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Polychromatic Pixels

compoundsemiconductor.net

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Re: Polychromatic Pixels

#101

Post by cubefox »

jiggawatts wrote: post #99
cubefox wrote: post #98

Earlier quoted context omitted.

No, normal monitors use additive color mixing, but dithering isn't additive, it's averaging. With just red, green, blue, black you couldn't dither cyan, magenta, yellow, white, just some much darker versions of them. E.g. you get grey instead of white. You can check this by trying to dither a full color image in a program like Photoshop. It doesn't work unless you use at least the 8 colors. In fact, ink jet printers…

The article is talking about microLEDs, which are an emissive light source.

You can dither not just in print but also on illuminated screens. For example:

http://caca.zoy.org/study/out/lena6-1-2.png

This picture has only pixels of the aforementioned eight colors.

Re: Polychromatic Pixels

#102

Post by mistercow »

MT4K wrote: post #96
mistercow wrote: post #15

Earlier quoted context omitted.

If the refresh rate is high enough, a single LED could flip between multiple wavelengths to dither to non spectral colors.

Or if pixel density is high enough, adjacent pixels could display the colors to combine with no flickering. Unlike regular RGB subpixels, this would only be needed for areas where the color cannot be displayed by an individual pixel alone.

Yeah, and both techniques can be combined, which common with LCD screens, although it does sometimes lead to visible moving patterns when viewed close up.

There’s more flexibility with tunable wavelengths, though, since there will often be multiple solutions for what colors and intensities can be combined to create a particular photoreceptor response. By cycling through different solutions, I wonder if you could disrupt the brain’s ability to spot any patterns, so that it’s just a very faint noise that you mostly filter out.

Re: Polychromatic Pixels

#104

Post by exmadscientist »

layer8 wrote: post #44
Retr0id wrote: post #37

Earlier quoted context omitted.

Can you produce "white" with just two wavelengths?

Yes, mix two complementary colors like orange and cyan. You just need two wavelengths that hit all three cone types [0] in the right ratio. There’s the possibility that it’s subject to more variation across individuals though, as not everyone has exactly the same sensitivity curves. [0] https://upload.wikimedia.org/wikipedia/commons/f/f1/1416_Col...

Human vision in the yellow (~590nm) region is known to be extremely sensitive to particular wavelengths. Observe how quickly things go from green through yellow to amber/orange!

So this is probably a nonstarter.

Re: Polychromatic Pixels

#105

Post by exmadscientist »

duskwuff wrote: post #79
PaulHoule wrote: post #57

Earlier quoted context omitted.

See also https://en.wikipedia.org/wiki/Spectral_color This reminds me of the observation I had in high school that I could immerse LEDs in liquid nitrogen and run them at higher than usual voltage and watch the color change. I got a PhD in condensed matter physics later on but never got a really good understanding of the phenomenon but I think it has something to do with https://www.digikey.com/en/articles/identifyin…

> I got a PhD in condensed matter physics later on but never got a really good understanding of the phenomenon but I think it has something to do with The color of most* LEDs is controlled by the band gap of the semiconductor they're using. Reducing the temperature of the material widens the band gap, so the forward voltage of the diode increases and the wavelength of the emitted light gets shorter https://www.scienc…

> phosphor-converted LEDs, which are uncommon

No, they're extremely common. Every white LED in the market is phosphor-converted: they're blue LEDs, usually ~450nm royal blue, with yellow-emitting phosphors on top. Different phosphors and concentrations give different color temperatures for the final LED, from about 7500K through 2000K. (Last I looked, anything below about 2000K didn't look right at all, no matter what its manufacturer claimed.)

Bigger LEDs are often phosphor-converted as well. Most industrial grow lamps use this type of LED. So they're around! You're probably looking at some right now!

Re: Polychromatic Pixels

#106

Post by exmadscientist »

KennyBlanken wrote: post #63

This appears to be done by varying current, from a slide in this 'webinar': https://youtu.be/MI5EJk8cPwQ?t=238 That's not hugely surprising given that (I believe) LEDs have always shifted spectrum-wise a bit with drive current (well, mostly junction temperature, which can be a function of drive current.) I guess that means they're strictly on/off devices, which seems furthered by this video from someone stopping by t…

> if they made 5050-sized LEDs

I doubt they can. Probably the process only works (or yields) small pieces, otherwise they'd be doing exactly what you suggest.

I also notice that their blues look terrible in the provided images. Which will be a problem. I don't think they get much past 490nm or so? That would also explain why they don't talk at all about phosphors, which seem like a natural complement to this tech... I don't think they can actually pump them. Which is disappointing :(

Re: Polychromatic Pixels

#108

Post by ajuc »

mensetmanusman wrote: post #75
jessriedel wrote: post #58

Earlier quoted context omitted.

It also can't produce white or anything else in the interior of this diagram (as well as, as you mention, shades of magenta and purple that lie on the flat lower edge): https://upload.wikimedia.org/wikipedia/commons/b/ba/Planckia...

The human eye will see white when a pixel flashes through all of the colors quickly in time.

But that means it has reduced refresh rate.

Re: Polychromatic Pixels

#109

Post by ajuc »

pfg_ wrote: post #93
GrantMoyer wrote: post #45

A single wavelength can't reproduce all visible colors. These pixels are variable wavelength, but can only produce one at a time, so you'd still need at least 2 of these pixels to reproduce any visible color. The fundamental problem is that color space is 2D[1] (color + brightness is 3D, hence 3 subpixel on traditional displays), but monochromatic light has only 1 dimension to vary for color. [1]: https://en.wikipedi…

This seems like a non-problem, cut the display resolution in half on one axis and reserve two 'subpixels' for each pixel. Then you have a full color display with only one physical pixel type and that needs one less subpixel. These displays could even produce some saturated colors with specific wavelengths that can't be represented on regular rgb displays.

You'd still be unable to produce different brightness pixels. You'd get white but no grayscale.

I guess you could cheat it by moving the wavelength outside the visible spectrum?

Re: Polychromatic Pixels

#110

Post by incrudible »

cubefox wrote: post #101
jiggawatts wrote: post #99

Earlier quoted context omitted.

The article is talking about microLEDs, which are an emissive light source.

You can dither not just in print but also on illuminated screens. For example: http://caca.zoy.org/study/out/lena6-1-2.png This picture has only pixels of the aforementioned eight colors.

Emissive means additive, not averaging. Cyan, magenta and yellow are not primaries here. Red and green light adds up to perceptual yellow. Red, green and blue adds up to perceptual white (or grey, at very low luminance). Treating each of these pixels like subpixels (which is arguably a form of dithering) will produce a full color image (at a lower resolution), but given that they did not demonstrate it, color reproduction and/or luminance likely is far from competitive at this point.
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