Setting a Pixel

Initial Task: Turning on a pixel (loading the frame buffer/bit-map). Assume the simplest case, i.e., an 8-bit, non-interlaced graphics system. Then each byte in the frame buffer corresponds to a pixel in the output dispaly.

To find the address of a particular pixel (X,Y) we use the following formula:

addr(X, Y) = addr(0,0) + Y rows * (Xm + 1) + X (all in bytes)

addr(X,Y) = the memory address of pixel (X,Y)
addr(0,0) = the memory address of the initial pixel (0,0)
Number of rows = number of raster lines.
Number of columns = number of pixels/raster line.

Example:

For a system with 640 480 pixel resolution, find the address of pixel X = 340, Y = 150

addr(340, 150) = addr(0,0) + 150 * 640 (bytes/row) + 340
= base + 96,340 is the byte location

Graphics system usually have a command such as set_pixel (x, y) where x, y are integers.

 

Output Primitives menu
HyperGraph Table of Contents.
HyperGraph Home page.

Last changed May 13, 1998, G. Scott Owen, owen@siggraph.org