TWI763049B - Camera device and image processing method for automatic exposure - Google Patents

Abstract

A camera device includes a photosensitive module, an image signal processor, a first exposure table and a second exposure table. The photosensitive module has a plurality of photosensitive elements configured to receive an ambient light and generate a sensing image. The image signal processor is configured to receive the sensing image and correspondingly set an automatic exposure target brightness. When the automatic exposure target brightness does not match the first exposure table, the image signal processor performs image processing on the sensing image to generate a first image and compensates the first image according to the brightness of the first image and the second exposure table to generate a second image, so that the brightness of the second image meets the automatic exposure target brightness. The brightness value of each pixel of the first image is the sum of the brightness values of at least two corresponding adjacent pixels in the photosensitive image.

Description

Image pickup device and image processing method for automatic exposure

The present disclosure relates to a camera device, and more particularly, to a camera device capable of reducing image noise.

With the development of technology, many electronic devices (such as smart phones) nowadays have the function of taking pictures or videos. Through the camera module disposed on the electronic device, the user can operate the electronic device to capture various photos.

The design of today's electronic devices is constantly developing towards the trend of miniaturization, so that various components or structures of the camera module must also be continuously reduced in order to achieve the purpose of miniaturization. However, when the miniaturized photosensitive element needs to output high pixels, the pixel size on the photosensitive element must be reduced. However, the reduction of the pixel size will lead to insufficient sensitivity of the photosensitive element. Therefore, when the ambient light source is insufficient, the image generated by the camera module will have obvious noise.

Therefore, how to improve the sensitivity of the photosensitive element and reduce the noise of the image is a topic worthy of discussion and resolution.

In view of this, the present disclosure proposes a camera device to solve the above problems.

The present disclosure provides a camera device including a photosensitive module, an image signal processor, a first exposure table and a second exposure table. The photosensitive module has a plurality of photosensitive elements configured to receive an ambient light and generate a sensing image. The image signal processor is configured to receive the sensing image and set an automatic exposure target brightness correspondingly. When the brightness of the automatic exposure target does not meet the first exposure table, the image signal processor performs image processing on the sensed image to generate a first image, and compensates the first image according to the brightness of the first image and the second exposure table to generate a first image. The second image, so that the brightness of the second image matches the automatic exposure target brightness. The luminance value of each pixel of the first image is the sum of the luminance values of at least two corresponding adjacent pixels in the photosensitive image.

The present disclosure provides an image processing method for automatic exposure, which includes: receiving an ambient light by a photosensitive module to generate a sensing image; receiving the sensing image through an image signal processor and correspondingly setting an automatic exposure Target brightness; when the brightness of the sensed image is less than the automatic exposure target brightness, the image signal processor determines whether the automatic exposure target brightness conforms to a first exposure table; when the automatic exposure target brightness does not meet the first exposure table, the image signal The processor performs image processing on the sensing image to generate a first image, wherein the luminance value of each pixel of the first image is the sum of the luminance values of at least two adjacent pixels in the sensing image; and an image signal processor The first image is compensated according to the brightness of the first image and a second exposure meter to generate a second image, so that the brightness of the second image can meet the target brightness of automatic exposure.

The present disclosure provides an image processing method for automatic exposure, comprising: detecting an illuminance of an ambient light by a photosensitive module and generating a sensing image; judging by an image signal processor whether the illuminance is less than a first Threshold; when the illuminance is less than the first threshold, the image signal processor further determines whether the illuminance is less than a second threshold; when the illuminance is less than the first threshold and greater than or equal to the second threshold, the image signal processor will sense The image is subjected to image processing to generate a first image, wherein the brightness value of each pixel of the first image is the sum of the brightness values of at least two adjacent pixels in the photosensitive image; and the image signal processor is based on the first image. The brightness and a second exposure meter compensate the first image to generate a second image, so that the brightness of the second image conforms to an automatic exposure target brightness, wherein the automatic exposure target brightness corresponds to the illuminance of ambient light.

The present disclosure provides a camera device including a photosensitive module and an image signal processor. The photosensitive module is configured to receive an ambient light and generate a sensing image. The image signal processor sets an automatic exposure target brightness according to the brightness of the sensing image, and further performs image processing on the sensing image to generate a brightness that meets the automatic exposure target. image to achieve automatic exposure function.

