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better rounding in vips_flatten() 

thanks allesandro
This commit is contained in:
John Cupitt 2014-02-04 19:50:13 +00:00
parent 281b0e91d8
commit 5989a2a37e
2 changed files with 28 additions and 78 deletions
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1
ChangeLog
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@ -3,6 +3,7 @@
- background render thread cleans up and quits neatly
- colourspace has a source_space option
- operations can be tagged as "deprecated"
- better rounding in vips_flatten()
22/1/14 started 7.38.3
- undeprecate VIPS_MASK_IDEAL_HIGHPASS and friends, ruby-vips was using them,

105
libvips/conversion/flatten.c
View File

@ -2,6 +2,9 @@
*
* Author: John Cupitt
* Written on: 18/6/12
*
* 4/1/14
* - better rounding
*/
/*
@ -70,24 +73,9 @@ typedef VipsConversionClass VipsFlattenClass;
G_DEFINE_TYPE( VipsFlatten, vips_flatten, VIPS_TYPE_CONVERSION );
/* Shift A down N places, rounding to nearest.
*
* This calculates A / B, rounding the result to nearest, ie.
*
* (a + (b / 2)) / b
*
* We mustn't overflow during the add, so we actually do:
*
* ((a / 2) + (b / 4)) / (b / 2)
*
* slightly less accurate, but safe from overflow.
/* Flatten with black background.
*/
#define SHIFT_ROUND( A, N ) \
((((A) >> 1) + (1 << ((N) - 2)) - 1) >> ((N) - 1))
/* Flatten with shift + round, black background.
*/
#define VIPS_FLATTEN_INT_BLACK( TYPE, N ) { \
#define VIPS_FLATTEN_BLACK( TYPE, MAX ) { \
TYPE *p = (TYPE *) in; \
TYPE *q = (TYPE *) out; \
\
@ -96,67 +84,28 @@ G_DEFINE_TYPE( VipsFlatten, vips_flatten, VIPS_TYPE_CONVERSION );
int b; \
\
for( b = 0; b < bands - 1; b++ ) \
q[b] = SHIFT_ROUND( p[b] * alpha, N ); \
q[b] = (p[b] * alpha) / (MAX); \
\
p += bands; \
q += bands - 1; \
} \
}
/* Flatten with shift + round, any background.
/* Flatten with any background.
*/
#define VIPS_FLATTEN_INT( TYPE, N ) { \
#define VIPS_FLATTEN( TYPE, MAX ) { \
TYPE *p = (TYPE *) in; \
TYPE *q = (TYPE *) out; \
\
for( x = 0; x < width; x++ ) { \
TYPE alpha = p[bands - 1]; \
TYPE nalpha = ((1 << (N)) - 1) - alpha; \
TYPE nalpha = (MAX) - alpha; \
TYPE *bg = (TYPE *) flatten->ink; \
int b; \
\
for( b = 0; b < bands - 1; b++ ) \
q[b] = SHIFT_ROUND( p[b] * alpha, (N) ) + \
SHIFT_ROUND( bg[b] * nalpha, (N) ); \
\
p += bands; \
q += bands - 1; \
} \
}
/* Flatten via float division, black background.
*/
#define VIPS_FLATTEN_FLOAT_BLACK( TYPE, SCALE ) { \
TYPE *p = (TYPE *) in; \
TYPE *q = (TYPE *) out; \
\
for( x = 0; x < width; x++ ) { \
TYPE alpha = p[bands - 1]; \
int b; \
\
for( b = 0; b < bands - 1; b++ ) \
q[b] = ((double) p[b] * alpha) / (SCALE); \
\
p += bands; \
q += bands - 1; \
} \
}
