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DLP 6500 EVM, 8bit greyscale image repetition rate

user4263665
Prodigy 40 points

I am working with the DLP Light Crafter 6500 EVM (v1) and control it with the provided GUI (version 1.1.0). We illuminate the DLP homogeneously with a single LED and image the DLP with a standard projection lens. In the pattern-on-the-fly mode, when I try to display a static, monochromatic 8-bit greyscale image with an exposure setting of 100000us and a darktime setting of 0 in repeated play-mode, I observe non-static images with a CMOS camera chip placed at the image plane using 100ms exposure:

10 observations at ~1Hz acquisition rate with 100ms camera exposure of a gradient image (tiff stack, with 10frames, 520x95 pixels):
gradient_usb_100imgs_exp100ms_substack1-10.tif

According to the specs, the repetition rate of 8bit greyscale images of the DLP 6500 is supposed to be 250Hz, so I would expect the image at an exposure of 100ms to appear almost static. Why do I observe these (rather slow) variations?

Thanks for your help, best,

Stefan

  • 0
    TI__Expert 6370 points

    Hello Stefan,

    I believe the inconsistency you are observing here is caused by the camera integration capturing a partial exposure from the LightCrafter 6500.

    You mentioned that you set the exposure to 100000us (=100ms). If you set this value in the GUI, the exposure will not be for the maximum LightCrafter 6500 speed, 4046us, it will be for 1000000us.  So, both the camera and LightCrafter6500 are exposing at 10 Hz (the LightCrafter 6500 is not exposing at 250Hz).

    In theory, the matched exposure time should mean that the camera should integrate one complete exposure from the LightCrafter 6500, but that cannot be guaranteed. The only way to ensure the exposures happen in a synchronized fashion is to trigger the LightCrafter 6500 off of the camera or vice versa. Our TI Design for 3D scanning with the LightCrafter 6500 covers the process of making a trigger.

    Let me know if you have any other questions or if there is something I can clarify.

    Best regards,

    Trevor

  • 0 in reply to Trevor Dowd
    Prodigy 40 points
    Dear Trevor,

    Thanks for your response. Actually, I have to revise my indications on camera exposure, because I interpreted it wrongly. After double-checking the setting with the camera manual I understood, that in reality it was a camera exposure time of 2ms (setting 100 on our camera corresponds to 100 x 20us = 2ms). So it makes sense that some partial exposures of the greyscale pattern was observed.

    Best wishes,

    Stefan
  • 0 in reply to user4263665
    TI__Expert 6370 points
    Stefan,

    Excellent! Let me know if everything is not working properly now or if you have additional questions.

    Best regards,
    Trevor