Adaptive quantization of orthogonal transform coefficients for setting a target amount of compression
First Claim
1. An image signal compressing device, comprising:
- means for applying an orthogonal transformation to original image data to obtain orthogonal transformation coefficients for each of a plurality of spatial frequencies that include a first spatial frequency and a second spatial frequency, said orthogonal transformation coefficients being deemed to be equivalent to quantized orthogonal transformation coefficients obtained using a first set of quantization coefficients;
means for encoding said quantized orthogonal transformation coefficients, said encoding means arranging said quantized orthogonal transformation coefficients in a predetermined one-dimensional array with respect to said plurality of spatial frequencies, said encoding means once performing an encoding calculation based on said arranged quantized orthogonal transformation coefficients to obtain encoded data for each of said plurality of spatial frequencies during an operation of said image signal compressing device;
means for setting a target value which defines a degree of compression by which an amount of said encoded data is compressed, said target value being replaceable by said amount of said encoded data for each of said plurality of spatial frequencies;
means for estimating an amount of said encoded data of said first spatial frequency based on a statistical value of said encoded data of said second spatial frequency, said first spatial frequency being provided adjacent to said second spatial frequency in said one-dimensional array; and
means for obtaining a second quantization coefficient, associated with one quantization coefficient of said first set of quantization coefficients, corresponding to said first spatial frequency, so that said estimated amount of said encoded data of said first spatial frequency does not exceed said target value, said encoding means classifying said quantized orthogonal transformation coefficients into categories, based on a value of said quantized orthogonal transformation coefficients, and obtaining a run length based on a number of consecutive "0"'"'"'s of said quantized orthogonal transformation coefficients, said estimating means estimating said amount of said encoded data of said first spatial frequency based on said categories and said run length, said encoding means once performing said encoding calculation on said quantized orthogonal transformation coefficients after said estimating means estimates said amount of encoded data and said obtaining means obtains said second quantization coefficient.
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Abstract
An image signal compressing device having a spatial frequency data amount setting unit and a quantization table generation unit. A set data amount is set in the spatial frequency data amount setting unit for each of a plurality of spatial frequencies based on a preset total data amount and a discrete cosine transformation (DCT) data statistical amount corresponding to quantized DCT coefficients using a quantization table in which all quantization coefficients are "1". An amount of encoded data obtained using a predetermined quantization coefficient is estimated in the quantization table generation unit. The predetermined quantization coefficient is adopted as a resultant quantization coefficient of the quantization table when the estimated data is not greater than the set data amount set in the spatial frequency data amount setting unit.
54 Citations
17 Claims
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1. An image signal compressing device, comprising:
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means for applying an orthogonal transformation to original image data to obtain orthogonal transformation coefficients for each of a plurality of spatial frequencies that include a first spatial frequency and a second spatial frequency, said orthogonal transformation coefficients being deemed to be equivalent to quantized orthogonal transformation coefficients obtained using a first set of quantization coefficients; means for encoding said quantized orthogonal transformation coefficients, said encoding means arranging said quantized orthogonal transformation coefficients in a predetermined one-dimensional array with respect to said plurality of spatial frequencies, said encoding means once performing an encoding calculation based on said arranged quantized orthogonal transformation coefficients to obtain encoded data for each of said plurality of spatial frequencies during an operation of said image signal compressing device; means for setting a target value which defines a degree of compression by which an amount of said encoded data is compressed, said target value being replaceable by said amount of said encoded data for each of said plurality of spatial frequencies; means for estimating an amount of said encoded data of said first spatial frequency based on a statistical value of said encoded data of said second spatial frequency, said first spatial frequency being provided adjacent to said second spatial frequency in said one-dimensional array; and means for obtaining a second quantization coefficient, associated with one quantization coefficient of said first set of quantization coefficients, corresponding to said first spatial frequency, so that said estimated amount of said encoded data of said first spatial frequency does not exceed said target value, said encoding means classifying said quantized orthogonal transformation coefficients into categories, based on a value of said quantized orthogonal transformation coefficients, and obtaining a run length based on a number of consecutive "0"'"'"'s of said quantized orthogonal transformation coefficients, said estimating means estimating said amount of said encoded data of said first spatial frequency based on said categories and said run length, said encoding means once performing said encoding calculation on said quantized orthogonal transformation coefficients after said estimating means estimates said amount of encoded data and said obtaining means obtains said second quantization coefficient. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. An image signal compressing device, comprising:
