Is the 4th Yellow Pixel of Sharp Quattron Hype? 511
Nom du Keyboard writes "Sharp Aquos brand televisions are making a big deal about their Quattron technology of adding a 4th yellow pixel to their RGB sets. While you can read a glowing review of it here, the engineer in me is skeptical because of how all the source material for this set is produced in 3-color RGB. I also know how just making a picture brighter and saturating the colors a bit can make it more appealing to many viewers over a more accurate rendition – so much for side-by-side comparisons. And I laugh at how you are supposed to see the advantages of 4-color technology in ads on your 3-color sets at home as you watch their commercials. It sounds more like hype to extract a higher profit margin than the next great advance in home television. So is it real?"
RGB (Score:5, Informative)
Not necessarily fake (Score:5, Informative)
Adding an extra phosphor can extend your gamut, increase your dynamic range within your gamut, or give you finer quantization within the gamut, or some combination of all three. The fact that your source material is provided as three quantities (YCbCr, not RGB) doesn't mean four phoshors won't help.
Doesn't mean it will, either.
Re:Human retinas (Score:3, Informative)
You can't tell the difference, assuming of course that the RGB phosphors are evenly matched with your cones.
Take for instance printers. We have CMYK precisely because C+M+Y doesn't equal to black, as the inks aren't perfect. I think some sort of muddy brown actually results. So a black ink is needed to fix that imperfection. There exist printers with 6 ink colors as well, because that still doesn't make it perfect.
I think better monitors would be a good thing, but I'm more interested in a higher bit depth. Real life has quite a few things that you can see just fine, but which are challenging to photograph and can't be accurately reproduced on a monitor.
Comment removed (Score:2, Informative)
It does work (Score:2, Informative)
Re:RGB (Score:5, Informative)
That 1931 color gamut is misleading because it overempasizes greens. In fact, the original NTSC green primary was much closer to the peak, but as a result, yellows were too muted, so they changed it. But you're right - a turquoise primary would increase the RGB gamut significantly.
The ideal would be that all color information in video would be in device-independent xy color space instead of RGB. See LogLUV encoding for example: http://www.anyhere.com/gward/papers/jgtpap1.pdf
Re:AVSforum take on it (Score:1, Informative)
here [avsforum.com]
It *could* be good (Score:5, Informative)
First, check out http://en.wikipedia.org/wiki/Gamut [wikipedia.org] for reference. The sample gamut picture in the top right shows a typical CRT--lets assume for the sake of argument that LCDs are similar.
If you add a yellow LED to that it just isn't going to add much. The yellow part of the spectrum is already fairly well represented.
*But* if they also change the hue of the green LED toward the blue spectrum then it has a good chance of really opening up the gamut.
The people saying RGB is enough don't understand chromaticity--go look for gamut plots of your favorite output devices and see how little of the full spectrum of colors they can actually reproduce. Printers are especially embarrassing. Your eyes can really see a whole lot of color detail.
Re:Human retinas (Score:3, Informative)
Some women have 4 cones..
Re:Human retinas (Score:4, Informative)
Generally speaking, the human eye is less sensitive to blue and most sensitive to red (more yellow, actually) and green. Making sure that the blue pixels are the brightest in the screen and changing the red pixel to something a little more yellow (assuming the firmware adjusts when recreating colors) would probably be the best approaches to catering to the human eye.
Re:Of course it's hype, just SHARPer :-) (Score:3, Informative)
A 120 Hz display provides a better result for 24 fps input (from film sources) than will a 60 Hz display. With 120 Hz, each frame is displayed for 1000/24 ms instead of varying between 1000/30 ms and 1000/20 ms on a 60 Hz display.
Re:Of course it's hype, just SHARPer :-) (Score:3, Informative)
Except you're completely missing the point. It's not about sharpness or speed. It's about being an even multiple of 24hz so you can display film material (e.g. about everything you'd really want on a 1080p set) without any tricks that ruin the smoothness of motion.
Re:Human retinas (Score:1, Informative)
The human eye has only three kinds of color receptors (plus one grayscale, but only in the peripheral field of view). You could therefore come to the conclusion that you only need three different stimuli to recreate all possible color impressions. This is not the case, due to the overlap in the response curves of the different receptors. There is no single color which can stimulate just the green receptor without also stimulating either the red receptor or the blue receptor. To be able to create all color impressions, you'd need many different greens in addition to a red and a blue light source (which are both sufficiently pure to avoid stimulating the green receptor).
