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Projecting 8 bit infrared image using Lightcommander

Nikhil Naik
Prodigy 30 points

Hi 
I am trying to project a grayscale image using the Lightcommander in infrared. When I project a linear ramp (from 0 to 255), I see a linear ramp in visible light, but in Infrared, the IR camera sees a binary image (anything >128 is set to 255 and <128 is set to 0).  I am using a solution with 8 bit resolution. 

Please let me know if there is a way to project an 8 bit image in IR. Thanks

  • 0
    TI__Mastermind 30875 points

    Hello Nikhil Naik,

    There is OSRAM's SFH 4750 IR LED on the Kit. As far as DMD and IR LED modulation to generate a 8-bit grayscale image, it is treated same as R G B Visible LEDs.

    Attaching LED characteristics

     

    We have tried using IR channel for capturing grayscale images for three phase structured light decoding algorithm, so although we haven't have measured values for grayscale linearity plot, since we used the algorithm successfully, we can derive that we are able to generate proper grayscale values.

    Few suggestions - 

    1. Check your IR camera sensor capture curve, if it is able to capture around 870nm.

    2. You could also put a detector infront of the kit, and look at the signals on the oscilloscope, you should see a PWM signal in the given frame time. 

    3. Also try increasing the LED current to 100%. Test it in dark to room since the light o/p strength with IR led is considerable less than the other visible LEDs. 

    Regards,
    Sanjeev

  • 0
    Intellectual 590 points

    Whats the exposure time of the camera and whats the frame time of the Ligthcommander (or whatever its called in the setup software)?

    DLPs are doing pulse width modulation. So I am assuming that the exposure time is lower than the frame time. So you only look at 1 bit of the modulation. For a short test increase the exposure time. Does the image change?

    C.

  • 0 in reply to Curtis Newton
    TI__Mastermind 30875 points

    Good point Curtis.

    Regards,
    Sanjeev

  • 0 in reply to Sanjeev
    Prodigy 30 points

    Thanks Curtis and Sanjeev.  My IR camera has a maximum exposure of 2500 microseconds, which I am using.  The minimum "LED Illumination Time (Camera Exposure Time)" that the LightCommander GUI allows me to set is 1368 microseconds. But I still observe different bit planes at this exposure time when I project a ramp from 0 to 255.  Is that correct? Does 1368 microseconds include the integration of all 8 bit planes? 

  • 0 in reply to Curtis Newton
    Prodigy 30 points

    Thanks Curtis. Just copying my post here in direct reply

    My IR camera has a maximum exposure of 2500 microseconds, which I am using.  The minimum "LED Illumination Time (Camera Exposure Time)" that the LightCommander GUI allows me to set is 1368 microseconds. But I still observe different bit planes at this exposure time when I project a ramp from 0 to 255.  Is that correct? Does 1368 microseconds include the integration of all 8 bit planes? 

  • 0 in reply to Nikhil Naik
    TI__Mastermind 30875 points

    Hello Nikhil,

    How you are synchronizing camera with the projector? Have you connected the trigger out (BNC connector) to the Camera?

    Just to get the basic things setup, you can start like 60Hz i.e., 16667us exposure and then go on reducing the exposure time.

    If you are seeing problem with simple 60Hz, 100Hz, 200Hz pattern exposure and trigger rate, then there is something wrong in the configuration or setup.

    We haven't tried IR LED capture at 716Hz frame-rate for 8bit pattern display.

    Regards,

    Sanjeev