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Many printers use CMY or CMYK whereas most computer monitors and TVs use RGB. Many cameras, film cameras, image and movie formats use YUV. Why don't they use the same color representation?

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marked as duplicate by Mokubai, mpy, Dave M, Simon Sheehan, Baarn Oct 24 '13 at 17:45

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A CRT monitor will need to 'turn on' Red/Green/Blue components to display a color(because the screen is 'black' by default. For a printer, the paper is already White(which is a mix of all other base colors), so it needs to 'turn off' some light components and 'leave on' those representing the desired color.

Each color system is capable of representing a certain group of colors(a "color space"), but none of them is able to actually cover all visible colors. These color spaces do not completely overlap, so there will always be colors that can be represented in some color systems while not having a direct correspondent in others. So converting from a color system/space to another is a rather complex problem.

There are many color systems defined, but they can be grouped into "additive" and "subtractive" systems:

  • some devices (e.g. Monitors) use "additive" color systems, like RGB(Red, Green, Blue): the base color is Black, and you can "add" red/green/blue to obtain other colors. You obtain "White" by using the maximum amount of all three components.

  • other devices ( printers ) will use "subtractive" color systems(like CMY or CMYK), where the base color is "White", and you "mask" some components to obtain other colors. In CMY, you get to "Black" by mixing the maximum amounts of all three components.

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Monitors emit light, paper reflects light. When emitting light, it turns out that you can use a bigger spectrum of colors, plus you have more variation in intensity. This is only improving as monitors get better, have more contrast, etc.

When creating color for a specific medium, you can take this into account. If you want to create an advertisement for a magazine in Photoshop, you use CMYK. You could of course send in your image with RGB color-space, but the result might be that some colors are out of the spectrum, which would result in loss of quality. In that case, the printer translates the RGB value that cannot be printed into the nearest CMYK value.

OK you think, what does it matter if I do this or if the printer (or the image-editing program of the printer shop) does it?! Sometimes it doesn't matter. But for high quality printing where the graphic designer wants absolute control, it does matter.

Aside from CMYK and RGB, there are color spaces like Adobe RGB. These are more specific. You can use a calibrated monitor. When the image is then send over to another user, with another monitor, in another lighting condition, the other user will see the image like the creator did, if his monitor is calibrated as well. That's the idea at least.

In my experience color handling is something very tricky. I don't calibrate my monitor, I don't use color profiles, except for the standard ones installed by default. If you don't know what you're doing, it can work against you.

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