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RGB to become RGBCMY
elgatozorbas writes "The basic color elements of television have not changed much since 1954; a half-century after RCA introduced the first color set, the RGB (red, green and blue) system used then still prevails. But Israeli company Genoa Color Technologies has broken the RGB barrier by adding one to three primary colors such as yellow, cyan and magenta, thus expanding - from 55 to 95 percent - the coverage of the visible color gamut. The promised result of this multi-primary color (MPC) technology is a television picture that, with its truer, more vibrant color and brighter image, looks more like cinema than video. Also covered in IEEE Spectrum."
Does this mean I should hold off on buying an HDTV?
It's almost enough to make me wish I was a mutant mother of a color blind son.
A truly revolutionary idea would be to include and project IR and UV in addition to RGB/CMY. Even though our eyes can't exactly 'see' IR and UV, they still form an important part of our realistic image perception. It's not unlike sounds above 20-25kHz in pitch; we don't 'hear' them, but our brain perceives them nonetheless and they are used for stereo imaging of a space.
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Cheers,
Erick
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Sometimes the most mundane improvements can be the best. All the people who swear by HDTV will be SOL, because they'll have hi-res, but improperly colored, television/movies.
My friends are going to be viridian with envy!
There are a couple of factual errors in this story that makes me feel uneasy.
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From the spectrum article:
While film used in cinema contains pigments that can create an infinitely large number of color variations, TV sets combine discrete amounts of red, green, and blue light to create a much more limited color range.
This isn't true: color slide film uses three layers, just like monitors do: http://www.imx.nl/photosite/technical/E100G/E100G
He says that in printing it's common to have inkjet devices that use six, seven, or even eight primaries.
There are good reasons printing uses so many primaries, but it's usually to make an evener tone. My consumer-grade printer has the traditional CMYK (cyan magenta yellow blacK), but it also has two additional colors: light-cyan and light-magenta. They chose these lighter colors so make the blending smoother and the ink spots less noticible; it wasn't to increase the gamut. Printers also use spot-color to make particular colors (such as a company logo) print without needing to use a halftone. These are all just gimicks to get around the fact that printing isn't continuous tone -- in projectors that are continuous tone, these tricks aren't needed.
Basically, it comes down to eyeballs... if you emulate the response curves that your eye is sensitive to, then you can't perceptually do any better.
The traditional RGB's and CMY's don't match these curves, so they define a gamut that can be improved on. For example, take this projector's gamut -- its green is far away from the eye's green, so it can't display the cyans well. But, the color model my company is using for its video product uses a much truer green so we can cover much more of the gamut.
disclaimer: IANACE (color expert), but my most recent project has been color calibration to precise standards.
HIV Crosses Species Barrier... into Muppets
16 million colors should be enough for anyone.
There are three primary additive colors and three primary subtractive colors. Cecil explains it rather well.
Most folks don't realize, but there really are four primary colors. Most geeky types are familiar with the red, green, and blue cone cells in our eyes -- but the rod cells that are used for night vision have their own separate response spectrum, weighted heavily toward the blue/violet end of the spectrum.
That means you have four separate "detector systems" in your eye, each of which is sensitive to a different slice of the optical spectrum. In particular, you can distinguish shades of violet and magenta that differ only in the blue-cone/rod response levels.
Ever think about why blue light is used universally to signify "darkness" or "moonlight" on stage? It's because, in low light levels, your cones shut down and your rods -- which in bright light connote blueness -- are the only part of your retina that works well.
It's also the reason why night-vision flashlights are red, and why blue LEDs appear so bright when used as flashlights. The red light doesn't stimulate your rods, preserving their sensitivity; and the blue light gives you extra rod stimulation per unit power, making blue LEDS very efficient as nighttime illumination.
CMY(K) are Subtractive Colours. (You add them together to get black)
... RGB + CMYK negate each other.
... while LCD's naturally use a CMYk approach
Hehe! No, this is quite false, quite a number of ways.
First of all, colors of light are additive, colors of pigment are subtractive. This is true regardless of which colors you choose. If you had a monitor using the CYM model, you could not produce red, because monitors, being light emitting devices, are always additive, never subtractive, mixing C and Y would add their lights, not subtract leaving just the G. Because of this, you cannot get a lot of colors. However, you can get white, by adding C, M, and Y together. Since monitors are additive, adding CYM makes white, not black.
The LCDs we use today are light emitting, not light reflecting. Thus, they naturally use an RGB color model. If they did not emit light on their own but only reflected like, like a sheet of paper, then their natural color model would be CYM(K). But that's just not how things work.
