436 lines
10 KiB
C
436 lines
10 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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* 5/9/13
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* - redo as a class
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* 9/9/13
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* - any number of bands
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* 20/1/17
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* - add contrast limit
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* - sum to <= target, not < target, since cumulative hists include the
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* current value
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* - scale result by 255, not 256, to avoid overflow
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* - off by 1 fix for odd window widths
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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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#include <vips/internal.h>
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typedef struct _VipsHistLocal {
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VipsOperation parent_instance;
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VipsImage *in;
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VipsImage *out;
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int width;
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int height;
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int max_slope;
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} VipsHistLocal;
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typedef VipsOperationClass VipsHistLocalClass;
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G_DEFINE_TYPE( VipsHistLocal, vips_hist_local, VIPS_TYPE_OPERATION );
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/* Our sequence value: the region this sequence is using, and local stats.
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*/
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typedef struct {
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VipsRegion *ir; /* Input region */
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/* A 256-element hist for every band.
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*/
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unsigned int **hist;
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} VipsHistLocalSequence;
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static int
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vips_hist_local_stop( void *vseq, void *a, void *b )
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{
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VipsHistLocalSequence *seq = (VipsHistLocalSequence *) vseq;
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VipsImage *in = (VipsImage *) a;
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VIPS_UNREF( seq->ir );
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if( seq->hist &&
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in ) {
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int i;
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for( i = 0; i < in->Bands; i++ )
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VIPS_FREE( seq->hist[i] );
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VIPS_FREE( seq->hist );
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}
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VIPS_FREE( seq );
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return( 0 );
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}
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static void *
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vips_hist_local_start( VipsImage *out, void *a, void *b )
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{
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VipsImage *in = (VipsImage *) a;
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VipsHistLocalSequence *seq;
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int i;
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if( !(seq = VIPS_NEW( NULL, VipsHistLocalSequence )) )
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return( NULL );
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seq->ir = NULL;
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seq->hist = NULL;
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if( !(seq->ir = vips_region_new( in )) ||
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!(seq->hist = VIPS_ARRAY( NULL, in->Bands, unsigned int * )) ) {
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vips_hist_local_stop( seq, NULL, NULL );
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return( NULL );
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}
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for( i = 0; i < in->Bands; i++ )
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if( !(seq->hist[i] = VIPS_ARRAY( NULL, 256, unsigned int )) ) {
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vips_hist_local_stop( seq, NULL, NULL );
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return( NULL );
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}
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return( seq );
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}
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static int
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vips_hist_local_generate( VipsRegion *or,
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void *vseq, void *a, void *b, gboolean *stop )
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{
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VipsHistLocalSequence *seq = (VipsHistLocalSequence *) vseq;
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VipsImage *in = (VipsImage *) a;
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const VipsHistLocal *local = (VipsHistLocal *) b;
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VipsRect *r = &or->valid;
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const int bands = in->Bands;
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const int max_slope = local->max_slope;
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VipsRect irect;
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int y;
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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 = r->left;
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irect.top = r->top;
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irect.width = r->width + local->width;
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irect.height = r->height + local->height;
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if( vips_region_prepare( seq->ir, &irect ) )
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return( -1 );
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lsk = VIPS_REGION_LSKIP( seq->ir );
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centre = lsk * (local->height / 2) + bands * (local->width / 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 * restrict p =
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VIPS_REGION_ADDR( seq->ir, r->left, r->top + y );
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VipsPel * restrict q =
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VIPS_REGION_ADDR( or, r->left, r->top + y );
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VipsPel * restrict p1;
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int x, i, j, b;
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/* Find histogram for start of this line.
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*/
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for( b = 0; b < bands; b++ )
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memset( seq->hist[b], 0, 256 * sizeof( unsigned int ) );
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p1 = p;
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for( j = 0; j < local->height; j++ ) {
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for( i = 0, x = 0; x < local->width; x++ )
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for( b = 0; b < bands; b++, i++ )
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seq->hist[b][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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for( b = 0; b < bands; b++ ) {
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/* Sum histogram up to current pel.
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*/
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unsigned int * restrict hist = seq->hist[b];
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const int target = p[centre + b];
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int sum;
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sum = 0;
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/* For CLAHE we need to limit the height of the
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* hist to limit the amount we boost the
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* contrast by.
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*/
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if( max_slope > 0 ) {
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int sum_over;
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sum_over = 0;
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/* Must be <= target, since a cum hist
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* always includes the current element.
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*/
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for( i = 0; i <= target; i++ ) {
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if( hist[i] > max_slope ) {
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sum_over += hist[i] -
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max_slope;
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sum += max_slope;
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}
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else
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sum += hist[i];
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}
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for( ; i < 256; i++ ) {
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if( hist[i] > max_slope )
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sum_over += hist[i] -
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max_slope;
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}
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/* The extra clipped off bit from the
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* top of the hist is spread over all
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* bins equally, then summed to target.
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*/
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sum += (target + 1) * sum_over / 256;
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}
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else {
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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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}
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/* This can't overflow, even in
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* contrast-limited mode.
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*
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* Scale by 255, not 256, or we'll get
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* overflow.
