Method of coding video signals and transmission system thereof
First Claim
1. A method for compressing a frame of video data to be transmitted, comprising:
- discrete cosine transform coding said frame of video data to provide discrete cosine transform coded video data;
quantizing said discrete cosine transform coded video data with a quantizing step of variable size to provide quantized video data;
variable length coding said quantized video data to provide a variable length code; and
controlling the size of said quantizing step by accumulating a first total absolute value of said frame of video data, dividing said frame of video data into a plurality of subregions thereof, accumulating a second total absolute value of each said sub-region of video data, distributing a total bit amount allowed for transmission of said first total absolute value to a bit amount allowed for transmission of each said subregion in proportion to said second total absolute value, and determining said size of the quantization step in response to said bit amount allowed for transmission of the respective region so that said size of the quantizing step is controlled in response to at least one characteristic of said frame of video data which influences the quality of a respective picture displayed therefrom.
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Abstract
In a video signal coding method for generating transmission data, a digital video signal is quantized by a quantization step which is controlled on the basis of significant picture information to be transmitted. The significant picture information is, for example, the quantity of information in a main region and in a sub region, the quantity of picture information to be coded, the picture motion in coded regions, the amount of variations in picture information between regions to be coded, or the components of spatial frequency with respect to regions to be coded. By reason of such control of the quantization step, deterioration of picture quality of the transmission data can be avoided, while the quantity of transmitted data is reduced.
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Citations
13 Claims
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1. A method for compressing a frame of video data to be transmitted, comprising:
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discrete cosine transform coding said frame of video data to provide discrete cosine transform coded video data; quantizing said discrete cosine transform coded video data with a quantizing step of variable size to provide quantized video data; variable length coding said quantized video data to provide a variable length code; and controlling the size of said quantizing step by accumulating a first total absolute value of said frame of video data, dividing said frame of video data into a plurality of subregions thereof, accumulating a second total absolute value of each said sub-region of video data, distributing a total bit amount allowed for transmission of said first total absolute value to a bit amount allowed for transmission of each said subregion in proportion to said second total absolute value, and determining said size of the quantization step in response to said bit amount allowed for transmission of the respective region so that said size of the quantizing step is controlled in response to at least one characteristic of said frame of video data which influences the quality of a respective picture displayed therefrom. - View Dependent Claims (2, 3)
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4. A method for compressing a frame of video data to be transmitted, comprising:
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discrete cosine transform coding said frame of video data to provide a discrete cosine transform coded video data; quantizing said discrete cosine transform coded video data with a quantizing step of variable size to provide quantized video data; variable length coding said quantized video data to provide a variable length code; controlling said size of the quantizing step in response to at least one characteristic of said frame of video data which influences the quality of a respective picture displayed therefrom; dividing each said frame of video data into a plurality of sub-regions each containing a predetermined number of pixels and corresponding to a transmission unit block; accumulating a total absolute value of transmission data for each said transmission unit block; determining from said total absolute value of transmission data a mean value thereof for each said pixel; further controlling said size of the quantizing step on the basis of said mean value; transmitting said variable length code through a transmission buffer memory having a predetermined buffer capacity; determining the remaining quantity of said buffer capacity; calculating a size of the quantizing step from a product of said mean value of transmission data and a ratio of said remaining quantity to said buffer capacity; and substituting predetermined minimum and maximum values of said quantizing steps in the event that the calculated size of the quantizing step is below or above, respectively, said minimum and maximum values.
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5. A method for compressing a frame of video data to be transmitted, comprising:
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discrete cosine transform coding said frame of video data to provide a discrete cosine transform coded video data; quantizing said discrete cosine transform coded video data with a quantizing step of variable size to provide quantized video data; variable length coding said quantized video data to provide a variable length code; transmitting said variable length code through a transmission buffer memory having a predetermined buffer capacity; determining the quantity of said buffer capacity remaining in said buffer memory; detecting motion in a picture from successive frames of said video data; and controlling the size of said quantizing step in accordance with said motion in a picture that is detected and with said remaining quantity of said buffer capacity.
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6. The method for compressing a frame of video data to be transmitted, comprising:
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discrete cosine transform coding said frame of video data to provide a discrete cosine transform coded video data; quantizing said discrete cosine transform coded video data with a quantizing step of variable size to provide quantized video data; variable length coding said quantized video data to provide a variable length code; transmitting said variable length code through a transmission buffer memory having a predetermined buffer capacity; determining the quantity of said buffer capacity remaining in said buffer memory; dividing each said frame of video data into a plurality of sub-regions each containing a predetermined number of pixels of data to be coded; generating a feed back quantization step of the basis of said remaining quantity of buffer capacity; comparing said data of each of said pixels with said feedback quantization step for detecting motion in a picture; and controlling the size of said quantizing step in accordance with said motion in a picture that is detected and with said remaining quantity of said buffer capacity. - View Dependent Claims (7, 8, 9, 10)
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11. A method for compressing a frame of video data to be transmitted, comprising:
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discrete cosine transform coding said frame of video data to provide discrete cosine transform coded video data; quantizing said discrete cosine transform coded video data with a quantizing step of variable size to provide quantized video data; variable length coding said quantized video data to provide a variable length code; transmitting said variable length code through a transmission buffer memory having a predetermined buffer capacity; determining the quantity of said buffer capacity remaining in said buffer memory; generating a feedback quantization step on the basis of the proportion of said remaining buffer capacity to said predetermined buffer capacity; dividing each said frame of video data into a plurality of sub-regions each containing a predetermined number of pixels of data to be coded; and controlling of the size of said quantizing step by determining a mean value for said pixels in one of said sub-regions to be coded, determining a mean value for said pixels in each of a plurality of said sub-regions surrounding said one-sub region to be coded, determining a maximum difference between said mean value associated with said sub-region to be coded and said mean values associated with said surrounding sub-regions, selecting a feedback quantization step transform ratio in accordance with the amount of said maximum difference, and calculating said size of the quantizing step from said feedback quantization step and said feedback quantization step transform ratio. - View Dependent Claims (12)
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13. A method for compressing a frame of video data to be transmitted, comprising:
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discrete cosine transform coding said frame of video data to provide discrete cosine transform coded video data; quantizing said discrete cosine transform coded video data with a quantizing step of variable size to provide quantized video data; variable length coding said quantized video data to provide a variable length code; controlling said size of the quantizing step in response to at least one characteristic of said frame of video data which influences the quality of a respective picture displayed therefrom; dividing each said frame of video data into a plurality of blocks; generating predictive data for each of said blocks; providing deviation data as the difference between the video data and predictive data for each of said blocks; accumulating a first total absolute value of said deviation data for each said frame; dividing said first total absolute value by the number of said blocks in a frame so as to obtain a mean value of the absolute value of said deviation data for each said block; setting a threshold level in accordance with said mean value; calculating a second total absolute value of said deviation data for each of said blocks; determining whether or not said second total absolute value is greater than said threshold level; applying to said discrete cosine transform coded data a weighting coefficient having a gradient when said second total absolute value is greater than said threshold level; and applying to said discrete cosine transform coded data a flat weighting coefficient when said second total absolute value is less than said threshold value.
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Specification