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Play with --gamma=oklab.
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This code is used only in dithering (it is not used in color space
choice, i.e., `--method=diversity` or `--method=median-cut`).
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@kohler
kohler committed Feb 19, 2024
1 parent 233036b commit 99f4845
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Showing 7 changed files with 146 additions and 35 deletions.
3 changes: 2 additions & 1 deletion configure.ac
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
dnl Process this file with autoconf to produce a configure script.
AC_INIT([gifsicle],[1.95])
AC_INIT([gifsicle],[1.96])
AC_PREREQ([2.69])
AC_CONFIG_SRCDIR([src/gifsicle.h])
AC_CONFIG_HEADERS([config.h])
Expand Down Expand Up @@ -129,6 +129,7 @@ AC_DEFINE_UNQUOTED(RANDOM, ${random_func}, [Define to a function that returns a
AC_REPLACE_FUNCS([strerror])
AC_CHECK_FUNCS([strtoul mkstemp snprintf])
AC_SEARCH_LIBS([pow], [m], [AC_DEFINE([HAVE_POW], [1], [Define to 1 if you have the `pow' function.])])
AC_SEARCH_LIBS([cbrtf], [m], [AC_DEFINE([HAVE_CBRTF], [1], [Define to 1 if you have the `cbrtf' function.])])


dnl
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42 changes: 31 additions & 11 deletions src/gifsicle.c
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Expand Up @@ -1969,26 +1969,46 @@ main(int argc, char *argv[])
}

case GAMMA_OPT: {
#if HAVE_POW
char* ends;
MARK_CH(output, CH_GAMMA);
if (clp->negated) {
MARK_CH(output, CH_GAMMA);
def_output_data.colormap_gamma_type = KC_GAMMA_NUMERIC;
def_output_data.colormap_gamma = 1;
} else if (strcmp(clp->val.s, "sRGB") == 0
|| strcmp(clp->val.s, "srgb") == 0)
def_output_data.colormap_gamma = 1.0;
break;
}
if (strlen(clp->val.s) == 4
&& tolower((unsigned char) clp->val.s[0]) == 's'
&& tolower((unsigned char) clp->val.s[1]) == 'r'
&& tolower((unsigned char) clp->val.s[2]) == 'g'
&& tolower((unsigned char) clp->val.s[3]) == 'b') {
MARK_CH(output, CH_GAMMA);
def_output_data.colormap_gamma_type = KC_GAMMA_SRGB;
else {
break;
}
#if HAVE_CBRTF
if (strlen(clp->val.s) == 5
&& tolower((unsigned char) clp->val.s[0]) == 'o'
&& tolower((unsigned char) clp->val.s[1]) == 'k'
&& tolower((unsigned char) clp->val.s[2]) == 'l'
&& tolower((unsigned char) clp->val.s[3]) == 'a'
&& tolower((unsigned char) clp->val.s[4]) == 'b') {
MARK_CH(output, CH_GAMMA);
def_output_data.colormap_gamma_type = KC_GAMMA_OKLAB;
break;
}
#endif
#if HAVE_POW
{
char* ends;
double gamma = strtod(clp->val.s, &ends);
if (*clp->val.s && !*ends && !isspace((unsigned char) *clp->val.s)) {
MARK_CH(output, CH_GAMMA);
def_output_data.colormap_gamma_type = KC_GAMMA_NUMERIC;
def_output_data.colormap_gamma = gamma;
} else
Clp_OptionError(clp, "%O should be a number or %<srgb%>");
break;
}
}
#else
Clp_OptionError(clp, "this version of Gifsicle does not support %O");
#endif
Clp_OptionError(clp, "%O not supported");
break;
}

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1 change: 1 addition & 0 deletions src/gifsicle.h
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Original file line number Diff line number Diff line change
Expand Up @@ -266,6 +266,7 @@ void resize_stream(Gif_Stream* gfs, double new_width, double new_height,
**/
#define KC_GAMMA_SRGB 0
#define KC_GAMMA_NUMERIC 1
#define KC_GAMMA_OKLAB 2
void kc_set_gamma(int type, double gamma);

