Rainbow – an attempt to display colour on a B&W monitor

The aim of this project was to display a colour image on a black and white monitor, by overlaying an acetate bayer filter over the monitor and mosaicing a colour image.

I obtained an Eizo B&W monitor from ebay, which I was intending for use viewing B&W photos and was curious if I could replicate an effect similar to Autochrome Lumière ( see wikipedia ) where they overlay colour filters over a B&W photographic plate, using starch grains, which creates a colour image.

The following image shows a 500x microscope image of the pixels that make up the B&W LCD display, taken using a very cheap USB microscope. It looks to me as if each pixel, is represented by 4 sub-pixel elements, please correct me if this appears not be the case.

A pdf was created of the bayer display, with the dimensions 433.1mm x 324.8mm. The monitor has a resolution of 2048×1536 and I assumed the pixels had the same width as height.

You can see an example of the pdf I created below, where for example a blue element, should be represented by 2×2 pixels from the B&W monitor.

I created 3 pdfs:

  • bayer_1.pdf – each element, is represented by 1 pixel from the display
  • bayer_2.pdf – each element, is represented by 2×2 pixels from the display (this is the acetate used in the video)
  • bayer_4.pdf – each element is represented by 4×4 pixels from the display

The following image shows the printed acetate with the bayer pattern:

The following, is a B&W image with mosaicing applied from the colour image:

How it works

The monitor I am using seems to generally be used portrait, to make it landscape on linux:

xrandr --output HDMI1 --rotate left

Image of effect

As you can see the effect of my attempt is quite slight, but you can see in the centre the different colours of the balloons.

Video of effect

The effect is also demonstrated in the following video, with the following parameters:

 mpv out.mkv --fullscreen --loop --brightness=10 --contrast=20

Microscope images of the bayer filter (2×2 scaling)

2×2 bayer filter, I tried to design it so that for example the ‘red’ square covers 2×2 pixels on the monitor

Chess board

As suggested by Olivier, I’ve just created 2 chess board images. Olivier was correct that a single pixel consists of 3 sub-pixels 🙂

1×1 (the white patch is 1 pixel), monitor in landscape, image in correct orientation from microscope (left, towards left monitor, top, towards top of monitor)

2×2

Possible improvements

I wonder if by measuring the exact pixel width/height under a microscope, if the effect could possibly be improved somewhat, as that information could be used when creating the acetate filter.

Alignment is also a key issue, I need to think of ways to improve that possibly using a microscope while aligning the acetate.

I’d be interested in other improvements I could make too!

Source

The sourcecode to generate the PDFs for the acetate and the mosaiced images and videos is at:

https://www.github.com/anfractuosity/rainbow


13 Comments
  • Olivier Parmentier
    June 27, 2020 Reply

    Seems to me that the screen has exactly the same structure as a color screen.
    Each block of “<<“ structure is a subpixel on a color screen so I would guess that a pixel is 3 of those blocks addressed by the controller as one b&w pixel.
    You can test this hypothesis by sending a chessboard pattern on the screen et look with the microscope.

    To adjust the dpi of the bayer print. Guess a good enough approximate. Print it, then when it’s on the screen display one color (red for example) and count the moire effects. That would give you the information to adjust the dpi of the print.

    • admin
      June 27, 2020 Reply

      Thanks a lot for your comment. I’ll definitely have to try that, regarding the
      chessboard pattern and microscope, and the dpi information you gave!

  • Peter McNeeley
    June 27, 2020 Reply

    Ive done some experiments with lenticular sheets so im aware of some of the difficulties here.

    Im wondering if in addition to alignment issues you also dont have a parallax viewing issue. You might need to adjust for that.

    • admin
      June 28, 2020 Reply

      Thanks :), it does look like the camera needs to be pretty parallel to the monitor. I will look at this more.

  • Michael
    June 27, 2020 Reply

    I notice the color is clearer in the center and more grey on the edges. Is this an old tube monitor? The glass is usually curved, so the geometry may not be an even grid. You might need to create a curved projection for your color filter,

    • admin
      June 27, 2020 Reply

      That’s a good point, but it’s a B&W LCD monitor. I’ll have to have a think why
      the colour is more prevalent in the centre.

      • Xyzzy
        June 28, 2020 Reply

        If you move the camera, and the centre-spot of colour moves with it, it’s likely parallax? The more oblique the viewing angle, the less the three components (camera, acetate, LCD panel) line up.

        • admin
          June 28, 2020 Reply

          Thanks for your comment, I will look into this more, it does seem like the camera does
          need to be pretty parallel to the monitor.

  • Douglas
    June 27, 2020 Reply

    One trick would be to do it all back to front. Instead of saying, “this pixel will be green”, then very precisely placing a green mask over just that pixel, you could place a mask that is pretty close over the screen, iterate over the pixels lighting one up at a time, recording what colour it goes (some combination of red green and blue). To show a colour image, lighten the pixels based on how much of that composite colour is needed.

    • admin
      June 27, 2020 Reply

      That’s a very cool idea. I think that would be really interesting to try!

  • Anna
    June 27, 2020 Reply

    I have nothing to say beyond – this is incredible. Nice!

  • tepe
    June 27, 2020 Reply

    This is cool. It’s essentially how the original OLPC screen did color. (See http://wiki.laptop.org/go/Display#Screen)

  • owen
    June 28, 2020 Reply

    This is impressive stuff.. doing more with less is a noble venture. Think of all we could achieve if we weren’t wasting compjting power on react interfaces.

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