Reduction of errors during computation of inverse discrete cosine transform

Abstract

Techniques are described to reduce rounding errors during computation of discrete cosine transform using fixed-point calculations. According to these techniques, an inverse discrete cosine transform a vector of coefficients is calculated using a series of butterfly structure operations on fixed-point numbers. Next, a midpoint bias value and a supplemental bias value are added to a DC coefficient of the matrix of scaled coefficients. Next, an inverse discrete cosine transform is applied to the resulting matrix of scaled coefficients. Values in the resulting matrix are then right-shifted in order to derive a matrix of pixel component values. As described herein, the addition of the supplemental bias value to the DC coefficient reduces rounding errors attributable to this right-shifting. As a result, a final version of a digital media file decompressed using these techniques may more closely resemble an original version of a digital media file.

Description

[0001] This application asserts U.S. Provisional Application Nos. 60 / 816,697, filed June 26, 2006, U.S. Provisional Application Nos. 60 / 841,362, filed August 30, 2006, 60 / 847,194, U.S. Provisional Application No. 60 / 829,669, filed October 16, 2006, and U.S. Provisional Application No. 60 / 869,530, filed December 11, 2006, the above provisional applications The entire content of is incorporated herein by reference. technical field [0002] This invention relates to computer graphics and multimedia, and more particularly to the compression of graphics, image and video information. Background technique [0003] Many existing image and video encoding standards use compression techniques in order to allow high resolution images and video to be stored or transmitted as relatively compact files or data streams. Such encoding standards include Joint Photographic Experts Group (JPEG), Moving Pictures Experts Group (MPEG)-1, MPEG-2, MPEG-4 Part 2, H.261, H.263 and Other image or vid...

AI Technical Summary

Problems solved by technology

Furthermore, errors resulting from mismatches between the encoder's implementation of the IDCT and the decoder's implementation of the IDCT can accumulate during the encoding and decoding of the predicted frame sequence

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