"Convictions are more dangerous enemies of truth than lies."
As I recall, a linear combination of RGB can express any possible color -- if you allow for negative amounts of the components. A really bright yellow might be 1 R + 1 G - .2 B for example.
That's still a linear combination, but just one that's not particular useful in the real world of phosphors and filters.
Thad
I love Mondays. On a Monday, anything is possible.
CMY are really "combinations" of R G and B.
This is false. C, Y, and M are different wavelengths of light from R, G, and B. Because the human eye only has receptors for R, G, and B, we can't distinguish between equal quantities of R and G and a single wavelength in between the two, namely Y. In other words, we are able to trick the eye into perceiving a full color spectrum using only three different wavelengths of light.
Trees can't go dancing
So do them a big favor
Pretend dancing stinks!
CMY are really "combinations" of R G and B.
They are on your standard RGB monitor, but not in the general case. For example, take a look at the CIE "Tongue" chart displayed e.g. here. With you monitor, you can only display colors in the red, green, blue triangle, but one could add pure cyan at 490nm and actually increase the area/gamut.
Second, there are colors that your eye can perceive that are not representable by the RGB system.
That would be the good old RCA, phosphor based RGB system. If you ran your display with e.g. lasers with 410, 520 and 700nm respectively, you could get a gamut that's almost indistinguishable from the full gamut the average eye can percieve. The smaller area covered in the green region on top of the chart would probably be neglegible due to the decreased capability of the eye to distinguish between greens. So, not RGB is the problem, but the technology to record and display it.
... you're going to need a format that preserves color information in the new 5 color system if you're going to exploit the real improvements in this color technology: closer reproductions of actual color.
Absolutely not true.
For people with normal color vision, in addition to the "rod" pigment (which is not a significant player in color perception and daylight central vision) there are three color receptor pigments located in the "cone" cells, which have broad reception peaks with well-known shapes. The response of those three sets of cells to an image can be accurately modeled by using three sets of sensors and filters that model the three pigments' frequency response.
The problem comes when, given this measurement, you try to stimulate a viewer's cone cells to produce the response equivalent to the light you measured. If you just pick three color phosphors at the peak of the three dyes' response curves, you find that the colors don't stimulate JUST the cones you intended. The green light, for instance, will strongly stimulate the green-responsive cones. But it will also weakly stimulate the red and blue cones. Similarly, red light will strongly stimulate red cones, weakly stimulate green cones, and very weakly stimulate blue cones. Ditto the other way around with blue light.
This has two effects:
First: Even within the range of combinations of stimulus the three light sources can produce, simply playing back the signal will cause the results to be somewhat more pastel than the orignal scene. This can be compensated for to some extent - by subtracting out appropriate amounts of each color's signal from the signals going to the others color emitters.
Second: You can't make the emitters emit a negative amount of light. The result is that there are scene colors, saturated and nearly-saturated colors between the phosphor colors you chose for reproduction, that can produce color sensations that these three screen colors can't reproduce. These scene colors will ALWAYS apper somewhat washed-out if you only reproduce the image with three screen colors.
So with three values you can accurately transmit any color a normal eye can see. But with three phosphors you can't make the eye see some of these colors.
The two-dimensional representation of the relative responses of the three dies looks something like a spearment leaf with the base sliced off. (See figure 12 of this web page. And thank you, canavan) The edge of the leaf represents the response to a pure spectral color, and regions within it to mixes of colors. If you try to reproduce the response with three phosphor colors, you are picking three points on the leaf edge and drawing a triangle between them. By adjusting the relative amounts of light from the three phosphors you can produce a stimulus corresponding to any point WITHIN the triangle. But you can't produce one corresponding to the arcs of the leaf that are outside the triangle.
But by picking more points along the leaf edge you can draw a polygon and hit any point within it. This covers more of the leaf and leaves fewer colors missing. (Indeed, just a couple extra points can give you most of the leaf.)
You still send the signal with the three values corresponding to the response you want from the eye. But now your monitor processes it into more than three colors to put on the screen, to get the eye to respond more closely to the response it would have had to the original scene.
(Note that people with some forms of color blindness have cones with pigments that have abnormal frequency responses. Such people will not see a color TV image as right even with this upgrade, because the camera will not have correctly encoded what THEIR eyes would have seen. They need a camera with a different response, and yet another set of phosphors in the monitor, to get a good match.)
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the human eye only has receptors for R, G, and B
Mantis shrimp have at least eleven different receptors, and lots of birds and fish have four or five. So I guess it's the logical direction to go once the human market for RGB monitors reaches saturation.