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psd: LAB conversion speed improved

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Using an approximated pow function improves the conversion speed of LAB images by more than 50% without an appreciable visual difference.
This commit is contained in:
Mirco Miranda
2023-01-27 23:19:48 +00:00
committed by Albert Astals Cid
parent 5cc7a2b45c
commit 21211cd63b
4 changed files with 40 additions and 3 deletions
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8
src/imageformats/psd.cpp
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@ -32,6 +32,7 @@
* color management engine (e.g. LittleCMS).
*/
#include "fastmath_p.h"
#include "psd_p.h"
#include "util_p.h"
@ -50,7 +51,7 @@ typedef quint8 uchar;
* This should not be a problem because the Qt's QColorSpace supports the linear
* sRgb colorspace.
*
* Using linear conversion, the loading speed is improved by 4x. Anyway, if you are using
* Using linear conversion, the loading speed is slightly improved. Anyway, if you are using
* an software that discard color info, you should comment it.
*
* At the time I'm writing (07/2022), Gwenview and Krita supports linear sRgb but KDE
@ -898,8 +899,9 @@ inline double gammaCorrection(double linear)
#ifdef PSD_FAST_LAB_CONVERSION
return linear;
#else
// NOTE: pow() slow down the performance by a 4 factor :(
return (linear > 0.0031308 ? 1.055 * std::pow(linear, 1.0 / 2.4) - 0.055 : 12.92 * linear);
// Replacing fastPow with std::pow the conversion time is 2/3 times longer: using fastPow
// there are minimal differences in the conversion that are not visually noticeable.
return (linear > 0.0031308 ? 1.055 * fastPow(linear, 1.0 / 2.4) - 0.055 : 12.92 * linear);
#endif
}