Shaded picture signal processing system and method

Claim 2

A shaded picture signal processing method for obtaining an output picture signal by quantizing an input picture signal having gradations of p bits per picture element into gradation levels of q bits per picture element with said input picture signal formed in a block of m×n picture elements, comprising the steps of: calculating a quantized value x qij by quantizing in q bits per picture element x ij in a spatial address (i, j) in said block; calculating a higher quantization value x uij by adding predetermined quantization step data to said quantized value x qij ; calculating a quantization error e ij which is a difference between said picture element x ij and said quantized value x qij ; and providing a threshold pattern in m×n matrix form in correspondence to said one block; selecting one of said quantized value x qij and said higher quantization value x uij in response to a comparison of said quantization error e ij with a threshold c ij at a spatial address (i, j) in said threshold pattern to output an output picture signal y ij of q bits per picture element corresponding to said spatial address thereby to reproduce halftones.

Claim 3

A shaded picture signal processing method in which an input picture signal is formed in a block m×n picture elements, comprising the steps of: calculating an average value x from picture elements x ij of said block; dividing said block into a region A in which picture elements x ij ≧average value x and a region B in which picture elements x ij <average value x; calculating average values x 1 and x 0 of said picture elements x ij in said regions A and B; calculating quantized values x 1q and x 0q by quantizing in q bits said average values x 1 and x 0 ; calculating higher quantization values x 1u and x 0u obtained by adding said quantized values x 1q and x 0q to predetermined quantization step data; calculating quantization errors e 1 and e 0 which are differences between said average value x 1 and said quantized value x 1q and between said average value x 0 and said quantized value x 0q ; providing a threshold pattern in m×n matrix form in correspondence to said block; and obtaining an output picture signal y ij in which each picture element comprises q bits corresponding to a spatial address (i, j) in said threshold pattern by selecting one of said quantized value and higher quantization value by comparing said quantization error with a threshold c ij in said spatial address, wherein, when said spatial address (i, j) is in said region A said quantization error e 1 , quantized value x 1q and higher quantization value x 1u are employed and when said spatial address is in said region B, said quantization error e 0 , quantized value x 0 q and quantization higher value x 0u are employed; and outputting one of said quantized value x 1q and quantization higher value x 1u , and said quantized value x 0q and quantization higher value x 0u to reproduce halftones.

Claim 4

A shaded picture signal processing method in which an input picture signal is formed in a block m×n picture elements, comprising the steps of: calculating an average value x from picture elements x ij of said block; dividing said block into a region A in which picture elements x ij ≧average value x and a region B in which picture elements x ij <average value x; calculating average values x 1 and x 0 of said picture elements x ij in said regions A and B; calculating quantized values x 1q and x 0q by quantizing in q bits said average values x 1 and x 0 ; calculating higher quantization values x 1u and x 0u obtained by adding said quantized values x 1q and x 0q to predetermined quantization step data; calculating quantization errors e 1 and e 0 which are differences between said average value x 1 and said quantized value x 1q and between said average value x 0 and said quantized value x 0q ; providing a threshold pattern in m×n matrix form in correspondence to said block; and obtaining an output picture signal y ij in which each picture element comprises q bits corresponding to a spatial address (i, j) in said threshold pattern by selecting one of said quantized value and higher quantization value by comparing said quantization error with a threshold c ij in said spatial address, wherein, when said spatial address (i, j) is in said region A said quantization error e 1 , quantized value x 1q and higher quantization value x 1u are employed and when said spatial address is in said region B, said quantization error e 0 , quantized value x 0 q and quantization higher value x 0u are employed; and outputting one of said quantized value x 1q and quantization higher value x 1u , and said quantized value x 0q and quantization higher value x 0u to reproduce halftones.

Claim 5

The system as claimed in claim 1 or 2 wherein said quantization step data is set to 2.sup.(p-q).

Claim 6

The system as claimed in claim 1 or 2 wherein said threshold c ij in said threshold pattern is fixed independent of input picture signals.

Claim 7

The system as claimed in claim 1 or 2 wherein said threshold pattern is varied according to the magnitudes of said picture elements x ij in said block so as to be suitably variable for blocks.