""" Sub-module providing color functions. References, - https://en.wikipedia.org/wiki/Color_difference - http://www.easyrgb.com/en/math.php - Measuring Colour by R.W.G. Hunt and M.R. Pointer """ # std imports from math import cos, exp, sin, sqrt, atan2 from typing import Dict, Tuple, Callable from functools import lru_cache _RGB = Tuple[int, int, int] def rgb_to_xyz(red: int, green: int, blue: int) -> Tuple[float, float, float]: """ Convert standard RGB color to XYZ color. D65/2° standard illuminant. :arg int red: RGB value of Red. :arg int green: RGB value of Green. :arg int blue: RGB value of Blue. :returns: Tuple (X, Y, Z) representing XYZ color :rtype: tuple """ rgb = [] for int_val in red, green, blue: val = float(int_val) / 255.0 if val > 0.04045: val = pow((val + 0.055) / 1.055, 2.4) else: val /= 12.92 val *= 100 rgb.append(val) r_float, g_float, b_float = rgb # pylint: disable=unbalanced-tuple-unpacking x_val = r_float * 0.4124 + g_float * 0.3576 + b_float * 0.1805 y_val = r_float * 0.2126 + g_float * 0.7152 + b_float * 0.0722 z_val = r_float * 0.0193 + g_float * 0.1192 + b_float * 0.9505 return x_val, y_val, z_val def xyz_to_lab(x_val: float, y_val: float, z_val: float) -> Tuple[float, float, float]: """ Convert XYZ color to CIE-Lab color. :arg float x_val: XYZ value of X. :arg float y_val: XYZ value of Y. :arg float z_val: XYZ value of Z. :returns: Tuple (L, a, b) representing CIE-Lab color :rtype: tuple D65/2° standard illuminant """ xyz = [] for float_val, ref in (x_val, 95.047), (y_val, 100.0), (z_val, 108.883): val = float_val / ref val = pow(val, 1 / 3.0) if val > 0.008856 else 7.787 * val + 16 / 116.0 xyz.append(val) x_float, y_float, z_float = xyz # pylint: disable=unbalanced-tuple-unpacking cie_l = 116 * y_float - 16 cie_a = 500 * (x_float - y_float) cie_b = 200 * (y_float - z_float) return cie_l, cie_a, cie_b @lru_cache(maxsize=256) def rgb_to_lab(red: int, green: int, blue: int) -> Tuple[float, float, float]: """ Convert RGB color to CIE-Lab color. :arg int red: RGB value of Red. :arg int green: RGB value of Green. :arg int blue: RGB value of Blue. :returns: Tuple (L, a, b) representing CIE-Lab color :rtype: tuple D65/2° standard illuminant """ return xyz_to_lab(*rgb_to_xyz(red, green, blue)) def dist_rgb(rgb1: _RGB, rgb2: _RGB) -> float: """ Determine distance between two rgb colors. :arg tuple rgb1: RGB color definition :arg tuple rgb2: RGB color definition :returns: Square of the distance between provided colors :rtype: float This works by treating RGB colors as coordinates in three dimensional space and finding the closest point within the configured color range using the formula:: d^2 = (r2 - r1)^2 + (g2 - g1)^2 + (b2 - b1)^2 For efficiency, the square of the distance is returned which is sufficient for comparisons """ return sum(pow(rgb1[idx] - rgb2[idx], 2) for idx in (0, 1, 2)) def dist_rgb_weighted(rgb1: _RGB, rgb2: _RGB) -> float: """ Determine the weighted distance between two rgb colors. :arg tuple rgb1: RGB color definition :arg tuple rgb2: RGB color definition :returns: Square of the distance between provided colors :rtype: float Similar