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External Pattern for structured light App

Jeffrey Chung
Prodigy 100 points

Have anyone successful use the External Pattern for structured light App? I turn to mode 7, and the light become purple color, and my fringe pattern is not smooth, what happen ? Am i doing any thing wrong, I find that it is very difficult to work with this projector...

  • 0
    TI__Genius 9935 points

    Jeffrey,

    Are you using the application report DLPA021: "Using the DLP Pico 2.0 Kit for Structured Light" ? (Go to http://ti.com/mems and click on 0.17 HVGA Chip Set, then look under "Applications Notes".

    The input must be 640x480@60Hz. The pattern will be cropped from the upper left corner 480x320. You must reduce the LED currents to avoid LED degradation. (See the caution at the bottom of page 5 of the App Note.) Then you must choose which mode you wish to use. This sets the pattern rate and bit depth used. The App Note shows how the various modes work.

    I have tried all of these modes, and they do work according to the descriptions in the App Note. However, the results are sometimes not what you may be expecting - until you understand the details in the App Note.

    Best regards,

    Pascal

  • 0 in reply to Pascal DLP
    Prodigy 100 points

    Hi Pascal,

    In fact, I need to use structured light mode, because i need to sync between camera and projector, and i need to project white light (8 bit on each color), so which mode will you advise me to set in structured light mode?

    Thanks.

  • 0 in reply to Jeffrey Chung
    TI__Genius 9935 points

    Jeffrey,

    All of the structured light modes for the Pico Kit v2 are described in the document DLPA021 - Using the DLP Pico 2.0 Kit for Structured Light Applications (available at: http://www.ti.com/litv/pdf/dlpa021).

    There is no "8 bit per color" structured light mode which produces white light (uses all 3 LEDs - RGB). There is a 4 bit per color RGB 120 Hz mode, though.

    In order to achieve a 8-bit ("gray" scale), you must use a monochrome mode - "120 Hz, 8-bit Monochrome". In this mode, only one of the LEDs may be enabled. (Note that also, the LED current must be reduced when using the monochrome modes. There is a "CAUTION" note at the bottom of Page 5 of DLPA021.)

    The "white" light mode (sequential RGB) with 8-bit per color depth is only available in video mode (640x480@60Hz), but the sync on AUXSYNC output is not available, as it is in the SL (Structured Light) modes. In order to synchronize the camera, it is necessary to sync to the VSYNC signal - but there is a latency involved, which should be measured for precision - but will be around 25 ms after the VSYNC which ends a frame on the input.

    Best regards,

    Pascal

  • 0 in reply to Pascal DLP
    Prodigy 100 points

    Hi Pascal,

    I've do some experiment on the structured light mode, and i will make a summary based on Mode 4 (8 bit green color) and Mode 7 (4 bit white color), cause i think these two modes can represent all the options in structured light mode selection.

    Mode 4:

    Result is as good as mode 0, but because it project green light, object's color without green element will not reflect green light, so it show dark in the image. For example, pure red and pure blue color will be impacted. So, this mode is not practical, unless, your target object is tend to green color.

    Mode 7

    Result is not as good as mode 0, outcome tend to be jaggy (not smooth), i think this is because it only use 16 type of color to form the sinusoidal curve. No doubt it is faster, but it also loss information.

    So i can conclude that, all the structured light mode is not practical enough, except it provide SYNC. 

    Correct me if I'm wrong.  Sorry for so direct, I just try to make thing work!

    Thanks.

     

  • 0 in reply to Jeffrey Chung
    TI__Genius 9935 points

    Jeffrey,

    Your summaries look accurate to me. The limitation of no white (rather than monochrome) 8-bit SL mode for the Pico Kit v2 is that of the chipset design - in the monochrome modes, only one LED can be active. We understand that this can be a limiting factor for the reasons you summarize - especially the non-monochrome nature of the object being measured.

    It is possible to use the chipset demonstrated by the Pico Kit v2 (DLP1700 chip set) with a different light engine especially designed for white light. This could be done by using only one LED strobe (green) to drive 3 LEDs (RGB) simultaneously, or possibly by using a "white" LED.

    The Pico Kit v2 does not have the right LED strobe signals or the thermal capacity to do this - but such a light engine could certainly be designed. DLP has a network of Design House partners who could possibly help you with this, should you desire. (http://ti.com/mems - "Getting Started", "DLP Design Houses".

    Best regards,

    Pascal

  • 0 in reply to Pascal DLP
    Prodigy 100 points

    Hi Pascal,

    Thanks for your input and support. And I have contacted one of the design house on this.

    But temporarily, i have to use this projector to meet the project dead line.

    I have one work around, not sure whether it work, need your advice on it.

    Work Around:

    I skip some commands used to set the external structured light pattern mode, and only execute 2 of them,

    1. Select "Parallel RGB" input source

    4. Disable all non-linear pixel processing

    I do this because i have to used Mode 0. The side effect is i do not have Sync from projector to my camera.

    To overcome this, i have to put some fix delay for my camera to snap image, and i set the exposure time to 16.7 millisecond.

    why 16.7 ms? , because i found that, the projector will repeat the same image on every 16.7ms interval, i confirmed this thru the observation under Hi-Speed camera on 1ms interval.  

    So, this is my work around, hope you can give me some advice.

    Thanks! 

    Best Regards,

    Jeffrey

  • 0 in reply to Jeffrey Chung
    TI__Genius 9935 points
    Jeffrey, This sounds reasonable to me. The only advice that I can offer is to try it. Let me know how it works. Best regards, Pascal
  • 0 in reply to Pascal DLP
    Prodigy 100 points

    Hi Pascal,

    Thanks! 

    Good support from you!

    Best regards,

    Jeffrey

  • 0 in reply to Jeffrey Chung
    TI__Genius 9935 points
    You are welcome.