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DLP6500FYE: The gray scale of projection is nonlinear

ke zhang
Prodigy 10 points
Part Number: DLP6500FYE
Other Parts Discussed in Thread: DLPC900

Hi everyone,

I am experimenting with SLM composed of DLP6500+DLPC900.Recently,I tried to perform grayscale calibration.I made a monochrome grayscale map of 0-255, and projected one sheet at a time.


1. I use a reflective DMD + external LED parallel light source, and the gray scale is discontinuous during projection, they change in steps. A typical point is that there must be a jump at 128bit, and linear changes cannot be achieved.
The camera exposure time is about 4ms, the projection exposure time is 100,000us, and the dark time is set to 80,000us. I see someone in the forum has achieved linearity by changing the camera parameters, but  I did not get the ideal linear result by the adjustment. I think the reason is that I am not clear about the reason for the discontinuous grayscale change. So how should it be adjusted?
2. In addition, how many 8bit images can be projected at one time for the 6500. The effect of projecting 20 grayscale images at a time is different from that of a single projection 20 times. Each time the grayscale calibration is projected one by one is very time-consuming.

Hope everyone can help! ! Grateful! !

  • 0
    TI__Expert 3825 points

    Hello Ke Zhang,

    Welcome to DLP forum and thank you for your interest in DLP technology.

    We will soon get back to you on this.

    Regards

    Akhil

  • 0
    TI__Guru 54705 points

    Hello Ke Zhang,

    The DLPC900 based systems depend on light modulation as part of the grayscale values.  You should connect to the LED enable(s) to turn off and on the LEDs during a frame. Without solid state modulation, there will be times that the light is on contributing to the gray value of the bit when it should not.

    Even with modulation, the grayscale LED modulation for the 6500 assumes that the LED switching time is zero, which it not in reality.  

    This also looks like your video driver may have RGB "Limited" turned on instead of RGB "Full" since the "0" value is not near 0..  Changing this setting (if it is set0 will depend on the video software and/or video driver you are using;

    Fizix

  • 0 in reply to Fizix
    Prodigy 10 points

    Hello Fizix,

    Thank you for answer my question! But I still feel puzzled about how to change it. I did not find any setting option related to LED enable or LED switch time in the GUI software interface. Futher more,I have tried to change all options about LED ,but it didn't work. 

    So could you please describe more details on this question and tell me What should I do?

    I am sorry to bother you again.Hope for your reply!

    Ke Zhang

  • 0 in reply to ke zhang
    TI__Guru 54705 points

    Hello again Ke,

    The "limited" vs "full" is not a setting on the DLPC900 system.  It is a video card setting. You will have to read or search online to see how your video system sets this. For example, on the lab system I have used the video card is an nVidia Quadro and the setting was in the nVidia control panel.

    You may have an Intel, AMD, nVidia or other graphics chipset and will need to consult the GPU documentation on adjusting this output.

    The other thing that needs to be done is to connect your LED system to the LED enable(s) on the EVM.  If you are using a single color LED with Video Mode, then you will need to combine the R, G, & B LED enables with AND gates.

    If you are using Pre-stored Pattern, Pattern on-the-fly, or Video pattern Modes, then choose an LED color in the GUI and connect to the corresponding LED enable to modulate the LED output of your LED driver system.

    Fizix