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gifsave: expose bitdepth property (#2429) 

Provides control over the maximum number of colours in the output
image palette, making the API more closely match that of pngsave.

Lowering the bitdepth to 7 (from the default value of 8), which
halves the maximum number of colours from 255 to 127, typically
reduces encoding time by ~20%.
This commit is contained in:
Lovell Fuller 2021-09-10 08:57:12 +01:00 committed by GitHub
parent cfd9dc3f01
commit f7619cf33e
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2 changed files with 24 additions and 1 deletions
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20
libvips/foreign/cgifsave.c
View File

@ -52,6 +52,7 @@ typedef struct _VipsForeignSaveCgif {
double dither;
int effort;
int bitdepth;
VipsTarget *target;
} VipsForeignSaveCgif;
@ -120,7 +121,8 @@ vips_foreign_save_cgif_build( VipsObject *object )
/* Generate indexed image (t[0]) and palette (t[1])
*/
if( vips__quantise_image( save->ready, &t[0], &t[1],
255, 100, cgif->dither, cgif->effort, TRUE ) )
(1 << cgif->bitdepth) - 1, 100, cgif->dither,
cgif->effort, TRUE ) )
return( -1 );
/* Convert palette to RGB
@ -224,6 +226,13 @@ vips_foreign_save_cgif_class_init( VipsForeignSaveCgifClass *class )
G_STRUCT_OFFSET( VipsForeignSaveCgif, effort ),
1, 10, 7 );
VIPS_ARG_INT( class, "bitdepth", 12,
_( "Bit depth" ),
_( "Number of bits per pixel" ),
VIPS_ARGUMENT_OPTIONAL_INPUT,
G_STRUCT_OFFSET( VipsForeignSaveCgif, bitdepth ),
1, 8, 8 );
}
static void
@ -231,6 +240,7 @@ vips_foreign_save_cgif_init( VipsForeignSaveCgif *gif )
{
gif->dither = 1.0;
gif->effort = 7;
gif->bitdepth = 8;
}
typedef struct _VipsForeignSaveCgifTarget {
@ -410,6 +420,7 @@ vips_foreign_save_cgif_buffer_init( VipsForeignSaveCgifBuffer *buffer )
*
* * @dither: %double, quantisation dithering level
* * @effort: %int, quantisation CPU effort
* * @bitdepth: %int, number of bits per pixel
*
* Write a VIPS image to a file as GIF.
*
@ -417,6 +428,11 @@ vips_foreign_save_cgif_buffer_init( VipsForeignSaveCgifBuffer *buffer )
* and @effort to control the CPU effort (1 is the fastest,
* 10 is the slowest, 7 is the default).
*
* Use @bitdepth (from 1 to 8, default 8) to control the number
* of colours in the palette. The first entry in the palette is
* always reserved for transparency. For example, a bitdepth of
* 4 will allow the output to contain up to 15 colours.
*
* See also: vips_image_new_from_file().
*
* Returns: 0 on success, -1 on error.
@ -445,6 +461,7 @@ vips_gifsave( VipsImage *in, const char *filename, ... )
*
* * @dither: %double, quantisation dithering level
* * @effort: %int, quantisation CPU effort
* * @bitdepth: %int, number of bits per pixel
*
* As vips_gifsave(), but save to a memory buffer.
*
@ -494,6 +511,7 @@ vips_gifsave_buffer( VipsImage *in, void **buf, size_t *len, ... )
*
* * @dither: %double, quantisation dithering level
* * @effort: %int, quantisation CPU effort
* * @bitdepth: %int, number of bits per pixel
*
* As vips_gifsave(), but save to a target.
*

5
test/test-suite/test_foreign.py
View File

@ -1229,6 +1229,11 @@ class TestForeign:
large_effort = self.colour.gifsave_buffer(effort=10)
assert len(little_effort) > len(large_effort)
# Reducing bitdepth will typically reduce file size (and reduce quality)
bitdepth8 = self.colour.gifsave_buffer(bitdepth=8,effort=1)
bitdepth7 = self.colour.gifsave_buffer(bitdepth=7,effort=1)
assert len(bitdepth8) > len(bitdepth7)
if have("webpload"):
# Animated WebP to GIF
x1 = pyvips.Image.new_from_file(WEBP_ANIMATED_FILE, n=-1)