Definition of a Digital Image

An image is a two-dimensional array of values representing light intensity. For the purposes of image processing, the term image refers to a digital image. An image is a function of the light intensity

f(x, y)

where f is the brightness of the point (x, y) and x and y represent the spatial coordinates of a picture element (abbreviated pixel).

By convention, the spatial reference of the pixel with the coordinates (0,0) is located at the top, left corner of the image. Notice in the following image that the value of x increases moving from left to right, and the value of y increases from top to bottom.

In digital image processing, an imaging sensor converts an image into a discrete number of pixels. The imaging sensor assigns each pixel a numeric location and a gray level or color value that specifies the brightness or color of the pixel.