Its a bit depth

 Bit depth is the colour information stored within an image this is sampling as it makes the colours components (the things that make up its colour) its purpose is to store the bits per pixel within an image the higher the bits per pixel the more colours a colour pallet will hold.

A monochrome pallet for example consists of only 2 colours black and white this is a 1 bit image.

A low colour pallet is an 8 bit image and contains 256 colours

(http://www.ceb.cam.ac.uk/data/images/currentstudents/it/bit8.gif)

Anything above a 16 bit image is a high colour pallet and can contain up to 65536 colours. To people with  normal vision eye this might look like real life however as is said in web designer’s guide to graphics PNG,GIF&JPEG ‘folks with sensitive eyes might be able to see the difference.’

(http://upload.wikimedia.org/wikipedia/commons/d/d1/RGB_16bits_palette.png)

A 24 bit image is true colour and has around 16777216 colours meaning it is true to life colours.















(http://www.ulillillia.us/images/truecolorpalette.png)