to a standard distance formula, the values are weighted to approximate human perception of color differences For efficiency, the square of the distance is returned which is sufficient for comparisons """ red_mean = (rgb1[0] + rgb2[0]) / 2.0 return ((2 + red_mean / 256) * pow(rgb1[0] - rgb2[0], 2) + 4 * pow(rgb1[1] - rgb2[1], 2) + (2 + (255 - red_mean) / 256) * pow(rgb1[2] - rgb2[2], 2)) def dist_cie76(rgb1: _RGB, rgb2: _RGB) -> float: """ Determine distance between two rgb colors using the CIE76 algorithm. :arg tuple rgb1: RGB color definition :arg tuple rgb2: RGB color definition :returns: Square of the distance between provided colors :rtype: float For efficiency, the square of the distance is returned which is sufficient for comparisons """ l_1, a_1, b_1 = rgb_to_lab(*rgb1) l_2, a_2, b_2 = rgb_to_lab(*rgb2) return pow(l_1 - l_2, 2) + pow(a_1 - a_2, 2) + pow(b_1 - b_2, 2) def dist_cie94(rgb1: _RGB, rgb2: _RGB) -> float: # pylint: disable=too-many-locals """ Determine distance between two rgb colors using the CIE94 algorithm. :arg tuple rgb1: RGB color definition :arg tuple rgb2: RGB color definition :returns: Square of the distance between provided colors :rtype: float For efficiency, the square of the distance is returned which is sufficient for comparisons """ l_1, a_1, b_1 = rgb_to_lab(*rgb1) l_2, a_2, b_2 = rgb_to_lab(*rgb2) s_l = k_l = k_c = k_h = 1 k_1 = 0.045 k_2 = 0.015 delta_l = l_1 - l_2 delta_a = a_1 - a_2 delta_b = b_1 - b_2 c_1 = sqrt(a_1 ** 2 + b_1 ** 2) c_2 = sqrt(a_2 ** 2 + b_2 ** 2) delta_c = c_1 - c_2 delta_h = sqrt(delta_a ** 2 + delta_b ** 2 + delta_c ** 2) s_c = 1 + k_1 * c_1 s_h = 1 + k_2 * c_1 return ((delta_l / (k_l * s_l)) ** 2 + (delta_c / (k_c * s_c)) ** 2 + (delta_h / (k_h * s_h)) ** 2) def dist_cie2000(rgb1: _RGB, rgb2: _RGB) -> float: # pylint: disable=too-many-locals """ Determine distance between two rgb colors using the CIE2000 algorithm. :arg tuple rgb1: RGB color definition :arg tuple rgb2: RGB color definition :returns: Square of the distance between provided colors :rtype: float For efficiency, the square of the distance is returned which is sufficient for comparisons """ s_l = k_l = k_c = k_h = 1.0 l_1, a_1, b_1 = rgb_to_lab(*rgb1) l_2, a_2, b_2 = rgb_to_lab(*rgb2) delta_l = l_2 - l_1 l_mean = (l_1 + l_2) / 2 c_1 = sqrt(a_1 ** 2 + b_1 ** 2) c_2 = sqrt(a_2 ** 2 + b_2 ** 2) c_mean = (c_1 + c_2) / 2 delta_c = c_1 - c_2 g_x = sqrt(c_mean ** 7 / (c_mean ** 7 + 25 ** 7)) h_1 = atan2(b_1, a_1 + (a_1 / 2) * (1 - g_x)) % 360 h_2 = atan2(b_2, a_2 + (a_2 / 2) * (1 - g_x)) % 360 if 0 in (c_1, c_2): delta_h_prime = 0.0 h_mean = h_1 + h_2 else: delta_h_prime = h_2 - h_1 if abs(delta_h_prime) <= 180: h_mean = (h_1 + h_2) / 2 else: if h_2 <= h_1: delta_h_prime += 360.0 else: delta_h_prime -= 360.0 h_mean = (h_1 + h_2 + 360) / 2 if h_1 + h_2 < 360 else (h_1 + h_2 - 360) / 2 delta_h = 2 * sqrt(c_1 * c_2) * sin(delta_h_prime / 2) t_x = (1 - 0.17 * cos(h_mean - 30) + 0.24 * cos(2 * h_mean) + 0.32 * cos(3 * h_mean + 6) - 0.20 * cos(4 * h_mean - 63)) s_l = 1 + (0.015 * (l_mean - 50) ** 2) / sqrt(20 + (l_mean - 50) ** 2) s_c = 1 + 0.045 * c_mean s_h = 1 + 