This is jbsmooth.c in view mode; [Download] [Up]
/*
* jbsmooth.c
*
* Copyright (C) 1991, 1992, Thomas G. Lane.
* This file is part of the Independent JPEG Group's software.
* For conditions of distribution and use, see the accompanying README file.
*
* This file contains cross-block smoothing routines.
* These routines are invoked via the smooth_coefficients method.
*/
#include "jinclude.h"
#ifdef BLOCK_SMOOTHING_SUPPORTED
/*
* Cross-block coefficient smoothing.
*/
METHODDEF void
smooth_coefficients (decompress_info_ptr cinfo,
jpeg_component_info *compptr,
JBLOCKROW above,
JBLOCKROW currow,
JBLOCKROW below,
JBLOCKROW output)
{
QUANT_TBL_PTR Qptr = cinfo->quant_tbl_ptrs[compptr->quant_tbl_no];
long blocks_in_row = compptr->downsampled_width / DCTSIZE;
long col;
/* First, copy the block row as-is.
* This takes care of the first & last blocks in the row, the top/bottom
* special cases, and the higher-order coefficients in each block.
*/
jcopy_block_row(currow, output, blocks_in_row);
/* Now apply the smoothing calculation, but not to any blocks on the
* edges of the image.
*/
if (above != NULL && below != NULL) {
for (col = 1; col < blocks_in_row-1; col++) {
/* See section K.8 of the JPEG standard.
*
* As I understand it, this produces approximations
* for the low frequency AC components, based on the
* DC values of the block and its eight neighboring blocks.
* (Thus it can't be used for blocks on the image edges.)
*/
/* The layout of these variables corresponds to text and figure in K.8 */
JCOEF DC1, DC2, DC3;
JCOEF DC4, DC5, DC6;
JCOEF DC7, DC8, DC9;
long AC01, AC02;
long AC10, AC11;
long AC20;
DC1 = above [col-1][0];
DC2 = above [col ][0];
DC3 = above [col+1][0];
DC4 = currow[col-1][0];
DC5 = currow[col ][0];
DC6 = currow[col+1][0];
DC7 = below [col-1][0];
DC8 = below [col ][0];
DC9 = below [col+1][0];
#define DIVIDE_256(x) x = ( (x) < 0 ? -((128-(x))/256) : ((x)+128)/256 )
AC01 = (36 * (DC4 - DC6));
DIVIDE_256(AC01);
AC10 = (36 * (DC2 - DC8));
DIVIDE_256(AC10);
AC20 = (9 * (DC2 + DC8 - 2*DC5));
DIVIDE_256(AC20);
AC11 = (5 * ((DC1 - DC3) - (DC7 - DC9)));
DIVIDE_256(AC11);
AC02 = (9 * (DC4 + DC6 - 2*DC5));
DIVIDE_256(AC02);
/* I think that this checks to see if the quantisation
* on the transmitting side would have produced this
* answer. If so, then we use our (hopefully better)
* estimate.
*/
#define ABS(x) ((x) < 0 ? -(x) : (x))
#define COND_ASSIGN(_ac,_n,_z) if ((ABS(output[col][_n] - (_ac))<<1) <= Qptr[_z]) output[col][_n] = (JCOEF) (_ac)
COND_ASSIGN(AC01, 1, 1);
COND_ASSIGN(AC02, 2, 5);
COND_ASSIGN(AC10, 8, 2);
COND_ASSIGN(AC11, 9, 4);
COND_ASSIGN(AC20, 16, 3);
}
}
}
/*
* The method selection routine for cross-block smoothing.
*/
GLOBAL void
jselbsmooth (decompress_info_ptr cinfo)
{
/* just one implementation for now */
cinfo->methods->smooth_coefficients = smooth_coefficients;
}
#endif /* BLOCK_SMOOTHING_SUPPORTED */
These are the contents of the former NiCE NeXT User Group NeXTSTEP/OpenStep software archive, currently hosted by Netfuture.ch.