A preset first exposure table is stored in the camera device, and the image signal processor can compensate the sensed image according to the first exposure table, so that the brightness of the final output image conforms to the target brightness of automatic exposure. However, in some embodiments, when the camera device is located in a dark environment, using the setting of the first exposure meter may cause the output image to have too much noise, so the image signal processor can image the sensing image. The processing generates a first image, and the first image is compensated according to the second exposure table. Since the gain and exposure time to achieve the required automatic exposure target brightness in the second exposure table are smaller than those in the first exposure table, noise in the output image can be effectively reduced.

The words "including" and "including" mentioned in the entire specification and the scope of the patent application are open-ended terms, so they should be interpreted as "including but not limited to". The word "substantially" means that within an acceptable error range, those skilled in the art can solve the technical problem within a certain error range and achieve the basic technical effect.

Various embodiments of the present invention are described in detail with reference to the accompanying drawings. The use of the same reference numbers in the figures refers to the same or similar elements. These examples are intended to illustrate the general principles of the invention and should not be construed in a limiting sense. Detailed descriptions of well-known functions and structures will be omitted to avoid obscuring the subject matter of the present invention.

Notably, references to different "an" or "one" embodiment in this disclosure are not necessarily the same embodiment, and references are to at least one. Furthermore, when a particular feature, structure or characteristic is described in connection with an embodiment, it will be recognized that a person of ordinary skill in the art, whether described in detail or not, would be within the purview of the art to assign such feature. , structures or characteristics are linked to the remaining embodiments.

The ordinal numbers in this specification and the scope of the patent application, such as "first", "second", "third", etc., do not have a sequential relationship with each other, and are only used to mark and distinguish two identical different elements of the name.

Please refer to FIG. 1. FIG. 1 is a schematic block diagram of a camera device 100 according to an embodiment of the present disclosure. The camera device 100 can be installed on an electronic device or a portable electronic device, such as a digital camera, a notebook computer, a tablet computer, a smart phone, etc., and the camera device 100 can generate a digital image or a digital image after receiving an external light. digital video.

In this embodiment, the camera device 100 may include an image sensor 102 , a memory 108 , an encoder 110 and an image output interface 112 . The image sensor 102 may include a photosensitive module 104 and an image signal processor 106 . The photosensitive module 104 generates a sensing image to the image signal processor 106 after receiving external light, and the photosensitive module 104 may include a lens, a shutter (not shown in the figure) and a photosensitive element 105 (FIG. 2).

Please refer to FIG. 2 , which is a schematic diagram of a photosensitive element 105 according to an embodiment of the present disclosure. In this embodiment, the photosensitive element 105 has a plurality of photosensitive pixels 1051, such as 8*8 photosensitive pixels, arranged in a matrix manner. The size of the photosensitive pixels is, for example, 0.8 μm, but the size and number thereof are not limited thereto.

The image signal processor 106 (Image Signal Processor, ISP) is a processing chip, which can perform image processing on the sensed image, such as adjusting the gain of the sensed image, and can also control the shutter to adjust the exposure time, so as to make the camera The device 100 achieves the function of automatic exposure. After the image signal processor 106 processes the sensed image, a processed image can be generated and provided to the memory 108 .

The memory 108 can be a random access memory (RAM), a flash memory, or the like, which serves as a buffer memory for storing multiple frames of processed images.

The encoder 110 may include, for example, a JPEG encoder and an image encoder configured to compress the plurality of processed images and output them to the image output interface 112 . The image output interface 112 is, for example, a display panel for displaying the compressed image or video to the user for viewing.

Please refer to FIGS. 1 to 3. FIG. 3 is a flowchart of an image processing method 300 for automatic exposure according to an embodiment of the present disclosure. In step 302, the photosensitive module 104 receives external light (ambient light) to generate a sensing image.

In step 304, the image signal processor 106 calculates the brightness Y of the sensed image after receiving the sensed image, and the brightness Y can be, for example, a grayscale value. Next, the image signal processor 106 can correspondingly set an auto exposure target (auto exposure target, AE target for short) according to the luminance Y.

In step 306, the brightness Y of the sensing image is compared with the brightness of the automatic exposure target. For example, in one embodiment, the brightness Y is 100, and the automatic exposure target brightness is 110, which is greater than the brightness Y.