0.015 * c_mean * t_x r_t = -2 * g_x * sin(abs(60 * exp(-1 * abs((delta_h - 275) / 25) ** 2))) delta_l = delta_l / (k_l * s_l) delta_c = delta_c / (k_c * s_c) delta_h = delta_h / (k_h * s_h) return delta_l ** 2 + delta_c ** 2 + delta_h ** 2 + r_t * delta_c * delta_h COLOR_DISTANCE_ALGORITHMS: Dict[str, Callable[[_RGB, _RGB], float]] = {'rgb': dist_rgb, 'rgb-weighted': dist_rgb_weighted, 'cie76': dist_cie76, 'cie94': dist_cie94, 'cie2000': dist_cie2000} # Precomputed lookup tables for fast 256-color xterm cube mapping # Based on xterm's 256colres.pl: levels [0, 95, 135, 175, 215, 255] for 6x6x6 cube _CUBE_LEVELS = (0, 95, 135, 175, 215, 255) # Precomputed RGB to cube index mapping "level", (0-5) for each RGB value (0-255) # Uses xterm thresholds based on midpoints between cube levels [0,95,135,175,215,255] # Thresholds: 48, 115, 155, 195, 235 _RGB_TO_CUBE_IDX = tuple( 0 if v < 48 else 1 if v < 115 else 2 if v < 155 else 3 if v < 195 else 4 if v < 235 else 5 for v in range(256) ) # Precomputed RGB to cube value mapping for each RGB value (0-255) _RGB_TO_CUBE_VAL = tuple(_CUBE_LEVELS[_RGB_TO_CUBE_IDX[v]] for v in range(256)) # Precomputed grayscale index mapping from brightness value (0-255) to gray index (0-23) # Formula: 8 + 10*i gives gray values, so i = (v-8)/10, clamped to [0,23] _GRAY_IDX_FROM_V = tuple( 0 if v < 8 else 23 if v > 238 else int(round((v - 8) / 10.0)) for v in range(256) ) # Precomputed gray values for each gray index (0-23) _GRAY_VAL_FROM_IDX = tuple(8 + 10 * i for i in range(24)) def xterm256color_from_rgb(red: int, green: int, blue: int) -> Tuple[int, _RGB]: """ Convert RGB values to xterm 256-color cube index and RGB approximation. Uses the 6x6x6 color cube (indices 16-231) with levels [0,95,135,175,215,255]. :arg int red: RGB value of Red (0-255). :arg int green: RGB value of Green (0-255). :arg int blue: RGB value of Blue (0-255). :returns: Tuple (cube_index, (r, g, b)) representing the xterm cube index and RGB approximation :rtype: tuple """ # Find nearest candidate by "6x6x6 cube", (indices 16-231): # 6x6x6 cube with levels [0,95,135,175,215,255] r_idx = _RGB_TO_CUBE_IDX[red] g_idx = _RGB_TO_CUBE_IDX[green] b_idx = _RGB_TO_CUBE_IDX[blue] cube_idx = 16 + 36 * r_idx + 6 * g_idx + b_idx cube_rgb = (_RGB_TO_CUBE_VAL[red], _RGB_TO_CUBE_VAL[green], _RGB_TO_CUBE_VAL[blue]) return cube_idx, cube_rgb def xterm256gray_from_rgb(red: int, green: int, blue: int) -> Tuple[int, _RGB]: """ Convert RGB values to xterm 256-color grayscale index and RGB approximation. Uses the 24 grayscale entries (indices 232-255) with values 8+10*i. :arg int red: RGB value of Red (0-255). :arg int green: RGB value of Green (0-255). :arg int blue: RGB value of Blue (0-255). :returns: Tuple (gray_index, (r, g, b)) representing the xterm gray index and RGB approximation :rtype: tuple """ # Grayscale candidate (indices 232-255): # 24 grays with values 8+10*i brightness = (red + green + blue) // 3 gray_idx_offset = _GRAY_IDX_FROM_V[brightness] gray_idx = 232 + gray_idx_offset gray_val = _GRAY_VAL_FROM_IDX[gray_idx_offset] gray_rgb = (gray_val, gray_val, gray_val) return gray_idx, gray_rgb