An image can be defined as a 2D signal that varies over the spatial coordinates x and y and can be written mathematically a f(x,y).

In general, the image can be written as a mathematical function f(x,y) as a matrix of values, comprising of rows and columns.

The image f(x,y) is divided into X rows and Y columns. Thus, the coordinate ranges are x = {0, 1,......, X-1} and y = {0, 1,......, Y-1}.

The value of the function f(x,y) at every point indexed by a row and a column is called the gray value or intensity of the image. Generally, the value of the pixel is the intensity value of the image at that point.

The number of rows in the digital image is called vertical resolution. The number of columns in the digital image is called horizontal resolution. The number of rows and columns describes the dimensions of the image.

The number of bits necessary to encode the pixel value is called bit depth.

The set of all colors that can be represented by the bit depth is called the gamut or palette.

So, the total number of bits necessary to represent the image is equal to Number of rows x Number of columns x Bit depth.