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change vips_flatten() alpha rules

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now match vips_premultiply()

add tests

foreign knows about new logic
This commit is contained in:
John Cupitt 2015-05-09 12:10:42 +01:00
parent 9dda68f8cd
commit ec52d1b922
7 changed files with 109 additions and 60 deletions
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1
ChangeLog
View File

@ -1,5 +1,6 @@
7/5/15 started 8.1.0
- add vips_premultiply(), vips_unpremultiply()
- change the alpha range rules for vips_flatten() to match vips_premultiply()
4/5/15 started 8.0.2
- fix a refcount error in C++ wrapper, thanks huskier

6
TODO
View File

@ -1,9 +1,3 @@
- looks like flatten has some confusion with flatten->in and in
change rules for flatten alpha max ... copy the premultiply thing of being
255 + a param, look at convert savveable
- are the mosaic functions calling vips_fastcor()? it must be very slow

96
libvips/conversion/flatten.c
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@ -5,6 +5,8 @@
*
* 4/1/14
* - better rounding
* 9/5/15
* - add max_alpha to match vips_premultiply() etc.
*/
/*
@ -67,6 +69,10 @@ typedef struct _VipsFlatten {
*/
VipsPel *ink;
/* Use this to scale alpha to 0 - 1.
*/
double max_alpha;
} VipsFlatten;
typedef VipsConversionClass VipsFlattenClass;
@ -75,7 +81,7 @@ G_DEFINE_TYPE( VipsFlatten, vips_flatten, VIPS_TYPE_CONVERSION );
/* Flatten with black background.
*/
#define VIPS_FLATTEN_BLACK( TYPE, MAX ) { \
#define VIPS_FLATTEN_BLACK( TYPE ) { \
TYPE * restrict p = (TYPE *) in; \
TYPE * restrict q = (TYPE *) out; \
\
@ -84,7 +90,7 @@ G_DEFINE_TYPE( VipsFlatten, vips_flatten, VIPS_TYPE_CONVERSION );
int b; \
\
for( b = 0; b < bands - 1; b++ ) \
q[b] = (p[b] * alpha) / (MAX); \
q[b] = (p[b] * alpha) / max_alpha; \
\
p += bands; \
q += bands - 1; \
@ -93,19 +99,19 @@ G_DEFINE_TYPE( VipsFlatten, vips_flatten, VIPS_TYPE_CONVERSION );
/* Flatten with any background.
*/
#define VIPS_FLATTEN( TYPE, MAX ) { \
#define VIPS_FLATTEN( TYPE ) { \
TYPE * restrict p = (TYPE *) in; \
TYPE * restrict q = (TYPE *) out; \
\
for( x = 0; x < width; x++ ) { \
TYPE alpha = p[bands - 1]; \
TYPE nalpha = (MAX) - alpha; \
TYPE nalpha = max_alpha - alpha; \
TYPE * restrict bg = (TYPE *) flatten->ink; \
int b; \
\
for( b = 0; b < bands - 1; b++ ) \
q[b] = (p[b] * alpha) / (MAX) + \
(bg[b] * nalpha) / (MAX); \
q[b] = (p[b] * alpha) / max_alpha + \
(bg[b] * nalpha) / max_alpha; \
\
p += bands; \
q += bands - 1; \
@ -115,7 +121,7 @@ G_DEFINE_TYPE( VipsFlatten, vips_flatten, VIPS_TYPE_CONVERSION );
/* Same, but with float arithmetic. Necessary for int/uint to prevent
* overflow.
*/
