METHOD AND APPARATUS FOR ENCODING AND DECODING IMAGE DATA

A method and apparatus for encoding and decoding image data in which continuous still images are compressed and decompressed. The apparatus divides a plurality of multivalue image data into blocks each comprising a plurality of pixels, the pixels in the block are orthogonal converted and compressed, and the original image data is decompressed from the encoded data. The apparatus detects the block having an image change as an effective block. For a macro block including a plurality of effective blocks, a compressing order of the macro blocks is decided by the order according to appearance frequencies of the effective blocks or a predetermined order and the image data is compressed every macro block. As encoded data, the order information and code information of the macro block are sequentially transmitted. In this instance, the code amount is monitored. When the code amount exceeds a predetermined threshold value, the compression is stopped and the compression of the next image is performed. The encoded data is sequentially sent to the decompressing side and is decompressed in accordance with the order from the macro block of a portion of large change in the image. Even when the compression is stopped during the image processing because of a limitation of a code transmission amount, the image is reconstructed from the portion to which a person more carefully observes, so that a discrete motion or a background block noise does not occur.