42 lines
1.2 KiB
Forth
42 lines
1.2 KiB
Forth
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// Uchimura 2017, "HDR theory and practice"
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// Math: https://www.desmos.com/calculator/gslcdxvipg
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// Source: https://www.slideshare.net/nikuque/hdr-theory-and-practicce-jp
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vec3 uchimura(vec3 x, float P, float a, float m, float l, float c, float b) {
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float l0 = ((P - m) * l) / a;
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float L0 = m - m / a;
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float L1 = m + (1.0 - m) / a;
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float S0 = m + l0;
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float S1 = m + a * l0;
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float C2 = (a * P) / (P - S1);
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float CP = -C2 / P;
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vec3 w0 = vec3(1.0 - smoothstep(0.0, m, x));
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vec3 w2 = vec3(step(m + l0, x));
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vec3 w1 = vec3(1.0 - w0 - w2);
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vec3 T = vec3(m * pow(x / m, vec3(c)) + b);
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vec3 S = vec3(P - (P - S1) * exp(CP * (x - S0)));
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vec3 L = vec3(m + a * (x - m));
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return T * w0 + L * w1 + S * w2;
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}
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vec3 uchimura(vec3 x) {
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const float P = 1.0; // max display brightness
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const float a = 1.0; // contrast
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const float m = 0.22; // linear section start
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const float l = 0.4; // linear section length
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const float c = 1.33; // black
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const float b = 0.0; // pedestal
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return uchimura(x, P, a, m, l, c, b);
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}
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out vec4 color;
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void main(void) {
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vec2 uv = TEXCOORD.st;
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vec4 src = texture2D(iChannel0, uv);
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color = vec4( uchimura(src.xyz), src.a);
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}
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