Adaptive graylevel image compression system
First Claim
1. A differential pulse code modulation (DPCM) data compression system in which a predicted value P is subtracted from an input signal value X to provide a difference signal value which is to be quantized, the system comprising:
- a plurality of selectable quantizers for quantizing a difference signal input;
a plurality of selectable predictor calculators;
entropy encoder means for producing code outputs in response to decision inputs and state inputs, the state inputs providing a context for the decision inputs received;
activity indicator means for indicating the level of input signal activity based on quantized difference history;
first selector means, which receives the output of the activity indicator means as input, for selecting one of the quantizers based on the activity indicator output; and
second selector means, which receives the output of the activity indicator means as input, for selecting as the predictor P the output of one of the predictor calculators based on the activity indicator output;
wherein said entropy encoding means receives the output of the activity indicator means as a state input thereto.
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Accused Products
Abstract
Apparatus and method for modelling differential pulse code modulation (DPCM) input data for entropy coding. In particular, the sign and magnitude of one piece of DPCM data after another are modelled to provide a magnitude state input and a sign state input to provide context for DPCM magnitude input and DPCM sign input, respectively, to an entropy encoder or decoder. That is, the DPCM magnitudes of earlier pieces of (context) DPCM magnitude data are re-mapped for each such earlier piece of data, the re-mapped data being aggregated to form a combined value indicative of the magnitude state input. Similarly, the DPCM signs of earlier pieces of (context) DPCM sign data are re-mapped for each such earlier piece of data, the re-mapped data being aggregated to form a combined value indicative of the sign state input. In an image data compression system, the magnitude state input serves as an activity indicator for picture elements (pixels) neighboring a "subject" pixel. According to the invention, the DPCM signal is derived from a difference value calculated by subtracting one of a plurality of predictor values from the graylevel value X of the subject pixel. The selection of predictor value P is based on the value of the magnitude state (activity indicator). In addition, the difference value is subject to adaptive quantization in which one of a plurality of quantizers is employed in assigning the (X-P) difference value to a quantization level. The selection of quantizers is also based on the value of the magnitude state (activity indicator).
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Citations
16 Claims
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1. A differential pulse code modulation (DPCM) data compression system in which a predicted value P is subtracted from an input signal value X to provide a difference signal value which is to be quantized, the system comprising:
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a plurality of selectable quantizers for quantizing a difference signal input; a plurality of selectable predictor calculators; entropy encoder means for producing code outputs in response to decision inputs and state inputs, the state inputs providing a context for the decision inputs received; activity indicator means for indicating the level of input signal activity based on quantized difference history; first selector means, which receives the output of the activity indicator means as input, for selecting one of the quantizers based on the activity indicator output; and
second selector means, which receives the output of the activity indicator means as input, for selecting as the predictor P the output of one of the predictor calculators based on the activity indicator output;wherein said entropy encoding means receives the output of the activity indicator means as a state input thereto. - View Dependent Claims (2, 3, 4)
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5. In a data compression system including an entropy encoder which encodes decision inputs in a context defined by a corresponding state input, a machine-implemented method of modelling differential pulse code modulation (DPCM) image data for entropy coding comprising the steps of:
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(a) for a subject pixel, evaluating a predictor value P; (b) subtracting P from a graylevel value X for the subject pixel to provide a difference value; (c) quantizing a DPCM signal having a sign and a magnitude from the difference value; (d) modelling the DPCM signal sign to provide a sign state input to the entropy encoder; (e) modelling the DPCM signal magnitude to provide a magnitude state input to the entropy encoder; (f) the entropy encoder encoding the DPCM signal sign in the context defined by the sign state input; and (g) the entropy encoder encoding the DPCM signal magnitude in the context defined by the magnitude state input. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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Specification