Encoder capable of faithfully and adaptively encoding a moving image

An encoder for use in encoding a moving image into a sequence of encoded image codes in response to a sequence of coefficient blocks, each coefficient block being composed of a plurality of orthogonal transform coefficients resulting from orthogonal transform of predictive error signals which are produced by predictively coding a plurality of picture elements of said moving image at every picture block, said encoder comprising a quantization unit having a plurality of quantization characteristics, a code conversion unit having a plurality of code conversion characteristics, and a coefficient selection unit having a plurality of coefficient selection characteristics, each of said coefficient blocks being processed through said quantization unit, said code conversion unit, and said coefficient selection unit into said encoded image codes by selecting said quantization characteristics, said code conversion characteristics, and said coefficient selection characteristics, wherein the improvement comprises:

• classifying means responsive to said coefficient blocks for classifying each of said coefficient blocks into a selected one of statistically determined classes with reference to the orthogonal transform coefficients included in each of said coefficient blocks, to produce a control signal representative of said selected one of the classes;
• and
• delivering means for delivering said control signal to at least two of said quantization unit, said code conversion unit, and said coefficient selection unit to select at least two of said quantization characteristics, said code conversion characteristics, and said coefficient selection characteristics.