Image compression with color interpolation for a single sensor image system
First Claim
1. Apparatus for transmitting and receiving a color image signal representing the amplitudes of a single image plane of pixels, each one of said pixels representing a respective one of three different colors whereby pixels of pairs of said colors are missing at sites of respective individual pixels, one of said three colors being more closely related to luminance than the remaining colors, said apparatus comprising:
- A) transmitting means comprising;
1) means for transforming the amplitude of each of said pixels to a Γ
-space amplitude by changing its original value A to A1/Γ
, where Γ
is a real number, whereby the Γ
-space amplitudes of the pixels of said one color comprise a first input color data plane;
2) first means for inferring by interpolation the Γ
-space amplitudes of the missing pixels of said one color;
3) means for forming second and third input color data planes of respective color difference signals by subtracting the Γ
-space amplitudes of said missing pixels of said one color from the Γ
-space amplitudes of corresponding pixels of each of said remaining colors, respectively;
4) means for compressing each of said input color data planes to form corresponding first, second and third compressed color data planes;
B) receiving means comprising;
1) means for decompressing said first, second and third compressed color data planes to form, respectively, first, second and third decompressed color data planes;
2) means for converting said first, second and third decompressed color data planes to first, second and third output color data planes, respectively, of Γ
-space amplitudes of pixels of respective ones of said three colors;
3) means for edge enhancing said first, second and third output color data planes; and
4) means for back-transforming each of the Γ
-space amplitudes A1/Γ
of the pixels of said output color data planes to amplitudes A.
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Accused Products
Abstract
In accordance with the present invention, the R,G,B color image signals from a single sensor having a color filter array are all transformed to Γ-space by changing them to R1/Γ, G1/Γ, B1/Γ, respectively, where Γ is approximately 2.4. In this space, all operations such as color differencing, interpolation of those missing pixels required for color differencing, compression, decompression, edge enhancement and final interpolation of all missing pixels are performed without further transformation of the image signals. For the same final bit rate, noise in the reproduced image is reduced by refraining from interpolating the missing color pixels prior to compression of the image data. In order to avoid over-emphasizing features of the image which are already sufficiently sharp, the combined outputs of horizontal and vertical sharpening processes are subjected to a paring process of the invention which suppresses strong high-spatial frequency components as a function of their amplitude. In the compression-decompression process of the invention, each spatial frequency coefficient of the spatial frequency-transformed image is divided by a normalization factor determined by cascading in the spatial frequency domain the human visual system contrast sensitivity function, the edge enhancement modulation transfer function and the image display modulation transfer function and inversing the resulting matrix elements.
97 Citations
62 Claims
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1. Apparatus for transmitting and receiving a color image signal representing the amplitudes of a single image plane of pixels, each one of said pixels representing a respective one of three different colors whereby pixels of pairs of said colors are missing at sites of respective individual pixels, one of said three colors being more closely related to luminance than the remaining colors, said apparatus comprising:
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A) transmitting means comprising; 1) means for transforming the amplitude of each of said pixels to a Γ
-space amplitude by changing its original value A to A1/Γ
, where Γ
is a real number, whereby the Γ
-space amplitudes of the pixels of said one color comprise a first input color data plane;2) first means for inferring by interpolation the Γ
-space amplitudes of the missing pixels of said one color;3) means for forming second and third input color data planes of respective color difference signals by subtracting the Γ
-space amplitudes of said missing pixels of said one color from the Γ
-space amplitudes of corresponding pixels of each of said remaining colors, respectively;4) means for compressing each of said input color data planes to form corresponding first, second and third compressed color data planes; B) receiving means comprising; 1) means for decompressing said first, second and third compressed color data planes to form, respectively, first, second and third decompressed color data planes; 2) means for converting said first, second and third decompressed color data planes to first, second and third output color data planes, respectively, of Γ
-space amplitudes of pixels of respective ones of said three colors;3) means for edge enhancing said first, second and third output color data planes; and 4) means for back-transforming each of the Γ
-space amplitudes A1/Γ
of the pixels of said output color data planes to amplitudes A. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. Apparatus for transmitting and receiving image data as arrays of pixels comprising:
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means for sectioning the arrays of pixels into plural blocks of pixels; means for spatial frequency transforming each of said blocks of pixels to form two-dimensional arrays of spatial frequency coefficients; means for determining the number of cycles per pixel of each of said spatial frequency coefficients from the number of pixels in each row and column of a two-dimensional array of pixels wherein each pixel is associated with two positional indices; edge enhancement modulation transfer function means for associating the two positional indices of each spatial coefficient with an associated value of an edge enhancement modulation transfer function at a corresponding spatial frequency in cycles per pixel to form an edge enhancement modulation transfer function array; means for determining the number of cycles per unit distance of each of said spatial frequency coefficients form pixel spacing; display modulation transfer function means for associating the two positional indices of each spatial frequency coefficient with an associated value of the display modulation transfer function in cycles per unit distance to form a display modulation transfer function array; means for determining the number of cycles per degree of visual angle of each of said spatial frequency coefficients from a viewing distance; human visual contrast sensitivity means for associating the two positional indices of each spatial frequency coefficient with an associated value of a human visual contrast sensitivity function in cycle per degree to form a visual contrast sensitivity function array; and means for combining said function arrays together to form a cascaded array the output of which is a normalization array. - View Dependent Claims (22, 23, 24)
