
Show HN: Rainbow – an attempt to display colour on a B&W monitor - anfractuosity
https://www.anfractuosity.com/projects/rainbow/
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Jetroid
Very neat, the outcome probably isn't what you were hoping for, but it has a
beautiful and ethereal quality to it. It's like an art piece.

From the photos and video, only a small section of the screen has colour. Does
that change as you move around, or is the coloured section static?

Off topic, but the visual effect seen here is a lot like how my memories and
dreams feel; only the thing I'm currently focussing on has any colour or
detail, whilst everything else is muted and fuzzy.

~~~
anfractuosity
Yeah I would like to improve the effect. I think the main colour region seems
to stay the same.

I'm wondering if I can get acetate that's ever so slightly adhesive, so it
sticks better to the monitor, which I'm wondering might help the colours show
better all over.

~~~
pbhjpbhj
Acetate sheets for use on Over-Head Projectors (OHP), used to come on a plain
white backing sheet. The top was glossy smooth, and the back was a little
tacky; if you can find those ...

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myself248
Tektronix did it with a totally wild set of LCD color filter shutters over the
whole face of the CRT, and then sequential color fields. It meant you got the
whole spatial resolution of the display, but one third the temporal
resolution. Similar to color-wheels in DLP projectors, really.

The system was called NuColor, if you want more detail.

The Bayer filter method in TFA is sensitive to perfect alignment between the
filter and the image, which proved impractical in the real world. Sure makes
for a neat experiment, though.

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tootie
JVC built a working model with that approach. There's a neat breakdown of the
tech on this YT channel:

[https://youtu.be/z-q8ehzHeQQ](https://youtu.be/z-q8ehzHeQQ)

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jeffbee
Man, that was the golden age of analog video right there. In the 90s it became
just barely possible to do a lot of processing of analog video using a
shitload of expensive electronics, and people did. Those were the days of
"line doubling" deinterlacers that were as big as shoeboxes and as expensive
as cars.

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Exuma
Can someone explains how this works? I have frustratingly been googling for 30
minutes now trying to learn how autochrome works. Being tech oriented it's so
frustrating when people sum it up in 1 sentence "its made of potato starch and
magically it makes color!"

How does it work? Do they hand paint the screen? How does it actually add red
or blue to an arbitrary shade of gray which lacks any chroma? Does it work
with video too?

~~~
Jetroid
The trick is because the shade of grey DOES have chroma. You can't just apply
any autochrome panel to the image (unlike what the OP is trying to do with
Rainbow), instead, the negative is generated using the chrominance filter

Imagine that each grain is blocking a 'pixel' of the negative. For simplicity
of this explanation, I'll pretend the grains are red, green, and blue. If
there's a blue grain, only blue light can get through, and thus the luminance
is baked in specific to the amount of blue in that region. The same is true
for the red, and the green.

Thus, each 'pixel' of the negative isn't determining a monochromatic
luminosity (ie black and white), but instead telling the luminosity of a
single channel of red, green, or blue.

When the grain filter and the developed negative are combined, we get natural
colour. The same filter is used for generation and display.

Another way to think of it is like this: Each pixel on our screen is actually
3 subpixels, each defining red, green, and blue, and we format our image to
alternate between telling the red, green, and blue channels how bright to be.
This is doing the same, but the subpixels are distributed randomly because
that's much easier to make.

EDIT:

If you organise the grains in a geometric pattern, you get Dufaycolor[1].

[1]
[https://en.wikipedia.org/wiki/Dufaycolor](https://en.wikipedia.org/wiki/Dufaycolor)

~~~
jacobush
Does it mean the filter has to very very precisely aligned when booth shooting
and printing from the negative?

I may be daft, and your explanation sounds reasonable but I still feel "magic
+ potato starch" :-D

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CrazyStat
The filter is part of the photographic plate, and the plate is developed
directly into a positive. So there's no alignment issue.

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Normille
This was actually a "thing" back in the 1950s. Apparently the results were
awful:

[http://www.earlytelevision.org/color_filter.html](http://www.earlytelevision.org/color_filter.html)

~~~
tyingq
They appear to just be green on the bottom, yellow in the middle, and blue on
the top.

Such that it might be plausible for outdoor scenery, but useless otherwise.

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jjeaff
Yes, that's how they were. I believe it worked for the occasional western or
other outdoor filming.

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fhars
Oh, I hoped to see something based on Fechner colours
([https://en.m.wikipedia.org/wiki/Fechner_color](https://en.m.wikipedia.org/wiki/Fechner_color)).
It gave me quite some creeps when a misconfigured XFree86 server managed to
draw a bright red line right across the black and white LCD screen of my first
laptop...

~~~
yread
Wikipedia has it animated, too

EDIT: warning! strobing!

[https://en.m.wikipedia.org/wiki/Benham%27s_top#/media/File%3...](https://en.m.wikipedia.org/wiki/Benham%27s_top#/media/File%3ABenham's_disc_\(animated\).gif)

~~~
stordoff
Does anyone have an explanation of what I should be seeing here? I've been
staring at it for a while (both full-screen and in the article), and I haven't
noticed anything other than black and white.

~~~
sundarurfriend
In the spinning animation, the black bands in the white parts quickly turn
another colour (brown for me, apparently blue or other colours for others)
while the image is spinning.

The effect is much reduced if I tap on the image to make it full screen on
mobile. The larger size seems to reduce the velocity of the spin, which seems
to be an essential part of it. Could this be the reason you don't see it, are
you perhaps on a low performance device for eg.?

Just for the sake of completion, the effect is incomplete for me - the outer
black bands are always brown, but the inner two switch between black and
brown. The middle one is more often black than brown, but it seems when that
one's brown, the innermost one instead turns black.