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an orthogonal transformation coefficient applying device that applies an orthogonal transformation to original image data to obtain an orthogonal transformation coefficient for each spatial frequency of a plurality of spatial frequencies, said orthogonal transformation coefficient applying device dividing said original image data into a plurality of blocks to obtain said orthogonal transformation coefficient; a quantizer that obtains quantized orthogonal transformation coefficients using a quantization table composed of predetermined quantization coefficients; an encoder that encodes said quantized orthogonal transformation coefficients, said quantized orthogonal transformation coefficients being arranged in a predetermined one-dimensional array with respect to said plurality of spatial frequencies, said encoder performing an encoding calculation based on said arranged quantized orthogonal transformation coefficients to obtain encoded data for each of said plurality of spatial frequencies; a target value setting device that sets a target value defining a degree of compression by which an amount of encoded data is compressed, said target value being replaced by said amount of encoded data for each of said plurality of spatial frequencies; an estimator that estimates said amount of encoded data for each of said plurality of spatial frequencies without having to encode said quantized orthogonal transformation coefficients, by classifying a first spatial frequency of said quantized orthogonal transformation coefficients into a plurality of categories in accordance with a value of each quantized orthogonal transformation coefficient, by obtaining a run length distribution of a category "0" of said first spatial frequency based on a number of blocks forming a single image, a number of blocks corresponding to category "0" and a number of blocks corresponding to other than category "0", a run length/category table of said first spatial frequency being generated based upon said run length distribution, a category distribution of an "i"th spatial frequency being generated, a run length distribution of category "0" of said "i"th spatial frequency being generated based upon the number of blocks of category "0" of an "i-1"th spatial frequency and a run length distribution of category "0" of said "i-1"th spatial frequency, a run length/category table of said "i"th spatial frequency being generated from i=2 through i=n, so that a run length/category table of each of a second spatial frequency through in "n"th spatial frequency is generated, an amount of encoded data obtained for each spatial frequency being based on said run length/category table of each spatial frequency and a table of code lengths of code words, determined by a combination of said category and run length; and an obtainer that obtains a modified quantization coefficient corresponding to each of said plurality of spatial frequencies, so that said estimated amount of encoded data does not exceed said target value, where "i" is a natural number and "n" represents a maximum value. - View Dependent Claims (13, 14, 15, 16)
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17. An image signal compressing device, comprising:
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an orthogonal transformation coefficients applying device that applies an orthogonal transformation to original image data to obtain orthogonal transformation coefficients for each spatial frequency of a plurality of spatial frequencies; a quantizing device that quantizes said orthogonal transformation coefficients using a quantization table composed of predetermined quantization coefficients, to obtain quantized orthogonal transformation coefficients; an encoding device that encodes said quantized orthogonal transformation coefficients in a predetermined one-dimensional array with respect to said plurality of spatial frequencies, an encoding calculation being based on said arranged quantized orthogonal transformation coefficients to obtain encoded data for each of said spatial frequency of said plurality of spatial frequencies; a target value setting device that sets a target value defining a degree of compression by which an amount of said encoded data is compressed, said target value varying by said amount of said encoded data for each said spatial frequency of said plurality of spatial frequencies, said target value setting device having a default quantization table, in which all quantization coefficients are "1", said target value setting device further having a predetermined filtering table, said target value being set based upon a ratio of said amount of compressed image data quantized by said default quantization table for each said spatial frequency of said plurality of spatial frequencies to values of said predetermined filtering table; and an obtaining device that obtains a modified quantization coefficient corresponding to each said spatial frequency of said plurality of spatial frequencies, so that an estimated amount of said encoded data does not exceed said target value.
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Specification