number supplied from the division means 16 is added by the addition means 22 to the rounding coefficient r supplied by the r variation means 21 and the digits to the right of the decimal point are discarded by the truncation means 23 the dct coefficient thus quantized and rounded to an integer finally is subjected to variable length coding by the variable length coding means 18 so that it is recorded or transmitted in a compression data form the configuration described above is similar to a basic configuration of a common image compression method that employs the dct such as the configuration of the mpeg or the jpeg except for the following characteristic the rounding means 17 of the present invention is capable of varying the rounding coefficient r flexibly according to a category in which an image block is classified by the classification means 13 according to the result of detection by the feature detection means 12 conventionally a value having a fraction part generated as a result of a calculation is rounded off so that the value is rounded to an integer commonly this is because the rounding off operation causes a rounding error to be minimized arithmetically however in the case where all the blocks are subjected to the rounding off operation uniformly blocks with a great significance in image display and blocks with a small significance in image display each have a uniform rounding error presuming that the processing system of compression decompression is made irreversible by the quantization process the reduction of coding distortion of a significant block that attracts attention on a screen.