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*/
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q[b] = 255 * sum /
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(local->width * local->height);
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/* Adapt histogram --- remove the pels from
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* the left hand column, add in pels for a
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* new right-hand column.
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*/
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p1 = p + b;
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for( j = 0; j < local->height; j++ ) {
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hist[p1[0]] -= 1;
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hist[p1[bands * local->width]] += 1;
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p1 += lsk;
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}
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}
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p += bands;
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q += bands;
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}
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}
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return( 0 );
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}
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static int
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vips_hist_local_build( VipsObject *object )
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{
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VipsObjectClass *class = VIPS_OBJECT_GET_CLASS( object );
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VipsHistLocal *local = (VipsHistLocal *) object;
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VipsImage **t = (VipsImage **) vips_object_local_array( object, 3 );
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VipsImage *in;
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if( VIPS_OBJECT_CLASS( vips_hist_local_parent_class )->build( object ) )
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return( -1 );
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in = local->in;
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if( vips_image_decode( in, &t[0] ) )
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return( -1 );
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in = t[0];
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if( vips_check_format( class->nickname, in, VIPS_FORMAT_UCHAR ) )
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return( -1 );
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if( local->width > in->Xsize ||
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local->height > in->Ysize ) {
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vips_error( class->nickname, "%s", _( "window too large" ) );
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return( -1 );
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}
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/* Expand the input.
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*/
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if( vips_embed( in, &t[1],
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local->width / 2, local->height / 2,
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in->Xsize + local->width - 1, in->Ysize + local->height - 1,
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"extend", VIPS_EXTEND_MIRROR,
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NULL ) )
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return( -1 );
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in = t[1];
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g_object_set( object, "out", vips_image_new(), NULL );
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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( vips_image_pipelinev( local->out,
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VIPS_DEMAND_STYLE_FATSTRIP, in, NULL ) )
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return( -1 );
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local->out->Xsize -= local->width - 1;
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local->out->Ysize -= local->height - 1;
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if( vips_image_generate( local->out,
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vips_hist_local_start,
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vips_hist_local_generate,
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vips_hist_local_stop,
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in, local ) )
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return( -1 );
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local->out->Xoffset = 0;
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local->out->Yoffset = 0;
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vips_reorder_margin_hint( local->out, local->width * local->height );
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return( 0 );
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}
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static void
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vips_hist_local_class_init( VipsHistLocalClass *class )
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{
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GObjectClass *gobject_class = G_OBJECT_CLASS( class );
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VipsObjectClass *object_class = (VipsObjectClass *) class;
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gobject_class->set_property = vips_object_set_property;
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gobject_class->get_property = vips_object_get_property;
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object_class->nickname = "hist_local";
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object_class->description = _( "local histogram equalisation" );
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object_class->build = vips_hist_local_build;
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VIPS_ARG_IMAGE( class, "in", 1,
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_( "Input" ),
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_( "Input image" ),
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VIPS_ARGUMENT_REQUIRED_INPUT,
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G_STRUCT_OFFSET( VipsHistLocal, in ) );
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VIPS_ARG_IMAGE( class, "out", 2,
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_( "Output" ),
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_( "Output image" ),
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VIPS_ARGUMENT_REQUIRED_OUTPUT,
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G_STRUCT_OFFSET( VipsHistLocal, out ) );
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VIPS_ARG_INT( class, "width", 4,
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_( "Width" ),
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_( "Window width in pixels" ),
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VIPS_ARGUMENT_REQUIRED_INPUT,
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G_STRUCT_OFFSET( VipsHistLocal, width ),
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1, VIPS_MAX_COORD, 1 );
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VIPS_ARG_INT( class, "height", 5,
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_( "Height" ),
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_( "Window height in pixels" ),
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VIPS_ARGUMENT_REQUIRED_INPUT,
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G_STRUCT_OFFSET( VipsHistLocal, height ),
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1, VIPS_MAX_COORD, 1 );
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VIPS_ARG_INT( class, "max_slope", 6,
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_( "Max slope" ),
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_( "Maximum slope (CLAHE)" ),
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VIPS_ARGUMENT_OPTIONAL_INPUT,
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G_STRUCT_OFFSET( VipsHistLocal, max_slope ),
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0, 100, 0 );
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}
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static void
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vips_hist_local_init( VipsHistLocal *local )
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{
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}
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/**
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* vips_hist_local:
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* @in: input image
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* @out: output image
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* @width: width of region
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* @height: height of region
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* @...: %NULL-terminated list of optional named arguments
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*
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* Optional arguments:
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*
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* * @max_slope: maximum brightening
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*
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* Performs local histogram equalisation on @in using a
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* window of size @width by @height centered on the input pixel.
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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 mirroring the input image outwards.
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*
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* If @max_slope is greater than 0, it sets the maximum value for the slope of
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* the cumulative histogram, that is, the maximum brightening that is
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* performed. A value of 3 is often used. Local histogram equalization with
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* contrast limiting is usually called CLAHE.
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*
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* See also: vips_hist_equal().
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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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vips_hist_local( VipsImage *in, VipsImage **out, int width, int height, ... )
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{
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va_list ap;
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int result;
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va_start( ap, height );
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result = vips_call_split( "hist_local", ap, in, out, width, height );
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va_end( ap );
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return( result );
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}
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