4 ms·
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
by GrantMoyer 2y ago
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.wikipedia.org/wiki/Chromaticity https://en.wikipedia.org/wiki/Chromaticity
- FriedPickles 2y agoIt can produce all the colors of the rainbow. But no magenta. Perhaps they can quickly pulse the LED enough between multiple wavelengths.
- PaulHoule 2y agoSee also https://en.wikipedia.org/wiki/Spectral_color 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/identifying-the-causes-of-led-efficiency-droop https://www.digikey.com/en/articles/identifying-the-causes-o... Here is a video of people doing it https://www.youtube.com/watch?v=5PquJdIK_z8 https://www.youtube.com/watch?v=5PquJdIK_z8
- duskwuff 2y ago> 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/0031891467900626 https://www.sciencedirect.com/science/article/abs/pii/003189... *: With the exception of phosphor-converted LEDs, which are uncommon.
- exmadscientist 2y ago> 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!
- jessriedel 2y agoIt 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/PlanckianLocus.png https://upload.wikimedia.org/wikipedia/commons/b/ba/Planckia...
- mensetmanusman 2y agoThe human eye will see white when a pixel flashes through all of the colors quickly in time.
- ajuc 2y agoBut that means it has reduced refresh rate.
- wmertens 2y agoThe two are not related at all. Refresh rate is how fast it can accept input, whereas this is how fast it can do TDM of colors and intensities
- deleted 2y ago[deleted]
- Etherlord87 2y agoHow quickly? Surely well above 1 kHz (1000 FPS). Otherwise you will see flickering.
- jessriedel 2y agoAccording to this, humans can't see flicker above 100 Hz for most smooth images, but if the image has high frequency spatial edges then they can see flicker up to 500-1000 Hz. It has to do with saccades. https://www.nature.com/articles/srep07861 https://www.nature.com/articles/srep07861
- jessriedel 2y agoHa, 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 red herring. But they also mention mass transfer ("positioning of the red, green and blue chips to form a full-colour pixel") which plausibly is a much bigger effect: If you replace a process that needs to delicately interweave 3 distinct parts with one that lays down a grid of identical (but individually controllable) parts, you potentially get a much bigger manufacturing efficiency improvement that could go way beyond 3x. I think that's probably the better sales pitch.
- etrautmann 2y agoIt 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?
- formerly_proven 2y agoPure 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:PlanckianLocus.png https://en.wikipedia.org/wiki/Chromaticity#/media/File:Planc...
- Y_Y 2y agoPresumably they wouldn't need to do a pixel-to-pixel mapping, but could account for the wavelengths of neighbouring pixels to produce a more faithful colour reproduction at an effectively lower resolution.
- meindnoch 2y agoIt's going to be the spectral locus.
- jmu1234567890 2y agoHowever, you would have more flexibility to do tricks sub-pixel to improve resolution?
- thomassmith65 2y agoSurely the 'tricks' we have for RGB displays would be more effective when every element has the same color range as every other. For example, the subpixel rendering of typography for RGB displays had an unavoidable rainbow halo that would no longer be an issue for most colors of text with polychromatic pixels.
- Remnant44 2y agoThis is definitely a problem; if the control circuitry is up for it you could PWM the pixel color, basically dithering in time instead of space to achieve white or arbitrary non-spectral colors.
- brookst 2y agoYep. DLP color wheels come to mind.
- TJSomething 2y agoOne 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.
- mensetmanusman 2y agoThose are the densities needed for near eye displays. The best displays can still show pixelization to the human eye up close.
- golergka 2y ago> 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.
- paipa 2y agoYou 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.
- GrantMoyer 2y agoHumans 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.
- a-priori 2y agoAccording the opponent process model of colour perception you need three axes to represent all colours: luminosity [L+M+S+rods], red-green [L-M] and blue-yellow [S - (L+M)].
