Week 11: Homework 4 - Depth Perception

This week you'll use applications contained in the "StereoStuff" folder in the Honors 185 folder in the Electronic Classroom. For these exercises you'll need a pair of red/green glasses (called "anaglyphs") for viewing the video monitor. They will be distributed in class on Tuesday. Before you get started, be aware that there are some really nice webpages on stereopsis, with super demonstrations and tutorials. You can see an index of those sites by navigating to this site and then selecting the "Stereograms" option.

Ready to start? First: change the colors to 256 using the application in the folder ("Set to 256 color mode"). Log-in and copy that folder to the local workspace of your computer (this exercise must be done in the EC).

1. Stereograms. Open the application called "Stereograms" and click on the "Begin" button. This will bring up a blank screen with menu options. Start simply by looking at some of the "picure" stereograms under the Pictures menu. Select each of the options and look at them using the red/green glasses - to start be sure the glasses are viewed with the green lens in front of your left eye, red in front of the right. (You should also try reversing the glasses - green/right; red/left - just to see what happens.) When you get to the picture called "Tilted Sinewave" you'll need to specify the magnitude of the "difference" between the two pictures. The default is set to 0.40, but you should start with 0.10. You should see the grating slanting in depth, with the righthand side tilted away from you (that's with the green lens of the glasses in front of the left eye). Now systematically increase the "slant" in steps of 0.05 :

• what happens as the percentage difference increases?
• at what percentage difference does the depth effect breakdown (meaning that the right-hand edge no longer looks slanted away from you)?
• what happens when you view with the green lens in front of your right eye?

2. Next try the "cube" under the "Outlines" menu. For this exercise, you'll vary the "pixel disparity" between the two eyes' views. Start with the disparity at 0 and work your way up in steps of 5 pixels.get instructions about details of using this file and changing variables. For this exercise position your head approximately 12 " from the video screen.

• what happens as you increase the pixel disparity?
• what is the largest disparity at which you can still see good depth?
• set the disparity to 20 and, holding that constant, compare what you see when the cube is viewed from 12" vs from 24" (double your viewing distance)
• try the same set of exercises with one of the other figures

3. Next select go to the Random Dots menu item and select "Square". Set the dot density to 98 (the default value), the pixel disparity to 5 and the object size (which is cued in the window that appears after you do density and disparity) to 100.

• when viewed from about 12" with green in front of the left eye, what do you see? what happens when you reverse the glasses?
• increase the disparity in steps of 10 to discover the value at which the stereo depth effect is abolished
• repeat steps 1 and 2 with a dot density of 50.
• now select "Sinewave" under the Random Dots menu and again specify a dot density of 98. For this stimulus you are to discover the largest dot disparity that gives rise to a sense of depth for sinewave frequencies of 1, 5 and 10. Use the 12" viewing distance.
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4. Quit the application, double click on the "Stereopsis and Depth" application, read the "information" section to get instructioins for operating the software, then test yourself by clicking on "Begin". When you've finished both the crossed and uncrossed disparity tests, select "Results" to see the data and print the graph.

5. Quit this application and open the one called 3D Dots 1.1. This program allows you to create "magic eye" type stereo-pictures. It also contains a nice explanation of how they're made and how they're to be viewed. After teaching yourself how to use the software, create your own, original stereogram (be creative!), save it using your last name as part of the file name, and once you've quit copy it to the homework folder. I will select one or two of the creations to post on the web.

Your answers and data for all these questions should be turned in by the end of the week (Friday March 26).