Aren't the standard additive primary colors enough? (RGB)

[Alaric Darconville]

Sharp's got a new LCD TV (Quattron) using 4 colors (adding yellow to the RGB setup). I surmise it'll get you yellower yellows than before (since typically it's R+G that makes yellow), but will it really matter much since things are produced using RGB? (Maybe Sony will make a new camera with a 4-color CCD...)

 

[blasterman]

I saw this new set and also wondered at the problem it was trying to solve.

I'm assuming there's an issue with R+G not being able to produce a sufficient enough yellow because of specific spectral lines of LEDs. I have some RGB mixing PARs and they don't produce a good yellow no matter how you mix R+G.

 

[alpg88]

i,ve seen that commercial too, sounds like new marketing trick.
however, my friend works in large electronic store, they have few dozens tv's on the wall, i,m sure you would see the difference if 2 tv's (3 color and 4 color) are side by side, and same channel is on. but if you bring only 1 at home, you'll be very satisfied with either.
most likely this weekend i will be at his store again, i'll look at that 4 color tv, if they have it on display, and post my findings.

 

[jeeves]

I assume it's meant to speed up image rendering (refresh rate) and reduce energy consumption.
Instead of needing two LEDs to produce yellow, you use a dedicated (real) yellow. This free's up the R + G LEDs to produce other (more vivid) colors/pixels.

I don't know enough about LED tv projection but this might also allow for something I'll just call hybrid-color rendering. Instead of only subtractive color you could potentially 'overlay' colors to utilize the additive spectrum (Y+B = G).


My $0.02.

 

[Canuke]

The main problem with standard RGB is that certain colors will be left out by necessity.

See this diagram for reference.

The outside edge of the CIE diagram represents pure wavelengths. Inside this curve are colors that we see when wavelengths are mixed. Any particular color that we see is a function of which particular wavelengths (components) are used, and the relative intensity of each component.

If we were to mix two components, the resulting range or set of possible perceived colors for that combination -- the gamut -- would be represented on this diagram by a straight line linking the wavelengths of your two components. For example, if you want to see the color range of a 635nm red source and a 505nm bluish green source, locate these two wavelengths on the curve and draw a straight line linking them, across the CIE diagram. The line shows you the set of all possible colors that can be realized using that particular gamut.

Side note: this is how you can detect "metamerisms", i.e. combinations of different components that look the same to the human eye. Simply draw the gamuts of your particular component combination, and anywhere those lines intersect, is the one color where the human eye cannot distinguish between them. This occurs because this use of discrete wavelengths to represent a spectrum of wavelengths, is a sampling process, which is subject to all the errors inherent in such things.

That is also how you can determine which combinations of two wavelengths will result in "white" to the human eye: any line that crosses the midpoint "E" in the diagram includes "white" in its gamut. So, if you wanted to determine what second wavelength you need to make "white" with 635nm red, draw a line through "E" to the other side, which hits at about 495nm.

Conversely, you can link up two standard wavelengths to see their gamut; if you link your standard 590nm amber and 470nm blue, the line does not cross "E", but gets closest to it somewhere to the "southwest" of it, which is in the pink-purple zone (And sure enough, that's the color I see when I mix those).

Now, as you can see, using only two components comes nowhere near the possible gamut available to us (in fact, using two components approximates the color gamut of red-green colorblindness). In order to cover an area of the possible colors, we need to use three components.

The gamut of three-component systems can be visualized on the CIE diagram in the same manner -- except now, you get a triangle instead of a line segment. This is what we see in the diagram.

As you can see, a triangle is not a perfect fit; some possible colors are necessarily left out of the possible gamut.

Now, note that the saturation of any particular hue is a function of its distance from the white point "E". This signifies that for any three-color combination intended to reproduce all possible hues (i.e. surrounds and includes "E"), the out-of-gamut colors will always be the most saturated ones.

In the case of the sRGB gamut, presented in the diagram, the colors that can't be reached are the very saturated emerald bluish-greens. (The Sharp TV adds yellow, rather than emerald green; that suggests to me that their green component may ot be sRGB green, but in the 510nm zone perhaps.) For sRGB, displaying those colors represent a conundrum: if you display the most accurate possible hue of emerald, it cannot be as saturated as it looked in reality, nor in comparison with the other colors that it can display. The only way to improve saturation -- get further away from "E" -- is to change the hue, towards green or blue.

And sure enough, as anyone of you who have cyan LED's or argon lasers in the 480-510nm range can attest, it can be a real bear to get beamshots that look right.

By adding a fourth component, Sharp is seeking to expand the display gamut by adding another "corner" to the gamut, so it can cover a larger area and thusly "reach" more saturated colors further away from "E". Described another way, they are taking more "samples" in color space to increase its resolution.

Now that I've explained that, I need to tackle a few loose ends to round things out.

First: the diagram assumes completely pure wavelengths. In reality, the RGB sources we use, be they phosphors on CRT's, LED's, or filtered sources, they are not in fact pure, or completely saturated. This means that they are closer to "E" than pure wavelengths; the gamut therefore shrinks inward on the diagram. (The purest practical light sources we have are lasers; this is one reason why laser TV's and projectors are a hot area of development at the moment.)