- dahart 2y agoThere is a fair point there, but a few things - HSV and Lab are only models, they don’t necessarily capture all visible colors (esp. when it comes to tetrachromats). Brightness is a dimension, and can affect the perception of a color, esp. as you get very bright - HSV and Lab are 3D spaces. Arguing that brightness should be ignored or factored out is problematic and only a small step from arguing that saturation should be factored out too and that color is mostly one dimensional.
- BurningFrog 2y agoIn this sense our hearing is much better than our color vision. We can distinguish the combination a huge number of frequencies between 20-20000Hz. But we can only distinguish 3 independent colors of light. Of course our vision is vastly better than hearing for determining where the sound/light comes from.
- cubefox 2y ago> These pixels are variable wavelength, but can only produce one at a time Citation needed. The article doesn't say anything about how the colors are generated, and whether they can only produce one wavelength at a time. Assuming they are indeed restricted to spectral colors, dithering could be used to increase the number of colors further. However, dithering needs at least 8 colors to cover the entire color space: red, green, blue, cyan, magenta, yellow, white, black. And two of those can't be produced using monochromatic light -- magenta and white. This would be a major problem.
- jiggawatts 2y agoDithering just black, red, green, and blue is sufficient to produce a full-colour image. Everything else is a combination of those. That's effectively how normal LCD or OLED monitors work!
- cubefox 2y agoNo, 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 do something similar: They use subtractive color mixing to create red, green and blue dots (in addition to cyan, magenta, yellow and black ink and white paper), then all the remaining shades are dithered from those eight colors. It looks something like that: https://as2.ftcdn.net/v2/jpg/01/88/80/47/1000_F_188804787_u1tuOtXIheifDiUCHxl6UYbLTf0nYQKJ.jpg https://as2.ftcdn.net/v2/jpg/01/88/80/47/1000_F_188804787_u1... (though there black is also created with subtractive color mixing). The color mixing type used by dithering is sometimes called "color blending". Apart from dithering it's also used when simulating partial transparency (alpha).
- jiggawatts 2y agoThe article is talking about microLEDs, which are an emissive light source.
- pfg_ 2y agoThis 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.
- ajuc 2y agoYou'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?
- mark-r 2y agoI hate to think of the damage large amounts of IR or especially UV would do to the eye.
- enragedcacti 2y agoAssuming they can PWM the brightness while getting consistent color (seems reasonable since microLEDs have extremely fast response time) then I think what you're saying would work great. It would be akin to 4:2:2 chroma subsampling where luminance (which we have higher acuity for) gets more fidelity and the resulting image quality is closer to full-res than half-res.
- Bumblonono 2y agoThere are plenty of monochromatic cases. Right now hw has a lot of orange. Dynamic resolution / subpixel rendering. Retina looks really good already, not sure if the effect would be relevant or interesting but it might open up something new
- creshal 2y agoWhat Apple sells as "retina" still doesn't match common print densities, there's definitely room for improvement.
- Bumblonono 2y agoYou make it sound like there is still an easy to spot difference. When i look at the print quality of pictures on a news paper, its the opposite and at least for me, i don't need more than retina and i was very eager to switch to 4k to have higher dpi. But 14' with retina im very happy. I'm actually more surprised by hdr on my lg oled 4k. Its actually quite nice when done well.
- creshal 2y agoNewspapers are famously printed on the lowest quality recycled paper and cheapest print process available, because they're disposable. Compare a retina screen to a coffee table style reference book with high resolution photos – the kinds you can use a magnifying glass on - and you'll still notice differences. Or just look at what companies do when manufacturing technologies allow them to push for higher densities: iPhones now exceed 450 dpi, and the 8" iPads exceed 300; if the technology allowed it, Apple would most likely introduce higher densities on larger iPads and Macbooks as well.
- deleted 2y ago[deleted]
- meatmanek 2y agoI'm assuming that in most cases they'll just make these act as RGB displays, either by sequentially tuning the wavelength of each pixel to red, green, blue in a loop, or by assigning each pixel to be red, green, or blue and just having them act as subpixels.