System and method for suppressing blocking artifacts in decoded transform coded images

Claim 1

A method for removing blocking artifacts in regions of slowly varying intensity in an electronic image decoded from a transform coded representation of an image, comprising the steps of: receiving signals indicative of DC and AC coefficient values of transformed blocks of image data representative of the image regions; evaluating whether the region of the image being decoded is varying slowly or rapidly in intensity, and producing signals indicative of the results of said evaluation; when said evaluation signals indicate said region is varying rapidly, applying no blocking correction to the received signals; and when said evaluation signals indicate said region is varying slowly, applying a blocking correction to said received signals.

Claim 4

A method for removing blocking artifacts in regions of slowly varying intensity in an electronic image decoded from a transform coded representation of an original image, comprising the steps of: receiving signals indicative of DC and AC coefficient values of transformed blocks of image data representative of the image regions; determining whether the AC prediction value of one of said blocks of transformed image data is within a selected range with respect to the received AC coefficient value; and if said AC prediction value of said one block is within said selected range, using said AC prediction value in decoding said block; and if said AC prediction value of said one block is not within said selected range, using said received AC coefficient value in decoding said block.

Claim 7

A method for removing blocking artifacts in regions of slowly varying intensity in an electronic image decoded from a transform coded representation of an image, comprising the steps of: receiving signals indicative of DC and AC coefficient values of transformed blocks of image data representative of the image regions; evaluating whether the region of the image being decoded is varying slowly or rapidly in intensity, and producing signals indicative of the results of said evaluation; when said evaluation signals indicate said region is varying rapidly, applying no blocking correction to the received signals; and when said evaluation signals indicate said region is varying slowly, applying a blocking correction to said received signals, and wherein said blocking correction comprises the steps of: determining whether the AC prediction value of one of said blocks of compressed image data is within a selected range with respect to the received AC coefficient value, and producing a signal indicative of the results of said determination; when said signal indicative of the results of said determination indicates said AC prediction value of said one block is within said selected range, using said AC prediction value in decoding said block; and when said signal indicative of the results of said determination indicates said AC prediction value of said one block is not within said selected range, using said received AC coefficient value in decoding said block, wherein said selected range preferably comprises the range of original coefficient values that would have been quantized to the decoded quantized value during the forward transform coding of said original image block and/or wherein said evaluating step preferably comprises using at least one of the following: spatial edge detection; frequency edge detection; zonal classification; and threshold classification.

Claim 8

A system for removing block artifacts in regions of slowly varying intensity in an electronic image decoded from a transform coded representation of an image, comprising: means for receiving signals indicative of DC and AC coefficient values of compressed blocks of image data representative of the image regions to be decoded; means, responsive to signals from said receiving means, for evaluating whether the region of the image being decoded is varying slowly or rapidly in intensity, and producing a signal indicative of the results of said evaluating; means for applying a blocking correction to said received signals when said signal indicative of said evaluating results indicates said region is varying slowly; and means for avoiding a blocking correction to said received signals when said signal indicative of said evaluating results indicates said region is varying rapidly, wherein said evaluating means preferably comprises means for testing using at least one of the following: spatial edge detection; frequency edge detection; zonal classification; and threshold classification.

Claim 9

A system for removing blocking artifacts in regions of slowly varying intensity in an electronic image decoded from a transform coded representation of an original image, comprising: means for receiving signals indicative of DC and AC coefficient values of transformed blocks of image data representative of the image regions; means, responsive to signals from said receiving means, for determining whether the AC prediction value of one of said blocks of transformed image data is within a selected range with respect to the received AC coefficient value and producing a signal indicative of the results of said determination: means for using said AC prediction value in decoding said block when said results signal indicates that said AC prediction value of said one block is within said selected range; and means for using said received AC coefficient value in decoding said block when said results signal indicates that said AC prediction value of said one block is not within said selected range, wherein said means for determining said selected range preferably comprises means for determining the range of original coefficient values that would have been quantized to the decoded quantized value during the forward transform coding of said original image block.