如何創建Display P3顏色的不飽和版本？

Question

我有一個顏色UIColor(displayP3Red: 1, green: 0, blue: 0.8, alpha: 1)。我想創建一個不飽和的版本 - 具有相同的色調和亮度，但較少的飽和度，如原始飽和度的一半。我該怎麼做呢？

Answer 1

extension UIColor {  
    // Calling this with 0.5 as argument returns a color whose saturation is 50% of that of the receiver. 
    func desaturatedBy(fraction: CGFloat) -> UIColor { 
    var hue: CGFloat = 0 
    var saturation: CGFloat = 0 
    var brightness: CGFloat = 0 
    var alpha: CGFloat = 0 
    let success = getHue(&hue, saturation: &saturation, brightness: &brightness, alpha: &alpha) 
    assert(success) 

    saturation *= fraction 

    return UIColor(hue: hue, saturation: saturation, brightness: brightness, alpha: alpha) 
    } 
} 

這工作，因爲第e getter在擴展的sRGB色彩空間中返回HSB，而UIColor的初始化程序也在擴展的sRGB色彩空間中獲取HSB。所以我們不需要做任何色彩空間轉換。

Answer 2

考慮到您可以計算DCI-P3的歸一化主矩陣（NPM），它應該很簡單：NPM的中間一行代表亮度因子。我將舉例說明這一點使用Colour，它假設你正在使用線性值：

import numpy as np 
import colour 

# Computing the sRGB Luminance Equation, you should be familiar with the 
# resulting Luminance factors. 
print(colour.RGB_luminance_equation(
    colour.sRGB_COLOURSPACE.primaries, 
    colour.sRGB_COLOURSPACE.whitepoint)) 
# Y = 0.212639005872(R) + 0.715168678768(G) + 0.0721923153607(B) 

# Computing the DCI-P3 Luminance Equation. 
print(colour.RGB_luminance_equation(
    colour.DCI_P3_COLOURSPACE.primaries, 
    colour.DCI_P3_COLOURSPACE.whitepoint)) 
# Y = 0.209491677913(R) + 0.721595254161(G) + 0.0689130679262(B) 

# Computing Luminance of given RGB colour, this is assuming it is representing linear values. 
DCI_P3_LUMINANCE_FACTORS = np.array([0.209491677913, 0.721595254161, 0.0689130679262]) 
RGB = np.array([1.0, 0.0, 0.8]) 
Y = np.dot(RGB, DCI_P3_LUMINANCE_FACTORS) 
print(Y) 
# 0.264622132254 

隨着Ÿ代表您給出顏色的亮度，如果你想在50％飽和度，你可以做這樣的事情：

線性插值（RGB，[Y，Y，Y]，0.5）