Method and apparatus for adaptive transform coding of picture signals
First Claim
1. A method for adaptive transform coding of picture signals comprising the steps of:
- transforming the picture signals in accordance with a unitary orthogonal transform to obtain a plurality of coefficient value signals representative of picture energy in a series of subpictures, the coefficient value signals being grouped into a plurality of sequence classes, each sequence being associated with a distinct, fixed threshold signal value;
comparing each of the coefficient value signals with its associated threshold signal value and counting the number of coefficient value signals in each sequence class which exceed the associated threshold signal,quantizing said coefficient value signals, the number and range of quantization levels applied to each coefficient value signal being determined by the combinations of the number of coefficient value signals in each class which exceed the associated threshold signal value.
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Abstract
A method and apparatus to reduce the redundancy for the transmission or storage of picture signals using transforms. The basis coefficients are arranged in a sequence and thereafter quantized in the customary manner. The basis coefficients obtained from the transformation are sequentially examined to see if they exceed a predetermined value, for example the average value across the entire picture. The number of times the value is exceeded is counted. If, in a sequence class, the number of coefficients exceeding the predetermined value is more than half the total number in the sequence class then the associated sequences are quantized with a larger number of bits. For this purpose, activity classes are formed which indicate which sequences in the picture are active and the characteristic of the quantizer is controlled by this class information.
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Citations
5 Claims
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1. A method for adaptive transform coding of picture signals comprising the steps of:
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transforming the picture signals in accordance with a unitary orthogonal transform to obtain a plurality of coefficient value signals representative of picture energy in a series of subpictures, the coefficient value signals being grouped into a plurality of sequence classes, each sequence being associated with a distinct, fixed threshold signal value; comparing each of the coefficient value signals with its associated threshold signal value and counting the number of coefficient value signals in each sequence class which exceed the associated threshold signal, quantizing said coefficient value signals, the number and range of quantization levels applied to each coefficient value signal being determined by the combinations of the number of coefficient value signals in each class which exceed the associated threshold signal value. - View Dependent Claims (2, 3, 4)
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5. Apparatus for adaptive transform coding of picture signals comprising:
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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.
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Specification