Hello,
I am trying to use Matlab's Psychtoolbox to control the Lightcrafter 4500 in Pattern Sequence Mode (pattern source: video port). Specifically, the pattern sequence is 3 6-bit patterns (one using G0-G5, one using R0-R5, and one using B0-B5), each driving the blue LED, so I can present 3 different 6-bit images during one frame. However, I find that the actual light intensity displayed and the RGB values I generate with Psychtoolbox don't correspond in an understandable way. That is, I've tried each possible set of 6 bits, but I still can't get the Lightcrafter to present brighter pixels as the value I feed in increases. White and black are fine, but the mapping in between is sometimes brighter and sometimes dimmer. This happens even when I use only one 6-bit pattern or one 8-bit pattern. However, if I'm in video mode, the presentation behaves appropriately, monotonically increasing in brightness as the RGB values increase.
My goal is to have a linear relationship between input values and light intensity of the blue LED in 6-bit mode. I assumed I would have to gamma correct, but currently, the relationship between input values and light intensity is not such a function.
I'm using a photodiode to measure light intensity and averaging over the intensities during a 1-second period to get the light intensity at each input value. However, the issue I'm seeing is obvious even without that. If I present an image that is a smooth gradient (either grayscale or one color) from black to white, I see a smooth gradient in video mode but a pattern that is sometimes brighter and sometimes darker in pattern sequence mode.
An explanation about how to relate RGB values sent through the video port to output light intensities in pattern sequence mode would be much appreciated.
Thanks,
Helen
