Bit Depth

‘Bit’ means basic unit of information in computing and digital compressions. Bit depth in digital audio is the number of bits of information in each sample, directly corresponding to the resolution of each sample. Most digital devices operate on 8 bit (8 bits of information making up the image). It is on or off, 1 or 0, and black or white. Regarding images, bit depth measures how many unique colours are available in the images colour palette. For example in Adobe Photoshop you can select a colour bit by picking an exact colour using the sampling tool.

Images can have different bits per pixel (BPP) such as 8bpp, 16bpp and 32bpp. In a single image pf 8bpp there can be up to 256 shades of the same colour, which is what a gif format supports. 24bpp has 16777216 colours plus transparency which is more than the human eye can perceive. This is why having an image above 24bpp can be seen as unnecessary. Monochrome is when there are multiple shades of the same colour (image below). Each monochromatic image is only 1bp, using only two colours which are often black and white.

There is a difference between high colour and true colour; high colour has a depth of 15bpp which is split equally between red, green and blue, whereas true colour supports 24bpp split between the three colours and therefore has a much higher total of colour variations making the quality of the image better.