When obtaining pictures with differing pixel densities by converting the pixel density of the original still picture, the technique here is to reproduce pictures with the highest fidelity to the original. It is related to the picture compression coding system and is employed in the international JBIG standards and the international standards for facsimiles.

1. In the figure, memory 1 stores picture data adjacent to the original picture data and memory 2 stores image data after the pixel density of the original picture data is converted. The pixel conversion station for converting the pixel density of original picture data performs conversion referring to picture data in memories 1 and 2 and outputs picture data with a different pixel density from the original picture. Because the system is designed to determine pixel-converted data by referring to image data after conversion of the pixel density of the original picture data and image data adjacent to the original image data, in addition to pixels at a corresponding zone of the original picture, the original image data can be reproduced with the highest fidelity when obtaining a picture with a different in pixel density.
2. This picture conversion system is employed in ITU-T recommendation T.82 and ISO/IEC standard 1154).

JBIG: Joint Bi-level Image Group of ITU-T/ISO/IEC

JPEG: Joint Photographic Experts Group of ITU-T/ISO/IEC

ITU-T recommendation T.82, ISO/IEC standard 11544: Progressive binary picture compression

OA equipment such as FAX, PPC and printers, and broadcast editing units