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DLP & MEMS
DLP LightCommander Development Platform
DMD stability concern operating under high frequency
Dear Texas Instruments,I have the following concern when I was conducting my experiments using the DLP light commander.
When I was projecting fringe images using the light commander, I have the setting as 716hz, projecting image using 1024 x 768, 8 bits.I projected a progressive fringe patterns, using the so-called sinusoidal technique; having the darkest part (as black) at the centre and slowly fading away toward both sides (white). Though, when I viewed it with a video camera with resolution of 640x 480, frame rate of 200fps, the projected image seems to be unstable.
Firstly, it shows discontinuity between each projected pixel. Secondly, the centre of the image doesn't seem to be projecting stable dark image; it fluctuates between black and grey. Thirdly, the flickering also occur on suppose-to-be white zones; flickering black lines sometimes occur. Furthermore, instead of being perfectly black right at the centre line, an area around the centre line tend to be in the same colour as the centre line.
I am wondering if this is due to DMD instability when operating under high frequency(716Hz).Regards,Wayne
It is definitely not a "stability" issue with the DMD. I believe that what you are seeing is the result of "beat" frequencies between the camera shutter rate and the DMD subframe rates.
You mention that you are using 8 bit images on the LightCommander. This means that each image is being displayed as a series of 8 subframes of varying duration (to obtain the gray scale). If the camera is running at 200 fps, it will not be synchronized with the total frame rate of 716 Hz, and certainly not with the varying length subframes of each displayed image.
So, what you are seeing is the fact that the camera is seeing a different part of the image sequence every frame. This would lead to the appearance which you are describing.
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