Is the 4th Yellow Pixel of Sharp Quattron Hype?

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?"

Comments

RGB

[Kell Bengal]

It strikes me that a better use of a fourth colour pixel would be to represent all those greens the RGB colour space doesn't actually represent.

Re:RGB

[Anonymous Coward]

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:RGB

[forkazoo]

Only one problem. No Y encoded in the data stream, so it has to be interpolated.

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:RGB

[rduke15]

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.

Re:RGB

[jareds]

You seem to be under the impression that every fully saturated color is a spectral color, but this is false. If "hue" only includes the pure visible spectrum, then HSB will not include magenta (or, actually, the whole triangle defined by white, red, and violet, on CIE chromaticity diagram). Look in particular at the color wheel and the visible spectrum on the magenta page. People do use HSB, but the range of the hue must include a non-spectral "line of purples" to wrap around.

Not necessarily fake

[russotto]

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.

It *could* be good

[__david__]

First, check out http://en.wikipedia.org/wiki/Gamut 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.

Pictures just about sums it up

[phantomcircuit]

http://regmedia.co.uk/2010/05/07/quattron_4.jpg That just about sums up the entire article.

Re:Yellow... yawn

[eggnoglatte]

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:Careful What You Laugh At

[iwaybandit]

Didn't see that ad myself, but they probably used this effect.
Fechner color

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.