Images in computer are stored as digital values. Here the basic process of obtaining image and representing them as digital values in computers is explained.

A camera is the first basic and widely used device to take a picture. In the past the images were stored as analog signals on a film. Nowadays, digital camera, computer camera and mobile camera have replaced the analog camera. With digital camera the pictures taken are stored as digital signals values inside the camera memory. An image is a 2D function f(x,y) where x and y are spatial coordinates. The amplitude of f(x,y) at any point (x,y) is called intensity. The image can black and white or it can be colored. When the image is black and white the image is said to be gray level or monochrome image. If the image is colored then the image is called RGB image, where R means read, G means green and B means blue.

An image is in continuous analog form before the picture via the camera is taken. It is the digitizer within the camera(or computer) that converts the continuous analog image signal to digital form. The digitizer receives the analog signal performs sampling and quantification. Then the quantized samples are given coordinate values x and y. The origin is usually taken to be (0,0). The next is (0,1) and goes along the first row upto (0,N). The next row is filled starting from (1,0) upto (1,N). This keeps repeating until (M,N) is reached. Thus what we end up with is a MxN matrix. M is the number of rows and N is the number of column. Each point of the digitized/quantized value f(x,y) is called pixel.

The coordinate system with pixel at some point is shown below.

How images are represented in Computer

By using such coordinate system the image can be stored as matrix in a computer. Representing an image as matrix also facilates in doing image processing in CAD such as matlab software. For more detailed information you should read the digital image processing using matlab by gonzalez pdf.

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