Digital images, bits, bytes and pixels

A digital image is made up from a very large number of squares each of a single colour, these are called pixels. Because there are so many and they are so small we cannot usually make out individual pixels. There are well over 100,000 in this small photograph.

A digital image might have millions of pixels

Even when a part of it is blown up, the individual pixels are hard to see, but if we magnify it further then these pixels become evident. The colour/shade of each of these pixels is transmitted or stored as a binary number.

 

The individual pixels are hard to see

 

 

If the image is enlarged the individual pixels can be seen

 

 

 

 

 

 

 

 

A very simple image, such a black and white monochrome picture will only be one digit, thatʼs called one bit, that is either 1 or 0 recording black or white. A shaded monochrome image may record 16 shades of grey, thats 4 bits. 42 = 16. A colour image is likely to have a least 8 bits, that is 82 = 256 colours.

A binary number of 8 digits, 8 bits, is called a byte. 1 byte = 8 bits The final number is divided by 8 if we want to measure in bytes.

The amount of information recorded in an image, measured in bits, is therefore: no. of pixels x no of bits per pixel. A high quality image will have a large number of pixels so show tiny details and a high number of bits per pixel to give accurate colour and shade.

If you would like to learn more about digital signal processing there are some notes sheets in PDF format which you can download here:

There are two other notes pages here: