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DLP4500: Issue with not completely black screen in video mode

Romain Strady
Prodigy 30 points
Part Number: DLP4500

Hello, I am currently working with a LightCrafter, and I encountered an issue when using the video mode, because, when using HDMI input source, and displaying a black screen (all pixels are set to zero using python in a tkinter window) there is still light projected, I can clearly see a lighter rectangle detaching itself from the projection surface. This problem also happens with an image uploaded to the flash memory, even though I also checked that the background pixels of my image are really set to zero in the RGB matrix. Finally, even with the internal test pattern input source, when setting the foreground and background color to be zero for red, green and blue, I can still see the frame. The problem is worse when using HDMI than when using internal test pattern or flash memory image as input source, so I think there might be an additional problem when using HDMI. From what I gathered, HDMI is quite notorious for this not completely black screen thing. I would like to know if there is any way to solve these issues.

Respectfully

Romain

  • 0
    TI__Expert 7080 points

    Hello Romain,

    In the GUI you can try setting the LED Driver current at the top right to all 0's. 

    Thanks,

    Alex Chan

  • 0 in reply to Alexander Chan
    Prodigy 30 points

    Hello Alexander, this indeed provides a complete black screen, however that does not solve my problem, as I still want something to be displayed, for example the image I send attached, with the right dimensions of course, with only the area around my shape being completely black, and the shape itself being properly displayed.

    Regards 

    Romain

  • 0 in reply to Romain Strady
    TI__Expert 7080 points

    Hello Romain,

    There are many factors that can play a part in how the black content looks. Every projector is going to have black levels and also contrast based on the f-number of the aperture. It also can vary or depend on what surface you are projecting onto and ambient light.  

    Even with an all black test pattern, the LED driver control is still on so there is going to be some light.

    Alternatively, what black are you testing with hdmi? I do not see much difference between black internal test pattern vs hdmi on my system in the lab. 

    One test I would recommend is using powerpoint and fill background color and ensure you are using a color with r,g,b set to all 0's to represent actual black as a random image from the internet with black in it may not be actual black or I am not sure what content you are trying to display through hdmi. 

    Do you have access to a photodetector? You can use one and connect with an oscilloscope to double check waveform behavior between hdmi and internal test pattern. I did not notice any varying waveform activity between hdmi with all black screen from powerpoint and the all black internal test pattern. I left the LED driver values alone during testing and did not set them to 0. 

    Regards,

    Alex Chan