Gamma is a term that describes the relationship between the brightness of a projected image, and the digital values (or codes) used to create that image. Gamma correction adjusts an image's brightness to match how the human eye perceives brightness.
Gamma correction is also used to adjust the brightness of dark and mid-tone areas of the image and the overall contrast of the picture.
Regarding home theater projectors, gamma is usually measured in a value between 1.8 and 2.2. A value of 2.2 is considered the standard for home theater projectors, and it's the value used to match the way the human eye perceives brightness. A value of 1.8 is a low gamma setting, which will result in a brighter image and less detail in the dark areas of the picture. A value of 2.2 is a high gamma, resulting in a darker appearance and more detail in the dark regions of the image.
Most projectors have the option to adjust the gamma value in their menus. It's important to note that the gamma value can be affected by various factors, such as the projector's lamp, the projector's color wheel, and the ambient light, so it's essential to ensure that the projector is set up correctly and calibrated to match the intended use of the projector.