Picture signal coding apparatus
First Claim
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1. A picture signal coding apparatus comprising:
- threshold value setting means for setting at least one threshold value for each of a plurality of coding blocks into which a frame of a gray-scaled picture is divided, based on the luminance distribution in each block;
means for classifying the luminance level of each picture element of each coding block into any one of level ranges defined by the threshold value to obtain a resolution component;
typical luminance level calculating means for obtaining at least two typical luminance levels from the classification result and the brightness levels of the picture elements of each coding block;
decoding means for decoding the picture elements of each coding block based on the resolution component and the threshold value;
error calculating means for a calculating a coding error in the coding of the coding block from each decoded picture element and its original picture element;
block size changing means for comparing the calculated error with a set value to change the size of each coding block in accordance with the compared output; and
means for providing, as true coded outputs, the resolution component and the typical luminance levels when the error is in a predetermined range.
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Abstract
A frame of a gray-scaled picture is divided into blocks, in each of which the mean luminance of picture elements is used as a threshold value for comparison with each picture element signal to classify it into 0 or 1 according to its magnitude to provide a resolution component. From the resolution component and each picture element signal in the block are calculated two gray components; the resolution component and the two gray components are used as coded outputs for each block. The size of each block is changed in accordance with the property of the picture in the portion corresponding to the block.
72 Citations
10 Claims
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1. A picture signal coding apparatus comprising:
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threshold value setting means for setting at least one threshold value for each of a plurality of coding blocks into which a frame of a gray-scaled picture is divided, based on the luminance distribution in each block; means for classifying the luminance level of each picture element of each coding block into any one of level ranges defined by the threshold value to obtain a resolution component; typical luminance level calculating means for obtaining at least two typical luminance levels from the classification result and the brightness levels of the picture elements of each coding block; decoding means for decoding the picture elements of each coding block based on the resolution component and the threshold value; error calculating means for a calculating a coding error in the coding of the coding block from each decoded picture element and its original picture element; block size changing means for comparing the calculated error with a set value to change the size of each coding block in accordance with the compared output; and means for providing, as true coded outputs, the resolution component and the typical luminance levels when the error is in a predetermined range. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 10)
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9. A picture signal coding apparatus according to claim 9, wherein said threshold value setting means obtains a mean value of the luminance levels of the picture elements of each block, and wherein said typical luminance level calculating means calculate mean values a0 and a1 of the luminance levels of the picture elements below and above the threshold value.
Specification