sergiotarxz/libvips
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

better rounding behaviour for sRGB <-> XYZ

Browse Source
This commit is contained in:
John Cupitt 2012-11-06 21:32:13 +00:00
parent 26d1f76469
commit 6a1753577d
1 changed files with 7 additions and 24 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
libvips/colour/LabQ2sRGB.c
View File

@ -2,6 +2,10 @@
* inaccurate: for display only! Note especially that this dithers and will * inaccurate: for display only! Note especially that this dithers and will
* give different results on different runs. * give different results on different runs.
* *
* The XYZ <-> sRGB transform implemented is this one:
*
* http://en.wikipedia.org/wiki/SRGB
*
* 5/11/97 Steve Perry * 5/11/97 Steve Perry
* - adapted from old ip code * - adapted from old ip code
* 7/11/97 JC * 7/11/97 JC
@ -130,7 +134,7 @@ calcul_tables( int range, int *Y2v, float *v2Y )
else else
v = (1.0 + 0.055) * pow( f, 1.0 / 2.4 ) - 0.055; v = (1.0 + 0.055) * pow( f, 1.0 / 2.4 ) - 0.055;
Y2v[i] = (range - 1) * v; Y2v[i] = VIPS_RINT( (range - 1) * v );
} }
/* Copy the final element. This is used in the piecewise linear /* Copy the final element. This is used in the piecewise linear
@ -172,8 +176,7 @@ vips_col_make_tables_RGB_8( void )
} }
} }
/* Computes the transform: r,g,b => Yr,Yg,Yb. It finds Y values in /* RGB to XYZ.
* lookup tables and calculates X, Y, Z.
* *
* @range is eg. 256 for 8-bit data, * @range is eg. 256 for 8-bit data,
*/ */
@ -204,11 +207,6 @@ vips_col_sRGB2XYZ( int range, float *lut,
return( 0 ); return( 0 );
} }
/* Computes the transform: r,g,b => Yr,Yg,Yb. It finds Y values in
* lookup tables and calculates X, Y, Z.
*
* rgb are in the range 0 to 255,
*/
int int
vips_col_sRGB2XYZ_8( int r, int g, int b, float *X, float *Y, float *Z ) vips_col_sRGB2XYZ_8( int r, int g, int b, float *X, float *Y, float *Z )
{ {
@ -241,11 +239,6 @@ vips_col_make_tables_RGB_16( void )
} }
} }
/* Computes the transform: r,g,b => Yr,Yg,Yb. It finds Y values in
* lookup tables and calculates X, Y, Z.
*
* rgb are in the range 0 to 65535,
*/
int int
vips_col_sRGB2XYZ_16( int r, int g, int b, float *X, float *Y, float *Z ) vips_col_sRGB2XYZ_16( int r, int g, int b, float *X, float *Y, float *Z )
{ {
@ -325,11 +318,6 @@ vips_col_XYZ2sRGB( int range, int *lut,
return( 0 ); return( 0 );
} }
/* Turn XYZ into display colour. Return or=1 for out of gamut - rgb will
* contain an approximation of the right colour.
*
* r, g, b are scaled to fit the range 0 - 255.
*/
int int
vips_col_XYZ2sRGB_8( float X, float Y, float Z, vips_col_XYZ2sRGB_8( float X, float Y, float Z,
int *r, int *g, int *b, int *r, int *g, int *b,
@ -340,11 +328,6 @@ vips_col_XYZ2sRGB_8( float X, float Y, float Z,
return( vips_col_XYZ2sRGB( 256, vips_Y2v_8, X, Y, Z, r, g, b, or ) ); return( vips_col_XYZ2sRGB( 256, vips_Y2v_8, X, Y, Z, r, g, b, or ) );
} }
/* Turn XYZ into display colour. Return or=1 for out of gamut - rgb will
* contain an approximation of the right colour.
*
* r, g, b are scaled to fit the range 0 - 65535.
*/
int int
vips_col_XYZ2sRGB_16( float X, float Y, float Z, vips_col_XYZ2sRGB_16( float X, float Y, float Z,
int *r, int *g, int *b, int *r, int *g, int *b,
@ -356,7 +339,7 @@ vips_col_XYZ2sRGB_16( float X, float Y, float Z,
X, Y, Z, r, g, b, or ) ); X, Y, Z, r, g, b, or ) );
} }
/* Build Lab->disp tables. /* Build Lab->disp dither tables.
*/ */
static void * static void *
build_tables( void *client ) build_tables( void *client )