#define COLORMAP_DIVERSITY 0
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117 changes: 97 additions & 20 deletions src/kcolor.c
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Expand Up @@ -89,9 +89,44 @@ static const uint16_t srgb_revgamma_table_256[256] = {
32313, 32370, 32427, 32484, 32541, 32598, 32654, 32711
};

uint16_t* gamma_tables[2] = {
(uint16_t*) srgb_gamma_table_256,
(uint16_t*) srgb_revgamma_table_256
static const float linear_srgb_table_256[256] = {
0.00000, 0.04984009, 0.08494473, 0.11070206, 0.13180381, 0.1500052, 0.1661857, 0.18085852,
0.19435316, 0.20689574, 0.21864912, 0.22973509, 0.2402475, 0.25026038, 0.25983337, 0.26901522,
0.27784654, 0.28636143, 0.29458886, 0.3025538, 0.31027776, 0.31777957, 0.32507575, 0.33218095,
0.33910814, 0.34586892, 0.35247374, 0.35893196, 0.3652521, 0.3714419, 0.37750843, 0.38345808,
0.38929683, 0.39503005, 0.40066284, 0.40619975, 0.41164514, 0.417003, 0.42227703, 0.42747074,
0.4325873, 0.4376298, 0.44260103, 0.4475037, 0.45234028, 0.45711315, 0.46182457, 0.4664766,
0.47107124, 0.4756104, 0.4800958, 0.4845292, 0.48891217, 0.49324623, 0.49753287, 0.5017734,
0.5059693, 0.5101216, 0.5142317, 0.5183006, 0.5223295, 0.5263194, 0.53027135, 0.53418624,
0.53806514, 0.54190874, 0.5457181, 0.54949385, 0.5532369, 0.556948, 0.5606278, 0.5642771,
0.56789654, 0.5714868, 0.57504845, 0.5785821, 0.5820884, 0.58556795, 0.58902115, 0.59244865,
0.59585094, 0.5992285, 0.60258186, 0.60591143, 0.60921764, 0.612501, 0.61576194, 0.6190008,
0.622218, 0.62541395, 0.62858903, 0.6317436, 0.63487804, 0.6379926, 0.6410878, 0.6441637,
0.64722085, 0.6502595, 0.6532799, 0.65628237, 0.65926725, 0.6622347, 0.6651851, 0.66811866,
0.67103565, 0.6739363, 0.67682093, 0.6796897, 0.6825429, 0.6853807, 0.6882034, 0.69101113,
0.69380414, 0.6965826, 0.69934684, 0.70209694, 0.7048331, 0.7075556, 0.7102645, 0.71296,
0.7156424, 0.7183118, 0.7209683, 0.7236121, 0.7262435, 0.7288625, 0.73146933, 0.73406404,
0.73664695, 0.73921806, 0.7417776, 0.74432564, 0.7468624, 0.749388, 0.75190246, 0.7544061,
0.7568989, 0.759381, 0.76185256, 0.7643137, 0.7667645, 0.7692052, 0.7716358, 0.7740564,
0.77646714, 0.77886814, 0.78125954, 0.78364134, 0.7860138, 0.7883768, 0.79073066, 0.7930754,
0.795411, 0.7977377, 0.80005556, 0.8023647, 0.8046651, 0.80695695, 0.8092403, 0.8115152,
0.8137818, 0.81604016, 0.8182903, 0.8205324, 0.8227665, 0.8249926, 0.8272109, 0.8294214,
0.8316242, 0.8338194, 0.836007, 0.8381871, 0.84035975, 0.84252506, 0.8446831, 0.84683394,
0.84897757, 0.85111415, 0.8532437, 0.85536623, 0.8574819, 0.8595907, 0.8616927, 0.86378807,
0.8658767, 0.8679587, 0.87003416, 0.87210315, 0.87416565, 0.8762218, 0.8782716, 0.8803151,
0.8823524, 0.8843835, 0.8864085, 0.8884274, 0.8904402, 0.8924471, 0.89444804, 0.8964431,
0.8984324, 0.9004158, 0.90239346, 0.9043654, 0.9063318, 0.9082925, 0.91024756, 0.9121972,
0.9141413, 0.91608, 0.9180133, 0.9199412, 0.92186373, 0.92378104, 0.9256931, 0.92759997,
0.92950165, 0.9313982, 0.93328965, 0.9351761, 0.9370575, 0.9389339, 0.9408054, 0.9426719,
0.9445336, 0.94639045, 0.9482424, 0.9500897, 0.9519322, 0.95377004, 0.9556032, 0.9574316,
0.9592555, 0.9610748, 0.96288955, 0.9646998, 0.9665055, 0.9683068, 0.9701037, 0.9718961,
0.9736842, 0.9754679, 0.97724736, 0.9790225, 0.9807934, 0.9825601, 0.98432255, 0.9860808,
0.987835, 0.989585, 0.9913309, 0.99307275, 0.9948106, 0.99654436, 0.99827415, 1.00000
};

