Working of an Interactive Graphics Display

Interactive graphics display consists of three components

a) A display controller

b) A digital memory or frame buffer

c) A television monitor

d) A video controller

The display controller gets the inputs and commands from the user and determines the image to be displayed on the monitor. The display controller will divide the image into a number of pixels. This image which is to be displayed is stored in the frame buffer. The image will be stored as a matrix of intensity values.

The image will be displayed onto the television monitor and the video controller will act as a simple interface that passes the contents of the frame buffer to the monitor. The image must be repeatedly passed to the monitor, 30 or more times a second. This helps you to maintain a steady picture on the screen.

In the frame buffer the image is stored as a pattern of binary digital numbers. These binary digital numbers represents a rectangular array of picture elements or pixels (a picture can be divided into a number of picture elements or pixels. You will learn more about pixels in the coming lectures.).

So corresponding to each pixel you have a binary digital number in the frame buffer. If your image is a black and white image you can represent the black pixels by 0 s and white pixels by 1s. Therefore a 16 X 16 array of black and white pixels could be represented by the binary values stored in the 32 8-bit bytes. Now what happens to this data?

The video controller simply reads each successive byte of data from the frame buffer and converts its 0s and 1s into the corresponding video signal. This signal is then fed into the TV monitor, producing a black and white pattern on the screen. The video controller repeats this operation 30 times a second in order to maintain a steady picture on the TV screen.

Now what should be done to change or modify this image?

All we need is to modify the frame buffers contents. Set the frame buffer with a new set of values so that it represents the new image. In this way we can achieve effects like a rotating wheel and a wheel that grows and shrinks.

The figure given below gives an idea about the graphics display system