How many color shades the maximum can be obtained if you encode the color of each point of the bitmap with two bits.

To encode a color with two bits means to allocate two bits for each code, i.e. two characters in binary notation.
The codes will be as follows: 00, 01, 10, 11. There can be no others. This means that 4 color shades can be encoded in this way.
In this problem, the formula N = 2 ^ i is also applicable, where i is the number of bits allocated for 1 color, and N is the number of colors obtained.