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Structured Light in LCR4500 vs LCR

Pete Thompson
Intellectual 465 points


Hello,

I'm looking to see if it's possible for us to migrate to the LCR4500 because of its brighter display compared to the older Lightcrafter model. 

Here's what we did with the older model:

- 16 4bit images were stored in flash (15 binary+phase images, plus 1 focus pattern)

- 15 images were displayed in a sequence (by using the camera to trigger to the next pattern), with exposure time of 1600us.

- focus pattern (16th image) is displayed at all other times when in idle mode.  (It's part of the sequence to avoid the load time delay since it's far faster to display an image from the sequence than switching to/from static image mode)

- No HDMI cable is needed.

In summary, the projector would be triggered by the camera to run through the first 15 images in the sequence as fast as possible, limited by the camera speed.  We've had up to 200fps capture rates, which we were very happy with.  Unfortunately the Lightcrafter simply wasn't bright enough for general use. 

My question is: Can we do the same or something similar with the Lightcrafter4500? 

I've read the user guides, which seems to indicate that it is not possible... but I'm hoping that I'm just misreading the guide and there's a way to make this work  :)

Here's what I learned about using structured light mode from the LCR4500 guide:

- 4 bits = 588Hz, 1700us minimum exposure  (perfect!)

- 12 patterns maximum (uh oh....)

Is there any thing I'm missing in the guide, and it's actually possible to go through a sequence of 15 (or more?) patterns at high speed using the LCR4500?  If so, how? 

I'm not worried about the focus pattern since 200ms image load wait time is acceptable when switching between idle and capture mode.  However, that brings up another question:  Would this mean it takes about 200ms to begin the sequence?  Or 400ms to fill the two buffers before the sequence can start? Or is there a better way to display a focus pattern when idling?

Finally, since we generated 4bit images to load into the Lightcrafter, do they need to be in 24bits to load into the LCR4500?  If so, are they then downsampled to 4bits which will effect the image palette?  We picked very specific values for each pixel in the image, so I'm hoping they'll remain intact.

  • 0
    TI__Expert 4720 points

    Hello Pete,

    My short answer is yes, I think what you need is possible. You have a lot of information within your post and I think I understand your problem, but I have a question regarding your sequence before I go into a more detailed answer.

    You said, "16 4bit images were stored in flash (15 binary+phase images, plus 1 focus pattern."

    If your patterns are binary, why did you store them as 4-bit images? Did you store them as 4-bit values because your phase images and/or focusing pattern need to be 4-bits/pixel? 

    Please tell me the bit-depth for each pattern that your system requires (not necessarily how many bitdepths each pattern has when you store it in flash on the LightCrafter). 

    For example,

    • Pattern 1 = 1bpp
    • Pattern 2 = 1bpp
    • ...
    • Pattern 16 = 4bpp

    After I know this information, I can better assist you. 

    Best regards,

    Blair Conner

  • 0 in reply to Blair Conner
    Intellectual 465 points

    Ah... coming from the Lightcrafter, I assumed that all images had to be 4 bits.  So the 4500 supports using mixed image formats in a sequence?  If so, then that sounds like that'll solve our biggest problem! 

    I'm still experimenting with the 4500 to understand its differences from the older Lightcrafter.  I'm still a little confused about how to load the images into the 4500, and whether it's possible to pre-load into 48 bit planes in structured light mode or not.  Is structured light mode a different mode from simply using "Pattern Sequence + Flash pattern source"?  According to page 40 of the user's guide: 

    "In structured light mode, the 48 bit-planes can be pre-loaded from flash memory and then sequenced with
    a combination of patterns with different bit depths."

    Contrast that with this (same page):

    "If the pattern sequence is less than 24 bit fields, the patterns are displayed from a pre-loaded buffer. Once the patterns are loaded, the pattern sequence repeats from the internal display memory with no buffer load penalty. If the pattern sequence is greater than 24 bit-fields, the 24 bit-field pattern sequence display time must be longer than the full buffer load time."

    Can this be clarified or elaborated on?  Is it possible to play through 48 bits at full speed without the 200ms wait at the 24bit barrier?

  • 0 in reply to Pete Thompson
    TI__Expert 4720 points

    Hello Pete,

    Yes, the LightCrafter 4500 supports mixed pattern formats in a sequence. Structured light mode is Pattern Sequence Mode in the LightCrafter 4500. The source can be either flash or the RGB888 external video interface. 

    It is possible to run a sequence of 48 bit-planes from only one or two images at full speed without the image load time. It is also possible to run full speed with a sequence that has 24 or less bit-planes from a single image.

    This is a section of the User's Guide that must be clarified and I apologize for the confusion. Let me know if I can explain the pattern sequence mode more clearly.

    Best regards,

    Blair

  • 0 in reply to Blair Conner
    Intellectual 465 points

    Thanks for the confirmation!  The pattern sequence seems to be working well now.