Image Representation - Colour by Numbers

Images are everywhere on computers. Some are obvious, like photos on web pages and icons on buttons, but others are more subtle: a font is really a collection of images of characters, and a fax machines is really a computer that is good at scanning and printing.

This activity explores how images are displayed, based on the pixel as a building block. In particular, the great quantity of data in an image means that we need to use compression to be able to store and transmit it efficiently. The compression method used in this activity is based on the one used in fax machines, for black and white images.

Although the main activity is based on coloring a few dozen black pixels with a pencil, in live shows wen like to demonstrate it on a larger scale. One way to do this is to use a can of black spray paint and a square stencil to make a giant picture pixel-by-pixel. Another is to process a photograph of (say) a teacher to the kidfax code, and have a whole class decode the mystery photo.