Next, in step 308, when the brightness Y of the sensed image is less than the automatic exposure target brightness, the image signal processor 106 further determines whether the automatic exposure target brightness conforms to a first exposure table. The first exposure table is a preset exposure table in the camera device 100 and is stored in the image signal processor 106 . The first exposure table can be, for example, Table 1 below.

[Table I] Ambient Illuminance (Lux) Gain Exposure time Lux index AE target brightness (AE target) 2000 1.3 0.03 ms 100 50 500 4 0.039 ms 200 70 100 8 0.0975 ms 295 110 50 10 0.0156 ms 320 120 20 10 0.016 ms 350 130

The image signal processor 106 inquires whether there is a setting in the first exposure table that meets the target brightness of the automatic exposure. It can be seen from Table 1 that the setting corresponding to the illuminance index 295 can conform to the situation that the target brightness of the automatic exposure is 110. That is, the brightness of the automatic exposure target conforms to the first exposure table. In this case, step 310 can be further performed.

In step 310, when the automatic exposure target brightness conforms to the first exposure table, the image signal processor 106 adjusts the light sensitivity according to the brightness Y of the sensed image, the automatic exposure target brightness, and the setting corresponding to the selected illuminance index 295 of the first exposure table The module 104 has a shutter time (exposure time) and a gain value to compensate the sensing image.

In addition, in other embodiments, when the camera device 100 is located in a dark environment, for example, when the ambient light intensity is less than 20 lux, the image signal processor 106 correspondingly sets the automatic exposure target brightness to be, for example, 140. It can be seen from Table 1 that the image signal processor 106 cannot find the illuminance index corresponding to the automatic exposure target brightness of 140 in the first exposure table, which means that the automatic exposure target brightness does not conform to the first exposure table.

In step 312, when the brightness of the automatic exposure target does not meet the first exposure table, the image signal processor 106 performs image processing on the sensed image to generate a first image, wherein the brightness value of each pixel of the first image is The sum of the brightness values of at least two adjacent pixels in the photosensitive image.

Specifically, please refer to FIGS. 4 and 5. FIG. 4 is a schematic diagram of a photosensitive image SG according to an embodiment of the present disclosure, and FIG. 5 is a schematic diagram of a first image IG1 according to an embodiment of the present disclosure. . The photosensitive image SG has M*N pixels, where M and N are natural numbers. In this embodiment, as shown in FIG. 4 , M=8 and N=8, which correspond to the number of photosensitive elements 105 in FIG. 2 . In other embodiments, M may not be equal to N.

In Figure 5, the first image IG1 has 4*8 pixels, wherein the brightness (gray value) of the pixel PB1 of the first image IG1 is the brightness value (gray value) of the two adjacent pixels PA1 and PA2 of the photosensitive image SG The luminance value of the pixel PB2 of the first image IG1 is the sum of the luminance values of the two adjacent pixels PA3 and PA4 of the photosensitive image SG, and the luminance value of the pixel PB3 of the first image IG1 is the photosensitive image. The sum of the luminance values of two adjacent pixels PA5 and PA6 of SG, and so on.

Next, in step 314, the image signal processor 106 compensates the first image IG1 according to the brightness (eg, average brightness) of the first image IG1 and a second exposure table to generate a second image, so that the brightness of the second image is Matches the AE target brightness. The second exposure table can be, for example, the second table below.

[Table II] Ambient Illuminance (Lux) Gain Exposure time Lux index AE target brightness (AE target) 2000 1 0.015 100 50 500 2 0.015 200 90 100 8 0.0375 295 140 50 8 0.075 320 150 20 10 0.08 350 170

In this embodiment, the image signal processor 106 inquires whether there is a setting in the second exposure table that complies with the automatic exposure target brightness of 140. It can be seen from Table 2 that the setting corresponding to the illuminance index 295 can conform to the situation that the target brightness of the automatic exposure is 140. Therefore, the image signal processor 106 uses the setting of the illuminance index 295 to adjust the shutter time and gain value of the photosensitive module 104 to compensate the first image IG1 to obtain the second image, so that the brightness of the second image is approximately equal to 140.

Since the exposure time and gain value used in Table 2 are relatively small, the noise problem of the image output by the image sensor 102 can be reduced.

