Author Archives: ssp

The Porter/Duff Over operator, also known as the “Normal” blend mode in Photoshop, computes the amount of light that is reflected when a pixel partially covers another: The fraction of bg that is covered is denoted alpha. This operator is … Continue reading →

Pixels with 8 bits per channel are normally sRGB encoded because that allocates more bits to darker colors where human vision is the most sensitive. (Actually, it’s really more of a historical accident, but sRGB nevertheless remains useful for this … Continue reading →

A new version 1.1.8 of Sysprof is out. This is a release candidate for 1.2.0 and contains mainly bug fixes.

If you are compositing pixels with 16 bits per component, you often need this computation: uint16_t a, b, r; r = (a * b + 0x7fff) / 65535; There is a well-known way to do this quickly without a division: … Continue reading →