PNG_GAMMA_LINEAR 2117 pngread.c               png_ptr->colorspace.gamma = PNG_GAMMA_LINEAR;
PNG_GAMMA_LINEAR 3674 pngread.c                  input_gamma_default = PNG_GAMMA_LINEAR;
PNG_GAMMA_LINEAR 3695 pngread.c               output_gamma = PNG_GAMMA_LINEAR;
PNG_GAMMA_LINEAR 2187 pngwrite.c           png_set_gAMA_fixed(png_ptr, info_ptr, PNG_GAMMA_LINEAR);