US 6,983,079 B2
Reducing blocking and ringing artifacts in low-bit-rate coding
Changick Kim, San Jose, Calif. (US)
Assigned to Seiko Epson Corporation, Tokyo (Japan)
Filed on Oct. 23, 2001, as Appl. No. 10/37,767.
Claims priority of provisional application 60/323986, filed on Sep. 20, 2001.
Prior Publication US 2003/0053711 A1, Mar. 20, 2003
Int. Cl. G06K 9/40 (2006.01)
U.S. Cl. 382—275 19 Claims
OG exemplary drawing
 
1. A method for reducing artifacts in digital data, comprising the steps of:
(a) obtaining a reconstructed block-based pixel representation of the digital data;
(b) extracting a DC coefficient for each block in the pixel representation based on values of selected pixels in that block to generate a map of DC coefficients;
(c) for each pixel block, predicting a select number of lower frequency AC coefficients using the DC coefficient for that pixel block and a select number of neighboring DC coefficients in the DC coefficient map to construct a corresponding partial transform-coefficient block;
(d) classifying each pixel block as a low-activity block or a high-activity block based on the predicted AC coefficients in the corresponding partial transform-coefficient block; and
(e) selectively performing a low-pass filtering operation on select pixels in select pixel blocks on a block-by-block basis based on the classification of that block, the locations and values of predicted non-zero AC coefficients in the corresponding partial transform block, and certain pixel values in that block, wherein a low-pass filter of a first strength is applied to a given pixel region in a given low-activity block if a minimum condition for that pixel region is satisfied, and wherein a low-pass filter of a second strength is applied to a given pixel region in a given high-activity block if a minimum condition for that pixel region is satisfied.