However, this only applies to very saturated colors. As soon as you desaturate a color, stimulating the other receptors is no longer a problem. The color space which a device can reproduce (actually the impressions of which the device can reproduce) is called its "gamut". [wikipedia.org] It's usually represented by a triangle in a horseshoe shaped CIE chromaticity diagram (The corners of the triangle are the impressions created by the three base colors of the device.) Adding a fourth color can extend the color space. The typical RGB display however mostly lacks in the green-cyan area, so that's where additional base colors would create more "new" colors. But even then, it's only about very saturated colors. When was the last time you looket at #00FFFF and said to yourself "That doesn't pop, more saturation"?
LCD screens have a related problem: The colors are created by subtracting (absorbing) colors from a backlight. If the spectrum of the backlight has very distinct spikes, then the resulting base colors are very pure. If the spikes are not only very distinct but also at frequencies which avoid the overlap in the response curves of the receptors as much as possible, you have a wide gamut display. If on the other hand the backlight is a continuous spectrum light source or the red and blue peaks are too close to green, then the gamut is limited by the backlight. For example, CCFL backlit LCDs often have an "orange" red where the red always stimulates the green receptor a little as well. On such a display, a pure red is simply impossible. You can however avoid the color shift by desaturating the colors: Add a little blue too and you get the right hue, just with less saturation.
Re:RGB (Score:2, Informative)
Actually the eye is more sensitive to yellows than reds if you look at that wikipedia page you cited.
As it is now there is a slight dip in the yellow part of the color spectrum on displays because they use a pretty narrow band of red.
Cameras on the other hand for the red color uses a filter that basically takes all light between yellow and infrared.
So the input is both yellow an red combined while the output is just red, by adding yellow the display can correct some of that loss.
Though i would like to see cameras/displays combos that use more natural light spectrum's than just adding yellow.
Re:Human retinas (Score:3, Informative)
As I understand it, only in a small, relatively isolated Northern population. And it's not for yellow. Still cool though.
Re:RGB (Score:5, Informative)
In some cases, it could actually be useful. While most cameras shoot with RGB sensors, most video compression is in some variation of YUV (1) color space. If you shoot on something like a Red One (2) camera, you get a RAW format with more than 8 bits (3) of color information. If you have a sensible post pipeline, you can go to YUV for your distribution format and have plenty of color data to completely fill out the 8 bit YUV data. YUV and RGB don't have identical color reproduction and gamut, so you can wind up with the odd situation where you shot on an RGB sensor, and you decimated to 8 bit data for distribution, but a normal 8 bit RGB display can't quite show every color that you have.
I wouldn't expect brick-shittingly amazing results on such a system. I'd need to see it in person and see a measured gamut chart to have any particular opinion on this particular display, but I can't dismiss the concept out of hand.
(1) : Y in YUV isn't Yellow, it's Luma. Still, the imperfect conversion between YUV and RGB means that a fourth primary could make it possible to more accurately show YUV data on an RGBY display.
(2) : "Red" is a brand name. "Red" in the name of the camera doesn't specifically imply any relationship to RGB color space or anything like that. The camera does use a standard RGB Bayer pattern sensor, though.
(3) : 8 bit color in this context is always "per component" rather than "per pixel" and doesn't imply old school 256 total colors palleted mode. In a X11 config file for example, this would be referred to as 24 bit color. Video guys are more interested in per-component colors because they always do operations on components. When you are writing misc. GUI software, you are generally more concerned with bits per-pixel because you would never care about how much space it takes to upload a fraction of a pixel to a video card since you have to upload a full pixel to display it.
(4) : This footnote doesn't correspond to anything in the text. After all that, I'm now just in the habit of writing footnotes.
Re:Yellow... yawn (Score:4, Informative)
Pictures just about sums it up (Score:5, Informative)
http://regmedia.co.uk/2010/05/07/quattron_4.jpg That just about sums up the entire article.
Re:Better frequency coverage? (Score:3, Informative)
OPPS! The chart should have been:
red -- 610 to 760 nm
gap - 570 to 610 nm
green -- 500 to 570 nm
blue -- 450 to 500 nm
"And I laugh at how you are supposed to see..." (Score:2, Informative)
Re:RGB (Score:4, Informative)
Nit: sRGB isn't synonymous RGB, nor even with RGB as used in displays.
Plenty of RGB colorspaces don't have the green-deficiency problem, and it's nothing innately required by an RGB LED system if it's willing to do a non-sRGB display.
Re:RGB (Score:5, Informative)
I have the impression that you are implying that the bits per channel are related to the color gamut. That more bits per pixel or channel produce a wider color gamut. That is not the case, and the 2 are unrelated. More bits per pixel only give you more shades within a given gamut. In practice, more bits per channel are desirable in video production to allow finer control over color correction, without producing artifacts like banding.
