Method and apparatus for encoding and decoding dither signals for reproduction of the halftone of a picture

Claim 1

A method for encoding and decoding dither signals for reproduction of the halftone of an original picture, in which there are provided the same dither thresholds on both an encoding side and a decoding side, picture signals, which are obtained pel by pel by scanning the original picture, are converted into signals for transmission by using the dither thresholds, on the encoding side, and the converted signals for transmission are reconverted into the dither signals by using the dither thresholds to reproduce the halftone of the picture, on the decoding side, characterized by the following steps; on the encoding side, first step of obtaining a predictive picture signal x ij of a pel (i, j) of j-th column on i-th scanning line, taking account of predictive picture signals of pels prior to the pel (i, j), which have been already obtained; second step of determining a two-level transposition signal d ij and calculating an approximation signal y ij , in accordance with the predetermined relations of an actual picture signal x ij of the pel (i, j) and the predictive signal x ij obtained in the first step to the thresholds t ij for the pel (i, j), the approximation signal y ij being available as the prior predictive picture signals in the first step for obtaining the predictive picture signal of a posterior pel; and third step of encoding the transposition signals d ij obtained in the second step and transmitting them to the decoding side; and, on the decoding side, fourth step of obtaining the predictive picture signal x ij of the pel (i, j), taking account of predictive signals of pels prior to the pel (i, j), which have been already obtained on the basis of the transposition signals previously transmitted; fifth step of calculating an approximation signal y ij in accordance with the predetermined relation of the predictive signal x ij of the pel (i, j) obtained in the fourth step to the thresholds t ij for the pel (i, j) and the transposition signal d ij transmitted from the encoding side; and sixth step of reproducing a dither signal z ij in accordance with the predetermined relation of the approximation signal y ij to the dither threshold t ij .

Claim 2

A method for encoding and decoding dither signals for reproduction of the halftone of an original picture, in which there are provided the same dither thresholds on both an encoding side and a decoding side, picture signals, which are obtained pel by pel by scanning the original picture, are converted into signals for transmission by using the dither thresholds, on the encoding side, and the converted signals for transmission are reconverted into the dither signals by using the dither thresholds to reproduce the halftone of the picture, on the decoding side, characterized by the following steps; on the encoding side, first step of obtaining a predictive picture signal x ij of a pel (i, j) of j-th column on i-th scanning line, taking account of predictive picture signals of pels prior to the pel (i, j), which have been already obtained; second step of determining a two-level transposition signal d ij and calculating an approximation signal y ij , in accordance with the predetermined relations of an actual picture signal x ij of the pel (i, j) and the predictive signal x ij obtained in the first step to the thresholds t ij for the pel (i, j), the approximation signal y ij being available as the prior predictive picture signals in the first step for obtaining the predictive picture signal of a posterior pel; and third step of encoding the transposition signals d ij obtained in the second step and transmitting them to the decoding side; and, on the decoding side, fourth step of obtaining the predictive picture signal x ij of the pel (i, j), taking account of predictive signals of pels prior to the pel (i, j), which have been already obtained on the basis of the transposition signals previously transmitted; fifth step of calculating an approximation signal y ij in accordance with the predetermined relation of the predictive signal x ij of the pel (i, j) obtained in the fourth step to the thresholds t ij for the pel (i, j) and the transposition signal d ij transmitted from the encoding side; and sixth step of reproducing a dither signal z ij in accordance with the predetermined relation of the approximation signal y ij to the dither threshold t ij .

Claim 9

An apparatus for encoding and decoding dither signals for reproduction of the halftone of an original picture, having, on an encoding side, means for scanning the original picture and producing multilevel picture signals pel by pel, a preprocessor for converting the picture signals into signals for transmission by using a dither matrix and means for encoding the signals converted by the preprocessor and transmitting the encoded signals, and on a decoding side, means for receiving and decoding the transmitted signals from the encoding side, a postprocessor for reconverting the decoded signals into the dither signals and means for reproducing the picture in accordance with the dither signals, characterized in that the preprocessor comprises; means for calculating a predictive picture signal x ij of a pel (i, j) of j-th column on i-th scanning line, taking account of predictive signals of pels prior to the pel (i, j), which have been already obtained and stored; means for storing a dither threshold t ij for the pel (i, j); means for comparing an actual picture signal x ij with the dither threshold t ij read out from said storing means to produce a first comparison output; means for comparing the predictive picture signal x ij with the dither threshold t ij to produce a second comparison output; means for generating a two-level transposition signal d ij in response to the logical operation of the first and second comparison outputs; means for correcting the predictive picture signal x ij in accordance with the predetermined relations of the actual picture signal x ij and the predictive picture signal x ij to the threshold t ij to produce and store an approximation signal y ij , which is available as the prior predictive picture signals for obtaining the predictive picture signal of a posterior pel; and

Claim 10

An apparatus for encoding and decoding dither signals for reproduction of the halftone of an original picture, having, on an encoding side, means for scanning the original picture and producing multilevel picture signals pel by pel, a preprocessor for converting the picture signals into signals for transmission by using a dither matrix and means for encoding the signals converted by the preprocessor and transmitting the encoded signals, and on a decoding side, means for receiving and decoding the transmitted signals from the encoding side, a postprocessor for reconverting the decoded signals into the dither signals and means for reproducing the picture in accordance with the dither signals, characterized in that the preprocessor comprises; means for calculating a predictive picture signal x ij of a pel (i, j) of j-th column on i-th scanning line, taking account of predictive signals of pels prior to the pel (i, j), which have been already obtained and stored; means for storing a dither threshold t ij for the pel (i, j); means for comparing an actual picture signal x ij with the dither threshold t ij read out from said storing means to produce a first comparison output; means for comparing the predictive picture signal x ij with the dither threshold t ij to produce a second comparison output; means for generating a two-level transposition signal d ij in response to the logical operation of the first and second comparison outputs; means for correcting the predictive picture signal x ij in accordance with the predetermined relations of the actual picture signal x ij and the predictive picture signal x ij to the threshold t ij to produce and store an approximation signal y ij , which is available as the prior predictive picture signals for obtaining the predictive picture signal of a posterior pel; and