OpenGLES滤镜开发汇总 —— 色彩转换

RGB转成HSL

HSL色彩模式

HSL色彩模式的定义，可以参考百度百科：
https://baike.baidu.com/item/HSL/1443144?fr=aladdin

HSL和RGB相互转换的OpenGLES实现

rgb转hsl：

vec3 convertRgbToHsl(vec3 c) { 
    vec4 K = vec4(0.0, -1.0 / 3.0, 2.0 / 3.0, -1.0); 
    vec4 p = mix(vec4(c.bg, K.wz), vec4(c.gb, K.xy), step(c.b, c.g)); 
    vec4 q = mix(vec4(p.xyw, c.r), vec4(c.r, p.yzx), step(p.x, c.r)); 
    
    float d = q.x - min(q.w, q.y); 
    float e = 1.0e-10; 
    return vec3(abs(q.z + (q.w - q.y) / (6.0 * d + e)), d / (q.x + e), q.x); 
} 

hsl 转 rgb:

vec3 convertHslToRgb(vec3 c) { 
    vec4 K = vec4(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0); 
    vec3 p = abs(fract(c.xxx + K.xyz) * 6.0 - K.www); 
    return c.z * mix(K.xxx, clamp(p - K.xxx, 0.0, 1.0), c.y);
} 

RGB转成HSB/HSV

HSB/HSV色彩模式

关于HSB/HSV色彩模式的定义，可以参考百度百科：
https://baike.baidu.com/item/HSV/547122
https://baike.baidu.com/item/hsb/10338413?fr=aladdin

HSB/HSV和RGB相互转换的OpenGLES实现

rgb转hsb/hsv:

vec3 convertRgbToHsv(vec3 c) {
    vec4 K = vec4(0.0, -1.0 / 3.0, 2.0 / 3.0, -1.0); 
    vec4 p = mix(vec4(c.bg, K.wz), vec4(c.gb, K.xy), step(c.b, c.g)); 
    vec4 q = mix(vec4(p.xyw, c.r), vec4(c.r, p.yzx), step(p.x, c.r)); 
    
    float d = q.x - min(q.w, q.y); 
    float e = 1.0e-10; 
    return vec3(abs(q.z + (q.w - q.y) / (6.0 * d + e)), d / (q.x + e), q.x); 
} 

hsb/hsv转rgb:

vec3 convertHsvToRgb(vec3 c) { 
    vec4 K = vec4(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0); 
    vec3 p = abs(fract(c.xxx + K.xyz) * 6.0 - K.www); 
    return c.z * mix(K.xxx, clamp(p - K.xxx, 0.0, 1.0), c.y); 
}