Image compression circuit for compressing pieces of image data of four adjacent pixels, image compression method, semiconductor device, and smartphone
First Claim
1. An image compression circuit that compresses pieces of image data of four adjacent pixels, the image compression circuit comprising:
- an image calculator for calculating a luminance of each pixel from said image data of each pixel expressed by an RGB color space;
a compression-system decision unit for deciding on a first RGB compression system compressing said image data of each pixel expressed by the RGB color space when a variation in luminance of all the pixels falls within a predetermined range based on the luminance of each pixel, which is calculated by said image calculator, deciding on a second RGB compression system, which differs from said first RGB compression system and compresses said image data of each pixel expressed by the RGB color space, when the variation in luminance of all the pixels does not fall within said predetermined range, and when the variation in luminance of the pixel included in a group falls within said predetermined range in each of two groups into which each pixel is divided based on the luminance of each pixel, and deciding on a YCbCr compression system when the variation in luminance of the pixel included in said group does not fall within said predetermined range in at least one of said two divided groups; and
a compression processor for compressing said image data into image data of one pixel expressed by the RGB color space based on the system decided on by said compression-system decision unit for said first RGB compression system, compressing said image data into image data of one pixel expressed by the RGB color space in each of said groups for said second RGB compression system, and compressing said image data into data including the luminances of the four pixels and image data of one pixel expressed by a YCbCr color space in each of said groups for said YCbCr compression system.
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Abstract
An image compression circuit 1 of the invention includes an image calculator 11, a compression-system decision unit 12, and a compression processor 13. Compression-system decision unit 12 determines a variation of pieces of image data of four adjacent pixels based on a variation in luminance Y of the pixels or variations in luminance Y and saturation S of the pixels, compresses the image data into image data of one or two pixels (RGB 888 and RGB 787) expressed by an RGB color space having a small quantization error in the case of the small variation of the pieces of image data, and compresses the image data into data including the luminances of the four adjacent pixels and pieces of image data of two pixels (YCbCr 422) expressed by a YCbCr color space having a large quantization error in the case of the large variation of the pieces of image data.
6 Citations
29 Claims
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1. An image compression circuit that compresses pieces of image data of four adjacent pixels, the image compression circuit comprising:
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an image calculator for calculating a luminance of each pixel from said image data of each pixel expressed by an RGB color space; a compression-system decision unit for deciding on a first RGB compression system compressing said image data of each pixel expressed by the RGB color space when a variation in luminance of all the pixels falls within a predetermined range based on the luminance of each pixel, which is calculated by said image calculator, deciding on a second RGB compression system, which differs from said first RGB compression system and compresses said image data of each pixel expressed by the RGB color space, when the variation in luminance of all the pixels does not fall within said predetermined range, and when the variation in luminance of the pixel included in a group falls within said predetermined range in each of two groups into which each pixel is divided based on the luminance of each pixel, and deciding on a YCbCr compression system when the variation in luminance of the pixel included in said group does not fall within said predetermined range in at least one of said two divided groups; and a compression processor for compressing said image data into image data of one pixel expressed by the RGB color space based on the system decided on by said compression-system decision unit for said first RGB compression system, compressing said image data into image data of one pixel expressed by the RGB color space in each of said groups for said second RGB compression system, and compressing said image data into data including the luminances of the four pixels and image data of one pixel expressed by a YCbCr color space in each of said groups for said YCbCr compression system. - View Dependent Claims (3, 4, 5, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 26, 27, 28, 29)
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2. An image compression circuit that compresses pieces of image data of four adjacent pixels, the image compression circuit comprising:
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an image calculator for calculating a luminance and a saturation of each pixel from said image data of each pixel expressed by an RGB color space; a compression-system decision unit for deciding on a first RGB compression system compressing said image data of each pixel expressed by the RGB color space when variations in luminance and saturation of all the pixels fall within a predetermined range based on the luminance and the saturation of each pixel, which are calculated by said image calculator, deciding on a second RGB compression system, which differs from said first RGB compression system and compresses said image data of each pixel expressed by the RGB color space, when the variations in luminance and saturation of all the pixels do not fall within said predetermined range, and when the variation in luminance and saturation of the pixel included in a group falls within said predetermined range in each of two groups into which each pixel is divided based on the saturation of each pixel, and deciding on a YCbCr compression system when the variations in luminance and saturation of the pixel included in said group do not fall within said predetermined range in at least one of said two divided groups; and a compression processor for compressing said image data into image data of one pixel expressed by the RGB color space based on the system decided on by said compression-system decision unit for said first RGB compression system, compressing said image data into image data of one pixel expressed by the RGB color space in each of said groups for said second RGB compression system, and compressing said image data into data including the luminances of the four pixels and image data of one pixel expressed by a YCbCr color space in each of said groups for said YCbCr compression system. - View Dependent Claims (6, 7, 8)
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24. An image compression method for compressing pieces of image data of four adjacent pixels, the image compression method comprising:
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a first step of calculating a luminance of each pixel from said image data of each pixel expressed by an RGB color space; a second step of deciding on a first RGB compression system compressing said image data of each pixel expressed by the RGB color space when a variation in luminance of all the pixels falls within a predetermined range based on the calculated luminance of each pixel, deciding on a second RGB compression system, which differs from said first RGB compression system and compresses said image data of each pixel expressed by the RGB color space, when the variation in luminance of all the pixels does not fall within said predetermined range, and when the variation in luminance of the pixel included in a group falls within said predetermined range in each of two groups into which each pixel is divided based on the luminance of each pixel, and deciding on a YCbCr compression system when the variation in luminance of the pixel included in said group does not fall within said predetermined range in at least one of said two divided groups; and a third step of compressing said image data into image data of one pixel expressed by the RGB color space based on the decided system for said first RGB compression system, compressing said image data into image data of one pixel expressed by the RGB color space in each of said groups for said second RGB compression system, and compressing said image data into data including the luminances of the four pixels and image data of one pixel expressed by a YCbCr color space in each of said groups for said YCbCr compression system.
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25. An image compression method for compressing pieces of image data of four adjacent pixels, the image compression method comprising:
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a first step of calculating a luminance and a saturation of each pixel from said image data of each pixel expressed by an RGB color space; a second step of deciding on a first RGB compression system compressing said image data of each pixel expressed by the RGB color space when variations in luminance and saturation of all the pixels fall within a predetermined range based on the calculated luminance and the calculated saturation of each pixel, deciding on a second RGB compression system, which differs from said first RGB compression system and compresses said image data of each pixel expressed by the RGB color space, when the variations in luminance and saturation of all the pixels do not fall within said predetermined range, and when the variation in luminance and saturation of the pixel included in a group falls within said predetermined range in each of two groups into which each pixel is divided based on the saturation of each pixel, and deciding on a YCbCr compression system when the variations in luminance and saturation of the pixel included in said group do not fall within said predetermined range in at least one of said two divided groups; and a third step of compressing said image data into image data of one pixel expressed by the RGB color space based on the decided system for said first RGB compression system, compressing said image data into image data of one pixel expressed by the RGB color space in each of said groups for said second RGB compression system, and compressing said image data into data including the luminances of the four pixels and image data of one pixel expressed by a YCbCr color space in each of said groups for said YCbCr compression system.
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Specification