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DLP4710: Can DLP DMD act as an optical shutter for a higher resolution image?

Ronald Walden
Prodigy 145 points
Part Number: DLP4710

What we want to essentially do is have a DLP4710 in an image plane of an 8K by 4K image and use the DMD to selectively block parts of the original image. I don't see why this wouldn't be possible as each micromirror is still just a mirror and if facing the other way will be blocking that part (4x4 pixel grid) of the original image. However I do see an issue due to the gaps between the pixels and diffraction from the DMD.

Those involved with the DLP development and aware of the unique features of this system, can you give us suggestion if what we want is possible, what we should and shouldn't expect to work and what potential issues?

Thank you.

  • 0
    TI__Mastermind 28005 points
    Ronald,

    Welcome to the E2E forums and thank you for your interest in our DLP technology.

    Can you describe your use case in a bit more detail? It sounds like you want to use a video projection that is completely separate from the DMD, and then use the DMD for the sole purpose of redirecting light to enable/disable specific sections of the screen. Is that correct?

    If so, you may encounter some difficulties with the DLP4710 chipset. The DLP4710 is a display chipset, so the software driving it includes algorithms for image quality optimization, so the mirrors may not always be 1:1 with what you want them to do. This sounds more like a light control application where you want to specifically create patterns on the DMD.

    Let me know if this is an accurate representation of your use case so we can assist further.

    Best Regards,
    Philippe Dollo
  • 0 in reply to Philippe Dollo
    Prodigy 145 points
    Hi Philippe,

    Feature-wise the DLP4710 chipset can do what we want. The question has more to do with the optical properties of DMDs, the pixel gaps and diffraction.
  • 0 in reply to Ronald Walden
    TI__Expert 4610 points
    Hi Ronald,

    Can you please describe your application in more details, it is not clear to us. First we want to understand the application (use case) then only we can suggest optical properties for that use case.

    What my understanding is " You want to display a 8K x 4K image and in the light path you want to add the DLP4710 to block the parts of image"

    If my understanding is correct, how you are displaying 8Kx4K image. how you want to place the DLP4710 in lightpath. I am not understanding how you want to block the parts of image.

    Can you please elaborate your use case and also the methodology to achieve that use case.

    If you do not want to share full application use case in public. You can share it in private also, i am sending you the request on e2e.

    Thanks,
    Navneet
  • 0 in reply to Navneet Singh
    Prodigy 145 points

    Hello. The idea is quite simple, we use a 4K LCoS panel to display 4K monochrome video at 240Hz, then with an optical actuator such as here ( www.ti.com/.../optical-module.html ) we shift the image by one pixel length each frame so we as a result turn the 240Hz 4K video into a 60Hz 8K video.


    The 1080p DLP has to come after the actuator to selectively block the image on an intermediate image plane. For reasons I cannot disclose the DLP can't come in the optical system before the LCoS, it has to be placed after the LCoS.

    I hope this made the general idea more clear to you.

  • 0 in reply to Navneet Singh
    Prodigy 145 points
    Looks like this isn't one of the easier questions you've received.
  • 0 in reply to Ronald Walden
    TI__Expert 4610 points
    Hi Ronald,

    Sorry for the delay. I was busy with some important work.

    Current DLP chipset support the traditional display application. The application you are using is not supported by DLP chipset.

    You should have to do this in Lcos itself.

    Thanks,
    Navneet
  • 0 in reply to Navneet Singh
    Prodigy 145 points
    Navneet, this has nothing to do with the chipset, but the optical properties of the DMD only. You're doing a disservice to your company by suggesting not to use DLP for this when it can clearly be used as I explain below.
    Some of your clients have already projected from one DLP chip to a secondary DLP chip which in turn projects through the actual projection lens. I am talking about the Zeiss Velvet projector. www.zeiss.com/.../zeiss-velvet-1600-sim.pdf

    Here I believe video is projected from a lower resolution DLP chip to a higher one to achieve a 2,500,000:1 contrast ratio, as stated in the spec sheet.

    What we intend to do instead is the opposite, project from a high res "DLP" onto a low res DLP chip which in turn will pass the projection to the final projection lens.

    Only concern here is the wider pixel gaps of the lower res DLP chip causing the high res projection to end up with the same screendoor as the low res second DLP chip. But this will happen only if the second low res DLP chip is perfectly on the intermediate image plane. I want to know if it won't be, can we assume the lower res screendoor will be mostly unnoticeable in cost of lower resolution "local dimming" of the second defocused DLP chip. I believe it will with LCoS or transmissive LCD panel, but DLP may have some more diffractive properties making this more difficult, hence my question.

    is it clearer now?
  • 0 in reply to Ronald Walden
    TI__Expert 4610 points
    Hello Ronald,

    Thanks for the more clarification. We are discussing with our optics team and get back to you with the possible cases in detail.