/* Flatten via float division, any background.
*/
#define VIPS_FLATTEN_FLOAT( TYPE, SCALE ) { \
TYPE *p = (TYPE *) in; \
TYPE *q = (TYPE *) out; \
\
for( x = 0; x < width; x++ ) { \
TYPE alpha = p[bands - 1]; \
TYPE nalpha = (SCALE) - alpha; \
TYPE *bg = (TYPE *) flatten->ink; \
int b; \
\
for( b = 0; b < bands - 1; b++ ) \
q[b] = ((double) p[b] * alpha) / (SCALE) + \
((double) bg[b] * nalpha) / (SCALE); \
q[b] = (p[b] * alpha) / (MAX) + \
(bg[b] * nalpha) / (MAX); \
\
p += bands; \
q += bands - 1; \
@ -184,37 +133,37 @@ vips_flatten_black_gen( VipsRegion *or, void *vseq, void *a, void *b,
switch( flatten->in->BandFmt ) {
case VIPS_FORMAT_UCHAR:
VIPS_FLATTEN_INT_BLACK( unsigned char, 8 );
VIPS_FLATTEN_BLACK( unsigned char, UCHAR_MAX );
break;
case VIPS_FORMAT_CHAR:
/* Alpha is 0 - 127? No idea, really.
*/
VIPS_FLATTEN_INT_BLACK( signed char, 7 );
VIPS_FLATTEN_BLACK( signed char, CHAR_MAX );
break;
case VIPS_FORMAT_USHORT:
VIPS_FLATTEN_INT_BLACK( unsigned short, 16 );
VIPS_FLATTEN_BLACK( unsigned short, USHRT_MAX );
break;
case VIPS_FORMAT_SHORT:
VIPS_FLATTEN_INT_BLACK( signed short, 15 );
VIPS_FLATTEN_BLACK( signed short, SHRT_MAX );
break;
case VIPS_FORMAT_UINT:
VIPS_FLATTEN_FLOAT_BLACK( unsigned int, UINT_MAX );
VIPS_FLATTEN_BLACK( unsigned int, UINT_MAX );
break;
case VIPS_FORMAT_INT:
VIPS_FLATTEN_FLOAT_BLACK( signed int, INT_MAX );
VIPS_FLATTEN_BLACK( signed int, INT_MAX );
break;
case VIPS_FORMAT_FLOAT:
VIPS_FLATTEN_FLOAT_BLACK( float, 1.0 );
VIPS_FLATTEN_BLACK( float, 1.0 );
break;
case VIPS_FORMAT_DOUBLE:
VIPS_FLATTEN_FLOAT_BLACK( double, 1.0 );
VIPS_FLATTEN_BLACK( double, 1.0 );
break;
case VIPS_FORMAT_COMPLEX:
@ -250,37 +199,37 @@ vips_flatten_gen( VipsRegion *or, void *vseq, void *a, void *b,
switch( flatten->in->BandFmt ) {
case VIPS_FORMAT_UCHAR:
VIPS_FLATTEN_INT( unsigned char, 8 );
VIPS_FLATTEN( unsigned char, UCHAR_MAX );
break;
case VIPS_FORMAT_CHAR:
/* Alpha is 0 - 127? No idea, really.
*/
VIPS_FLATTEN_INT( signed char, 7 );
VIPS_FLATTEN( signed char, CHAR_MAX );
break;
case VIPS_FORMAT_USHORT:
VIPS_FLATTEN_INT( unsigned short, 16 );
VIPS_FLATTEN( unsigned short, USHRT_MAX );
break;
case VIPS_FORMAT_SHORT:
VIPS_FLATTEN_INT( signed short, 15 );
VIPS_FLATTEN( signed short, SHRT_MAX );
break;
case VIPS_FORMAT_UINT:
VIPS_FLATTEN_FLOAT( unsigned int, UINT_MAX );
VIPS_FLATTEN( unsigned int, UINT_MAX );
break;
case VIPS_FORMAT_INT:
VIPS_FLATTEN_FLOAT( signed int, INT_MAX );
VIPS_FLATTEN( signed int, INT_MAX );
break;
case VIPS_FORMAT_FLOAT:
VIPS_FLATTEN_FLOAT( float, 1.0 );
VIPS_FLATTEN( float, 1.0 );
break;
case VIPS_FORMAT_DOUBLE:
VIPS_FLATTEN_FLOAT( double, 1.0 );
VIPS_FLATTEN( double, 1.0 );
break;
case VIPS_FORMAT_COMPLEX: