Image Representation

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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.

  • Posing
Videos 
Photos 
  • Mr. Idosaka explains the concept at Fujitsu Kids event with JOI, Japan

    Mr. Idosaka explains the concept at Fujitsu Kids event with JOI, Japan

  • Activity explained at Fujitsu Kids event with JOI, Japan

    Activity explained at Fujitsu Kids event with JOI, Japan

  • Image Representation

    Examples of worksheets from Susumu Kanmune

  • Kids' attempts at Fujitsu Kids event with JOI, Japan

    Kids' attempts at Fujitsu Kids event with JOI, Japan

Extension 
Other 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.

  • Wikipedia has useful articles on fax, run-length encoding and pixels

  • The Mathmaniacs website has a similar activity (lesson 3)

  • How Stuff Works: Fax Machine

  • Brian Myers from the University of Cincinnati has a related activity in Image Processing and Computer Vision called Healthcare Imaging where students explore x-rays by comparing them to light rays, and then explore how to create 3D images using CT imaging. This activity was developed for high school students.

  • Wikipedia: Flatland : A Romance of Many Dimensions is an 1884 satirical novella by the English schoolmaster Edwin Abbott. Writing pseudonymously as "a square", Abbott used the fictional two-dimensional world of Flatland to offer pointed observations on the social hierarchy of Victorian culture. However, the novella's more enduring contribution is its examination of dimensions; in a foreword to one of the many publications of the novella, noted science writer Isaac Asimov described Flatland as "The best introduction one can find into the manner of perceiving dimensions." As such, the novella is still popular amongst mathematics, physics, and computer science students. For some exciting resources on the movie, please visit the following sites:

  • 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.

  • stackoverflow has an interesting article called Twitter image encoding challenge which is worth a read about "...how their ideas about encoding can lead to more detail in the limited space that you have available"

  • Hobart and William Smith Colleges has the Data Representation Applet which is a small applet that shows how the same 32 bits stored in the memory of a computer can represent different things, depending on how they are interpreted.

  • SCIENCE BUDDIES offer the following activities:

  • TEACH Engineering has the following K-12 resources in image representation:

    • How Do You Store All This Data? allows students to start seeing the data structure they will use to store their images. Students will be introduced to two dimensional arrays and vector classes. Students will be guided to see that a vector class will be the most efficient way of storing the data for their images.
    • What Makes Up A Colour? helps students learn why image colour becomes important as we distort the outer boundaries of an image and have to interpolate pixels to fill in gaps created from our algorithm. Students learn what a digital image is, what pixels are, and learn to convert between RGB and hexadecimal values.
    • RGB to Hex Conversion Activity where students practice converting between RGB and hexadecimal (hex) formats. They learn about mixing primary colours in order to get the full spectrum of colours, and they learn how to average pixel values.
  • 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).

  • Wolfram Demonstrations Project has the following demonstration activities. Note: You will need to install the Wolfram CDF Player in order to use these activities. You can either download each demonstration or use your browser to run it.

    • Binary Run-Length Encoding which splits data into runs of zeros and ones. A list of binary distinctions can then be encoded as a list of run-lengths
  • Neuro Productions has Alice in Wonderland (the Bitmap) which is the full story, 12 chapters, more than 25000 words, all are crammed in one Bitmap!

  • Dane Court Computing has good class notes in Bitmaps and Vectors covering Run Length Encoding

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