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-rw-r--r--blackbody.c190
1 files changed, 156 insertions, 34 deletions
diff --git a/blackbody.c b/blackbody.c
index 6edc85a..78608c1 100644
--- a/blackbody.c
+++ b/blackbody.c
@@ -81,7 +81,7 @@ ciexyy_to_srgb(double x, double y, double Y, double *r, double *g, double *b)
/**
* Perform linear interpolation (considered very good)
- * between the CIE xyY values for two colour temperatures
+ * between the CIE xy 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
@@ -106,40 +106,29 @@ interpolate(double x1, double y1, double x2, double y2, double temp, double *r,
}
/**
- * 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
+ * Perform linear interpolation (considered very good)
+ * 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 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
+ * @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 x Output parameter for the CIE x value
+ * @param y Output parameter for the CIE y value
*/
+static void
+interpolate_xy(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;
+ *x = x1 * (1 - weight) + x2 * weight;
+ *y = y1 * (1 - weight) + y2 * weight;
+}
+
int
libred_get_colour(long int temp, double *r, double *g, double *b)
{
@@ -156,7 +145,7 @@ 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) {
x1 = xy_table[i].x;
@@ -172,6 +161,139 @@ libred_get_colour(long int temp, double *r, double *g, double *b)
return 0;
}
+
+int
+libred_get_colour_xy(long int temp, double *x, double *y) /* TODO test */
+{
+ 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_xy(x1, y1, x2, y2, (double)temp, x, y);
+ } else {
+ *x = xy_table[i].x;
+ *y = xy_table[i].y;
+ }
+
+ return 0;
+}
+
+double
+libred_get_temperature_xy(double x, double y, double *x_error, double *y_error) /* TODO man, test */
+{
+ size_t i, j;
+ double x1, y1, x2, y2, dx, dy, xd, yd, t, d2;
+ double best_temp = 0, 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;
+ }
+ }
+
+ return best_temp * LIBRED_DELTA_TEMPERATURE + LIBRED_LOWEST_TEMPERATURE;
+}
+
+/**
+ * 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)
+{
+ double s, z;
+
+ r *= s = r < 0 ? -1 : 1;
+ r = s * (r <= 0.0031306684425217108 * 12.92 ? r * 12.92 : pow((r + 0.055) / 1.055, 2.4));
+ g *= s = g < 0 ? -1 : 1;
+ g = s * (g <= 0.0031306684425217108 * 12.92 ? g * 12.92 : pow((g + 0.055) / 1.055, 2.4));
+ b *= s = b < 0 ? -1 : 1;
+ b = s * (g <= 0.0031306684425217108 * 12.92 ? b * 12.92 : pow((b + 0.055) / 1.055, 2.4));
+
+ *x = (0.41245744558236758 * r) + (0.35757586524551588 * g) + (0.18043724782639967 * b);
+ *y = (0.21267337037840828 * r) + (0.71515173049103176 * g) + (0.07217489913055987 * b);
+ z = (0.01933394276167346 * r) + (0.11919195508183859 * g) + (0.95030283855237174 * b);
+
+ *Y = *y;
+ s = *x + *y + z;
+ *x /= s;
+ *y /= s;
+ if (!isfinite(*x) || !isfinite(*y))
+ *x = *y = 0;
+}
+
+double
+libred_get_temperature(double r, double g, double b, double *y, /* TODO man, test */
+ 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, luma, &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
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