233 lines
5.1 KiB
C
233 lines
5.1 KiB
C
/* local histogram equalisation
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*
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* Copyright: 1991, N. Dessipris
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*
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* Author: N. Dessipris
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* Written on: 24/10/1991
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* Modified on :
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* 25/1/96 JC
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* - rewritten, adapting im_spcor()
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* - correct result, 2x faster, partial, simpler, better arg checking
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* 8/7/04
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* - expand input rather than output with new im_embed() mode
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* - _raw() output is one pixel larger
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* - sets Xoffset/Yoffset
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* 23/6/08
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* - check for window too small as well
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* 25/3/10
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* - gtkdoc
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* - small cleanups
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*/
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/*
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This file is part of VIPS.
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VIPS is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301 USA
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*/
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/*
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These files are distributed with VIPS - http://www.vips.ecs.soton.ac.uk
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*/
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#ifdef HAVE_CONFIG_H
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#include <config.h>
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#endif /*HAVE_CONFIG_H*/
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#include <vips/intl.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <vips/vips.h>
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/* Hold global stuff here.
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*/
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typedef struct {
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int xwin, ywin; /* Parameters */
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int npels; /* Pels in window */
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} LhistInfo;
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/* lhist generate function.
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*/
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static int
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lhist_gen( REGION *or, void *seq, void *a, void *b )
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{
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REGION *ir = (REGION *) seq;
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LhistInfo *inf = (LhistInfo *) b;
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Rect *r = &or->valid;
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Rect irect;
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int x, y, i, j;
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int lsk;
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int centre; /* Offset to move to centre of window */
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/* What part of ir do we need?
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*/
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irect.left = or->valid.left;
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irect.top = or->valid.top;
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irect.width = or->valid.width + inf->xwin;
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irect.height = or->valid.height + inf->ywin;
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if( im_prepare( ir, &irect ) )
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return( -1 );
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lsk = IM_REGION_LSKIP( ir );
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centre = lsk * (inf->ywin / 2) + inf->xwin / 2;
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for( y = 0; y < r->height; y++ ) {
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/* Get input and output pointers for this line.
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*/
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VipsPel *p = IM_REGION_ADDR( ir, r->left, r->top + y );
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VipsPel *q = IM_REGION_ADDR( or, r->left, r->top + y );
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VipsPel *p1;
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int hist[256];
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/* Find histogram for start of this line.
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*/
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memset( hist, 0, 256 * sizeof( int ) );
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p1 = p;
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for( j = 0; j < inf->ywin; j++ ) {
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for( i = 0; i < inf->xwin; i++ )
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hist[p1[i]] += 1;
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p1 += lsk;
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}
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/* Loop for output pels.
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*/
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for( x = 0; x < r->width; x++ ) {
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/* Sum histogram up to current pel.
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*/
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int target = p[centre];
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int sum;
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sum = 0;
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for( i = 0; i < target; i++ )
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sum += hist[i];
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/* Transform.
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*/
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q[x] = sum * 256 / inf->npels;
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/* Adapt histogram - remove the pels from the left hand
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* column, add in pels for a new right-hand column.
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*/
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p1 = p;
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for( j = 0; j < inf->ywin; j++ ) {
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hist[p1[0]] -= 1;
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hist[p1[inf->xwin]] += 1;
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p1 += lsk;
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}
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p += 1;
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}
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}
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return( 0 );
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}
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int
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im_lhisteq_raw( IMAGE *in, IMAGE *out, int xwin, int ywin )
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{
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LhistInfo *inf;
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if( im_check_mono( "im_lhisteq", in ) ||
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im_check_uncoded( "im_lhisteq", in ) ||
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im_check_format( "im_lhisteq", in, IM_BANDFMT_UCHAR ) ||
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im_piocheck( in, out ) )
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return( -1 );
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if( xwin > in->Xsize ||
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ywin > in->Ysize ) {
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im_error( "im_lhisteq", "%s", _( "window too large" ) );
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return( -1 );
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}
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if( xwin <= 0 ||
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ywin <= 0 ) {
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im_error( "im_lhisteq", "%s", _( "window too small" ) );
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return( -1 );
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}
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if( im_cp_desc( out, in ) )
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return( -1 );
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out->Xsize -= xwin - 1;
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out->Ysize -= ywin - 1;
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/* Save parameters.
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*/
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if( !(inf = IM_NEW( out, LhistInfo )) )
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return( -1 );
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inf->xwin = xwin;
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inf->ywin = ywin;
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inf->npels = xwin * ywin;
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/* Set demand hints. FATSTRIP is good for us, as THINSTRIP will cause
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* too many recalculations on overlaps.
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*/
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if( im_demand_hint( out, IM_FATSTRIP, in, NULL ) )
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return( -1 );
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if( im_generate( out,
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im_start_one, lhist_gen, im_stop_one, in, inf ) )
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return( -1 );
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out->Xoffset = -xwin / 2;
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out->Yoffset = -xwin / 2;
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return( 0 );
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}
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/**
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* im_lhisteq:
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* @in: input image
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* @out: output image
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* @xwin: width of region
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* @ywin: height of region
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*
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* Performs local histogram equalisation on @in using a
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* window of size @xwin by @ywin centered on the input pixel. Works only on
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* monochrome images.
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*
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* The output image is the same size as the input image. The edge pixels are
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* created by copy edge pixels of the input image outwards.
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*
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* See also: im_stdif(), im_heq().
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*
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* Returns: 0 on success, -1 on error
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*/
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int
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im_lhisteq( IMAGE *in, IMAGE *out, int xwin, int ywin )
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{
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IMAGE *t1;
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if( !(t1 = im_open_local( out, "im_lhisteq:1", "p" )) ||
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im_embed( in, t1, 1,
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xwin / 2, ywin / 2,
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in->Xsize + xwin - 1, in->Ysize + ywin - 1 ) ||
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im_lhisteq_raw( t1, out, xwin, ywin ) )
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return( -1 );
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out->Xoffset = 0;
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out->Yoffset = 0;
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return( 0 );
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}
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