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NAME

QccIMGImageComponentLBT, QccIMGImageComponentInverseLBT - lapped biorthogonal transform and inverse for an image component

SYNOPSIS

#include "libQccPack.h"

int QccIMGImageComponentLBT(const QccIMGImageComponent *image1, QccIMGImageComponent *image2, int overlap_sample, int block_size, double smooth_factor);
int QccIMGImageComponentInverseLBT(const QccIMGImageComponent *image1, QccIMGImageComponent *image2, int overlap_sample, int block_size, double smooth_factor);

DESCRIPTION

QccIMGImageComponentLBT() calculates the lapped biorthogonal transform (LBT) of input1. The result is returned in image2, which must be allocated prior to calling QccIMGImageComponentLBT(). Both image1 and image2 have the same number of rows and columns.

QccIMGImageComponentInverseLBT() calculates the inverse LBT of image1, returning its results in image2.

For both QccIMGImageComponentLBT() and QccIMGImageComponentInverseLBT(), overlap_sample and smooth_factor are parameters to the prefilter and postfilter of the LBT (see "ALGORITHM" below), while block_size is the size of the blocks used for the DCT.

RETURN VALUE

Both QccIMGImageComponentLBT() and QccIMGImageComponentInverseLBT() return 0 on success, 1 on error.

ALGORITHM

The lapped biorthogonal transform (LBT) implemented by these routines was proposed by Tran et al. In essence, the forward transform consists of a smoothing prefilter followed by a block-based DCT. The inverse is then a block-based inverse DCT followed by a corresponding postfilter. The prefilter is intended to reduce intra-block and inter-block correlation of the block-based DCT coefficients.

The parameters to the prefilter and postfilter operations are overlap_sample, which is the number of samples of overlap between DCT blocks in the prefilter and postfiler, and smooth_factor, which is the smoothing constant for the prefilter and postfilter. Although performance can varying for these parameters, sugegsted values are overlap_sample = block_size/2 and smooth_factor = 1.333333.

SEE ALSO

QccIMGImageComponentDCT(3) , QccPackIMG(3) , QccPack(3)

T. D. Tran, J. Liang, and C. Tu, "Lapped transform via time-domain pre- and post-filtering," IEEE Transactions on Signal Processing, vol. 51, no. 6, pp. 1557-1571, June 2003.

C. Tu and T. D. Tran, "Context-based entropy coding of block transform coefficients for image compression," IEEE Transactions on Image Processing, vol. 11, no. 11, pp. 1271-1283, November 2002.

AUTHOR

Copyright (C) 1997-2021 James E. Fowler

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