Digital Images. Activity J7. Tips and Suggestions. What s This Activity About? What Will Students Do? What Will Students Learn? Concepts.

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1 J7 Digital Images Activity J7 Grade Level: 7 2 Source: This activity was written by Tim Slater and Jeff Adams, who were part of the Conceptual Astronomy and Physics Education Research (CAPER) Team at Montana State University. It is 996 by Tim Slater and Jeff Adams. Permission is hereby granted to use this activity for any instructional purpose. However, reprinting the activity or selling it requires permission from the authors, at: timslaterwyo@ gmail.com; adams@physics.montana.edu. What s This Activity About? In our computer age, the term digital has become part of our everyday vocabulary. Whether we are dealing with a digitally recorded piece of music, or a digitized image, the idea is that information can be converted into numbers (digits) for easy transmission and storage. Images from astronomical satellites, such as the Yohkoh solar probe or the Hubble Space Telescope, are sent back to ground stations in digital form. Here students explore the basics of digital images. What Will Students Do? Students first create a digital image of their name. They then create a mystery picture on graph paper, which they must instruct other students to reproduce without showing it to them. Finally, they work on constructing a four-color digital image of the Sun from satellite data, and debrief on how the process worked and how it might have been speeded up. Tips and Suggestions A web version of this activity can be found at btc.montana.edu/ceres/html/pixel/pixel.html with more details, other examples, and links to the software mentioned in the activity. You can extend the discussion by having students read the article on the Meaning of Color in Hubble Images on the Hubble Space Telescope web site: meaning_of_color/index.php What Will Students Learn? Concepts Digital images Pixel Resolution File or data compression Telemetry Inquiry Skills Observing Recording Communicating Big Ideas Structure Patterns of change Page

2 Digital Images by Tim Slater and Jeff Adams (Montana State University) Students will learn about digital images and how satellites orbiting the Earth send information and pictures to us from space. Objectives By completing this activity, students will: observe magnified digital images use graph paper to create digital information create an information transfer protocol design encrypted messages or pictures decode a satellite image from space as a team discuss ways to improve digital image resolution and information exchange Materials Pixel Images handout (included) Rectangular graph paper, grey pencils, and black markers (or crayons) Four encrypted digital images from the Yohkoh satellite (included) Procedure Activity : Exploring Digital Encoding Ask students what a television image looks like if you sit really close to the screen. Distribute the handout Digital Images: The Effect of Pixel Size (found on pg. 9) to show that an electronic picture is composed of little squares, called picture elements or pixels. Normally, the pixels are too small for our eyes to detect and so the image looks smooth. Have students create an image of their name by blacking-out individual squares on rectangular graph paper. There should be no shading or half-squares colored in. First color in the squares; second, add numbers to identify colors. Provide students an example, such as the one shown below or on the next page. Two-Color Image ( = White; = Black) (rows are horizontal and columns are vertical) Page 2

3 Activity 2: Introducing Binary Encoding Computers often record and transfer information using a series of ones () and zeros (). This is called a binary system. For the images that students created, a computer would often record each box or picture element (pixel) with a zero () for white and a one () for black. Activity 3: Application to NASA Images Satellites send images from space to Earth by radio waves using a series of ones and zeros. In this activity students will decode an actual image from the Yohkoh satellite (for more information go to montana.edu/ypop). The process of sending data from a telescope to the Internet is called telemetry. Four Color Key Have students create a mystery word or mystery picture on graph paper and tell fellow students how to recreate the picture without showing the picture. Call white squares zero and black squares one. Suggest to students that they start in the upper left hand corner of the paper and read numbers (ones and zeros) all the way across the page to the end of the line, then go back to the left side and read the second row. Students should also think about ways to speed up the process of telling someone how to create the picture. (When scientists create ways to speed up the process, it is called file compression.) Zero = white One = gray pencil (light) Two = gray pencil (dark) Three = black marker Divide students into four or eight NASA imaging teams. Each team needs one of the four included data sheets, a sheet of graph paper, a black marker, and a gray pencil. Important: Students should read across rows, one row at a time. Encourage students to figure out ways to make the process go faster, but keep in mind it is very important to be as accurate as possible. Overlay the teams images as shown below with no gaps in the data. These four quadrants should combine to create an actual image of our Sun taken by the x-ray telescope on board the NASA and Japanese Yohkoh satellite. The black spots show the most active regions of our Sun, which generate x-rays. These energetic regions are places where sunspots can often be observed and where the particles are released that are responsible for creating the Northern Lights. Team Two Team One Team Three Team Four Page 3

4 Debriefing Digital images are recorded and transferred as pixels. A pixel is small element of the image that is a single color. The more pixels that are used, the better or more clear the image is (this is often referred to as resolution). However, the more pixels that are used to create an image, the more memory is required to receive or store it. Some images found on the Internet are 256 pixels long by 256 pixels wide, while many satellite images are 52 pixels long by 52 pixels wide. How many pixels are there in an Internet image? (256 x 256 = 65,536 pixels) How many pixels are there in a satellite image? (52 x 52 = 262,44) How long would it take you to read that many data points over the telephone at the rate of one per second? (262,44 seconds is more than 3 days working 24 hours a day non-stop.) This is one reason that scientists must work in teams to split up the work so the final product can be finished faster. NASA scientists are always trying to figure out ways to increase the speed at which digital information can be converted into pictures. Hopefully, your students were able to come up with strategies to increase the speed of the process. Have your students share these data compression routines. Enhancement If you have access to a computer as well as a document scanner or a digital camera, students can investigate electronic images of their own creation. Investigate the software program that came with your scanner and/or digital camera. These programs will often let you invert pixels, change the number of colors allowed, and even morph pictures to change their shape. These are powerful programs that users often forget they own. Also, any digital image from the Internet, scanner, or camera can be converted to a grid of pixels. If necessary, use a graphic converter program (such as GraphicConverter for Mac or PaintShopPro for PC) to convert the image to PICT or TIFF format. Open the file using an image-processing program (NIH Image for Mac or Scion ImagePC for PC) and export the file as TEXT. Then the file can be opened in a spreadsheet program such as MS Excel. Alternatively, any grid of numbers can be drawn in MS Excel by plotting a 3-D surface plot or by saving the data as TEXT and importing the data into your image processing program. Page 4

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9 DIGITAL IMAGES: THE EFFECT OF PIXEL SIZE Page 9