For those of you wondering why we don't simply move the green point up to the 520nm area: I suspect that this is a legacy of phosphor tech on CRT's which were dominant when the standards were defined. There may be more to the story; I understand that there are green diode lasers in development that lase around 515nm, which may address this.

 

[saabgoblin]

Red and Green are complimentary, meaning that they are on opposing sides of the color wheel and when mixed,they usually give you some form of muted orange brown. Red, Yellow, and Blue are the true primaries and Orange, Purple, and Green are secondary with all other colors in between being called tertiary. Red, Blue, and Yellow can be mixed together to create all colors that are visible to the human eye, some 350-360 some different colors can actually be differentiated by the human eye if I am not mistaken with the only exceptions being the colors that you see in tritium vials, such as Hot Pink, Ice Blue, Nuclear Green, I don't know how they get those colors:green:. I would imagine that adding Yellow to the spectrum would allow you to create much more natural colors and that is probably why the LED TV is starting to take hold in the market.

A true color plus White is called a tint.
A true color plus Black is called a shade.
A true color plus Grey is called a tone.

White=the absence of color.
Black=all colors.


A true color=any color not adulterated by either White, Black, and or Grey, a combination of Black and White.

 

[arek98]

Canuke, this is a great explanation :bow: Thanks!

 

[Ksailork]

My apologies for diluting the technical nature of this thread but the commercial for the Quattron starring George Takei makes me laugh every time I watch it. It is a breath of fresh air to see someone with a definite sense of humor and the ability to poke fun at himself.

Back to the yellow - a simple statement from wikipedia: "The Quattron released by Sharp uses RGB color and adds yellow as a sub-pixel, allowing an increase in the number of available colors." Whether it is perceivable by the general public and becomes successful is yet to be determined. I can see a notable difference side-by-side but I pay for that by being tone deaf.

 

[kitelights]

Mitsubishi has been using a 6 color system for a few years now that started with the color wheel on their DLPs. They use an additional yellow, red (magenta) and blue (cyan). The idea is that they can produce more colors and they can produce them faster.

They have a really neat control that allows you to adjust each of the 6 colors separately.

Sharp's 'addition' to RGB color is not new - Mitsubishi has had it for years.

The 'new' standard is x.v. color. Simply put, it's the difference in a box of crayons with 8 colors or one with 64 colors. Unfortunately, we don't yet
have the technology to fully take advantage of the additional colors that the new standard has the capability to produce.

 

[StarHalo]

It's a gimmick, and a strange choice of one in a time when we have a broad range of actual extras, like higher refresh rate, that manufacturers can choose from which make a much more notable difference when viewed in-store.

If you actually want more color, they'll have to take the advice I've been giving for some time and up the bit depth (which I would strongly prefer before another increase in resolution, and especially over that most-discussed but little-bought gimmick 3D.)

 

[gadget_lover]

The main problem with standard RGB is that certain colors will be left out by necessity.

Wow! That's the best description I've ever seen of the way light wavelengths blend and are perceived by the human eye. It makes it very clear why the television picture is almost never quite the same as what we see in real life.

Many thanks. I'm saving this one.

Daniel

 

[alpg88]

yesterday i want to a appliance store, watched 4 color tv for a while, like i said before the difference is noticeable when 2 tvs are right next to each other. 4 color sys. does appear to show better colors, picture is brighter, more vivid, but properly adjusted 3 color sets are not far behind, imo not enough to base my decision on that, thou price wise it is the same as normal 3 color sets.
what impressed me the most was 3d tv, sets already on sale, priced same as some regular led tvs, 50in 3d tv was $2600, it can work in 3d or 2 d modes, plus you need to get special glasses to see 3d picture, another $200, also there is only 1 3d cable channel, in my area, sometimes it shows 3d programs, but not all the time, i was told some sport programs there are in 3d, or you need special 3d dvd, and special 3d dvd player,
when you look at 3d tv with no glasses you see a double pics, like in old tvs that were out of focus.
very impressive, now a days there are only handful of 3d dvds (mostly cartoons), only few programs, but imo in few years it will be a as common as hd tv now.

 

[Pellidon]

Somewhat related my Sony digicam has added an Emerald layer to the mix. For me to get any benefit from it I have to use the "vivid" color space instead of the "standard" but it does give a boost to some colors. They probably found it easier to add a yellow layer to make some colors easier to be more vivid than with straight RGB.

 

[Alaric Darconville]

Red and Green are complimentary, meaning that they are on opposing sides of the color wheel and when mixed,they usually give you some form of muted orange brown. Red, Yellow, and Blue are the true primaries and Orange, Purple, and Green are secondary with all other colors in between being called tertiary.

White=the absence of color.
Black=all colors.


A true color=any color not adulterated by either White, Black, and or Grey, a combination of Black and White.

You're confusing subtractive color with additive color. Pigmentation is a subtractive process. How white does white look in the absence of light?

Television sets use additive color; painting and printing and coloring with crayons is a subtractive process.

 

[PhotonWrangler]

While I can see how a fourth color can expand the color rendering palette, and this will be important for the newer "deep color" HDMI standard, the source material is still only sampled as RGB. I suppose that the ability to interpolate more subtle hues at the receive end is good, but it can't be that much better until the source material is generated with a fourth color component (I'm primarily talking about cameras, not CGI scenes).