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-rw-r--r--blackbody.c252
1 files changed, 195 insertions, 57 deletions
diff --git a/blackbody.c b/blackbody.c
index 6edc85a..1abf133 100644
--- a/blackbody.c
+++ b/blackbody.c
@@ -11,6 +11,7 @@
# include <stddef.h>
+
/**
* Colour temperatures in CIE xy (xyY without Y)
*/
@@ -26,6 +27,7 @@ static struct rgb {double r, g, b;} rgb_table[] = {
};
+
#endif
/**
* Convert from CIE xyY to [0, 1] sRGB
@@ -41,9 +43,16 @@ static struct rgb {double r, g, b;} rgb_table[] = {
static void
ciexyy_to_srgb(double x, double y, double Y, double *r, double *g, double *b)
{
-#define SRGB(C) (((C) <= 0.0031308) ? (12.92 * (C)) : ((1.0 + 0.055) * pow((C), 1.0 / 2.4) - 0.055))
+#define LINEAR_TO_SRGB(C)\
+ do {\
+ double sign = (C) < 0 ? -1 : 1;\
+ (C) *= sign;\
+ (C) = (((C) <= 0.0031306684425217108) ? (12.92 * (C)) : (1.055 * pow((C), 1.0 / 2.4) - 0.055));\
+ (C) *= sign;\
+ } while (0)
+
double X, Z, max;
-
+
#if __GNUC__
# pragma GCC diagnostic push
# pragma GCC diagnostic ignored "-Wfloat-equal"
@@ -55,13 +64,16 @@ ciexyy_to_srgb(double x, double y, double Y, double *r, double *g, double *b)
# pragma GCC diagnostic pop
#endif
- /* Convert CIE XYZ to [0, 1] linear RGB (ciexyz_to_linear) */
- *r = ( 3.240450 * X) + (-1.537140 * Y) + (-0.4985320 * Z);
- *g = (-0.969266 * X) + ( 1.876010 * Y) + ( 0.0415561 * Z);
- *b = (0.0556434 * X) + (-0.204026 * Y) + ( 1.0572300 * Z);
-
- /* Convert [0, 1] linear RGB to [0, 1] sRGB */
- SRGB(*r), SRGB(*g), SRGB(*b);
+ /* Convert CIE XYZ to [0, 1] linear RGB */
+ *r = ( 3.24044625464773750067593027779366821050643920898438 * X)
+ + (-1.53713476182008057513428411766653880476951599121094 * Y)
+ + (-0.49853019302272871815517873983480967581272125244141 * Z);
+ *g = (-0.96926660624467975146956177923129871487617492675781 * X)
+ + ( 1.87601195978837020916785149893257766962051391601562 * Y)
+ + ( 0.04155604221443006535130493261931405868381261825562 * Z);
+ *b = ( 0.05564350356435283223577314970498264301568269729614 * X)
+ + (-0.20402617973596023914772956686647376045584678649902 * Y)
+ + ( 1.05722656772270329206264705135254189372062683105469 * Z);
/* Adjust colours for use */
max = fmax(fmax(fabs(*r), fabs(*g)), fabs(*b));
@@ -76,70 +88,124 @@ ciexyy_to_srgb(double x, double y, double Y, double *r, double *g, double *b)
*r = *r > 0.0 ? *r : 0.0;
*g = *g > 0.0 ? *g : 0.0;
*b = *b > 0.0 ? *b : 0.0;
+
+ /* Convert [0, 1] linear RGB to [0, 1] sRGB */
+ LINEAR_TO_SRGB(*r);
+ LINEAR_TO_SRGB(*g);
+ LINEAR_TO_SRGB(*b);
}
#ifndef LIBRED_COMPILING_PARSER
+
+/**
+ * Convert from [0, 1] sRGB to CIE xyY
+ *
+ * @param r The “red” value
+ * (Seriously, sRGB red is orange, just look at it fullscreen)
+ * @param g The green value
+ * @param b The blue value
+ * @param x Output parameter for The 'x' component
+ * @param y Output parameter for The 'y' component
+ * @param Y Output parameter for The 'Y' component
+ */
+static void
+srgb_to_ciexyy(double r, double g, double b, double *x, double *y, double *Y)
+{
+#define SRGB_TO_LINEAR(C)\
+ do {\
+ double sign = (C) < 0 ? -1 : 1;\
+ (C) *= sign;\
+ (C) = (((C) <= 0.0031306684425217108 * 12.92) ? ((C) / 12.92) : pow(((C) + 0.055) / 1.055, 2.4));\
