ISO (light sensitivity)

ISO stands for International Organization for Standardization. The standard that regulates the light sensitivity of digital cameras is ISO 12232:2006. It is common to use ISO for short when discusing the light sensitivity of cameras.

The common way to adjust sensitivity would be like this:

Pixel --> variable gain analog amplifier --> analog to digital converter --> digital multiplier

Each colour channel have a separate gain setting which would be part of the white balance system.

The digital multiplier is often referred to as uncalibrated or HI setting. Usually it multiplies the pixel value by a power of two, the same effect can be had by adjusting the brightess with image processing software. There may or may not be an advantage of letting the camera do it because it may affect how the noise reduction algorithms in the camera works. It needs to be tested on every camera model to find out what works best.