Colored Shadow Demo

This video is based on a visual perception demo given by Dr. Zygmunt Pizlo in a graduate psychology class at Purdue University.

The demo illustrated the perception of a green shadow when red and white light sources are mixed (Cornsweet, 1970).

The original demo used two slide projectors as light sources, a red filter, and the professor played the role of object that casted the shadows.

A problem informally posed to the class following the demo was: how to simulate the phenomena on a computer monitor instead of using two projectors.

Since this was a perception problem I was curious about whether or not the green shadow effect would translate after being captured by video. So I set up the prototype scenes you see here to test the effect.

I used only two 40watt light sources at very close range, a 320x240 webcam, some distant ambient light, a too-dark red filter, and an object just a little larger than a Q-Tip. The effect is weak due to the limitations of the source equipment, but the effect did in fact translate.

Setting up the environment took far more time than I expected, and reproducing it would have been a hassle too, so I decided to make the most of the moment by capturing some scenes.

In addition to illustrating the green shadow, I was also interested in the small scale effects of the weak light sources on a small object within the relationship between the white background and the limitations of the camera source.

Also a good experiment to test possibilities in a YouTube context.

tjr
---
Cornsweet TN (1970) Visual perception. New York: Academic.

Category:

Film & Animation

Tags:

• visual
• perception
• josh
• white
• etta
• leadbelly
• coletrain
• miles
• ellington
• james
• brown
• cole
• pizlo
• tjrogers