#define VIPS_FLATTEN_BLACK_FLOAT( TYPE, MAX ) { \
#define VIPS_FLATTEN_BLACK_FLOAT( TYPE ) { \
TYPE * restrict p = (TYPE *) in; \
TYPE * restrict q = (TYPE *) out; \
\
@ -124,26 +130,26 @@ G_DEFINE_TYPE( VipsFlatten, vips_flatten, VIPS_TYPE_CONVERSION );
int b; \
\
for( b = 0; b < bands - 1; b++ ) \
q[b] = ((double) p[b] * alpha) / (MAX); \
q[b] = ((double) p[b] * alpha) / max_alpha; \
\
p += bands; \
q += bands - 1; \
} \
}
#define VIPS_FLATTEN_FLOAT( TYPE, MAX ) { \
#define VIPS_FLATTEN_FLOAT( TYPE ) { \
TYPE * restrict p = (TYPE *) in; \
TYPE * restrict q = (TYPE *) out; \
\
for( x = 0; x < width; x++ ) { \
TYPE alpha = p[bands - 1]; \
TYPE nalpha = (MAX) - alpha; \
TYPE nalpha = max_alpha - alpha; \
TYPE * restrict bg = (TYPE *) flatten->ink; \
int b; \
\
for( b = 0; b < bands - 1; b++ ) \
q[b] = ((double) p[b] * alpha) / (MAX) + \
((double) bg[b] * nalpha) / (MAX); \
q[b] = ((double) p[b] * alpha) / max_alpha + \
((double) bg[b] * nalpha) / max_alpha; \
\
p += bands; \
q += bands - 1; \
@ -159,6 +165,7 @@ vips_flatten_black_gen( VipsRegion *or, void *vseq, void *a, void *b,
VipsRect *r = &or->valid;
int width = r->width;
int bands = ir->im->Bands;
double max_alpha = flatten->max_alpha;
int x, y;
@ -171,37 +178,35 @@ vips_flatten_black_gen( VipsRegion *or, void *vseq, void *a, void *b,
switch( flatten->in->BandFmt ) {
case VIPS_FORMAT_UCHAR:
VIPS_FLATTEN_BLACK( unsigned char, UCHAR_MAX );
VIPS_FLATTEN_BLACK( unsigned char );
break;
case VIPS_FORMAT_CHAR:
/* Alpha is 0 - 127? No idea, really.
*/
VIPS_FLATTEN_BLACK( signed char, CHAR_MAX );
VIPS_FLATTEN_BLACK( signed char );
break;
case VIPS_FORMAT_USHORT:
VIPS_FLATTEN_BLACK( unsigned short, USHRT_MAX );
VIPS_FLATTEN_BLACK( unsigned short );
break;
case VIPS_FORMAT_SHORT:
VIPS_FLATTEN_BLACK( signed short, SHRT_MAX );
VIPS_FLATTEN_BLACK( signed short );
break;
case VIPS_FORMAT_UINT:
VIPS_FLATTEN_BLACK_FLOAT( unsigned int, UINT_MAX );
VIPS_FLATTEN_BLACK_FLOAT( unsigned int );
break;
case VIPS_FORMAT_INT:
VIPS_FLATTEN_BLACK_FLOAT( signed int, INT_MAX );
VIPS_FLATTEN_BLACK_FLOAT( signed int );
break;
case VIPS_FORMAT_FLOAT:
VIPS_FLATTEN_BLACK_FLOAT( float, 1.0 );
VIPS_FLATTEN_BLACK_FLOAT( float );
break;
case VIPS_FORMAT_DOUBLE:
VIPS_FLATTEN_BLACK_FLOAT( double, 1.0 );
VIPS_FLATTEN_BLACK_FLOAT( double );
break;
case VIPS_FORMAT_COMPLEX:
@ -225,6 +230,7 @@ vips_flatten_gen( VipsRegion *or, void *vseq, void *a, void *b,
VipsRect *r = &or->valid;
int width = r->width;
int bands = ir->im->Bands;
double max_alpha = flatten->max_alpha;
int x, y;
@ -237,37 +243,35 @@ vips_flatten_gen( VipsRegion *or, void *vseq, void *a, void *b,
switch( flatten->in->BandFmt ) {
case VIPS_FORMAT_UCHAR:
