Decompression of standard ADCT-compressed document images

Details Decompression of standard ADCT-compressed document images Decompression of standard ADCT-compressed document images

1993-07-19

1994-10-25

Moore, David K.

Image analysis

Histogram processing

For setting a threshold

382 22, 382 54, 358433, G06K 936

Patent

active

053596765

ABSTRACT:
A method of improving the appearance of an ADCT decompressed document image while maintaining fidelity with an original document image from which it is derived, the method including the decompression steps of: a) receiving the encoded quantized transform coefficient blocks for the original image; b) removing any lossless encoding of the quantized transform coefficient blocks for the original image; c) multiplying each quantized transform coefficient in a block by a corresponding quantizing value from the quantization table to obtain a block of received transform coefficients; d) recovering the image by applying an inverse transform operation to the received transform coefficients; e) i) adaptively selecting on a block by block basis a filter threshold, ii) detecting edges within the block and forming a mapping of the edges occurring, and iii) iteratively filtering for a predetermined number of times the image with a smoothing filter, the filtering operation controlled by the derived edge map so as not to operate on image edges; f) comparing each block of new transform coefficients to a corresponding block of received transform coefficients and the selected quantization table, to determine whether the filtered recovered image is derivable from the original image; and g) upon the determination transferring the filtered recovered image to an output buffer.

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