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Polychromatic Pixels

compoundsemiconductor.net

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Re: Polychromatic Pixels

#71

Post by golergka »

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…

> color space is 2D

Human eyes have three different color receptors, each tuned for it's own frequency, so it's already 3d. However, apart from human perception, color, just like sound, can have any combinations of frequencies (when you split the signal with Fourier transform), and may animals do have more receptors than us.

Re: Polychromatic Pixels

#72

Post by formerly_proven »

etrautmann wrote: post #70
jessriedel wrote: post #54

Earlier quoted context omitted.

Ha, yea, in particular these monochromatic pixels can't simply be white. Notably ctrl-f'ing for "white" gives zero results on this page. Relatedly, the page talks a lot about pixel density, but this confused me: if you swap each R, G, or B LED with an adjustable LED, you naively get a one-time 3x boost in pixel area density, which is a one-time sqrt(3)=1.73x boost in linear resolution. So I think density is really a…

It would be interesting to plot all of the achievable colors of this LED on the chromaticity diagram. Presumably it'd be some sort of circle/ellipse around white but might have some dropouts in certain parts of the spectrum?

Pure wavelengths are on the horseshoe-shaped outline of the CIE 1931 space. The straight line connecting the ends of the horseshoe is the line of purples, which also isn't monochromatic.

https://en.wikipedia.org/wiki/Chromaticity#/media/File:Planc...

Re: Polychromatic Pixels

#73

Post by lsaferite »

FriedPickles wrote: post #61
jessriedel wrote: post #59

Earlier quoted context omitted.

Do you mean hyperspectral imager (i.e., camera), or a hyperspectral display ?

An imager/camera: by illuminating a scene (or light box) solely with the tunable LED, sweeping it across the spectrum, and capturing it with an achromatic camera.

> achromatic camera

Is that the same as a panchromatic camera?

Edit:

Asking because I have a 410x410px hyperspectral imager that has an aligned 1886x1886px panchromatic imager that is use to perform pan-sharpening of the HSI data bringing it up to 1886x1886. I'd never heard of a panchromatic camera before I got involved in this business and I've never heard of an achromatic camera either. All I seem to find is achromatic lenses.

Re: Polychromatic Pixels

#74

Post by mensetmanusman »

TJSomething wrote: post #69
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…

One thing I noticed is that they were talking about demoing 12,000 ppi displays, which is way more resolution than you're going to resolve with your eye. So using 2 pixels is still probably a win.

Those are the densities needed for near eye displays. The best displays can still show pixelization to the human eye up close.

Re: Polychromatic Pixels

#75

Post by mensetmanusman »

jessriedel wrote: post #58
FriedPickles wrote: post #52

Earlier quoted context omitted.

It can produce all the colors of the rainbow. But no magenta. Perhaps they can quickly pulse the LED enough between multiple wavelengths.

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.

Re: Polychromatic Pixels

#76

Post by mensetmanusman »

modeless wrote: post #49

I understand that one of the big issues with microLED is huge brightness variation between pixels. Due to some kind of uncontrollable (so far) variations in the manufacturing process, some pixels output 1/10 the light (or less) as others. Ultimately the brightness of the whole display is constrained by the least bright pixels because the rest have to be dimmed to match. Judging by their pictures they have not solved…

It is solvable with enough capital investment though, question is how much will it cost to solve.

Re: Polychromatic Pixels

#77

Post by mensetmanusman »

Retr0id wrote: post #13
maxrumpf wrote: post #10

I imagine color consistency will be such a pain here.

I'd hope that per-pixel calibration would solve that, but I wonder how much that calibration would drift over time.

Whatever the drift would be, inorganics would drift less than organic materials.

Re: Polychromatic Pixels

#78

Post by paipa »

golergka wrote: post #71
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…

> color space is 2D Human eyes have three different color receptors, each tuned for it's own frequency, so it's already 3d. However, apart from human perception, color, just like sound, can have any combinations of frequencies (when you split the signal with Fourier transform), and may animals do have more receptors than us.

You only need to mix two different wavelengths to render any human perceptible color. They give you four parameters to work with (wavelength1, brightness1, wavelength2, brightness2) which makes it an underdetermined system with an infinite number of solutions for all but the pure, spectral boundary of the gamut.

Re: Polychromatic Pixels

#79

Post by duskwuff »

PaulHoule wrote: post #57
FriedPickles wrote: post #52

Earlier quoted context omitted.

It can produce all the colors of the rainbow. But no magenta. Perhaps they can quickly pulse the LED enough between multiple wavelengths.

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.sciencedirect.com/science/article/abs/pii/003189...

*: With the exception of phosphor-converted LEDs, which are uncommon.

Re: Polychromatic Pixels

#80

Post by GrantMoyer »

golergka wrote: post #71
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…

> color space is 2D Human eyes have three different color receptors, each tuned for it's own frequency, so it's already 3d. However, apart from human perception, color, just like sound, can have any combinations of frequencies (when you split the signal with Fourier transform), and may animals do have more receptors than us.

Humans perceive all stimulation in the same raito of the L, M, and S cones to be the same color, but with different brightnesses. So only two dimensions are nessesary to represent human visible colors, hence HSV or L*a*b* space.
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