VIPS_FLATTEN( unsigned char, UCHAR_MAX );
VIPS_FLATTEN( unsigned char );
break;
case VIPS_FORMAT_CHAR:
/* Alpha is 0 - 127? No idea, really.
*/
VIPS_FLATTEN( signed char, CHAR_MAX );
VIPS_FLATTEN( signed char );
break;
case VIPS_FORMAT_USHORT:
VIPS_FLATTEN( unsigned short, USHRT_MAX );
VIPS_FLATTEN( unsigned short );
break;
case VIPS_FORMAT_SHORT:
VIPS_FLATTEN( signed short, SHRT_MAX );
VIPS_FLATTEN( signed short );
break;
case VIPS_FORMAT_UINT:
VIPS_FLATTEN_FLOAT( unsigned int, UINT_MAX );
VIPS_FLATTEN_FLOAT( unsigned int );
break;
case VIPS_FORMAT_INT:
VIPS_FLATTEN_FLOAT( signed int, INT_MAX );
VIPS_FLATTEN_FLOAT( signed int );
break;
case VIPS_FORMAT_FLOAT:
VIPS_FLATTEN_FLOAT( float, 1.0 );
VIPS_FLATTEN_FLOAT( float );
break;
case VIPS_FORMAT_DOUBLE:
VIPS_FLATTEN_FLOAT( double, 1.0 );
VIPS_FLATTEN_FLOAT( double );
break;
case VIPS_FORMAT_COMPLEX:
@ -304,7 +308,7 @@ vips_flatten_build( VipsObject *object )
/* Trivial case: fall back to copy().
*/
if( flatten->in->Bands == 1 )
if( in->Bands == 1 )
return( vips_image_write( in, conversion->out ) );
if( vips_check_noncomplex( class->nickname, in ) )
@ -380,12 +384,21 @@ vips_flatten_class_init( VipsFlattenClass *class )
VIPS_ARGUMENT_OPTIONAL_INPUT,
G_STRUCT_OFFSET( VipsFlatten, background ),
VIPS_TYPE_ARRAY_DOUBLE );
VIPS_ARG_DOUBLE( class, "max_alpha", 115,
_( "Maximum alpha" ),
_( "Maximum value of alpha channel" ),
VIPS_ARGUMENT_OPTIONAL_INPUT,
G_STRUCT_OFFSET( VipsFlatten, max_alpha ),
0, 100000000, 255 );
}
static void
vips_flatten_init( VipsFlatten *flatten )
{
flatten->background = vips_array_double_newv( 1, 0.0 );
flatten->max_alpha= 255.0;
}
/**
@ -397,19 +410,24 @@ vips_flatten_init( VipsFlatten *flatten )
* Optional arguments:
*
* @background: #VipsArrayDouble colour for new pixels
* @max_alpha: %gdouble, maximum value for alpha
*
* Take the last band of @in as an alpha and use it to blend the
* remaining channels with @background.
*
* The alpha channel is 0 - MAX for
* integer images and 0 - 1 for float images, where MAX means 100% image and 0
* means 100% background. Non-complex images only.
* @background defaults to zero (black). MAX is the largest possible positive
* value for that int type.
* The alpha channel is 0 - @max_alpha,
* where 1 means 100% image and 0
* means 100% background.
* Non-complex images only.
* @background defaults to zero (black).
*
* @max_alpha has the default value 255. You will need to set this to 65535
* for images with a 16-bit alpha, or perhaps 1.0 for images with a float
* alpha.
*
* Useful for flattening PNG images to RGB.
*
* See also: pngload().
* See also: vips_premultiply(), vips_pngload().
*
* Returns: 0 on success, -1 on error
*/

