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Thread: RGB vs CMY

  1. #1
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    Default RGB vs CMY

    Everybody has RBG lasers but every intelligent light that has colour mixing uses CMY, whats the difference and why?

    could you put RGB and CMY in the same laser?

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    Lightbulb

    I kinda asked this once. While you can get a "cyan" 488nm, and yellow 594nm lasers, there isn't a magenta wavelength...

    And with lasers you are using... (I get these backwards sometimes...) additive colors, RGB, the intelligent lighting fixtures are using subtractive colors (or vice versa, I know the thoeries, just not sure which is which ). I have no idea how intelligent lighting works, but I think they are like spot lights, using a white light and films to filter the light to change colors. They are taking colors away from the white light using CYM. I think...
    Love, peace, and grease,

    allthat... aka: aaron@pangolin

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    The color space for emitters is additive while it is subtractive for absorbers.

    The reason for not using CMY colors is that it would severely reduce the gamut as it would be impossible to reproduce for example blue or red.

    I don't know what "intelligent light" is, but I'm guessing it uses a white light source and color filters to make different colors. That is a subtractive system since the different filters absorb light. Here, you need to use CMY colored filters to remove the RGB colors one at a time. This can be a little confusing, but a material that appears for example red under white light has that color only because it absorbs blue and green. A CMY colored material absorbs only red, green or blue, meaning you can combine these filters to get the whole RGB space. From an efficiency point of view it is hardly an intelligent light though.
    Last edited by tocket; 07-13-2008 at 09:13.

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    Quote Originally Posted by tocket View Post
    I don't know what "intelligent light" is
    What they are really called is "intelligent lighting fixtures", they are basically any lighting fixture that can be controlled in someway by DMX control signals, be it the pan/tilt, colour, gobo etc. etc.
    Where as original lighting fixtures where controlled by some sort of dimmer pack and that was all they could do, dim.
    Most "intelligent lighting fixtures" use a bulb so the light is white, it then will have a dichroic filter put in front of it, usually a few fixed colours in a wheel that is turned in front of the beam. If it also has CMY mixing the the 3 colours Cyan, Magenta and Yellow are moved over the bulb in various amount to creat whatever colour you like.
    Most LED lights use the RBG system, in that they have a number of Red leds, a number of Green leds and a number of Blue leds, varying what colour leds are on or off and what intesity causes different colours to be produced. Some newer of the LED fixtures are now using a 20W white led which is sort of equivalent to a 250W halogen lamp. It then has the dichroic filters put in front to get the colours.

    I hope that helps expalin things abit better,

    André
    Last edited by Onge; 07-13-2008 at 09:36.

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    Color has been a fascination of mine ever since I can remember. There are many different models for synthesizing color.

    As tocket has already pointed out, the main difference is between emitters and absorber, additive and subtractive.

    A red laser is red because that is the only energy that you can see that it is emitting. A fire engine is red because some amount of light is illuminating it. That light must have at least some red in it. The paint will absorb every other color but the red. The red light will be dispersed off of the surface and you will see only that energy.

    Take a look at your computer monitor. When it is off it is nearly black. As you put a signal to it, it lights up. It can emit energy in red, green and blue. the more energy it emits the brighter it gets. It moves away from black toward white. That is additive.

    Take a look at a piece of paper. It is white! The more ink you put on it the darker it gets. It goes from white to black. That is subtractive.

    It turns out that the primary colors for additive are (approximately) the secondary colors for subtractive and vise versa.

    Look at it like this. Magenta ink will stain white paper so that it no longer reflects any green. So the ink has subtracted (absorbed) green from white; which leaves you with red and blue being reflected. Cyan will take out the red and reflect the green and blue. And yellow takes out the blue leaving the red and green.

    In general (computer inkjet) printing on paper is WAY different than a monitor in the fact that a monitor can mix varying amounts of energy to make all the colors and a printer (for the most part) can only either make a dot or not make a dot. Color mixing is done by creating a pattern of dots over an area. This is why you now see inkjet printers with pale magenta and pale cyan.

    There is also something else that I think is kinda' neat. There are color terms that are often misused, but they really have very specific meanings.

