Bit depth refers to the color information stored in an image. The higher the bit depth of an image, the more colors it can store. The simplest image, a 1 bit image, can only show two colors, black and white. That is because the 1 bit can only store one of two values, 0 (white) and 1 (black). An 8 bit image can store 256 possible colors, while a 24 bit image can display about 16 million colors.
Along with an image’s resolution, the bit depth determines the size of the image. As the bit depth goes up, the size of the image also goes up because more color information has to be stored for each pixel in the image.
While an image has a bit depth, so does your display. You can change the bit depth of your display by accessing the display preferences. To change the number of colors (bit depth), select System Preferences from the Apple menu, then click on the Displays button.
In the Display tab, select the number of colors using the Colors pulldown menu.
You can also change the resolution of your display using the Display tab. The bit depth, as well as the resolution, are actually determined by the capabilities of your graphics adapter.