Multilevel-coding apparatus and multilevel-coding method using an optimal sized window beginning from the smallest to a larger size

摘要

When image data binarized by a density-preserving type multilevel- coding method is to be recovered to multilevel image data, the size of a scanning window which includes as a central pixel point a pixel point to be subjected to multilevel coding is varied and the sums of data values of the binarized image data contained in the scanning windows corresponding to individual window sizes are sequentially calculated in the order of window size. If the sum of the binarized image data value reaches a predetermined threshold for each scanning window size, this window size is determined as a scanning window size for multilevel coding, and multilevel coding is executed. With this process, an optimum window size is determined which is suitable for use in effecting multilevel- coding with high image quality. Since multilevel coding employing the optimum window size is performed, multilevel coding with high image quality and high resolution is enabled.