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Due: &image-mosaics-due; Summary: In this assignment, you will use the basic pixel-manipulation techniques to create simple color mosaics from source images. Purposes: To give you more experience working with the basic pixel operations in the GIMP. To help you think about colors. To encourage you to build non-representational images. Expected Time: Two hours. Collaboration: We would prefer that you work in groups of size three. However, you may work alone, in a group of size two, or a group of size four. You may discuss this assignment and possible solutions with anyone you wish. If you discuss this assignment with people other than group members, make sure to include a citation (e.g., I consulted this person, who helped me do this). Submitting: Email your answer to &profemail;. The title of your email should have the form &image-mosaics-subject; and should contain your answers to all parts of the assignment. Scheme code should be in the body of the message. Warning: So that this assignment is a learning experience for everyone, we may spend class time publicly critiquing your work.

You now know a few simple techniques for dealing with raster graphics and the pixels through which we can describe raster images. In particular, you can load an image with image-load, create a new image with image-new, get the value of a pixel at a particular location with image-get-pixel, set the value of a pixel at a particular location with image-set-pixel!, and determine the width and height of an image with image-width and image-height. What can you do with this simple suite of procedures? One potentially interesting activity is to build new, simple, images from existing images. For example, you can take a small selection of pixels from one image and use those to build a new image- Such created images are a form of algorithmic images, images created by algorithm, rather than by hand.

a. Write a procedure, (image-mosaic-1 "image-file"), that builds and returns a new 4x4 image, each of whose pixels is taken from the image stored in "image-file". Which pixels should you choose? It is up to you. One natural technique is to divide the original image into sixteen portions, and take the middle pixel in each quadrant. b. Pick at least three images and generate mosaic images from them. Identify one that you find particularly appealing. c. If we're going to divide the image into sixteen quadrants, it might make sense to let the client specify where in each quadrant to grab the pixel. Write a procedure, (image-mosaic-2 "image-file" hoff voff), that divides the given image into a 4x4 grid and then builds and returns a new 4x4 image, each of whose pixels is taken from the pixel offset by hoff and voff from the top-left corner of the corresponding part of the grid. For example, supose our image is 100x200. All segments of the grid will have width 25 and height 50. One segment of the grid will start at (0,0), another at (25,0), another at (50,0), another at (75,0), another at (0,50), another at (25,50), and so on and so forth. If hoff is 3 and voff is 7, then the pixel we take from the segment starting at (25,50) would be at (28,57).

We will primarily look to see if you've tried something creative in choosing the pixels. We will also consider whether the algorithm you've come up with does anything interesting with typical pictures (whatever those are).

Please submit this work via email. The email should be titled &image-mosaics-subject; and should contain your answers to all parts of this assignment. Please include your Scheme work as the body of an email message. Attach one source image and the corresponding result image.