second threshold. The image processing apparatus according to claim 1, wherein at least one of the count numbers is used as the luminance distribution information.   The gamma correction unit includes a memory that stores a plurality of lookup tables including gamma correction data corresponding to input image data, and a selector that selects one lookup table in the memory according to the count number. An image processing apparatus according to claim 3.   The gamma correction unit selects a lookup table made of gamma correction data corresponding to input image data to be loaded from the outside according to the count number, and a loaded lookup table. An image processing apparatus according to claim 3, further comprising a memory for storing the image.   The gamma correction unit includes a memory storing a lookup table composed of gamma correction data corresponding to input image data, and a product-sum operation on a coefficient calculated from the count for the gamma correction data from the memory. The image processing apparatus according to claim 3, further comprising: an arithmetic unit that performs the operation.   The image processing apparatus according to claim 1, wherein the luminance distribution information calculation unit sets weighting corresponding to the position of the region of the image data, and calculates the luminance distribution information using the weighting.

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