const uint16_t* gamma_tables[2] = {
srgb_gamma_table_256,
srgb_revgamma_table_256
};

#if ENABLE_THREADS
Expand All @@ -114,44 +149,53 @@ const char* kc_debug_str(kcolor x) {
}

void kc_set_gamma(int type, double gamma) {
#if HAVE_POW
static int cur_type = KC_GAMMA_SRGB;
static double cur_gamma = 2.2;
int i, j;
if (type == cur_type && (type != KC_GAMMA_NUMERIC || gamma == cur_gamma))
uint16_t* g[2];
#if !HAVE_POW
if (type == KC_GAMMA_NUMERIC && gamma != 1.0) {
type = KC_GAMMA_SRGB;
}
#endif
if (type == cur_type && (type != KC_GAMMA_NUMERIC || gamma == cur_gamma)) {
return;
if (type == KC_GAMMA_SRGB) {
}
if (type != KC_GAMMA_NUMERIC) {
if (gamma_tables[0] != srgb_gamma_table_256) {
Gif_DeleteArray(gamma_tables[0]);
Gif_DeleteArray(gamma_tables[1]);
}
gamma_tables[0] = (uint16_t*) srgb_gamma_table_256;
gamma_tables[1] = (uint16_t*) srgb_revgamma_table_256;
gamma_tables[0] = srgb_gamma_table_256;
gamma_tables[1] = srgb_revgamma_table_256;
} else {
if (gamma_tables[0] == srgb_gamma_table_256) {
gamma_tables[0] = Gif_NewArray(uint16_t, 256);
gamma_tables[1] = Gif_NewArray(uint16_t, 256);
gamma_tables[0] = Gif_NewArray(uint16_t, 512);
gamma_tables[1] = gamma_tables[0] + 256;
}
g[0] = (uint16_t*) gamma_tables[0];
g[1] = (uint16_t*) gamma_tables[1];
for (j = 0; j != 256; ++j) {
gamma_tables[0][j] = (int) (pow(j/255.0, gamma) * 32767 + 0.5);
gamma_tables[1][j] = (int) (pow(j/256.0, 1/gamma) * 32767 + 0.5);
#if HAVE_POW
g[0][j] = (int) (pow(j / 255.0, gamma) * 32767 + 0.5);
g[1][j] = (int) (pow(j / 256.0, 1/gamma) * 32767 + 0.5);
#else
g[0][j] = (int) (j / 255.0 * 32767 + 0.5);
g[1][j] = (int) (j / 256.0 * 32767 + 0.5);
#endif
/* The ++gamma_tables[][] ensures that round-trip gamma correction
always preserve the input colors. Without it, one might have,
for example, input values 0, 1, and 2 all mapping to
gamma-corrected value 0. Then a round-trip through gamma
correction loses information.
*/
for (i = 0; i != 2; ++i)
while (j && gamma_tables[i][j] <= gamma_tables[i][j-1]
&& gamma_tables[i][j] < 32767)
++gamma_tables[i][j];
for (i = j ? 0 : 2; i != 2; ++i) {
while (g[i][j] <= g[i][j-1] && g[i][j] < 32767)
++g[i][j];
}
}
}
cur_type = type;
cur_gamma = gamma;
#else
(void) type, (void) gamma;
#endif
}

