Color breakup

Color-sequential displays (e.g. DLP projectors) typically show the red, green, and blue components of each frame in time-sequential order. If the frame rate of the display is 60Hz, the image should be updated 180 times per second, including all sub-frames. The visual system fortunately has a finite sensitivity to luminance change, and even lower sensitivity to chromatic variation, so it cannot detect the color change when a still image is presented by color-sequential displays.

However, a moving object can be problematic. Imagine a viewer tracking a bright object moving across a black background. The figure below illustrates such a situation, where the white arrow represents the direction of object movement. The viewer's fixation is moving smoothly over space, but all three sub-frames in a single frame would place the object at the same location on the screen. Consequently, the object gets displaced on the retina by each color components: the red component leads, the green component lags, and the blue component lags even more. This creates thin red and yellow (red + green) lines near the leading edge, and cyan (blue + green) and blue lines near the trailing edge. This is called color breakup, because the image appears to break up by color components.

Color Breakup

To understand the cause of color breakup, we developed a model that predicts the saliency of color breakup. The model is based on the chromatic contrast sensitivity function of the visual system. Using the model, we could predict when color breakup will occur, and find ways to minimize it. With tracking eye-movement, the retinal position of each color component is shifted, which obviously would result in color breakup. But without tracking eye-movement, there is no spatial shift among color components, only a temporal shift. Therefore, it is less obvious how color would appear. However, our model could predict when color breakup is visible or not, regardless of the existence of eye movement. We verified our model through psychophysical experiments.

Collaborator: Paul Johnson [home], Martin Banks

Related article: Johnson, P. V., Kim, J., and Banks, M. S. (2014). Color breakup and the means to reduce it, Journal of Vision (accepted)