Bitmaps and bit-depth

An important factor when the digital data for an image is captured, typically at the scanning stage, is its bit-depth. Bit-depth refers to the amount of digital storage space used to record information about the colour of a pixel. The more bits you use, the more colour of a pixel-but also, the larger the file size you end up with.

To output realistic images using PostScript technology an image should be able to represent 256 grey levels. A 24-bit scan is sufficient for recording 256 grey levels for each of the Red, Green and Blue channels, resulting in a possible combination of over 16 million colours.

Ideally, when you work on images in Photoshop you will do so using a 24-bit monitor capable of displaying over 16 million colours. This ensures that you see all the colour detail in the image. Although you can work on images using only thousands of colours, for best results, especially where colour reproduction is important, you need to work with as many colours as possible.