Gamma Correction

Changing gamma value to match a monitor's middle gray

Gamma correction compensates for the differences in color display on different output devices so that images look the same when viewed on different monitors.

A gamma value of 1 corresponds to an "ideal" monitor; that is, one that has a perfectly linear progression from white through gray to black. However, the ideal display device doesn't exist. Computer monitors are "nonlinear" devices. The higher the gamma value is set, the greater the degree of nonlinearity. The standard gamma value for NTSC video is 2.2. For computer monitors, gamma values in the range of 1.5 to 2.0 are common.

When you create an image on your computer, you base your color values and intensities on what you see on your monitor. Thus, when you save an image that looks perfect on your own monitor, you're compensating for the variance caused by the monitor gamma. The same image displayed on another monitor (or recorded to another media affected by gamma) will look different, depending on that media's gamma values.

Two basic procedures are required to compensate for changes in gamma:

The most important rule about gamma correction is to do it only once. If you do it twice, the image quality is over bright and loses color resolution.

With regard to output file gamma, video devices such as video tape recorders have their own hardware gamma-correction circuitry. Therefore, you need to decide whether to let the software do the output gamma correction or to let the output device handle it.

Gamma correction is not required for hardcopy print media.

Files coming into the software from programs such as Adobe Photoshop will have been gamma-corrected already. If you've been viewing the files on the same monitor and they look good, you won't need to set input file gamma.