Linear algebra and color gamut (Score:3, Informative)
Quick terminology: Spectral color- Pure, single wavelength color, like a laser. Composite color- A combination of many spectral colors of different intensity.
To truly reproduce a color, each pixel should be able to not only make one spectral color, but a combination of all of them.
This would be very expensive, and fortunately, our eye have sensors only for Red 580 nm, Green 540nm, and Blue 440 nm (RGB), if we exclude the low light rods. We can therefore get away with RGB screens. There are slight errors. For example, assume each R-G-B pixel emits light matching the eyes R-G-B sensors peak sensitivity. Now, we can reproduce any light stimulation by exiting a linear combination of the three emitters. The eye however is sensitive from 380 nm to 740 nm, and can obviously not create the stimulation for neither 400 nm light, nor 700 nm, as your linear combination of only positive values will not cover these spectral colors (outside the gamut of the display). Take a picture of a prism spectrum or rainbow, and compare the original with what you see on the monitor, and you can see this.
So bottom line, RGB covers almost all colors, but adding emitters allows linear combination to cover more of the possible stimulation, but a high cost for little value. It is primarily the near UV purplish blue below 440 nm and the warm reds near IR that can not be reproduced.
Re:Human retinas (Score:4, Informative)
But that assumes the "RGB" sensitivity of our eyes lines up with the emmision spectra of RGB screens; which is not true. Perhaps this Sharp screen brings it closer, actually shows more faithfully the colors which are in the signal; as far as human eye is concerned.
Re:Yellow... yawn (Score:5, Informative)
XYZ space is not perceptually uniform. In particular, the green/cyan area in XYZ occupies a much larger area than would be justified by the eye's ability to distinguish colors in that range. Yellow on the other hand is very under-represented in XYZ.
If you look at the gamuts in a perceptually uniform space such as LUV, you'll find that LCD panels are actually fairly limited in the yellows.
Re:Of course it's hype, just SHARPer :-) (Score:4, Informative)
Your talk of efficiency doesn't make sense at all. An LCD uses less electricity than a plasma. It doesn't matter what is hooked up to the display.
Re:Careful What You Laugh At (Score:4, Informative)
HDR is something which enables photographers to approach the dynamic range available in print photography while largely retaining the color saturation and other qualities of transparency film
That doesn't make much sense, because transparencies and computer displays have a higher dynamic range than prints, not lower.
I reality, HDR photography is about capturing a scene that has a very high contrast ration, beyond what cameras can capture or monitors display. It is done by using shots with different exposures, so parts of the image that would otherwise be over or under-exposed retain detail and don't just get clipped or blown out.
It does tend to be overdone, but so is saturation and the colors that people use in their photos/video don't particularly reflect reality very well either.
Actually, HDR photos are often a better representation of reality, because the human eye adjusts to different brightness levels, which is what the HDR process is doing.
Re:Of course it's hype, just SHARPer :-) (Score:3, Informative)
Nope. The "fluorescent" light in the back is a cold cathode fluorescent lamp driven by an inverter running anywhere from 20kHz to 50kHz. Beat effects with the backlight are not an issue (except on badly designed monitors that PWM too slowly to control brightness).
Some women can see four primary colours (Score:3, Informative)
Re:Clearly missing a trick. (Score:3, Informative)
This certainly accomplishes its goal, but the downsides are also pretty high. Variable backlighting means that color calibration goes completely and utterly out of whack - a different backlight level than what it was calibrated at changes the properties of the panel. So you can have more accurate darks, but you lose accurate colors in return.
Re:Careful What You Laugh At (Score:4, Informative)
Fechner color [wikipedia.org]
is an illusion of color seen when looking at certain rapidly changing or moving black-and-white patterns. They are also called pattern induced flicker colors (PIFCs). Not everyone sees the same colors.
Trying to solve problems that don't exist. (Score:3, Informative)
Color on RGB monitors currently is a fine match for standard broadcast/HDTV/Blu Ray gamut, and LCD monitors are plenty bright, this really doesn't solve a problem anyone was actually having.
Sharp has among the worse LCD tech(IMO) with weak (grey) blacks and a lot of viewing angle shift.
The first reviews that I read, say these problems persist, so Sharp didn't work on real (hard) they have with their technology. Instead they decided to tackle something they can use as a marketing differentiator to impress the rubes.
Re:RGB (Score:5, Informative)
Re:RGB (Score:2, Informative)