This lesson introduces students to GIMP and the concept of raster graphics. It covers basic image manipulation concepts, filters, and saving for the web.
Basic knowledge of computers.
Have a basic to advanced understanding of GIMP or a similar graphics editing program. If you are not familiar with GIMP, but have used other raster programs, spend an hour or so trying out the different features in GIMP. Pay special attention to the concept of pasting a new layer (anchoring the image is unique to GIMP), and if in OS X, the necessity to click a tool twice to select it rather than just once (once to select the tools window, once to select the tool itself). Also have the balloon with the grid ready before the lesson.
Keep food and drinks away from the computers.
Draw a grid on a balloon. Blow it up and explain the concept of raster graphics using the balloon:
"Raster graphics are similar. When we scale a raster graphic, the squares that make up the image are also scaled, creating what we call a 'pixelated' look. Note that if you deflate the balloon a little, it doesn't look nearly as bad as if you inflate the balloon."
Tell the students that this is the same with raster graphics. If you make the image smaller, the image still looks good, but if you make the image bigger, it is trying to "guess" what the image should look like by inferring from nearby pixels.
Hand out the GIMP cheat sheet (Download File) to students. Briefly go over the different tools in GIMP, focusing on the Select and Drawing tools. Give students a brief period of time to try those specific tools out, just so they have an idea of what they do when you explain it in-depth to them later.
There is no Exploration for this lesson.
Physical Modeling and Measurement
There is no Physical Modeling and Measurement for this lesson.
Layers (20 minutes)
For this activity, you may use the provided image of a blimp, or use your own photo. Just make sure the entire class is following along with the same photo.
Now have them create a new layer beneath the blimps and show them how to use the paintbrush tool to create clouds onto the background. Go through the different blending options and explain their purpose.
Have them save the file frequently (use XCF format).
Saving for Web Go over the different types of images used on the web, namely jpg, gif, and png. Tell them the benefits of each and discuss as a class what situations you would use each image type for.
If there is extra time before the break or at the end of class, you may choose to use the following activity:
Give students a few images to choose from that are too dark, have scratches, or need similar repairs to be made. Give them the opportunity to make the repairs, then challenge them to use some of the other tools they have learned so far.
Some examples are:
Saving For the Web