Q. How to calculate Colour Depth?

Colour Depth (or number of Colour Planes) is number of bits assigned to every pixel to code colour information in it. These are also known as Colour Planes since every bit of a pixel represents a particular colour and the bit at same position on each pixel represents same colour. Therefore the bits at same position can be thought of as creating a plane of a particular colour shade and these planes piled on top of each other give final colour at every point.  So if every pixel is defined by 3 bits one each for red, green and blue colour then there are 3 Colour Planes (one each for red, green and blue) and 6 colour planes if there are 6 bits - see Figure below.