

Google Earth Distortion

Artist Clement Valla posted a collection of distorted bridges gleaned from Google Earth. What happened here? Google Earth images are made from satellite pictures overlaid onto a 3D map of the terrain. The photographic images show bridges as they appear, but they don't fit over the terrain map, as they don't follow the terrain (if they did, they wouldn't be bridges). The software used to combine the photographs and the terrain map doesn't know the difference between a bridge and a road, and just lays the image down where the earth is.

Rolling Shutter Effect

Luke Mandle took this picture of his son with a digital camera. Notice that the child blinked when the picture was snapped. But... his reflection on the right of the picture show his eyes open! How did that happen?

A modern digital camera takes pictures by scanning from one side of the frame to the other (or top to bottom, depending on how you hold the camera). For most applications, that's fine. However, when objects move faster than the scanner, you get what is called the rolling shutter effect.

You see this same effect in a video of a moving propeller, taken with a scanning digital camera. The video below explains visually (and slowly) how the scanner cannot keep up with the speed of the propeller blades. Image by Flickr user Jason Mullins.


Even still scenes can be affected by the rolling shutter effect, if the movement is in the camera itself. If you want to do this on purpose, Wired has a tutorial.

This is an example of the rolling shutter effect done on purpose by moving the camera while shooting the picture. Image by Flickr user Matt Vinyl.

Stroboscopic Effect

You've noticed spoke-wheeled wagons in old films that appear to go backwards as the vehicle moves forward. When the movement of the wheel spoke (or in this case, propeller rotation) synchronizes with the frame rate, the rotation is seen as static, or moving in the other direction. This video was taken with a very short shutter speed, which kept the blades from blurring, and a frame rate that synchronized with the blade motion. Unless you can vary the frame rate while using the camera (which you can't), capturing this effect is purely by chance. Frame rates vary depending on the format, from 14 to 60 frames per second. A frame rate of 72 images per second is in the experimental phase. Converting motion pictures from one rate to another causes another set of problems.

The Moire Effect

A few days ago, I was watching a Three Stooges short from the 1930s. Larry Fine wore a striped shirt. The entire movie was in black and white, but Larry's shirt threw colors onto the TV screen like a prism. I've been told to never wear a striped shirt to a TV appearance, but there was no such restriction when filming with black and white analog film in the 1930s. Television is different. TV uses a raster scan, in which images are broadcast or relayed digitally by scanning lines from left to right and top to bottom. Each full scan is a frame of film or video. Movement in a striped pattern during a scan can cause a Moire effect, which you can manipulate on this page. The shirt you see was taken from a video illustrating the effect.

Encoding, recording, or broadcasting from one type of image capture to another can produce weird effects. Take an old movie recorded on analog film, or a TV show recorded with both color and black and white encoding, or encoded images from a different system (such as the European PAL system), and send it to a modern digital color TV, and you will see some weird effects, like the image above, which is an artifact of PAL decoding. As digital signals are more and more compressed to carry more information, there are trade offs in the ability to render older systems accurately.