RGB CMYK, what does GM have to do with it?

August 25, 2009

I miss the Canon TechNET Conferences. Canon use to hold them in Florida and California every year in August.  Yes it was Hot, Damn Hot to be in Florida in August but they were a great learning experience. i even took my young family to Disneyland a couple of times. But It was a working trip for me. It was where I learned much of my trade in a real world sense. IMHO there was no better technical training for an SE. The scope and depth of what you could get exposed to in a few days was unparalleled. From theory to hands on workshops I have never experienced a better run technical conference.

When Canon started doing the TechNET conferences EFI provided much of the technical expertize. But by the time they finished running them (thanks Arnold) Canon was doing most of the technical presentaions themselves, and doing a fine job. They use to do technology “primers” the first day. Stuff that was considered too basic for the experienced SE, but very, very important to those who were starting out.I personally attended these for the first few times I attended TechNET (I felt it was worth my time)

When it comes to color management, and color theory, especially on how it applies to the real world I will always remebr a phrase that I learned at one of my first Canon TechNET primers:

“Red Car BY GM”

What the heck does General Motors (GM) have to do with color management? Nothing, but if you remember that phrase and if you know how to draw triangles you will understand the relationship between RGB (Monitor) color and CMYK (Printed) color.

RGB (Monitor) color is represented by this first triangle

RGBCMY (we’ll talk about K later) is represented by this second triangle

CMYThe relationship between RGB and CMY is best described by

Red Car BY GM

Red Car BY GMThe relationship is R (red) to C (cyan), B (blue) to Y (yellow), and G (green) to M (magenta). Hence Red Car BY GM. When you draw your first triangle simply put an R, a G, and a B at separate points of the triangle. Now draw an inverse triangle so that is forms what looks like a star (or a star of David). And put the C (Cyan) opposite of the R (red), and the Y (yellow) opposite of the B (Blue), and the M (magenta) opposite of the G (green). So that your Color Star looks like the one above.

Now we can talk about the relationship between what we see on a Computer monitor (RGB) and what we see on a printer page (CMYK). The colors on each side of a color are directly proportionate. The Colors across from each other are inversely proportionate. What does that mean? Well if  the Graphic Artist says I want this to be more RED, most people will increase the Magenta because they think Magenta is directly proportionate to Red. But you only have it half right. Red is made up of Magenta AND YELLOW equally. since M & Y are on either side of R they are directly proportionate. So if I want more RED, I could increase BOTH my Magenta and Yellow. But I also could do something else. I could decrease my C (Cyan). Since C is across from R, they are inversely proportionate! I can reduce Cyan to shift the print to more Red. I still use this today, in fact I did use this today to help minimize a green hue in what the customer wanted to be a neutral tan.

So what about the “K” in the CMYK. What the heck is K anyway, and why doesn’t “K” show up in the triangles. . K = Black. And The triangles are theory. If you have R=0, G=0, B=0 you have black. And , in Theory if you were to mix equal portions of CMY together you would have Black at least at the maximum densities, at least in theory. in practice (read the real world) you most often get a muddy brown. So they add K or Black so that they can get a real, true black without mixing CMY.

Now this does not address a “cool black” or a “warm black” or a Pantone black versus an RGB Black vs a CMYK Black, And you thought that black was just black. Just for fun take Quark Express, or Indesign a draw a number of boxes and put each of the a fore mentioned blacks in them. Then print them out on your preferred MFD or high end printer and notice just how different they look. (Full disclosure: this was a Canon TechNET hands on exercise). It will be a learning experience.

Let’s consider this a Primer, a very basic instruction in the relationship between RGB and CMYK color. You can thank the folks who brought us the Canon TechNET conferences. I do wish they would bring them back. I think that the newer SEs could benefit greatly!

That’s My $0.02
Vince McHugh



  1. I have been working with color since I was old enough to hold an paintbrush, but I’ve never read such a clearly written, informative, useful explanation before. Spot on (no pun intended)! This post is a keeper, and with your permission I plan to share it with a couple of clients. Thanks, Vince!

  2. Shaja,

    Glad you found it useful. Feel free to share it.


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