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https://github.com/italicsjenga/slang-shaders.git
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31 lines
1.6 KiB
C
31 lines
1.6 KiB
C
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#define kMaxNitsFor2084 10000.0f
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#define kEpsilon 0.0001f
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vec3 InverseTonemap(vec3 sdr_linear, float max_nits, float paper_white_nits, float luma_ratio)
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{
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float luma = dot(sdr_linear, vec3(0.2126, 0.7152, 0.0722)); /* Rec BT.709 luma coefficients - https://en.wikipedia.org/wiki/Luma_(video) */
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/* Inverse reinhard tonemap */
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float max_value = (max_nits / paper_white_nits) + kEpsilon;
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float elbow = max_value / (max_value - 1.0f);
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float offset = 1.0f - ((0.5f * elbow) / (elbow - 0.5f));
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float hdr_luma_inv_tonemap = offset + ((luma * elbow) / (elbow - luma));
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float sdr_luma_inv_tonemap = luma / ((1.0f + kEpsilon) - luma); /* Convert the srd < 0.5 to 0.0 -> 1.0 range */
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float luma_inv_tonemap = (luma > 0.5f) ? hdr_luma_inv_tonemap : sdr_luma_inv_tonemap;
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vec3 per_luma = sdr_linear / (luma + kEpsilon) * luma_inv_tonemap;
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vec3 hdr_inv_tonemap = offset + ((sdr_linear * elbow) / (elbow - sdr_linear));
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vec3 sdr_inv_tonemap = sdr_linear / ((1.0f + kEpsilon) - sdr_linear); /* Convert the srd < 0.5 to 0.0 -> 1.0 range */
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vec3 per_channel = vec3(sdr_linear.x > 0.5f ? hdr_inv_tonemap.x : sdr_inv_tonemap.x,
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sdr_linear.y > 0.5f ? hdr_inv_tonemap.y : sdr_inv_tonemap.y,
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sdr_linear.z > 0.5f ? hdr_inv_tonemap.z : sdr_inv_tonemap.z);
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vec3 hdr = mix(per_luma, per_channel, vec3(luma_ratio));
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return hdr;
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}
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