SUCCEED

15 Minutes

Teacher Says:

• "We will be working with GIMP today. GIMP is a program for handling raster graphics."
• "Raster graphics are stored as a grid of pixels."
• "The words "raster" and "bitmap" are usually interchangeable. Some people use "pixmap" to describe a color raster graphic. Generally any graphic that is based off of a grid of pixels is a bitmap."

Draw a grid on a balloon. Blow it up and explain the concept of raster graphics using the balloon:
"When we blow up the balloon, the image gets bigger, but the squares also scale with the size of the image. We can draw new squares on the balloon, but the original image still looks blocky."

"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.

0 minutes

There is no Exploration for this lesson.

0 Minutes

There is no Physical Modeling and Measurement for this lesson.

35 Minutes

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.

Show students:

• How to open the image
• Have them copy the image to a new layer.
• Show them how to use the wand tool to select the background around the blimp (or if you're using a different image, whatever selection tool is appropriate) and have them remove the background.
• Have them duplicate the layer a few times, then show them how to move the layers around and scale them. Remind them that scaling down loses image detail, so there is no going back once you make an image smaller.

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).

15 minutes

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.

• gif - On/off Transparency, accepted by old IE, animation capabilities
• jpg - Intended for photos
• png--alpha transparency, small file size, not animated but maybe in future

optional

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:

• Duplicate a prominent aspect of the photo elsewhere in the image using the clone tool.
• Make a landscape photo look like it was taken at a different time of day (if they need a hint, tell them to use the Curves and Saturation tools)

Optional

Saving For the Web

• Show students how to add guides to the image to divide it into image to use on a web site. Point out that they would have to do this if there was a particular part of the image that they wanted to be clickable (since it's better to slice the image rather than create an image map).
• Have them use the rectangle selection tool to Copy each section in turn, then Paste as New. Show them how to save the image as a jpg.

Retouching

• Have students open a photo that is too dark and/or colored incorrectly, or have them continue to work with the blimp image.
• Show them how to use the Levels tool.
• Explain to them that sometimes an image is heavier in dark colors than light colors, or vice-versa. We often need to adjust for this. The Levels tool allows us to shift the balance between light and dark.
• Show them the Curves tool and explain to them that it is a more advanced version of the Levels tool.