Pixilation and Resolution
Subject Area:
Media and Technology
 
Age or Grade:
6 through 12th
 
Estimated Length:
1-2 days
 
Prerequisite knowledge/skills:     
  1. ✴Subsurface probing activity
  2. ✴Experience with a digital camera or LCD screen (or any digital image forming media)
 
Description of New Content:     
Students explore how pixilation occurs in a simple image
 
students will learn:
  1. ✴less pixilation occurs with a higher pixel density
  2. ✴what the common term "megapixel" means
  3. ✴that a digital image is formed by a matrix of pixels
  4. ✴how light intensities can be discretized to form a gray scale image
  5. ✴that a pixel stores or displays the average intensity of the light across the pixel area
 
Materials Needed:     
  1. ✴pixilation handout
  2. ✴pencils for shading
  3. ✴Pixilation Presentation
 
Procedure
 
Opener:
Discuss with students the outcome of their images and models from the subsurface probing activity. Discuss again the inaccuracies with the images and models. Tell students that we are going to explore one aspect of the cause of the problem.
 
Ask students what figure of merit is used to rate a good quality digital camera. They will have hopefully heard the term "megapixel" used to rate a camera. This figure of merit describes the density of the pixel array used to capture light and store the image - the higher the megapixel, the better the camera. For instance, a 6 megapixel camera has 6 million pixels to capture the image meaning that the picture is broken up into very small chunks of colors and intensities.
 
Have students explain where the have used or seen pixels. Students should realize that a pixel is simply a small element that makes up the part of an image. However, it should be made clear to students that a pixel used to capture or store a fraction of a picture, does not operate in the same way as a pixel used to display an image, but the term pixel is generically interchangeable.
 
Development:
Go through the pixilation handout with students. Use the bucket and ice analogy to explain why a pixel stores or displays the average intensity of light that hits the surface area of the pixel. Make it clear to students that a pixel can only store or display a single color with brightness. This means that a pixel does not know on what part of its surface area it receives, it only cares about the total light received
 
Closure:
Let students finish up the handout for homework. Show the Pixilation Presentation that shows how sampling resolution effects the quality of an image. This presentation shows that the pixel density (pixel size and spacing) govern the quality of the image. This presentation will hopefully show students the major factors that contributed to the pixilated images they made from the subsurface probing activity. From this activity and presentation, students should realize that their images of the mystery object would be most ideal with a very small size probe diameter and taking data at very small step increments.
 
 
Evaluation:
Collect the pixilation handouts and grade. Look out for students who draw a pixel as having stored the actual distribution of the light it sees as opposed to the average amount of light that it sees.