Please refer to FIG. 4 and FIG. 6. FIG. 6 is a schematic diagram of a first image IG1' according to another embodiment of the present disclosure. In another embodiment, as shown in FIG. 6, the first image IG1' generated in step 312 may have 8*4 pixels, wherein the luminance value (gray-scale value of the pixel PC1 of the first image IG1' is ) is the sum of the luminance values of the two adjacent pixels PA1 and PA5 of the photosensitive image SG, and the luminance value of the pixel PC2 of the first image IG1' is the sum of the luminance values of the two adjacent pixels PA2 and PA6 of the photosensitive image SG and the luminance value of the pixel PC3 of the first image IG1 ′ is the sum of the luminance values of the two adjacent pixels PA9 and PA10 of the photosensitive image SG, and so on.

Next, in step 314, the image signal processor 106 may also look up the setting corresponding to the automatic exposure target brightness in the second exposure table to compensate the first image IG1'.

Please refer to FIG. 4 and FIG. 7. FIG. 7 is a schematic diagram of a first image IG1'' according to another embodiment of the present disclosure. In this embodiment, as shown in FIG. 7 , the first image IG1 ″ generated in step 312 has 4*4 pixels, wherein the luminance value (gray-scale value of the pixel PD1 of the first image IG1 ″ is ) is the sum of the luminance values of the four adjacent pixels PA1, PA2, PA5 and PA6 of the photosensitive image SG, and the luminance value of the pixel PD2 of the first image IG1″ is the luminance value of the four adjacent pixels PA3 of the photosensitive image SG , the sum of the brightness values of PA4, PA7 and PA8, and so on.

Since the brightness of the first image IG1'' is greater than that of the first image IG1', in step 314, the image signal processor 106 can search a third exposure table to compensate the first image IG1''. The third exposure table can be, for example, the third table below.

[Table 3] Ambient Illuminance (Lux) Gain Exposure time Lux index AE target brightness (AE target) 2000 1 0.0019 100 50 500 2 0.0038 200 90 100 4 0.0094 295 140 50 8 0.0094 320 150 20 10 0.004 350 170

In this embodiment, it can be seen from Table 3 that the setting corresponding to the illuminance index 295 can conform to the situation where the automatic exposure target brightness is 140. Therefore, the image signal processor 106 uses the setting of the illuminance index 295 to adjust the shutter time and gain value of the photosensitive module 104, so as to compensate the first image IG1'' to obtain a second image, so that the brightness of the second image is approximately equal to 140.

In the case of corresponding to the same automatic exposure target brightness, since the exposure time and gain value used in Table 3 are smaller than those in Table 2, the noise problem of the image output by the image sensor 102 can be further reduced .

Please refer to Figure 8. FIG. 8 is a flowchart of an image processing method 800 for automatic exposure according to another embodiment of the present disclosure. In step 802 , the photosensitive module 104 detects an illuminance of an ambient light and generates a sensed image (eg, the photosensitive image SG in FIG. 4 ).

In step 803 , an automatic exposure target brightness is correspondingly set according to the brightness Y of the sensed image by the image signal processor 106 . In step 804, the image signal processor 106 determines whether the illuminance is less than a first threshold, wherein the first threshold is, for example, 100 lux.

In step 806, when the illumination of the environment is greater than the first threshold value, the image signal processor 106 can adjust the shutter time and gain value of the photosensitive module 104 according to the brightness of the sensed image and the preset first exposure table, thereby Compensate the sensed image.

In addition, when the illuminance is less than the first threshold, in step 808, the image signal processor 106 further determines whether the illuminance is less than a second threshold, for example, 50 lux.

When the illuminance is less than the first threshold and greater than or equal to the second threshold, in step 810 , the image signal processor 106 performs image processing on the sensed image to generate a first image (as shown in FIG. 5 or FIG. 6 ) , wherein the brightness value of each pixel of the first image is the sum of the brightness values of at least two adjacent pixels in the photosensitive image.

Next, in step 812, the image signal processor 106 compensates the first image to generate the second image according to the brightness of the first image and the second exposure table, so that the brightness of the second image conforms to the automatic exposure target brightness, wherein the automatic exposure target Brightness corresponds to the illuminance of ambient light.

