Image Representation

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 we 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.


Activity description (PDF)



  • Activity explained at Fujitsu Kids event with JOI, Japan
    Activity explained at Fujitsu Kids event with JOI, Japan

Related Resources

  •  An older version of this activity can be downloaded in PDF format here. The content is similar to the current version, but there’s some extra technical information.



  • Videos:
    • Taha Ben Brahim, Ph.D. candidate in Auburn University’s Department of Computer Science and Software Engineering has programmed this activity using the Textrix robot and RobotC. View the Videos:
    • The PrintBall is a graffiti Robot. It works like a giant Ink-Jet printer using a PaintBall Gun as print-head. The PaintBall gun is mounted on a custom made pan & tilt unit, which is connected to a software programmed with PrintWare 6.0. The pan & tilt is controlled by an Atmel chip [programmed in Basic] allowing the PrintWare 6.0 software to move the two stepper motors and to trigger the PaintBall Gun. The software allows the users to load, analyse and shot images. The resolution of the image can be adjusted according to the number of steps between each points. For videos of PrintBall in action visit the above site.
    • The students at the Fall 2010 Auburn Robo Camp have demonstrated combining this image representation activity with robotics; this video shows a robot decoding a binary image file (using the Textrix robot and RobotC).



Curriculum Links

Great Principles of Computer Science [info]
  • Recollection
ACM K12 Curriculum [info]
  • Level I (Grades K–2) Topic 11: Understand how 0s and 1s can be used to represent information, such as digital images and numbers.
New Zealand Curriculum [info]
  • Mathematics Level 1: Equations and expressions
    • Communicate and explain counting, grouping, and equal-sharing strategies, using words, numbers, and pictures.
  • Mathematics Level 2: Position and orientation
    • Create and use simple maps to show position and direction.
  • Technology Level 1: Technological systems
    • Understand that technological systems have inputs, controlled transformations, and outputs.
  • Technology Level 3: Technological systems
    • Understand that technological systems are represented by symbolic language tools and understand the role played by the “black box” in technological systems.