Method for image compression on a personal computer
First Claim
1. A method of compressing color image data signals, comprising the steps of:
- a) receiving, under foreground control of a processor and in real time, a sequence of the color image data signals representing a color image;
b) digitizing the data signals, thereby forming digitized data signals;
c) compressing the digitized data signals in real time to a first compression ratio using a first data compression algorithm under foreground control of the processor, thereby forming first compressed image data;
d) storing the first compressed image data in real time in a first quantity of digital memory under foreground control of the processor;
e) upon completion of step d), retrieving from storage the first compressed image data and decompressing the first compressed image data under background control of the processor, thereby forming a decompressed digital signal;
f) compressing the decompressed digital signal to a second compression ratio under background control of the processor, thereby forming second compressed image data; and
g) storing the second compressed image data in a second quantity of the digital memory wherein the second quantity of the digital memory is less than the first quantity.
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Abstract
A method and apparatus for image compression suitable for personal computer applications, which compresses and stores data in two steps. An image is captured in real-time and compressed using an efficient method and stored to a hard-disk. At some later time, the data is further compressed in non-real-time using a computationally more intense algorithm that results in a higher compression ratio. The two-step approach allows the storage reduction benefits of a highly sophisticated compression algorithm to be achieved without requiring the computational resources to perform this algorithm in real-time. A compression algorithm suitable for performing the first compression step on a host processor in a personal computer is also described. The first compression step accepts 4:2:2 YCrCb data from the video digitizer. The two chrominance components are averaged and a pseudo-random number is added to all components. The resulting values are quantized and packed into a single 32-bit word representing a 2×2 array of pixels. The seed value for the pseudo-random number is remembered so that the pseudo-random noise can be removed before performing the second compression step.
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Citations
9 Claims
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1. A method of compressing color image data signals, comprising the steps of:
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a) receiving, under foreground control of a processor and in real time, a sequence of the color image data signals representing a color image; b) digitizing the data signals, thereby forming digitized data signals; c) compressing the digitized data signals in real time to a first compression ratio using a first data compression algorithm under foreground control of the processor, thereby forming first compressed image data; d) storing the first compressed image data in real time in a first quantity of digital memory under foreground control of the processor; e) upon completion of step d), retrieving from storage the first compressed image data and decompressing the first compressed image data under background control of the processor, thereby forming a decompressed digital signal; f) compressing the decompressed digital signal to a second compression ratio under background control of the processor, thereby forming second compressed image data; and g) storing the second compressed image data in a second quantity of the digital memory wherein the second quantity of the digital memory is less than the first quantity. - View Dependent Claims (2, 3, 4)
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5. A method of compressing a digital video data signal using a personal computer for display on a screen having scanlines of pixels, comprising the steps of:
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a) reading two adjacent first pixels of a first scanline of the digital video data signal into the personal computer in real time; b) adding first pseudo-random number data to the first pixels of the digital video data signal, thereby generating modified pixels; c) masking and merging the modified pixels, thereby forming first compressed data; d) reading two adjacent second pixels of a second scanline of the digital video data signal in real time into the personal computer, wherein the second pixels are adjacent the first pixels; e) adding a second pseudo-random number to the second pixels of the digital video data signal, thereby generating modified second pixels; f) masking and merging the modified second pixels, thereby forming second compressed data; g) storing the first compressed data and the second compressed data in real time; h) retrieving from storage and decompressing the first compressed data and the second compressed data, thereby forming a decompressed signal; and i) compressing the decompressed signal under background control of the personal computer to generate a recompressed digital video data signal.
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6. An apparatus for compressing color image data signals, comprising:
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a) means for receiving, under foreground control of a processor and in real time, a sequency of the color image data signals representing a color image; b) means for digitizing the sequence of the color image data signals, thereby forming digitized data signals; c) means for compressing the digitized data signals in real time to a first compression ratio using a first data compression algorithm under foreground control of the processor, thereby forming first compressed image data; d) means for storing the first compressed image data in real time in a first quantity of digital memory under foreground control of the processor; e) means for retrieving from storage the first compressed image data and decompressing the first compressed image data under background control of the processor, thereby forming a decompressed digital signal; f) means for compressing the decompressed digital signal to a second compression ratio under background control of the processor, thereby forming second compressed image data; and g) means for storing the second compressed image data in a second quantity of the digital memory wherein the second quantity of the digital memory is less than the first quantity. - View Dependent Claims (7, 8)
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9. An apparatus for compressing a digital video data signal for display on a screen having scan lines of pixels, comprising:
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a) means for reading two adjacent first pixels of a first scanline of the digital video data signal under foreground control of a personal computer and in real time; b) means for adding a first pseudo-random number to the first pixels, thereby generating modified pixels; c) means for masking and merging the modified pixels under foreground control of the personal computer, thereby forming first compressed digital video data; d) means for reading two adjacent second pixels of a second scanline of the digital video data signal under foreground control of the personal computer and in real time, wherein the second pixels are adjacent the first pixels; e) means for adding a second pseudo-random number to the second pixels, thereby generating modified second pixels; f) means for masking and merging the modified second pixels under foreground control of the personal computer, thereby forming second compressed digital video data; g) means for storing the first compressed digital video data and the second compressed digital video data in real time; h) means for retrieving from storage and decompressing the first compressed digital video data and the second compressed digital video data, thereby forming a decompressed signal; and i) means for compressing the decompressed signal under background control of the personal computer to generate a recompressed digital video data signal.
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Specification