Abstract: An image signal encoding apparatus reads an image from an original and converts the image into color data values including lightness and chromaticity components. The data values are stored and divided into pixel blocks with data values of lightness components and pixel blocks with data values of chromaticity components. Average lightness component data values are computed for pixel blocks of lightness components and average chromaticity data values are computed for pixel blocks of chromaticity components. A region determination is made whether the pixel blocks correspond to color, monochrome or background region in the original based on the average pixel block data values of lightness components and chromaticity components. A switch outputs the lightness pixel block data values during the region determination, and outputs the lightness and chromaticity pixel block data values after the region determination.

Abstract: An image signal encoding apparatus reads an image from an original and converts the image into color data values including lightness and chromaticity components. The data values are stored and divided into pixel blocks with data values of lightness components and pixel blocks with data values of chromaticity components. Average lightness component data values are computed for pixel blocks of lightness components and average chromaticity data values are computed for pixel blocks of chromaticity components. A region determination is made whether the pixel blocks correspond to a color, monochrome or background region in the original based on the average pixel block data values of lightness components and chromaticity components. A switch outputs the lightness pixel block data values during the region determination, and outputs the lightness and chromaticity pixel block data values after the region determination.

Abstract: An image signal is divided into pixel blocks, each of which is subjected to orthogonal transform to be converted to transform coefficients. The transform coefficients are divided by respective thresholds set as a quantization matrix to become quantized coefficients. Coding symbols are constructed from the quantized coefficients using a coding symbol table which includes additional coding symbols corresponding to adaptive coding operations. The coding symbols are entropy-coded to become coded information. One of the adaptive coding operations is effected in accordance with identification information that is produced in accordance with a statistical parameter of the pixel blocks. The transform and quantizing operations are stopped during a block run, and after the end of the block run a coding symbol corresponding to the block-run detection is coded.

Abstract: An image coding and decoding apparatus to improve processing speed in searching for marker information such as control information when decoding, reduce the capacity of memory means for expanding compressed data and reduce the size of the unit of coding and decoding processing is disclosed, wherein divided coded data blocks CodeBlock 1-1, 1-2 and so forth are produced by dividing coded data obtained by coding image data for an image of a predetermined size into a predetermined size and control information values CodeSize1-1, 1-2 and so forth showing coded data block size are appended to each divided coded data block as control information.