2
libvips/conversion/premultiply.c
View File

@ -296,6 +296,8 @@ vips_premultiply_init( VipsPremultiply *premultiply )
* for images with a 16-bit alpha, or perhaps 1.0 for images with a float
* alpha.
*
* Non-complex images only.
*
* See also: vips_unpremultiply(), vips_flatten().
*
* Returns: 0 on success, -1 on error

2
libvips/conversion/unpremultiply.c
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@ -311,6 +311,8 @@ vips_unpremultiply_init( VipsUnpremultiply *unpremultiply )
* for images with a 16-bit alpha, or perhaps 1.0 for images with a float
* alpha.
*
* Non-complex images only.
*
* See also: vips_premultiply(), vips_flatten().
*
* Returns: 0 on success, -1 on error

3
libvips/foreign/foreign.c
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@ -1202,6 +1202,9 @@ vips_foreign_convert_saveable( VipsForeignSave *save )
if( vips_flatten( in, &out,
"background", save->background,
"max_alpha",
in->BandFmt == VIPS_FORMAT_USHORT ?
65535 : 255,
NULL ) ) {
g_object_unref( in );
return( -1 );

59
test/test_conversion.py
View File

@ -348,23 +348,12 @@ class TestConversion(unittest.TestCase):
self.assertAlmostEqualObjects(pixel, [20, 0, 41])
def test_flatten(self):
max_value = {Vips.BandFormat.UCHAR: 0xff,
Vips.BandFormat.USHORT: 0xffff,
Vips.BandFormat.UINT: 0xffffffff,
Vips.BandFormat.CHAR: 0x7f,
Vips.BandFormat.SHORT: 0x7fff,
Vips.BandFormat.INT: 0x7fffffff,
Vips.BandFormat.FLOAT: 1.0,
Vips.BandFormat.DOUBLE: 1.0,
Vips.BandFormat.COMPLEX: 1.0,
Vips.BandFormat.DPCOMPLEX: 1.0}
black = self.mono * 0.0
for fmt in noncomplex_formats:
mx = max_value[fmt]
for fmt in unsigned_formats + [Vips.BandFormat.SHORT,
Vips.BandFormat.INT] + float_formats:
mx = 255
alpha = mx / 2.0
nalpha = mx - alpha
test = self.colour.bandjoin(black + alpha).cast(fmt)
test = self.colour.bandjoin(alpha).cast(fmt)
pixel = test(30, 30)
predict = [int(x) * alpha / mx for x in pixel[:-1]]
@ -389,6 +378,46 @@ class TestConversion(unittest.TestCase):
for x, y in zip(pixel, predict):
self.assertLess(abs(x - y), 2)
def test_premultiply(self):
for fmt in unsigned_formats + [Vips.BandFormat.SHORT,
Vips.BandFormat.INT] + float_formats:
mx = 255
alpha = mx / 2.0
nalpha = mx - alpha
test = self.colour.bandjoin(alpha).cast(fmt)
pixel = test(30, 30)
predict = [int(x) * alpha / mx for x in pixel[:-1]] + [alpha]
im = test.premultiply()
self.assertEqual(im.bands, test.bands)
pixel = im(30, 30)
for x, y in zip(pixel, predict):
# we use float arithetic for int and uint, so the rounding
# differs ... don't require huge accuracy
self.assertLess(abs(x - y), 2)
def test_unpremultiply(self):
for fmt in unsigned_formats + [Vips.BandFormat.SHORT,
Vips.BandFormat.INT] + float_formats:
mx = 255
alpha = mx / 2.0
nalpha = mx - alpha
test = self.colour.bandjoin(alpha).cast(fmt)
pixel = test(30, 30)
predict = [int(x) / (alpha / mx) for x in pixel[:-1]] + [alpha]
im = test.unpremultiply()
self.assertEqual(im.bands, test.bands)
pixel = im(30, 30)
for x, y in zip(pixel, predict):
# we use float arithetic for int and uint, so the rounding
# differs ... don't require huge accuracy
self.assertLess(abs(x - y), 2)
def test_flip(self):
for fmt in all_formats:
test = self.colour.cast(fmt)