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nerdbaggy
Here is a good short video about how JVC did this with color shutters in the
front [https://youtu.be/z-q8ehzHeQQ](https://youtu.be/z-q8ehzHeQQ)

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ecpottinger
When I had a Commodore PET computer I tried making colour by flashing areas at
different rates. You can get a very limited colour by changing the length of
flashes but not only did I get it to work (poorly) I also got terrible eye
strain looking at those flashing squares.

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dbbbbbbbb
I had no idea B&W LCD monitors even existed, looks like they are primarily
marketed for medical imaging purposes, curious what advantage they have over
displaying grey-scale images on a good color monitor. I'm guessing by the sub-
pixels it is made from mostly the same panel as a color model.

~~~
avhon1
I perused Ezio's website, and found three B&W monitors they currently sell,
their "GX" series. Looking at the specs, the thing that stands out to me is
that they're _really_ bright: 1,200 cd/m^2 for the GX240 and GX340, and a
whopping 2,500 cd/m^2 for the GX560 ! I bet these monitors are brighter than
equivalently-backlit color displays from not having a Bayer filter in front.

Speculations on why medical monitors might be that bright: they can probably
be better read in brightly-lit medical settings, shine through overlays and
negatives placed over them, and be more easily read by some patients with poor
vision.

They also offer palettized grayscale: up to 1,024 tones from a palette of
16,369. I'm not sure how useful that is in practice, but is is a unique
feature.

[https://www.eizo.com/products/radiforce/gx240/](https://www.eizo.com/products/radiforce/gx240/)

[https://www.eizo.com/products/radiforce/gx340/](https://www.eizo.com/products/radiforce/gx340/)

[https://www.eizo.com/products/radiforce/gx560/](https://www.eizo.com/products/radiforce/gx560/)

~~~
artsyca
It reminds me of back in the 68k Mac days you you could set your screen to 256
colors or thousands of colors or thousands of greys, where you had to choose a
tradeoff of resolution and the greyscale mode was primarily for desktop
publishing applications ah QuarkXPress and PageMaker..

From their website --

> 10-Bit Simultaneous Grayscale Display

> 10-bit (1,024 tones) simultaneous grayscale display extends grayscale
> fidelity to the boundaries of human visual perception abilities and helps
> radiologists discern the finest nuances within an image.

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max_likelihood
The gentle gradients and transformations from black & white to color are
charming. It made me think of the scene in Wizard of Oz where Dorothy steps
into Technicolor.

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fortran77
One reason Color TV wasn't implemented like this is the need for a compatible
signal and the ability to decode the compatible signal with analog circuitry.

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jhiesey
I bet you could get a lot better color if you used the screen itself to
generate the bayer pattern on film rather than printing it with a printer.

Get some large format color negative film and thin cyan, magenta, and yellow
filters. Put a cyan filter on the LCD, followed by the film on top. In a
darkroom, light up the "red" pixels and to expose that part of the film.
Repeat with the magenta filter and "green" pixels, and finally the yellow
filter and "blue" pixels. Develop the film and reattach to the LCD.

This is kind of how the shadow mask was made in color CRT monitors. A
photographic process was used to put the red, green, and blue phosphor dots on
the screen by shining light through the shadow mask from the same angles the
electron guns would later illuminate the phosphors. This ensures that the red,
green, and blue phosphor dot pattern lines up (fairly) accurately with the
shadow mask.

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talideon
I'm reminded a bit of the JVC TM-L450TU LCCS
([http://www.earlytelevision.org/jvc_tm-l450tu.html](http://www.earlytelevision.org/jvc_tm-l450tu.html)),
which used some clever tricks to make a fundamentally B&W LCD show colour.

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elcomet
That's awesome! I guess diffraction of light between the original pixel and
the filter is also a reason for the low quality.

It would be nice if the author explained a bit more how he printed those pdfs
to such a resolution and precision. Is a home printer sufficient ?

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anfractuosity
The size of the acetate is around ~A2 size, I got the three acetate sheets
printed by printer service for around £35.

[https://github.com/anfractuosity/rainbow/blob/master/rainbow...](https://github.com/anfractuosity/rainbow/blob/master/rainbow_pdf.py)
is the code that I created to generate the pattern.

A home printer may work also though, as they're pretty high resolution these
days, I just don't have an inkjet printer at the moment.

I'm kind of curious about
[https://en.wikipedia.org/wiki/Duratrans](https://en.wikipedia.org/wiki/Duratrans)
too, instead of acetate and ink, but they seem very dear.

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EvanAnderson
An aside: I saw "Up" (the movie excerpted in the demo video) years ago, but I
never stopped and thought about the physics until today. The house would have
started rising as soon as sufficient balloons were inflated inside the house.
Releasing the balloons doesn't magically start making them buoyant-- they're
already buoyant when they're inside the house.

~~~
deberon
The balloons are under a tarp behind the house :)

~~~
dag11
Such a strong tarp!

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DonHopkins
I used to make screen captures of my Apple ][ monitor using Glow-In-The-Dark
Silly Putty.

It took a minute or so to capture the image, but then it was like Kai Power
Goo in non-Newtonian hardware!

[https://www.macworld.com/article/3005783/an-ode-to-kais-
powe...](https://www.macworld.com/article/3005783/an-ode-to-kais-power-
goo.html)

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tyingq
I wonder if a b/w CRT might work better.

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blt
I think the limiting factor of the color intensity is the dye/ink used to make
the mask. Probably each pixel is only blocking like 50% of the light in its
stop band.

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neoyagami
When my LHON was realy bad, this is how colors looked to me

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behnamoh
In an age with RGB monitors and displays, I don't know why such a project
could be useful.

~~~
markozivanovic
It's called 'hacker' news. Not all the things have to be useful. It's
interesting, at least to me. :)

