401 lines
9.6 KiB
C
401 lines
9.6 KiB
C
/* unpremultiply alpha
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*
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* Author: John Cupitt
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* Written on: 7/5/15
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*
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* 25/5/16
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* - max_alpha defaults to 65535 for RGB16/GREY16
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* 24/11/17 lovell
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* - match normalised alpha to output type
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* 27/2/21 jjonesrs
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* - revise range clipping and 1/x, again
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* 8/8/22
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* - look for alpha near 0, not just exactly 0
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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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/*
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#define VIPS_DEBUG
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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 <glib/gi18n-lib.h>
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#include <stdio.h>
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#include <string.h>
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#include <stdlib.h>
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#include <math.h>
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#include <vips/vips.h>
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#include <vips/internal.h>
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#include <vips/debug.h>
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#include "pconversion.h"
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typedef struct _VipsUnpremultiply {
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VipsConversion parent_instance;
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VipsImage *in;
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double max_alpha;
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int alpha_band;
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} VipsUnpremultiply;
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typedef VipsConversionClass VipsUnpremultiplyClass;
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G_DEFINE_TYPE( VipsUnpremultiply, vips_unpremultiply, VIPS_TYPE_CONVERSION );
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/* Unpremultiply an N-band image. Don't use clip_alpha to calculate factor: we
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* want over and undershoots on alpha and RGB to cancel.
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*/
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#define UNPRE_MANY( IN, OUT ) { \
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IN * restrict p = (IN *) in; \
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OUT * restrict q = (OUT *) out; \
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\
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for( x = 0; x < width; x++ ) { \
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IN alpha = p[alpha_band]; \
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OUT factor = alpha == 0 ? 0 : max_alpha / alpha; \
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\
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for( i = 0; i < alpha_band; i++ ) \
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q[i] = factor * p[i]; \
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q[alpha_band] = VIPS_CLIP( 0, alpha, max_alpha ); \
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for( i = alpha_band + 1; i < bands; i++ ) \
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q[i] = p[i]; \
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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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/* Unpremultiply an RGB (four band) image.
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*/
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#define UNPRE_RGBA( IN, OUT ) { \
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IN * restrict p = (IN *) in; \
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OUT * restrict q = (OUT *) out; \
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\
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for( x = 0; x < width; x++ ) { \
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IN alpha = p[3]; \
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OUT factor = alpha == 0 ? 0 : max_alpha / alpha; \
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\
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q[0] = factor * p[0]; \
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q[1] = factor * p[1]; \
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q[2] = factor * p[2]; \
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q[3] = VIPS_CLIP( 0, alpha, max_alpha ); \
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\
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p += 4; \
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q += 4; \
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} \
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}
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#define UNPRE( IN, OUT ) { \
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if( bands == 4 ) { \
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UNPRE_RGBA( IN, OUT ); \
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} \
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else { \
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UNPRE_MANY( IN, OUT ); \
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} \
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}
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/* For float-style images, we need to check for alpha near zero, or we'll get
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* +/- Inf in the output.
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*/
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#define FUNPRE_MANY( IN, OUT ) { \
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IN * restrict p = (IN *) in; \
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OUT * restrict q = (OUT *) out; \
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\
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for( x = 0; x < width; x++ ) { \
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IN alpha = p[alpha_band]; \
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OUT factor = VIPS_ABS( alpha ) < 0.01 ? 0 : max_alpha / alpha; \
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\
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for( i = 0; i < alpha_band; i++ ) \
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q[i] = factor * p[i]; \
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q[alpha_band] = VIPS_CLIP( 0, alpha, max_alpha ); \
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for( i = alpha_band + 1; i < bands; i++ ) \
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q[i] = p[i]; \
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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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#define FUNPRE_RGBA( IN, OUT ) { \
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IN * restrict p = (IN *) in; \
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OUT * restrict q = (OUT *) out; \
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\
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for( x = 0; x < width; x++ ) { \
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IN alpha = p[3]; \
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OUT factor = VIPS_ABS( alpha ) < 0.01 ? 0 : max_alpha / alpha; \
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\
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q[0] = factor * p[0]; \
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q[1] = factor * p[1]; \
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q[2] = factor * p[2]; \
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q[3] = VIPS_CLIP( 0, alpha, max_alpha ); \
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\
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p += 4; \
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q += 4; \
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} \
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}
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#define FUNPRE( IN, OUT ) { \
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if( bands == 4 ) { \
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FUNPRE_RGBA( IN, OUT ); \
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} \
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else { \
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FUNPRE_MANY( IN, OUT ); \
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} \
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}
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static int
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vips_unpremultiply_gen( VipsRegion *or, void *vseq, void *a, void *b,
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gboolean *stop )
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{
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VipsUnpremultiply *unpremultiply = (VipsUnpremultiply *) b;
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VipsRegion *ir = (VipsRegion *) vseq;
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VipsImage *im = ir->im;
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VipsRect *r = &or->valid;
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int width = r->width;
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int bands = im->Bands;
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double max_alpha = unpremultiply->max_alpha;
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int alpha_band = unpremultiply->alpha_band;
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int x, y, i;
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if( vips_region_prepare( ir, r ) )
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return( -1 );
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for( y = 0; y < r->height; y++ ) {
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VipsPel *in = VIPS_REGION_ADDR( ir, r->left, r->top + y );
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VipsPel *out = VIPS_REGION_ADDR( or, r->left, r->top + y );
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switch( im->BandFmt ) {
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case VIPS_FORMAT_UCHAR:
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UNPRE( unsigned char, float );
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break;
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case VIPS_FORMAT_CHAR:
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UNPRE( signed char, float );
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break;
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case VIPS_FORMAT_USHORT:
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UNPRE( unsigned short, float );
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break;
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case VIPS_FORMAT_SHORT:
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UNPRE( signed short, float );
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break;
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case VIPS_FORMAT_UINT:
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UNPRE( unsigned int, float );
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break;
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case VIPS_FORMAT_INT:
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UNPRE( signed int, float );
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break;
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case VIPS_FORMAT_FLOAT:
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FUNPRE( float, float );
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break;
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case VIPS_FORMAT_DOUBLE:
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FUNPRE( double, double );
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break;
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case VIPS_FORMAT_COMPLEX:
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case VIPS_FORMAT_DPCOMPLEX:
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default:
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g_assert_not_reached();
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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_unpremultiply_build( VipsObject *object )
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{
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VipsObjectClass *class = VIPS_OBJECT_GET_CLASS( object );
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VipsConversion *conversion = VIPS_CONVERSION( object );
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VipsUnpremultiply *unpremultiply = (VipsUnpremultiply *) object;
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VipsImage **t = (VipsImage **) vips_object_local_array( object, 1 );
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VipsImage *in;
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if( VIPS_OBJECT_CLASS( vips_unpremultiply_parent_class )->
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build( object ) )
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return( -1 );
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in = unpremultiply->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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/* Trivial case: fall back to copy().
