diff options
Diffstat (limited to '')
-rw-r--r-- | blackbody.c | 252 |
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 |