    Thanks,
    Navneet
  • 0 in reply to Navneet Singh
    Prodigy 145 points
    Hello, do you have any updates on this?
  • 0 in reply to Ronald Walden
    TI__Mastermind 22830 points

    Hi Ronald,
    Thank you for your patience. Information you provided is very help.
    It is technically feasible to achieve what your are targeting. However, the optical system could very complex and challenging to build.
    Typically, a  low resolution device should be placed earlier in the path to minimize artifacts and complexity.

    It is very difficult for to answer that de-focusing DMD would minimize the low frequency screen door. It may introduce other issues depending on your optical system design.
    What kind of optical architecture you intend to use - Telecentric or non-telecentric?

    regards,
    Vivek

  • 0 in reply to Vivek Thakur
    Prodigy 145 points
    Thank you Vivek.

    Indeed the optical design was not easy, but I think we have managed to get it to meet acceptable specifications.

    What issues do you have in mind and what characteristics of the optical design will those issues depend on?

    Right now the light cones are not perfectly telecentric, in the 1-2 degree variation range. The MTF graphs and image simulations look good with test patterns in Zemax.
  • 0 in reply to Ronald Walden
    TI__Mastermind 22830 points
    Hi Ronald,
    I made a little typo/missed a word in previous post. The line should read:
    "Typically, a low resolution device should be placed earlier in the path to minimize artifacts and complexity. "
    My concern is that if the second DMD is not focused or image plane then image on DMD will be blurry which may result in a blurry image on screen. Even though low frequency screen door will not be visible.

    You may have already considers other option, keep second DMD in image plane and use projection lens to soften the screen door. I am not sure which one will have better image on the screen.

    regards,
    Vivek
  • 0 in reply to Vivek Thakur
    Prodigy 145 points

    I believe if you defocus the focusing lens of the projection lens assembly, you will soften/blur the whole image, not just the screendoor (pixel gaps of the lower-res DLP DMD). Since the second DMD and its screendoor is lower resolution (bigger physical size) than the video beam it receives then when defocusing the pixels of the video beam will degrade sooner by softening and bleeding into each other before the screendoor will to a noticeable and practical amount. But correct me if we are missing something.

    But defocusing the second DMD itself instead, we assume the DMD is a selective mirror and would work very similarly like an ordinary first surface mirror between the second DMD and projection lens would: it wouldn't need to be on an image plane, provided all micromirrors were in the On-state.

    Difference between the DMD and a first surface mirror then to us seems that parts of the DMD can be selectively "turned off". Thus we assume, if we set the micromirrors on a central rectangular region on the second DMD to an On state and the other micromirrors to an Off state, the DMD acts as a basic reflective optical shutter ( i.imgur.com/eK2pSX3.png , i.imgur.com/IBdvVsF.png ). Then we assume, if we set this DMD slightly off from the image plane, the resulting image will simply have the edges of the central rectangular region as described above become feathered ( i.imgur.com/tE4jFFR.png , https://i.imgur.com/imS1ICY.png ) , rather than have all of the image defocused.

    But you seem to suggest that a slightly defocused DMD on an image plane acting as an optical shutter for the first DMD will somehow defocus the whole image ( i.imgur.com/yfUfdi3.png ) , while a first surface mirror wouldn't. Can you please explain why that is so, if I understood you correctly?

    (For reasons I cannot disclose, in our unique design it is simply not possible to have the lower resolution (1080p) DLP panel acting as an optical shutter in the optical system before the high resolution 8K spatial light modulator)

  • 0 in reply to Ronald Walden
    TI__Mastermind 22830 points
    Hi Ronald,
    I agree with your comments about de-focusing lens and softening of image. However, I defer with you on your assumption about the second DMD.

    "But defocusing the second DMD itself instead, we assume the DMD is a selective mirror and would work very similarly like an ordinary first surface mirror between the second DMD and projection lens would: it wouldn't need to be on an image plane, provided all micromirrors were in the On-state."

    The second DMD is not acting as a plane mirror. It is a pixel array with tilt angle. If you modulate mirror, it is acting as a shutter which is not in image plane and will blur image image. I hope this explain my concern.

    Regards,
    Vivek
  • 0 in reply to Vivek Thakur
    Prodigy 145 points

    I understand that, but from what I understand in the On-state each micromirror is perpendicular to an incoming light from a TIR prism. So if all micromirrors are in the On state, the DMD is not much different from a regular planar first surface mirror, of course excluding the pixel gaps which introduce issues on their own such as the screendoor.

    So unless I am missing something here, having Off state pixels surrounding a rectangular region with all pixels in the On state will be akin to having a cutout mirror on an image plane, which, if is slightly off from the image plane, will result in the edges of the mirror being feathered on the projection screen, rather than the whole image being blurred, even the portion being reflected from the middle of the mirror. Why would it be different with a DMD? My only concern was the diffraction from the pixel gaps but you seem to be concerned about something different.

