Abstract: A bit allocation method which facilitate control of the number of bits to be assigned to transform coefficients and block of image data with a deviation from the functional form. An image coding system which can implement an optimal bit allocation that minimizes quantization error under a predetermined information content or amount, in carrying out bit allocations of block-adaptive type and transform coefficient-adaptive type.

Abstract: An image compressing apparatus forms a synthetic image from a plurality of image data. The apparatus includes a device for sorting a plurality of image data into a plurality of image types in accordance with at least one of a nature and a use of each image data, a device for selecting an image compressing method out of a plurality of predetermined various image compressing methods for each image data in accordance with the sorted image type, and a device for compressing the image data in accordance with the selected image compressing method and recording the compressed image data in a recording medium.

Abstract: In an image data compression method to be employed in coding digital image data whose pixels are represented by n bits and which include 2.sup.n different types of runs, while a run length of a current run is counted, a value representing a run type of the current run is predicted. The prediction is repeated till a predicted value coincides with an actual value of the run type of the current run. When a predicted value does not coincide with the actual value of the run type of the current run, a run length for an imaginary run having the predicted value is regarded as zero and the run length 0 of the imaginary run is entropy coded. On the other hand, when a predicted value coincides with an actual value, the actual run length of the current run is entropy coded.