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25. Apparatus for edge enhancing a color image comprising three arrays of rows and columns of pixel amplitudes corresponding to three colors, one of said colors being more related to luminance than the others, comprising:
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means for bandpass filtering each column of pixel amplitudes of said color related to luminance to produce a corresponding column of bandpass filtered pixel amplitudes; means for bandpass filtering each row of pixel amplitudes of said color related to luminance to produce a corresponding row of bandpass filtered pixel amplitudes; means for combining said bandpass filtered pixel rows and columns to produce two-dimensionally bandpass filtered pixel amplitudes; means for paring said two-dimensionally bandpass filtered amplitudes so as to boost high spatial frequency components having lower amplitudes and so as to attenuate high spatial frequency components having higher amplitudes; and means for adding the two-dimensionally bandpass filtered pixel amplitudes to corresponding amplitudes of the pixels of each of said three colors. - View Dependent Claims (26, 27)
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28. Apparatus for transmitting a color image signal representing the amplitudes of a single image plane of pixels, each one of said pixels representing a respective one of three different colors whereby pixels of pairs of said colors are missing at sites of respective individual pixels, one of said three colors being more closely related to luminance than the remaining colors, said apparatus comprising:
-
means for transforming the amplitude of each of said pixels to a Γ
-space amplitude by changing its original value A to A1/Γ
, where Γ
is a real number, whereby the Γ
-space amplitudes of the pixels of said one color comprise a first input color data plane;first means for inferring by interpolation the Γ
-space amplitudes of the missing pixels of said one color;means for forming second and third input color data planes of respective color difference signals by subtracting the Γ
-space amplitudes of said missing pixels of said one color from the Γ
-space amplitudes of corresponding pixels of each of said remaining colors, respectively; andmeans for compressing each of said input color data planes to form corresponding first, second and third compressed color data planes. - View Dependent Claims (29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39)
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40. An apparatus for forming a normalization array, utilizing a two-dimensional array whose indices represent the spatial frequency coefficients resulting from the transformation of a digital image comprising:
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means for determining the number of cycles per pixel of each of said spatial frequency coefficients from the number of pixels in each row and column of a two dimensional array of pixels wherein each pixel is associated with two positional indices; edge enhancement modulation transfer function means for associating the two positional indices of each spatial coefficient with an associated value of an edge enhancement modulation transfer function at a corresponding spatial frequency in cycles per pixel to form an edge enhancement modulation transfer function array; means for determining the number of cycles per unit distance of each of said spatial frequency coefficients form pixel spacing; display modulation transfer function means for associating the two positional indices of each spatial frequency coefficient with an associated value of the display modulation transfer function in cycles per unit distance to form a display modulation transfer function array; means for determining the number of cycles per degree of visual angle of each of said spatial frequency coefficients from a viewing distance; human visual contrast sensitivity means for associating the two positional indices of each spatial frequency coefficient with an associated value of a human visual contrast sensitivity function in cycle per degree to form a visual contrast sensitivity function array; and means for combining said function arrays together to form a cascaded array the output of which is a normalization array. - View Dependent Claims (41, 42, 43)
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44. Apparatus for receiving a color image signal comprising compressed data corresponding to Γ
- -space amplitudes A1/Γ
of a single image plane of pixels, each one of said pixels representing a respective one of three different colors whereby pixels of pairs of said colors are missing at sites of respective individual pixels, one of said three colors being more closely related to luminance than the remaining colors, said compressed data comprising a first compressed color data plane comprising the Γ
-space amplitudes of the pixels of said one color and second and third compressed color data planes comprising respective color difference signals formed by subtracting interpolated Γ
-space amplitudes of missing pixels of said one color from the Γ
-space amplitudes of corresponding pixels of each of said remaining colors, respectively, said apparatus comprising;means for decompressing said compressed data to form first, second and third decompressed color data planes of Γ
-space amplitudes corresponding to said first, second and third compressed color data planes, respectively;means for converting said first, second and third decompressed color data planes to first, second and third output color data planes, respectively, of Γ
-space amplitudes of pixels of respective ones of said three colors;means for edge enhancing said first, second and third output color data planes; and means for back-transforming each of the Γ
-space amplitudes A1/Γ
of the pixels of said output color data planes to amplitudes A. - View Dependent Claims (45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62)
- -space amplitudes A1/Γ
Specification