Evaluating Madmapper For Keystone Correction With Gradient Correction / Corner Crop?
  • mdrejhon
    junior Member
    Posts: 1
    Joined: Sat Dec 15, 2018 12:31 am

    Evaluating Madmapper For Keystone Correction With Gradient Correction / Corner Crop?

    by mdrejhon » Sat Dec 15, 2018 3:08 am

    I want to shine a 5-figure lumens projector steeply angled upwards on the side of an apartment building.

    My projection mapping task is very rudimentary for a projection mapper, but more complex than a projector's built in keystone.
    I need extreme keystone correction far beyond the projector's adjustment range.

    Here are my diagrams.

    Image

    Image

    Image
    (Bottom edge will be above roughly the second storey level, due to steep-upwards projection angle)

    Image

    As many here probably know already, the top edge stretches a lot more than the bottom edge, and the top edge is much dimmer. (Fortunately the super excess lumens of the projector compensates). So I want to build compensating corrections into a custom-processed video file purposely generated for playback on this steeply-angled-upwards projector. I have to intentionally play a portrait video distorted into a 16:9 signal because the 16:9 projector is vertically stretching due to extreme angle into something more suitable for embedding a portrait video. So there's some weird aspect ratio remapping. Focus is not a problem (top and bottom is almost the same, the lenses are really good at the distances used), so I'll live with any imperfections.

    Everything works perfectly, I now just need to pre-distort a video file.

    My Questions:

    Since this is a simpler projection mapping task than the complex paid projection mappers but too complex for a projector's built-in keystone. I'm looking at a simple "Extreme Keystone" task that just barely veers into low-end projection mapping.

    How easy is it to use Madmapper to create a projection map that is merely an enhanced keystone correction:
    (A) brightness gradient correction
    (B) vertical stretch nonlinearity correction
    (C) major aspect ratio distortion since I'm embedding a squat portrait video in a 16:9 video file
    (D) keystone with intentional corner clipping
    (E) Black fill for outside boundaries (to avoid stray light)

    I presume Madmapper can already do it all, and I should try out the trial edition -- but it almost looks like Madmapper may be massive overkill (Like using a giant battleship cruiser to deliver one pizza)? Or it already easily does this with reasonably minimal steps?

    By the way, this is a community weekend project on a loaner lumen cannon and family-budget only. That's why we're fiddling with free tools but are considering inexpensive projection mappers such as Madmapper. But the 35-Euro rental may actually be acceptable if Madmapper is easy enough to do this extreme keystoning.

    Thank you!
  • mad-matt
    garageCube team
    Posts: 1475
    Joined: Mon Sep 09, 2013 5:50 pm

    Re: Evaluating Madmapper For Keystone Correction With Gradient Correction / Corner Crop?

    by mad-matt » Sun Dec 16, 2018 9:44 pm

    (A) brightness gradient correction

    You can do as following:
    Create a quad with your media mapped correctly
    Clone this quad (at the exact same position), set blending mode to "Multiply" and use for this quad a gradient image created in Photoshop or an image editor, that will do your gradient thing

    (B) vertical stretch nonlinearity correction

    This is automatically handle when mapping the quad

    (C) major aspect ratio distortion since I'm embedding a squat portrait video in a 16:9 video file

    No problem you can define your target by moving the 4 output handles, and crop in the input freely

    (D) keystone with intentional corner clipping

    I'm not sure I understand this one but your should try demo version and see the potential of the quad surface with mesh warping / masking + FX Soft-border that might make cleaner borders (avoid seeing pixels quantization). That should cover all your needs.

    (E) Black fill for outside boundaries (to avoid stray light)

    Where there is no surface, MadMapper will send a full black.

    > So I want to build compensating corrections into a custom-processed video file purposely generated for playback on this steeply-angled-upwards projector

    You don't need to pre-process, MadMapper will do it in real-time with no problem.

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