Bit Depth

In order select a specific shade of colour within a bit, sampling would be used to get the colour that meets your requirements. In Adobe Photoshop, there is a tool that allows you to do this very easily and is very accurate.

Bit depth can either mean the numbers of bits used to show the colour of a single pixel or the number of bits used for each colour component used in a single pixel. Overall, the bit depth counts how many colours are available in a certain image’s colour palette in terms of the number of bits available. The definition of a ‘Bit’ is the basic unit of information in computing and digital communications. To specify how many different bits are used within a pixel, we refer to this as bits per pixel (bpp).

Every pixel in an image is created through a combination of three different colours, red, green and blue (RGB). These colours are generally referred to as colour channels. The bit depth of each primary colour is known as ‘bits per channel’ (bpc).

When using Adobe Photoshop, there are 8bpp, 16bpp and 32bpp to choose from. The majority of digital cameras have 8-bits per channel and therefore they can use a total of 8 bits per pixels. The table below shows how many colours are available with each bit per pixel. As you can see, when using 8 bits per pixel, there are 256 colours available to use which is a large amount to produce a good coloured image (.GIF file format only supports this amount).

However, higher bits per pixel are available such as 16 bits per pixel which is commonly known as ‘high colour’. These colour depths are sometimes used in smaller digital devices such as mobile phones. In 16 bits per pixel, there can be 4 bits for each red, green and blue and then an extra 4 for transparency. Again, as you can see from the table, 65536 colours are available when using 16 bits per pixel (high colour).

There are also 24 and 32 bits per pixel available which are known as ‘true colour’ and there is 16777216 colours available for each. The only difference between 24bpp and 32bpp is that 32bpp also supports transparency. Usually true colour means that there will be 256 shades of each RGB colour resulting in a better quality image. However, the human eye can only identify 10 million colours and therefore using 24 or 32 bits per pixel might be too excessive.

On the lower end of the scale is 1 bit per pixel which is known as ‘monochrome’. This only includes two colours which are generally black and white.

In order select a specific shade of colour within a bit, sampling would be used to get the colour that meets your requirements. In Adobe Photoshop, there is a tool that allows you to do this very easily and is very accurate.