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*/
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if( in->Bands == 1 )
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return( vips_image_write( in, conversion->out ) );
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if( vips_check_noncomplex( class->nickname, in ) )
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return( -1 );
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if( vips_image_pipelinev( conversion->out,
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VIPS_DEMAND_STYLE_THINSTRIP, in, NULL ) )
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return( -1 );
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/* Is max-alpha unset? Default to the correct value for this
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* interpretation.
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*/
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if( !vips_object_argument_isset( object, "max_alpha" ) )
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if( in->Type == VIPS_INTERPRETATION_GREY16 ||
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in->Type == VIPS_INTERPRETATION_RGB16 )
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unpremultiply->max_alpha = 65535;
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/* Is alpha-band unset? Default to the final band for this image.
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*/
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if( !vips_object_argument_isset( object, "alpha_band" ) )
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unpremultiply->alpha_band = in->Bands - 1;
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if( in->BandFmt == VIPS_FORMAT_DOUBLE )
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conversion->out->BandFmt = VIPS_FORMAT_DOUBLE;
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else
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conversion->out->BandFmt = VIPS_FORMAT_FLOAT;
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if( vips_image_generate( conversion->out,
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vips_start_one, vips_unpremultiply_gen, vips_stop_one,
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in, unpremultiply ) )
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return( -1 );
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return( 0 );
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}
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static void
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vips_unpremultiply_class_init( VipsUnpremultiplyClass *class )
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{
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GObjectClass *gobject_class = G_OBJECT_CLASS( class );
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VipsObjectClass *vobject_class = VIPS_OBJECT_CLASS( class );
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VipsOperationClass *operation_class = VIPS_OPERATION_CLASS( class );
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VIPS_DEBUG_MSG( "vips_unpremultiply_class_init\n" );
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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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vobject_class->nickname = "unpremultiply";
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vobject_class->description = _( "unpremultiply image alpha" );
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vobject_class->build = vips_unpremultiply_build;
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operation_class->flags = VIPS_OPERATION_SEQUENTIAL;
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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( VipsUnpremultiply, in ) );
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VIPS_ARG_DOUBLE( class, "max_alpha", 115,
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_( "Maximum alpha" ),
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_( "Maximum value of alpha channel" ),
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VIPS_ARGUMENT_OPTIONAL_INPUT,
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G_STRUCT_OFFSET( VipsUnpremultiply, max_alpha ),
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0, 100000000, 255 );
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VIPS_ARG_INT( class, "alpha_band", 116,
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_( "Alpha band" ),
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_( "Unpremultiply with this alpha" ),
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VIPS_ARGUMENT_OPTIONAL_INPUT,
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G_STRUCT_OFFSET( VipsUnpremultiply, alpha_band ),
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0, 100000000, 3 );
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}
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static void
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vips_unpremultiply_init( VipsUnpremultiply *unpremultiply )
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{
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unpremultiply->max_alpha = 255.0;
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}
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/**
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* vips_unpremultiply: (method)
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* @in: input image
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* @out: (out): output image
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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_alpha: %gdouble, maximum value for alpha
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* * @alpha_band: %gint, band containing alpha data
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*
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* Unpremultiplies any alpha channel.
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* Band @alpha_band (by default the final band) contains the alpha and all
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* other bands are transformed as:
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*
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* |[
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* alpha = (int) clip( 0, in[in.bands - 1], @max_alpha );
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* norm = (double) alpha / @max_alpha;
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* if( alpha == 0 )
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* out = [0, ..., 0, alpha];
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* else
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* out = [in[0] / norm, ..., in[in.bands - 1] / norm, alpha];
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* ]|
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*
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* So for an N-band image, the first N - 1 bands are divided by the clipped
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* and normalised final band, the final band is clipped.
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* If there is only a single band, the image is passed through unaltered.
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*
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* The result is
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* #VIPS_FORMAT_FLOAT unless the input format is #VIPS_FORMAT_DOUBLE, in which
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* case the output is double as well.
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*
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* @max_alpha has the default value 255, or 65535 for images tagged as
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* #VIPS_INTERPRETATION_RGB16 or
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* #VIPS_INTERPRETATION_GREY16.
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*
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* Non-complex images only.
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*
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* See also: vips_premultiply(), vips_flatten().
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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_unpremultiply( VipsImage *in, VipsImage **out, ... )
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{
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va_list ap;
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int result;
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va_start( ap, out );
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result = vips_call_split( "unpremultiply", ap, in, out );
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va_end( ap );
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return( result );
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}
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