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DLPC3478: Something wrong when using dlpc3478 project gray-scale gradient pattern

gy qi
Prodigy 40 points
Part Number: DLPC3478

We are using dlpc3478 project gray-scale gradient pattern and using a camera sample the pattern.

But the frame we gain have some vertical stripes. 

The following two diagrams are the original and the camera sampling diagram.

Does anyone konw what the problem is?

What should we do to fix the problem?

  • 0
    TI__Expert 5485 points

    Hi Gy,

    Which pattern mode are you using to project this pattern: external, internal or splash pattern mode?

    Which trigger signal are you using to sync DLPC3478 with camera, if any?

    Is the pattern visible as expected to the naked eye? What exposure time have you specified for this pattern? Is this exposure time close to the camera's exposure time?

    Regards

    Azad

  • 0 in reply to Azad
    Prodigy 40 points

    Hi Azad,

    I use the extenal video port mode.

    I have tried trigger 1 or trigger 2.And I also use FPGA to generate a signal to trigger the camera.

    But the problem is not fix.

    The pattern projected is correct with naked eye.

    I config the dlpc3478 exposure like this.

    illumination time:11000

    preillumination time:1400

    postillumination time: 100

    The camera exposure time is fixed 8ms.

    The dlpc3478 is project at 60fps.

    Is the dlpc3478's exposure time must be close to the camera's exposure time?

    Thanks

  • 0 in reply to gy qi
    TI__Expert 5485 points

    Hi Gy,

    Yes, the camera exposure time should be such that it covers the whole of the projector's illumination time. This is because 8-bit grayscale patterns are projected as 8 separate bitplanes in a time-sequential manner, so if the camera's exposure time is less than the illumination time then the complete pattern may not be captured.

    For your case with a fixed camera exposure time of 8ms you can reduce the illumination time to <=8ms and use Trigger Out 2 to capture the patterns.

    Please try this out and let us know if the problem is resolved.

    Regards

    Azad

  • 0 in reply to Azad
    Prodigy 40 points

    Hi Azad,

    I have tried to make projector illumination time less than camera exposure time.

    The issue has improved but still exist.

    What kind of mode should I use in this case?

    And is there anything else to configure?

    Regards

  • 0 in reply to gy qi
    TI__Expert 5485 points

    Hi Gy,

    Ensure that the camera exposure covers the entire illumination period, sometimes this may not be the case due to pre-/post-dark times. 

    In case you plan to use 1D patterns only, you can also try internal pattern mode.

    Regards

    Azad

  • 0 in reply to Azad
    Prodigy 40 points

    Hi Azad,

    OK,I'll try the internal pattern mode.

    And I discover the projective images is not correct with the naked eye.

    It is also have some vertical stripe.

    Regards