PNG_GAMMA_THRESHOLD_FIXED 2522 3rdparty/libpng/png.c    return gamma_val < PNG_FP_1 - PNG_GAMMA_THRESHOLD_FIXED ||
PNG_GAMMA_THRESHOLD_FIXED 2523 3rdparty/libpng/png.c        gamma_val > PNG_FP_1 + PNG_GAMMA_THRESHOLD_FIXED;
PNG_GAMMA_THRESHOLD_FIXED 1493 3rdparty/libpng/png.h #define PNG_GAMMA_THRESHOLD (PNG_GAMMA_THRESHOLD_FIXED*.00001)