RGB vs. CMY Color Mixing
- Thread starterPadawanGeek
- Start date
Well they are really two different approaches entirly, and its not really a case of one of the other. For instance anytime you are using moving lights*, pars*, elipsodals* or anything of the sort you are pretty limited to cmy subtractive mixing. The only time as of right now where you might use RGB is for cyc lights, or with strip lights, but then color mixing is difficult since transparancy's are off with gels along with it being hard to get a true R, G or B.*
*This all gets thrown out the window when LED's getting improved output.
*This all gets thrown out the window when LED's getting improved output.
Chaos is Born
Active Member
It's hard to say one is better than the other, it's more a matter of which is possible for the type of application you are using.
"RGB" is an additive process and requires multiple light sources (typically Red, Green, and Blue) which are mixed together to make white. However, RGB isn't the only additive combination used. Selador's LED instruments use this technique but actually have 7 different colors mixing to make white.
"CMY" is a subtractive process and uses a single white source. A combination of Cyan, Magenta, and Yellow dichroic filters are moved in front of the light to subtract out colors in order to mix the color you want. (Seachanger adds a fourth "extreme Green" filter to extend the range of colors possible.)
"RGB" is an additive process and requires multiple light sources (typically Red, Green, and Blue) which are mixed together to make white. However, RGB isn't the only additive combination used. Selador's LED instruments use this technique but actually have 7 different colors mixing to make white.
"CMY" is a subtractive process and uses a single white source. A combination of Cyan, Magenta, and Yellow dichroic filters are moved in front of the light to subtract out colors in order to mix the color you want. (Seachanger adds a fourth "extreme Green" filter to extend the range of colors possible.)
PadawanGeek
Active Member
That is correct in that there is no scroller that could be loaded with red, green, and blue gel strings and give you any output. Putting any kind of color media, be it dichroic or gel you are creating the apparent color by either reflecting back the unused light (dichroic) or turning the unused light into heat (gel). If you put a combination of any two "pure" primary colors in front of a light (using either dichroic or gel) you will actually get no output. In short, there is no such thing as subtractive RGB mixing, it is impossible.
ON the other hand, if you have multiple sources RGB additive color mixing is the preferred method. If you play with the levels carefully and set your lights up well then you can create a wide range of colors from 3 sources or 3-circuit wash fixtures.
Chaos is Born said:
I find it interesting that you say this on account of the fact that in the graphics world, most printed graphics are created using some variation on the CMYK (Cyan, Magenta, Yellow, Black) printing process. Many new printers now use 8 inks, two tones of each color. Printing from an RGB palette is quite difficult, yes in pigment color theory it works, but have you tried it recently? It is very hard to create shading when you start with saturate primary colors.
Granted, a computer display is incapable of displaying graphics work in CMY space, but with all of the color conversion profiles today, it makes it much more beneficial to work in programs like Photoshop in CMY space especially if you are printing things yourself. CMY is the language your printer understands. If you are working for digital display then RGB is the color space you should work in.
Also important to note is that color theory is not the same for pigment and light. In pigment, R+G+B=some ugly brownish blackish color (you can't mix true black). In light, R+G+B=White. This is because of the same principals as color mixing above. Weather you paint the floor red and shine white light on it, or you put a red gel in front of a light, the red pigment in either case absorbs the rest of the spectrum only reflecting or allowing red wavelengths to pass. Thus, if you had a blue object you put in front of a red light it would appear black as there is no light in the blue wavelengths to reflect off the object.
There, color theory 101, a lot more than I thought I was going to say, hope it helps.
Just to add to what Wolf said... you could take three instruments with color scrollers, pack them in tight together and aim them carefully to hit the same space as close as possible and create a form of RGB type of mixing.
However, the gel in the scroller is actually subtractive. You are taking white light, subtracting everything but red, green, and blue in each instrument, then trying to put them back together to make white... that's nuts. (Just as nuts as taking a bunch of white LED's and filtering them to create Red when Red LED's will do the job so much better.)
In the end, LED's are best suited for RGB additive color mixing while Incandescent/Discharge instruments are best suited for CMY subtractive color.
Is this making sense?
Back to the original question, fine tuned a bit... LED's can produce colors with much more color saturation (deeper, richer, darker) than incandescents/discharge lamps with CMY filters... or just plain old gel. On the flip side, LED's have a harder time creating as good of a white light and they just aren't as bright.