kcolor kc_revgamma_transform(kcolor x) {
Expand Down Expand Up @@ -185,6 +229,39 @@ static void kc_test_gamma() {
}
#endif

kcolor kc_oklab_transform(int a0, int a1, int a2) {
#if HAVE_CBRTF
float cr = linear_srgb_table_256[a0];
float cg = linear_srgb_table_256[a1];
float cb = linear_srgb_table_256[a2];

float l = 0.4122214708f * cr + 0.5363325363f * cg + 0.0514459929f * cb;
float m = 0.2119034982f * cr + 0.6806995451f * cg + 0.1073969566f * cb;
float s = 0.0883024619f * cr + 0.2817188376f * cg + 0.6299787005f * cb;

float l_ = cbrtf(l);
float m_ = cbrtf(m);
float s_ = cbrtf(s);

float okl = 0.2104542553f*l_ + 0.7936177850f*m_ - 0.0040720468f*s_;
float oka = 1.9779984951f*l_ - 2.4285922050f*m_ + 0.4505937099f*s_;
float okb = 0.0259040371f*l_ + 0.7827717662f*m_ - 0.8086757660f*s_;

// On sRGB colors, `okl` ranges from 0 to 1,
// `oka` ranges from -0.23388740 to +0.27621666,
// `okb` ranges from -0.31152815 to +0.19856972.

kcolor kc;
kc.a[0] = okl * 32767;
kc.a[1] = (oka + 0.5) * 32767;
kc.a[2] = (okb + 0.5) * 32767;
return kc;
#else
/* fall back to sRGB gamma */
return kc_make8g(a0, a1, a2);
#endif
}


static int kchist_sizes[] = {
4093, 16381, 65521, 262139, 1048571, 4194301, 16777213,
Expand Down
4 changes: 3 additions & 1 deletion src/kcolor.h
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Original file line number Diff line number Diff line change
Expand Up @@ -43,7 +43,7 @@ typedef union kacolor {

/* gamma_tables[0]: array of 256 gamma-conversion values
gamma_tables[1]: array of 256 reverse gamma-conversion values */
extern uint16_t* gamma_tables[2];
extern const uint16_t* gamma_tables[2];


/* return the gamma transformation of `a0/a1/a2` [RGB] */
Expand Down Expand Up @@ -129,6 +129,8 @@ static inline kcolor kc_luminance_transform(int a0, int a1, int a2) {
return kc;
}

kcolor kc_oklab_transform(int a0, int a1, int a2);


/* wkcolor: like kcolor, but components are 32 bits instead of 16 */

Expand Down
11 changes: 9 additions & 2 deletions src/quantize.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1047,11 +1047,18 @@ colormap_stream(Gif_Stream* gfs, Gif_Colormap* new_cm, Gt_OutputData* od)

/* initialize kd3 tree */
new_gray = 1;
for (j = 0; new_gray && j < new_cm->ncol; ++j)
for (j = 0; new_gray && j < new_cm->ncol; ++j) {
if (new_col[j].gfc_red != new_col[j].gfc_green
|| new_col[j].gfc_red != new_col[j].gfc_blue)
new_gray = 0;
kd3_init_build(&kd3, new_gray ? kc_luminance_transform : NULL, new_cm);
}
if (new_gray) {
kd3_init_build(&kd3, kc_luminance_transform, new_cm);
} else if (od->colormap_gamma_type == KC_GAMMA_OKLAB) {
kd3_init_build(&kd3, kc_oklab_transform, new_cm);
} else {
kd3_init_build(&kd3, NULL, new_cm);
}

for (imagei = 0; imagei < gfs->nimages; imagei++) {
Gif_Image *gfi = gfs->images[imagei];
Expand Down
3 changes: 3 additions & 0 deletions src/win32cfg.h
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Expand Up @@ -13,6 +13,9 @@
/* Define if GIF LZW compression is off. */
/* #undef GIF_UNGIF */

/* Define to 1 if you have the `cbrtf' function. */
#define HAVE_CBRTF 1

/* Define to 1 if `ext_vector_type' vector types are usable. */
/* #undef HAVE_EXT_VECTOR_TYPE_VECTOR_TYPES */

Expand Down

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