When the illuminance is less than the second threshold, in step 814 , the image signal processor 106 performs image processing on the sensed image to generate a first image (as shown in FIG. 7 ), and the brightness of each pixel of the first image is The value is the sum of the brightness values of the corresponding adjacent four pixels in the photosensitive image, wherein the photosensitive image has M*N pixels, and the first image has M/2*N/2 pixels, and M, N are natural numbers .

Next, in step 816 , the image signal processor 106 compensates the first image to generate the second image according to the brightness of the first image and the third exposure table, so that the brightness of the second image matches the automatic exposure target brightness.

In addition, it should be noted that in other embodiments, the first image in step 814 may also have M/4*N/2 pixels, M/2*N/4 pixels, M/4*N/4 pixels pixels, etc., and so on for the rest.

The present disclosure provides a camera device 100 including a photosensitive module 104 and an image signal processor 106 . The photosensitive module 104 is configured to receive an ambient light and generate a sensed image. The image signal processor 106 sets an automatic exposure target brightness according to the brightness of the sensed image, and further performs image processing on the sensed image to generate an automatic exposure compliant The image of the target brightness to achieve the function of automatic exposure.

The camera device 100 stores a preset first exposure table, and the image signal processor 106 can compensate the sensed image according to the first exposure table, so that the brightness of the final output image conforms to the automatic exposure target brightness. However, in some embodiments, when the camera device 100 is located in a dark environment, using the setting of the first exposure table may cause the output image to have too much noise, so the image signal processor 106 can detect the image. The image processing is performed to generate a first image, and the first image is compensated according to the second exposure table. Since the gain and exposure time to achieve the required automatic exposure target brightness in the second exposure table are smaller than those in the first exposure table, noise in the output image can be effectively reduced.

Although the embodiments of the present disclosure and their advantages have been disclosed above, it should be understood that those skilled in the art can make changes, substitutions and modifications without departing from the spirit and scope of the present disclosure. In addition, the protection scope of the present disclosure is not limited to the process, machine, manufacture, material composition, device, method and steps in the specific embodiments described in the specification. It is understood that processes, machines, manufactures, compositions of matter, devices, methods and steps developed in the present or in the future can be used in accordance with the present disclosure as long as they can perform substantially the same functions or obtain substantially the same results in the embodiments described herein. Therefore, the protection scope of the present disclosure includes the above-mentioned processes, machines, manufactures, compositions of matter, devices, methods and steps. In addition, each claimed scope constitutes a separate embodiment, and the protection scope of the present disclosure also includes the combination of each claimed scope and the embodiments.

100: Camera device 102: Image sensor 104: Photosensitive module 105: Photosensitive element 1051: photosensitive pixel 106: Image Signal Processor 108: Memory 110: Encoder 112: Image output interface PA1, PA2, PA3, PA4, PA5, PA6, PA9, PA10: Pixels IG1, IG1', IG'': First image PB1, PB2, PB3, PC1, PC2, PC3, PD1, PD2: Pixels SG: Photosensitive Image 300, 800: method 302, 304, 306, 308, 310, 312, 314, 802, 803, 804, 806, 808, 810, 812, 814, 816: Steps

The present disclosure can be clearly understood from the following detailed description in conjunction with the drawings. It is emphasized that, in accordance with standard industry practice, the various features are not drawn to scale and are used for illustration purposes only. In fact, the dimensions of various features may thus be arbitrarily expanded or reduced for clarity of illustration. FIG. 1 is a block diagram of a camera device 100 according to an embodiment of the present disclosure. FIG. 2 is a schematic diagram of a photosensitive element 105 according to an embodiment of the present disclosure. FIG. 3 is a flowchart of an image processing method 300 for automatic exposure according to an embodiment of the present disclosure. FIG. 4 is a schematic diagram of a photosensitive image SG according to an embodiment of the present disclosure. FIG. 5 is a schematic diagram of a first image IG1 according to an embodiment of the present disclosure. FIG. 6 is a schematic diagram of a first image IG1' according to another embodiment of the present disclosure. FIG. 7 is a schematic diagram of a first image IG1'' according to another embodiment of the present disclosure. FIG. 8 is a flowchart of an image processing method 800 for automatic exposure according to another embodiment of the present disclosure.

