[Git][freetype/freetype-demos][master] * graph/gblender.c (gblender_set_gamma_table): Updated sRGB ramps.

[Alexei Podtelezhnikov (@apodtele)]

Alexei Podtelezhnikov pushed to branch master at FreeType / FreeType Demo Programs

Commits:

• af5c17e8
  by Alexei Podtelezhnikov at 2022-08-17T00:09:17-04:00

  * graph/gblender.c (gblender_set_gamma_table): Updated sRGB ramps.
  
  When we use finite approxination it is more appropriate to use the
  actual values for the linear portion instead of the standard ones.
  

1 changed file:

• graph/gblender.c

Changes:

graph/gblender.c

---

...	...	@@ -66,34 +66,53 @@ gblender_set_gamma_table( double gamma_value,
66	66	{
67	67	const int gmax = (256 << GBLENDER_GAMMA_SHIFT) - 1;
68	68	double p;
	69	+ int ii;
	70	+
69	71
70	72	if ( gamma_value <= 0 ) /* special case for sRGB */
71	73	{
72		- int ii;
	74	+ double d;
	75	+ int linear = 0;
	76	+
73	77
74	78	/* voltage to linear; power function using finite differences */
75		- for ( p = gmax, ii = 255; ii > (int)(255.*0.039285714); ii-- )
	79	+ for ( p = gmax, ii = 255; ii >= 0; ii--, p -= d )
76	80	{
77	81	gamma_ramp[ii] = (unsigned short)( p + 0.5 );
78		- p -= 2.4 * p / ( ii + 255. * 0.055 );
	82	+
	83	+ if ( linear )
	84	+ continue;
	85	+
	86	+ d = 2.4 * p / ( ii + 255. * 0.055 ); /* derivative */
	87	+
	88	+ if ( ii == 10 ) /* same as d < p / ii */
	89	+ {
	90	+ d = p / ii;
	91	+ linear = 1;
	92	+ }
79	93	}
80		- for ( ; ii >= 0; ii-- )
81		- gamma_ramp[ii] = (unsigned short)( gmax*ii/(255.*12.92321) + 0.5 );
82	94
	95	+ linear = 0;
83	96
84	97	/* linear to voltage; power function using finite differences */
85		- for ( p = 255., ii = gmax; ii > (int)(gmax*0.0030399346); ii-- )
	98	+ for ( p = 255., ii = gmax; ii >= 0; ii--, p -= d )
86	99	{
87	100	gamma_ramp_inv[ii] = (unsigned char)( p + 0.5 );
88		- p -= ( p + 255. * 0.055 ) / ( 2.4 * ii );
	101	+
	102	+ if ( linear )
	103	+ continue;
	104	+
	105	+ d = ( p + 255. * 0.055 ) / ( 2.4 * ii ); /* derivative */
	106	+
	107	+ if ( p < 10.02 ) /* same as d > p / ii */
	108	+ {
	109	+ d = p / ii;
	110	+ linear = 1;
	111	+ }
89	112	}
90		- for ( ; ii >= 0; ii-- )
91		- gamma_ramp_inv[ii] = (unsigned char)( 255.*12.92321*ii/gmax + 0.5 );
92	113	}
93	114	else
94	115	{
95		- int ii;
96		-
97	116	/* voltage to linear; power function using finite differences */
98	117	for ( p = gmax, ii = 255; ii > 0; ii-- )
99	118	{

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