Technology Trade-offs
Although video standards assume a display gamma of about 2.2, a gamma of about 2.5 is more realistic for CRT displays. However, this difference improves the viewing in a dimly lit environment. More accurate viewing in a brightly lit environment may be accomplished by applying another gamma factor of about 1.14 (2.5/2.2). It is also common to tweak the gamma curve in the display to get closer to the “film look.”
Early NTSC Systems
Early NTSC systems assumed a simple transform at the display, with a gamma of 2.2. RGB values are normalized to have a range
of 0 to 1:
To compensate for the nonlinear display, linear RGB data was “gamma-corrected” prior to transmission by the inverse transform.
RGB values are normalized to have a range of 0 to 1:
Early PAL and SECAM Systems
Most early PAL and SECAM systems assumed a simple transform at the display, with a gamma of 2.8. RGB values are normalized
to have a range of 0 to 1:
To compensate for the nonlinear display, linear RGB data was “gamma-corrected” prior to transmission by the inverse transform.
RGB values are normalized to have a range of 0 to 1:
Current Systems
Current NTSC, 480i, 480 p, and HDTV video systems assume the following transform at the display, with a gamma of [1/0.45]. RGB values are normalized to have a range of 0 to 1:
if (R′, G′, B′)<0.081
if (R′, G′, B′)≥0.081
To compensate for the nonlinear display, linear RGB data is “gamma-corrected” prior to transmission by the inverse transform. RGB values are normalized to have a range of 0 to 1:
if (R, G, B)<0.018
for (R, G, B)≥0.018
Although most PAL and SECAM standards specify a gamma of 2.8, a value of [1/0.45] is now commonly used. Thus, these equations are also now used for PAL, SECAM, 576i, and 576p video systems.
Non-CRT Displays
Since they are not based on CRTs, the LCD, LCOS, DLP, and plasma displays have different display transforms. To simplify interfacing to these displays, their electronics are designed to accept standard gamma-corrected video and then compensate for the actual transform of the display panel.
Instant summary
Color spaces are mathematical representations of a set of colors and many different models are and have been used in video technology. These include: