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DLP4500: Linear response of camera to projector

John Traynor
Intellectual 885 points
Part Number: DLP4500


hi guys,

A couple of questions all related to each other that I hope you can help with

  • Could you tell me how to check if a 4500 projector and Mono camera have a linear gray value response? (basically plot  input intensity to output intensity of the camera and projector)
  • Can the internal test patterns on the 4500 be used to plot this? (Horizontal ramp?) If not what should be used and how should it be created?
  • Do the light output values make a difference for this test (i,e, should we set Red to 128 or 255 or something different?)
  • What color should be used? (Red, Green, blue, or White - if white what mix of RGB should be used?)

Thanks

john

  • 0
    TI__Mastermind 20045 points
    Hello John,

    I believe if you are using a mono camera you could use any color you want (mono illumination or all of the RGBs at once to make white). The camera may have different sensitivity to different colors but I would check the manual of your camera.

    You could use the ramp test pattern to test. Alternatively, I would recommend you create your own test pattern with a custom set of bitplane sequences to precisely control what you are projecting.

    Thanks,
    Kyle
  • 0 in reply to Kyle Rakos
    Intellectual 885 points
    Hi Kyle,

    Thanks for the speedy reply

    We did try to use the horizontal ramp pattern and when we plot the graph, it is not linear. We also created our own patterns and they are not linear.

    When we check the camera linearity against a gray level ramp on a sheet of paper, while being illuminated with the projector with a solid white color, it is linear. So is there something in the projector settings / config that would stop it outputting a linear response. As far as I know no gamma correction is applied so I'm looking for advice on what it could be? How could I possibly debug a problem like this?

    Thanks

    John
  • 0 in reply to John Traynor
    TI__Mastermind 20045 points
    Hello John,

    Could you confirm how you are displaying the patterns? If you are displaying a test pattern in display mode it will not be using a linear gamma curve. You will want to use the pattern mode (where you create your own bitplanes). This mode uses linear gamma and will display the pixels without any processing from the input.

    Thanks,
    Kyle
  • 0 in reply to Kyle Rakos
    Intellectual 885 points

    Hi Kyle,

    Ahh- I'd say that is the issue. I thought there was no gamma correction applied to internal patterns. We'll give that a go and let you know how we get on.

    Thanks

    John

  • 0 in reply to John Traynor
    TI__Genius 10925 points
    Hi John, do you still need the answer to your question? I will be tentatively closing this thread due to inactivity, you can reopen anytime.

    Thanks & Regards,
    HIrak.