If I had an unlimited budget and wanted to wash a cyc with brilliant color, LED's win hands down. HOWEVER, LED's are dramaticlly more expensive at this point so it's out of the range of most theaters today to even consider.
If you want to wash a cyc with LED lights, bright enough that it doesn't get washed out by the other lighting on stage, you need to cover it with both top and bottom rows of instruments and you need LED instruments covering about 75% of the cyc's width. So a 50 foot cyc needs 50x.75= 37.5 feet of LED strips TOP AND BOTTOM... That's 75 feet of LED strip lights that cost around $1500 a foot (when you add the cost of diffusers, mounting hardware etc...). 75x$1500=$112,500. Who has that kind of cash laying around?
OR you can just use some Cyc lights and gel. In the future as LED's become more powerful and less expensive, they will be a great option, but for now it's an option only for big concert tours, Broadway, and Vegas.
If I had an unlimited budget and wanted to wash a cyc with brilliant color, LED's win hands down. HOWEVER, LED's are dramaticlly more expensive at this point so it's out of the range of most theaters today to even consider.
If you want to wash a cyc with LED lights, bright enough that it doesn't get washed out by the other lighting on stage, you need to cover it with both top and bottom rows of instruments and you need LED instruments covering about 75% of the cyc's width. So a 50 foot cyc needs 50x.75= 37.5 feet of LED strips TOP AND BOTTOM... That's 75 feet of LED strip lights that cost around $1500 a foot (when you add the cost of diffusers, mounting hardware etc...). 75x$1500=$112,500. Who has that kind of cash laying around?
OR you can just use some Cyc lights and gel. In the future as LED's become more powerful and less expensive, they will be a great option, but for now it's an option only for big concert tours, Broadway, and Vegas.
Last edited:
Chaos is Born
Active Member
this is true, however working in photoshop i have always found it easier to work RGB mixing than CMY on the color pallet. Granted when i'm doing photography editing with saturation in RAW images, i'm using ROYGABPM mixing seperatly to themselves, probably the best work is done with RAW images cause each color is a layer to iteself and it ends up working quite like CMY mixing on a slide that you would have, however i was trained in RGB since photoshop 4thats what i know and use in photoshop.
But what if you were to additive mix with CMY? I've never seen strip lights or cyc lights to be CMY (although I have seen RGB, RGB+Amber or RGB+N/C). Why is it that most striplights do not use cyan and magenta to create blue? I'm assuming it has something to do with the light output or the strength of color used?
However when I was learning color theory, you put a true red gel, you get red light. You use a magenta gel, the light has red and blue wavelengths, so it would seem as though that would allow more light to be let through.
Thanks!
JD
Well-Known Member
This has to do with another, almost unwanted characteristic-
LEDs (with exception to white) are monochromic.
A gelled "Primary Red" contains many color frequencies, where as a Primary Red led only contains one. The problem is, our eyes each see red at a slightly different center frequency. (Variance between people) The gelled primary red has enough slop to it that we all consider it red. The LED may be as red as it gets to some people, and slightly off to others. The "white" caused by an RGB led fixture contains only three frequencies of light! They effectively do not have a "color temperature." (White LEDs get their color temperature by the phosphorous they use to convert their UV output to visible light.) This may not look correct to some people. (Maybe everyone!)
Diachronic filters used in subtractive mixing are basically tight band-pass filters. There is still some output on either side of their center frequencies. Unfortunately, CMY subtraction is most often done using a discharge lamp, which itself has a lot of peaks and valleys in its spectral output.
Dichroic. "Diachronic" refers to language. See kids, no one is immune or above reproach; see this thread: http://www.controlbooth.com/forums/question-day/8599-cb-tech-form-english-class.html. JD used the wrong word once and was never corrected, so now he is wrong every time. <lecture /off>
JD
Well-Known Member
Ah, go tell Bill Gates! (I don't care if he retired!) I pre-type my posts into Word, and it auto-corrects it to Diachronic every time!
If you're a mac-ie, Safari does too. I think spell check is much more useful than auto-correct.
If you're a mac-ie, Safari does too. I think spell check is much more useful than auto-correct.
I thought Safari did it too, but I wasn't sure so I didn't write it. You can get Safari for Windows, too; I like Firefox because it's open source and the bookmarks feature works better than on Safari.