+ (C) *= sign;\
+ } while (0)
+
+ /* Convert [0, 1] sRGB to [0, 1] linear RGB */
+ double s, z;
+
+ SRGB_TO_LINEAR(r);
+ SRGB_TO_LINEAR(g);
+ SRGB_TO_LINEAR(b);
+
+ /* Convert [0, 1] linear RGB to CIE XYZ */
+ *x = 0.41245744558236757670854899515688885003328323364258 * r
+ + 0.35757586524551587814357844763435423374176025390625 * g
+ + 0.18043724782639966597308500695362454280257225036621 * b;
+ *y = 0.21267337037840827740353688568575307726860046386719 * r
+ + 0.71515173049103175628715689526870846748352050781250 * g
+ + 0.07217489913055986916479156434434116818010807037354 * b;
+ z = 0.01933394276167346020889326041469757910817861557007 * r
+ + 0.11919195508183859366635459764438564889132976531982 * g
+ + 0.95030283855237174250873977143783122301101684570312 * b;
+ *Y = z;
+
+ /* Convert CIE XYZ to CIE xyY */
+ *Y = *y;
+ s = *x + *y + z;
+ *x /= s;
+ *y /= s;
+ if (!isfinite(*x) || !isfinite(*y))
+ *x = *y = 0;
+}
+
+
/**
* Perform linear interpolation (considered very good)
- * between the CIE xyY values for two colour temperatures
- * and convert the result to sRGB. The two colours should
- * be the closest below the desired colour temperature,
- * and the closest above the desired colour temperature
+ * between the CIE xy values for two colour temperatures.
+ * The two colours should be the closest below the desired
+ * colour temperature, and the closest above the desired
+ * colour temperature
*
* @param x1 The 'x' component for the low colour
* @param y1 The 'y' component for the low colour
* @param x2 The 'x' component for the high colour
* @param y2 The 'y' component for the high colour
* @param temp The desired colour temperature
- * @param r Output parameter for the “red” value
- * @param g Output parameter for the green value
- * @param b Output parameter for the blue value
+ * @param x Output parameter for the CIE x value
+ * @param y Output parameter for the CIE y value
*/
static void
-interpolate(double x1, double y1, double x2, double y2, double temp, double *r, double *g, double *b)
+interpolate(double x1, double y1, double x2, double y2, double temp, double *x, double *y)
{
double weight = fmod(temp - (LIBRED_LOWEST_TEMPERATURE % LIBRED_DELTA_TEMPERATURE),
(double)LIBRED_DELTA_TEMPERATURE) / (double)LIBRED_DELTA_TEMPERATURE;
- double x = x1 * (1 - weight) + x2 * weight;
- double y = y1 * (1 - weight) + y2 * weight;
- ciexyy_to_srgb(x, y, 1.0, r, g, b);
+ *x = x1 * (1 - weight) + x2 * weight;
+ *y = y1 * (1 - weight) + y2 * weight;
}
-/**
- * Get the [0, 1] sRGB values of a colour temperature
- *
- * libred has a table of colour temperature values, this
- * function interpolates values that are missing. If you
- * don't want any interpolation the `temp` parameter can
- * be specified in one of the following ways:
- *
- * - floor:
- * (temp - LIBRED_LOWEST_TEMPERATURE) /
- * LIBRED_DELTA_TEMPERATURE *
- * LIBRED_DELTA_TEMPERATURE +
- * LIBRED_LOWEST_TEMPERATURE
- *
- * - ceiling:
- * (temp - LIBRED_LOWEST_TEMPERATURE +
- * LIBRED_DELTA_TEMPERATURE - 1) /
- * LIBRED_DELTA_TEMPERATURE *
- * LIBRED_DELTA_TEMPERATURE +
- * LIBRED_LOWEST_TEMPERATURE
- *
- * - round to nearest:
- * (temp - LIBRED_LOWEST_TEMPERATURE +
- * LIBRED_DELTA_TEMPERATURE / 2) /