100: Camera device 102: Image sensor 104: Photosensitive module 106: Image Signal Processor 108: Memory 110: Encoder 112: Image output interface

Claims (14)

A camera device, comprising: a photosensitive module with a plurality of photosensitive elements, configured to receive an ambient light and generate a sensed image; an image signal processor, configured to receive the sensed image and correspondingly set an automatic exposure target brightness; a first exposure table; and a second exposure table; wherein when the automatic exposure target brightness does not meet the first exposure table, the image signal processor performs image processing on the sensed image to generate a first image, and compensate the first image according to the brightness of the first image and the second exposure meter to generate a second image, so that the brightness of the second image conforms to the target brightness of the automatic exposure; wherein each of the first image The luminance value of a pixel is the sum of the luminance values of at least two adjacent pixels in the sensing image. The camera device of claim 1, wherein the sensing image has M*N pixels, and the first image has M/2*N pixels, wherein M and N are natural numbers. The camera device of claim 1, wherein the sensing image has M*N pixels, and the first image has M*N/2 pixels, wherein M and N are natural numbers. The camera device of claim 1, wherein the sensing image has M*N pixels, and the first image has M/2*N/2 pixels, where M and N are natural numbers. The camera device of claim 1, wherein when the automatic exposure target brightness conforms to the first exposure table, the image signal processor adjusts one of the photosensitive modules according to the brightness of the sensed image and the first exposure table The shutter time and a gain value are used to compensate the sensing image. An image processing method for automatic exposure, comprising: receiving an ambient light through a photosensitive module to generate a sensing image; receiving the sensing image through an image signal processor and correspondingly setting an automatic exposure target brightness ; When the brightness of the sensing image is less than the brightness of the automatic exposure target, determine whether the brightness of the automatic exposure target conforms to a first exposure table by the image signal processor; when the brightness of the automatic exposure target does not meet the first exposure table When , the image signal processor performs image processing on the sensing image to generate a first image, wherein the luminance value of each pixel of the first image is the luminance of at least two adjacent pixels corresponding to the sensing image and the image signal processor compensates the first image to generate a second image according to the brightness of the first image and a second exposure table, so that the brightness of the second image conforms to the automatic exposure target brightness. The image processing method for automatic exposure as claimed in claim 6, wherein when the automatic exposure target brightness conforms to the first exposure table, the image signal processing The device adjusts a shutter time and a gain value of the photosensitive module according to the brightness of the sensing image and the first exposure meter, so as to compensate the sensing image. The image processing method for automatic exposure according to claim 6, wherein the sensing image has M*N pixels, and the first image has M/2*N pixels, wherein M and N are natural numbers. The image processing method for automatic exposure according to claim 6, wherein the sensing image has M*N pixels, and the first image has M*N/2 pixels, wherein M and N are natural numbers. The image processing method for automatic exposure according to claim 6, wherein the sensing image has M*N pixels, and the first image has M/2*N/2 pixels, wherein M and N are natural number. An image processing method for automatic exposure, comprising: detecting an illuminance of an ambient light by a photosensitive module and generating a sensing image; judging by an image signal processor whether the illuminance is less than a first threshold ; When the illuminance is less than the first threshold, the image signal processor further determines whether the illuminance is less than a second threshold; when the illuminance is less than the first threshold and greater than or equal to the second threshold, the image The signal processor performs image processing on the sensing image to generate a first image, wherein the luminance value of each pixel of the first image is the sum of the luminance values of at least two adjacent pixels corresponding to the sensing image; and the image signal processor compensates the first image to generate a second image according to the brightness of the first image and a second exposure table, so as to make the brightness of the second image An automatic exposure target brightness is matched, wherein the automatic exposure target brightness corresponds to the illuminance of the ambient light. The image processing method for automatic exposure as claimed in claim 11, wherein when the illuminance is greater than the first threshold, the image signal processor adjusts the photosensitive mode according to the brightness of the sensed image and a first exposure meter A shutter time and a gain value are set to compensate the sensing image. The image processing method for automatic exposure as claimed in claim 11, wherein when the illuminance is less than the second threshold, the image signal processor performs image processing on the sensing image to generate the first image, and the The luminance value of each pixel of the first image is the sum of the luminance values of corresponding adjacent four pixels in the sensing image, wherein the sensing image has M*N pixels, and the first image has M/2 *N/2 pixels, where M and N are natural numbers. The image processing method for automatic exposure as claimed in claim 11, wherein the sensing image has M*N pixels, and the first image has M*N/2 or M/2*N pixels, wherein M , N is a natural number.

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