Image data compressing apparatus
First Claim
1. An image data compression apparatus for compressing image data comprising:
- DCT means for receiving block data obtained by dividing the image data into blocks of data and for obtaining DCT coefficients by performing a discrete cosine transformation of the block data;
main quantizing means for obtaining a optimum quantization output by quantizing, in accordance with an optimum quantization coefficient, the DCT coefficients obtained by the DCT means;
main encoding means for obtaining an encoded output by variable length encoding the optimum quantization output from the main quantizing means; and
optimum compression characteristic determining means for receiving the optimum quantization output from the main quantizing means, for generating the optimum quantization coefficient to be used by the main quantizing means, and for feeding back the optimum quantization coefficient to the main quantizing means;
wherein the optimum compression characteristic determining means generates the optimum quantization coefficient by;
quantizing the DCT coefficients through the use of a plurality of different quantization coefficients during a first scanning period corresponding to one frame of the image data so as to produce a plurality of quantization outputs;
encoding the plurality of quantization outputs;
obtaining a plurality of total bit counts corresponding to the encoded plurality of quantization outputs; and
executing a predetermined operation by using at least one of the plurality of total bit counts which is approximate to a target total bit count, and thereby generating the optimum quantization coefficient.
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Accused Products
Abstract
A DCT coefficient output from a DCT circuit 21 is quantized by different quantization outputs by quantization circuits 22 to 25, and code lengths obtained by encoding the respective quantization outputs are calculated by code length calculation circuits 28 to 31. The code lengths corresponding to one frame obtained by the code length calculation circuits 28 to 31 are accumulated by adders 33 to 36, thereby obtaining a plurality of calculated total bit counts corresponding to the plurality of quantization coefficients. A comparator 37, multipliers 38 and 39, and an adder 40 select, of the plurality of calculated total bit counts, two calculated total bit counts that are close to a target total bit count, and obtain a scale factor used for obtaining a quantization coefficient corresponding to the target total bit count. An optimum quantization coefficient for the subsequent second scanning operation is generated by a quantization coefficient generator 27 by using the scale factor.
38 Citations
13 Claims
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1. An image data compression apparatus for compressing image data comprising:
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DCT means for receiving block data obtained by dividing the image data into blocks of data and for obtaining DCT coefficients by performing a discrete cosine transformation of the block data; main quantizing means for obtaining a optimum quantization output by quantizing, in accordance with an optimum quantization coefficient, the DCT coefficients obtained by the DCT means; main encoding means for obtaining an encoded output by variable length encoding the optimum quantization output from the main quantizing means; and optimum compression characteristic determining means for receiving the optimum quantization output from the main quantizing means, for generating the optimum quantization coefficient to be used by the main quantizing means, and for feeding back the optimum quantization coefficient to the main quantizing means; wherein the optimum compression characteristic determining means generates the optimum quantization coefficient by; quantizing the DCT coefficients through the use of a plurality of different quantization coefficients during a first scanning period corresponding to one frame of the image data so as to produce a plurality of quantization outputs; encoding the plurality of quantization outputs; obtaining a plurality of total bit counts corresponding to the encoded plurality of quantization outputs; and executing a predetermined operation by using at least one of the plurality of total bit counts which is approximate to a target total bit count, and thereby generating the optimum quantization coefficient. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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Specification