Method and apparatus for adaptive transform coding of picture signals

Apparatus for adaptive transform coding of picture signals comprising:

• unitary orthogonal transform means connected to receive subpicture signals and to produce sequences of coefficient value signals therefrom, the coefficient value signals being grouped into a plurality of sequence classes;
• first memory means which store and supply a plurality of threshold signal values, each sequence of coefficient value signals being associated with a threshold signal;
• comparator means connected to receive coefficient value signals from the transform means and the associated threshold signal value from the first memory means and which supply a reference signal whenever a coefficient value signal exceeds the associated threshold signal value;
• first counter means connected to count the number of reference signals produced from coefficient value signals in each sequence class and to produce an activity signal whenever a predetermined count is exceeded for each sequence class;
• second memory means connected to receive and store the activity signals associated with each sequence class;
• logic means connected to receive and logically combine the activity signals derived from a subpicture signal, to produce quantizer control signals from the logical combination of signals, and to store the quantizer control signals;
• and
• quantizer means connected to receive the coefficient value signals produced from a subpicture signal together with the associated quantizer control signals and to quantize the coefficient value signals in accordance with a quantization characteristic which is uniquely determined by the quantizer control signals.