Method of and apparatus for eliminating interblock distortion due to compressed image data
AssigneeDainippon Screen Mfg. Co., Ltd.
InventorMasami Aragaki
Life of this patent
Estimating the term…
Abstract
Interblock distortion often appears on a boundary of pixel blocks in a reproduced image produced from compressed image data. The interblock distortion is eliminated by correcting a density distribution in the reproduced image. First, an average density (A.sub.ij) of a selected pixel block (B.sub.ij) is computed. Second, a standard deviation (.sigma..sub.ij) of a density distribution in the selected deviation is computed. If the standard deviation is equal to zero, correction value distributions (.DELTA.f.sub.m, .DELTA.f.sub.n) along a main scanning direction and a subscanning direction are obtained. Finally, corrected density distribution (f.sub.mn) is obtained as a sum of the average density and the correction value distributions.
Claims12
A method of eliminating interblock distortion, which is seen in a reproduced image produced on the basis of compressed image data obtained for each pixel block consisting of a prescribed number of pixels in said reproduced image and is defined as stepwise density difference on boundaries between said pixel blocks, by correcting a density distribution expressing densities for respective pixels in said pixel blocks, said method comprising the steps of:
- (a) sequentially selecting said pixel blocks one by one as an object pixel block,
- (b) obtaining a density distribution in said object pixel block on the basis of said compressed image data,
- (c) finding a statistical value expressing a standard deviation of said density distribution,
- (d) comparing said statistical value with a prescribed threshold value expressing a threshold standard deviation, thereby designating said object pixel block as either of a first type to be subjected to a processing for correcting said density distribution and a second type not to be subjected to said processing, and
- (e) performing said processing when said object pixel block is said first type, said processing comprising
- (e-1) obtaining respective average densities of said object pixel block and neighbor pixel blocks neighboring said object pixel block in a prescribed direction, and
- (e-2) correcting said density distribution through interpolation of quantities corresponding to said respective average densities so as to reduce said stepwise density differences on boundaries between said object pixel block and said neighbor pixel blocks, thereby obtaining a corrected density distribution in said object pixel block.
An apparatus for eliminating interblock distortion, which is seen in a reproduced image produced on the basis of compressed image data obtained for each pixel block consisting of a prescribed number of pixels in said reproduced image and is defined as stepwise density differences on boundaries between said pixel blocks, by correcting a density distribution expressing densities for respective pixels in said pixel blocks, said apparatus comprising:
- (a) a first processor means for sequentially selecting said pixel blocks one by one as an object pixel block,
- (b) a second processor means for obtaining a density distribution in said object pixel block on the basis of said compressed image data,
- (c) a third processor means for finding a statistical value expressing a standard deviation of said density distribution,
- (d) a fourth processor means for comparing said statistical value with a prescribed threshold value expressing a threshold standard deviation, thereby designating said object pixel block as either of a first type to be subjected to a processing for correcting said density distribution and a second type not to be subjected to said processing, and
- (e) a fifth processor means for performing said processing when said object pixel block is said first type, said processing comprising:
- (e-1) a six processor means for obtaining respective average densities of said object pixel block and neighbor pixel blocks neighboring said object pixel block in a prescribed direction, and (e-2) a seventh processor means for correcting said density distribution through interpolation of quantities corresponding to said respective average densities so as to reduce said stepwise density differences on boundaries between said object pixel block and said neighbor pixel blocks, thereby obtaining a corrected density distribution in said object pixel block.
Dependencies are inferred from the claim text.