    Hue, in its most pristine form is any single wavelength of light, analogous to a single line of energy emitted by a laser. Hue can also be synthesized using the RGB model. First of all you have to start with a balanced system. That is to say, you need to know that if you give it all the red, green and blue, you will get white. Now lets say you put your RGB channels on a scale of 0 to 255 (8 bits). If you start out with full on red, no green no blue. That is your first hue. Now, leave the red on and ramp up the green from 1 to 255. You have just made the next 255 hues that go from red, through orange up to yellow. Now ramp down the red from 255 to 0. There's another 256 hues from yellow to pure green. Now bring in the blue from 1 to 255 with the green still full on and you go from green through aqua to cyan. Ramp down the green back to 0 and you go from cyan to pure blue. With the blue still full on bring in the red from 1 to 255 and you go from blue to magenta. ramp down the blue with the red full on and you go from magenta back to pure red.

    Tint is even a bit more complicated to figure. Look at it like this if you could mix white light as a single component, you could make any one of the hues fade out to white light. Any color mixture in that direction is tint!

    Shade is the opposite. if you could fade any one hue to black that's shade.

    This is a full 2D map of all of the possible hues (1 pixel line horizontally through the center) the tints (anything above) and the shades (anything below)
    http://www.akrobiz.com/ezfb/graphics/ezfb_h_16.jpg

    What you do not see in this bitmap is the rest of the 16,777,216 mixtures of red, green and blue. Those are called tones
    Tone is what you get if you could mix a shade of gray with any one of the hues, so the color fades to a neutral gray. There are 254 combinations of gray, other than black and white.

    A shade of gray is what you get when you mix equal parts of red, green and blue. It has no tendency to look like any color (hue).

    James.
    Last edited by James Lehman; 07-13-2008 at 13:02.

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    I'm not absolutely sure, but I think there is a kind of polychromatic dicroic filter that will only pass a narrow portion of the spectrum. That wavelength is controled simply by the angle that the light passes through it. I think that is what I've seen waving back and forth on a stepper motor in front of a nice high output white lamp. That is an example of true hue! There is no RGB mixing in that at all. What you see is what it is!

    James.
    Last edited by James Lehman; 07-18-2008 at 11:42.

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    Quote Originally Posted by James Lehman View Post
    I'm not absolutely sure, but I think there is a kind of polychromatic dicroic filter that will only pass a narrow portion of the spectrum, that wavelength is controled simply by the angle that the light passes through it. I think that is what I've seen waving back and forth on a stepper motor in front of a nice high output white lamp. That is an example of true hue! There is no RGB mixing in that at all. What you see is what it is!

    James.
    I have a dicroic wheel with several continously changing sinusoidal bands on it, coated by OCLI (best in the world) for a major laser show company, what color do you want? There are 4 bands on the 5" wheel,makes some rather unique colors with a white laser, and thats the closest I've ever seen to cmy with a laser


    steve

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    Quote Originally Posted by mixedgas View Post
    I have a dicroic wheel with several continously changing sinusoidal bands on it, coated by OCLI (best in the world) for a major laser show company, what color do you want? There are 4 bands on the 5" wheel,makes some rather unique colors with a white laser, and thats the closest I've ever seen to cmy with a laser


    steve
    I think you missed the point. There is no such thing as additive color with CMY.

    There are a couple of ways to get color from an emitter, though. One way is to mix RGB and another way is to somehow filter a narrow bandwidth portion of the visible spectrum from a full spectrum white light source.

    James.

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    Uh... all my ColorKey DMX controllable intelligent lighting fixtures use RGBI... which is fairly reasonable since they're LED arrays.

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    Quote Originally Posted by James Lehman View Post
    I think you missed the point. There is no such thing as additive color with CMY.

    There are a couple of ways to get color from an emitter, though. One way is to mix RGB and another way is to somehow filter a narrow bandwidth portion of the visible spectrum from a full spectrum white light source.

    James.
    IS my Subtractive notch filter a RGB or A CMY? We could argue that for hours, but my wheel notches out, not adds!

    Steve

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