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use revised value K0 for SRGB

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This commit is contained in:
Ahmet Inan 2021-04-16 17:31:44 +02:00
commit a3c8d375c2
1 changed files with 2 additions and 2 deletions
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netpbm.hh
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@ -20,7 +20,7 @@ class ReadPNM : public ReadPEL<TYPE>
TYPE linear(int val) TYPE linear(int val)
{ {
int K0 = std::nearbyint(0.03928 * maxval_); int K0 = std::nearbyint(0.04045 * maxval_);
TYPE phi(12.92 * maxval_), a(0.055 * maxval_), gamma(2.4); TYPE phi(12.92 * maxval_), a(0.055 * maxval_), gamma(2.4);
return val <= K0 ? val / phi : std::pow((val + a) / (maxval_ + a), gamma); return val <= K0 ? val / phi : std::pow((val + a) / (maxval_ + a), gamma);
} }
@ -123,7 +123,7 @@ class WritePNM : public WritePEL<TYPE>
int srgb(TYPE val) int srgb(TYPE val)
{ {
TYPE K0(0.03928), a(0.055), phi(12.92), gamma(2.4); TYPE K0(0.04045), a(0.055), phi(12.92), gamma(2.4);
val = std::min(std::max(val, TYPE(0)), TYPE(1)); val = std::min(std::max(val, TYPE(0)), TYPE(1));
val = val <= K0 / phi ? val * phi : (1 + a) * std::pow(val, 1 / gamma) - a; val = val <= K0 / phi ? val * phi : (1 + a) * std::pow(val, 1 / gamma) - a;
return std::nearbyint(maxval_ * val); return std::nearbyint(maxval_ * val);