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DLPLIGHTCRAFTER: Minimum pattern exposure period in pattern sequence mode with video

robert sprowl
Prodigy 30 points

Part Number: DLPLIGHTCRAFTER

Hi,

I am using video input through the HDMI connector in pattern sequence mode and understand that the entire pattern sequence must fit within the period of 1 frame which is 16.7 msec at 60 Hz or 8.3 msec at 120 hz.

Why is the minimum pattern exposure 8.3 msec for a bit depth of 8  as shown in the allowable pattern combinations Table 4-1 ? How does this relate to the first paragraph of section 4.1 in the user guide that says that the maximum frame rate of 120 Hz is composed of 3 colors each allocated a 2.78 msec time slot ?

Finally, If 8 bits is allocated to each color for a 24 bit RGB image is the maximum frame rate in pattern sequence mode using video input 1/(3 x 8.3 msec) = 30 Hz for a 24 bit RGB image ?

I know similar questions have been answered before but it is still not clear to me.

Thanks !

  • 0
    TI__Mastermind 20045 points

    Hello Robert and welcome to the forums!

    Just to make sure, you are referencing the DLP LightCrafter EVM User's Guide, correct? Table 4-1 is for allowable external pattern combinations. This does not support the 120hz rate that is possible using some internal patterns.

    In table 4-3 we are talking about internal combinations. The minimum exposure time in this table references all three colors, not just a single color. Therefore, for 8 bits the maximum framerate is 1/(8.3ms)=120hz. However, each individual color is shown for 8.3/3 = 2.77ms like you said.

    Let me know if that makes sense or if there's anything else I can clear up!

    -Kyle

  • 0
    TI__Mastermind 30600 points
    Hi Robert,

    Welcome to the DLP forums and thank you for your questions! Just to clarify - are you using the DLPLIGHTCRAFTER or the DLPLCR4500EVM?

    When section 4.1 is discussing the frame rate with RGB input, that is for video mode, which has a different processing path than our pattern sequence mode. In video mode, there is no pixel accuracy and there are other video functions applied which make it non ideal for industrial applications (and also allows 24bit 120Hz).

    In pattern sequence mode the limitation is that you can only display 8 bits of the available 24bits at 120Hz. As you noted, if you wanted to replicate a "video" type scenario in pattern sequence mode (24bit image, sequential RGB) then you would have a maximum frame rate of 30Hz.

    I hope that's clear, please let me know if you have any further questions.

    Best,
    Paul
  • 0 in reply to Kyle Rakos
    Prodigy 30 points

    Hi Kyle, 

    Yes, I was referencing the Lightcrafter EVM user's guide.  Thanks for clearing that up. From reading the other posts it looks like the internal patterns can run at 120 hz but there is a limit of 48 bit planes at this rate due to the buffering time.

  • 0 in reply to Paul Goedeke
    Prodigy 30 points
    Thanks Paul. With your answer and Kyle's all of my questions were answered.