In MATLAB, a grey$-$scale image is stored a a matrix of numbers, all between $0($black$)$ and $255($white$).$ Since there are $256$ possible values, $8$ bits are needed or each pixel, in contrast to a normal integer, which is $64$ bits.To save memory, grey$-$scale images are stored with a special data type, uint$8($unsigned $8-$bit integer$).$ In computer terminology, $8$ bits $=1$ byte.