  • 0 in reply to Vivek Thakur
    Prodigy 145 points
    Hello again, did my previous message reach you?
  • 0 in reply to Ronald Walden
    TI__Mastermind 22830 points
    Hi Ronald,
    Thank you for your patience. I will draw few images to explain my concern. I will try to completed by end of day.
    regards,
    Vivek
  • 0 in reply to Vivek Thakur
    TI__Mastermind 22830 points

    DMDImagePlane.pdfHi Ronald,

    Please refer to the attached PDF with picture. I have tried to explain for a 17 degree tilt angle DMD with  F/1.7 optics. When DMD is in the image plane, if  you module  a mirror (pixel), it modulates only that pixel.

    When  DMD is not in the image plane ,  if you modulate a mirror, it  partially modulates the pixel and it also modulates part of the neighboring pixel. This effects will create a burring effect in the image.

    I hope this explain my concern. Finally , it will depend on your system design and target image quality.

    regards,

    Vivek

  • 0 in reply to Vivek Thakur
    Prodigy 145 points

    Thank you Vivek for taking the time for providing information and illustration. However, I think you didn't make your concerns clear. Let me explain:


    "When DMD is not in the image plane , if you modulate a mirror, it partially modulates the pixel and it also modulates part of the neighboring pixel. "

    I understand this. However, as I have already explained before, and I quote:

    "we assume, if we set the micromirrors on a central rectangular region on the second DMD to an On state and the other micromirrors to an Off state, the DMD acts as a basic reflective optical shutter ( https://i.imgur.com/eK2pSX3.png , https://i.imgur.com/IBdvVsF.png ). Then we assume, if we set this DMD slightly off from the image plane, the resulting image will simply have the edges of the central rectangular region as described above become feathered ( https://i.imgur.com/tE4jFFR.png , i.imgur.com/imS1ICY.png ) , rather than have all of the image defocused."


    Please do take the time to check the images I had provided.

    "So unless I am missing something here, having Off state pixels surrounding a rectangular region with all pixels in the On state will be akin to having a cutout mirror on an image plane, which, if is slightly off from the image plane, will result in the edges of the mirror being feathered on the projection screen, rather than the whole image being blurred, even the portion being reflected from the middle of the mirror."

    The part you wrote I quoted here seems to be concerned with just that, the edges of the rectangular region being defocused, rather than all of the rectangular central region, which in this instance for us is not an issue.

    "This effects will create a burring effect in the image." - I think you meant "blurring", like in the images I linked to. Correct?

    So , again, unless there is miscommunication, you seem to be concerned about an issue I have already posted about, quoted above.
    I again, don't see that as an issue if the state of each DMD when light cone(s) is perpendicular to it is used for displaying.

    Again, I was more concerned about what effect the gaps between the DMD micromirrors would have when having the DMD used in a way mentioned above, slightly off from image plane.

    Thank you.

  • 0 in reply to Ronald Walden
    TI__Mastermind 22830 points
    Hi Ronald,
    I understand. My comments will be not be applicable in your proposed use case. This will be only applicable for border pixel son the rectangular "ON" region.
    I do not see any known issue due to effect of mirror gap in your intended use case. I will discuss with few of my colleagues and get back to you.
    regards
    Vivek
  • 0 in reply to Vivek Thakur
    Prodigy 145 points
    Thank you. Keep me updated.
  • 0 in reply to Ronald Walden
    TI__Mastermind 22830 points
    Hi Ronald,
    No other update except ya typical diffraction through DMD mirrors.
    regards,
    Vivek
  • 0 in reply to Vivek Thakur
    Prodigy 145 points
    Hello.

    "except the typical diffraction through DMD mirrors."

    such as?
  • 0 in reply to Ronald Walden
    TI__Mastermind 22830 points

    Hi Ronald,

    I have uploaded a PDF file explaining the difference between reflection through plane mirror and through DMD.  The DMD is not exactly plane mirror in your use case, there is some diffraction effects. Hope this explains.DMDdiffraction.pdf

    regards,

    Vivek

    DMDdiffraction.pdf

  • 0 in reply to Vivek Thakur
    Prodigy 145 points
    I think if we make the flat state the one which reflects the light to the lens and the On state the one which deflects it from the lens instead we will not have this difference. But that said the issue in your illustration seems to be the different angle the beams will be reflected rather than illustrating diffraction.
    Thanks.
  • 0 in reply to Ronald Walden
    TI__Mastermind 22830 points
    Hi Ronald,
    I was not trying to highlight different angle, my intent was to show a difference between a DMD and plane mirror. The DMD does acts like a diffraction grating with tilted mirror.

    The DMD is a bi-state device - ON and OFF. The flat state is intended for non-operation and can not be controlled for application.

    regards,
    Vivek