Gamma Correction in the Mac Gamma Control Panel

Macintosh Gamma Control Panel - from Knoll Software
(released with Adobe Photoshop)
The Knoll software control panel for the Mac rewrites the look up table, (LUT) with a value of g/2.5 where g is the gamma the user selects. Thus selecting 1.8 will rewrite the LUT with 1.8/2.5 = 1/1.4 - the default setting. Therefore, the number that you set, is the number you get - ie your system gamma is the gamma you set in the control panel. The idea behind this control panel is to determine your system gamma. This is done by choosing your target gamma (probably 1.8) and adjusting it with the slider until the grey ribbon appears to be smooth when viewed from about 6-8 ft away. (We have reservations about this method although it is very common. Generally we feel it would be more accurate if the ribbon were much much larger and the patterns of alternating black and white dots were scaled a little bit lower - ie bigger dots. This is because the monitor may have trouble going from full on to full off in a space as short as one pixel. We have had better luck calibrating with large dot patterns and a viewing distance of over 15 feet!)