Process and device for the compression of image data by mathematical transformation effected at low cost, particularly for the transmission at a reduced rate of sequences of images
First Claim
1. Process of compression of data representative of an image signal, of the type consisting of decomposing the image into blocks forming arrays of pixels, of effecting a mathematical operation of transformation on each array of pixels according to a transform making it possible to obtain a resulting array of elements representative of the activity of the image, and of eliminating in each resulting array the elements of little psychovisual relevance by thresholding in relation to an array of reference thresholds, process characterized in that the said mathematical operation of transformation consists of the steps of:
- transposing the elements of the array of pixels by permutation of the indices of the said elements, so as to symmetrize the signal;
applying an interlacing of two series of one dimensional real value FFT, bearing successively on each line of the permuted array of pixels, then on each of the columns of the intermediate array resulting from the first series of one dimensional FFT.
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Abstract
Process and device for the compression of image data by a mathematical transformation implemented at low cost, particularly for the transmission at reduced speed of sequences of images.
The objective is to provide an economical method in "silicon area - processing speed" cost to implement a mathematical transformation of the DCT type, on arrays of pixels, suitable for image compression.
According to the invention, the method consists essentially of combining a permutation (1) of each block of pixels with a series of one dimensional FFT (211, 213). A series of variants is obtained by adding or not adding steps of matrix calculation (22) of reconstitution of a complex 2D-FET, of rotations (3) of reconstitution of the DCT, and/or of suppression of the imaginary coefficients.
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10 Claims
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1. Process of compression of data representative of an image signal, of the type consisting of decomposing the image into blocks forming arrays of pixels, of effecting a mathematical operation of transformation on each array of pixels according to a transform making it possible to obtain a resulting array of elements representative of the activity of the image, and of eliminating in each resulting array the elements of little psychovisual relevance by thresholding in relation to an array of reference thresholds, process characterized in that the said mathematical operation of transformation consists of the steps of:
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transposing the elements of the array of pixels by permutation of the indices of the said elements, so as to symmetrize the signal; applying an interlacing of two series of one dimensional real value FFT, bearing successively on each line of the permuted array of pixels, then on each of the columns of the intermediate array resulting from the first series of one dimensional FFT. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification