vec3 hueShift( vec3 color, float hueAdjust ){ | |
const vec3 kRGBToYPrime = vec3 (0.299, 0.587, 0.114); | |
const vec3 kRGBToI = vec3 (0.596, -0.275, -0.321); | |
const vec3 kRGBToQ = vec3 (0.212, -0.523, 0.311); | |
const vec3 kYIQToR = vec3 (1.0, 0.956, 0.621); | |
const vec3 kYIQToG = vec3 (1.0, -0.272, -0.647); | |
const vec3 kYIQToB = vec3 (1.0, -1.107, 1.704); | |
float YPrime = dot (color, kRGBToYPrime); | |
float I = dot (color, kRGBToI); | |
float Q = dot (color, kRGBToQ); | |
float hue = atan (Q, I); | |
float chroma = sqrt (I * I + Q * Q); | |
hue += hueAdjust; | |
Q = chroma * sin (hue); | |
I = chroma * cos (hue); | |
vec3 yIQ = vec3 (YPrime, I, Q); | |
return vec3( dot (yIQ, kYIQToR), dot (yIQ, kYIQToG), dot (yIQ, kYIQToB) ); | |
} |
There was a typo, this one works for me:
vec3 hueShift(vec3 color, float hue)
{
const vec3 k = vec3(0.57735, 0.57735, 0.57735);
float cosAngle = cos(hue);
return vec3(color * cosAngle + cross(k, color) * sin(hue) + k * dot(k, color) * (1.0 - cosAngle));
}
Does anyone know where the 0.57735
come from?
@RichardBray it's sqrt(3)/3
or 1/sqrt(3)
. It's one of those values that you see often in trigonometry, see e.g. http://mathforum.org/dr.math/faq/formulas/faq.trig.html (Not super often though; I had to do some digging to find this one too
@janpaul123 Thanks that makes more sense. But yeah I still can't figure out how that formula was reached.
Thank you so much for this! Contrary to what you seem to think though, your original function produces much more natural looking/beautiful results than the cheaper hueshift function provided by @viruseg. Of course it depends on context whether or not that's needed, but I for one deeply appreciate it!
EDIT but, I believe this is a faster implementation ->
vec2 rotate2(vec2 v, float fi) {
return v*mat2(cos(fi), -sin(fi), sin(fi), cos(fi));
}
// YIQ color rotation/hue shift
vec3 hueShiftYIQ(vec3 rgb, float hs) {
float rotAngle = hs*-6.28318530718;
const mat3 rgb2yiq = mat3(0.299, 0.596, 0.211,
0.587, -0.274, -0.523,
0.114, -0.322, 0.312);
const mat3 yiq2rgb = mat3(1, 1, 1,
0.956, -0.272, -1.106,
0.621, -0.647, 1.703);
vec3 yiq = rgb2yiq * rgb;
yiq.yz *= rot(rotAngle);
return yiq2rgb * yiq;
}
@viruseg Indeed, it is a more elegant solution, and simple to convert to GLSL, thanks.