- * LIBRED_DELTA_TEMPERATURE *
- * LIBRED_DELTA_TEMPERATURE +
- * LIBRED_LOWEST_TEMPERATURE
- *
- * @param temp The desired colour temperature
- * @param r Output parameter for the “red” value
- * @param g Output parameter for the green value
- * @param b Output parameter for the blue value
- * @return 0 on succeess, -1 on error
- * @throws EDOM The selected temperature is below 1000K
- */
+
+int
+libred_get_colour_xy(long int temp, double *x, double *y)
+{
+ double x1, y1, x2, y2;
+ size_t i;
+ long int tmp;
+
+ if (temp > LIBRED_HIGHEST_TEMPERATURE)
+ temp = LIBRED_HIGHEST_TEMPERATURE;
+
+ if (temp < LIBRED_LOWEST_TEMPERATURE) {
+ errno = EDOM;
+ return -1;
+ }
+
+ tmp = temp - LIBRED_LOWEST_TEMPERATURE;
+
+ i = (size_t)(tmp / LIBRED_DELTA_TEMPERATURE);
+ if (tmp % LIBRED_DELTA_TEMPERATURE) {
+ x1 = xy_table[i].x;
+ y1 = xy_table[i].y;
+ x2 = xy_table[i + 1].x;
+ y2 = xy_table[i + 1].y;
+ interpolate(x1, y1, x2, y2, (double)temp, x, y);
+ } else {
+ *x = xy_table[i].x;
+ *y = xy_table[i].y;
+ }
+
+ return 0;
+}
+
+
int
libred_get_colour(long int temp, double *r, double *g, double *b)
{
@@ -156,14 +222,16 @@ libred_get_colour(long int temp, double *r, double *g, double *b)
}
tmp = temp - LIBRED_LOWEST_TEMPERATURE;
-
+
i = (size_t)(tmp / LIBRED_DELTA_TEMPERATURE);
if (tmp % LIBRED_DELTA_TEMPERATURE) {
+ double x, y;
x1 = xy_table[i].x;
y1 = xy_table[i].y;
x2 = xy_table[i + 1].x;
y2 = xy_table[i + 1].y;
- interpolate(x1, y1, x2, y2, (double)temp, r, g, b);
+ interpolate(x1, y1, x2, y2, (double)temp, &x, &y);
+ ciexyy_to_srgb(x, y, 1, r, g, b);
} else {
*r = rgb_table[i].r;
*g = rgb_table[i].g;
@@ -172,6 +240,76 @@ libred_get_colour(long int temp, double *r, double *g, double *b)
return 0;
}
+
+
+double
+libred_get_temperature_xy(double x, double y, double *x_error, double *y_error)
+{
+ size_t i = 0, j;
+ double x1, y1, x2, y2, dx, dy, xd, yd, t, d2;
+ double best_temp = -1, best_d2 = INFINITY;
+
+ if (!x_error)
+ x_error = &dx;
+ if (!y_error)
+ y_error = &dy;
+
+ x1 = xy_table[0].x;
+ y1 = xy_table[0].y;
+
+ for (j = 1; j < sizeof(xy_table) / sizeof(*xy_table); j++) {
+ x2 = xy_table[j].x;
+ y2 = xy_table[j].y;
+ dx = x2 - x1;
+ dy = y2 - y1;
+
+ t = ((x - x1) * dx + (y - y1) * dy) / (dx * dx + dy * dy);
+ if (!isfinite(t))
+ continue;
+ t = t < 0 ? 0 : t;
+ t = t > 1 ? 1 : t;
+
+ xd = dx * t + x1 - x;
+ yd = dy * t + y1 - y;
+ d2 = xd * xd + yd * yd;
+
+ if (d2 < best_d2) {
+ *x_error = xd;
+ *y_error = yd;
+ best_d2 = d2;
+ t *= (double)(j - i);
+ best_temp = (double)i + t;
+ }
+
+ i = j;
+ }
+
+ return best_temp * LIBRED_DELTA_TEMPERATURE + LIBRED_LOWEST_TEMPERATURE;
+}
+
+
+double
+libred_get_temperature(double r, double g, double b, double *y,
+ double *r_error, double *g_error, double *b_error)
+{
+ double tx, ty, luma, x_error, y_error, ret;
+
+ srgb_to_ciexyy(r, g, b, &tx, &ty, &luma);
+ ret = libred_get_temperature_xy(tx, ty, &x_error, &y_error);
+ ciexyy_to_srgb(x_error, y_error, 1, &r, &g, &b);
+
+ if (y)
+ *y = luma;
+ if (r_error)
+ *r_error = r;
+ if (g_error)
+ *g_error = g;
+ if (b_error)
+ *b_error = b;
+
+ return ret;
+}
+
#endif
generated by cgit v1.2.3-70-g09d2 (git 2.48.0) at 2025-03-18 09:12:23 +0000