Remember that time when you were a kid, and you sat down with your so-called friend at a play date, each of you with your own colouring book and box of crayons? Remember how you proudly pulled out your set of 64 crayons…well actually it was 58 after the great dog-barfing-carpet-replacement incident of 1994. You opened the box to select a nice orange for the unicorn and to your horrors, your so-called friend pulls out a monster 2,000-crayon box, putting to shame your measly 58. Their unicorn emanates pink metallic fairy dust. You look in your crayon box, but alas, no pink metallic fairy dust in there. I ask, does the number of colours really matter? Read on, my Crayola-shamed friend.
Have you sometimes noticed the colour palette in your application has three colours labeled RGB, and sometimes it has four labeled CMYK. What is this alphabet soup of letters mean, and does it really matter which one it is?
Let’s start with CMYK. CMYK is short for Cyan, Magenta, Yellow, and Black (yeah, I know black doesn’t start with a K, but there is a good reason for it that’s not worth going into now). These are the ink colours used on printing presses. They put in a white piece of paper, and throw some ink dots at it and out comes greens, blues, pinks and oranges in addition to the cyan, magenta, yellow and black. You may have heard that it is a subtractive space. That’s because you have to take ink away to get to white.
CMYK is much like your box of 58 crayons. The number of possible colours described by a colour space is called the gamut (which means entire range or series). On your computer, these four colours go from 0% to 100% and represent what can be printed by a printing press (or your desktop printer). Compared to other colour spaces, CMYK’s gamut is the smallest. Designers will do all their work in RGB, save their files in RGB, and create a second version in CMYK if it is going to be printed. The reason you want to work in RGB is that it has a far bigger gamut – it’s like colouring with the crayon selection from the 2,000 colour box, not your 58 colours.
At home, you can print an RGB file because your printer software will convert the RGB data to CMYK on the fly. But you may not be happy with the results of how it decides to convert your colours. If you convert it yourself, you’ll still find the lack of range of colours disappointing, but at least you know what comes out of the printer is the best it can be. Looking at the image to the side, you can see the vibrant colours in the RGB space convert to dull colours in the CMYK space.
Now let’s take a boo at RGB. Have you seen those ceiling-mounted projectors with a red light, a green one, and a blue one? That’s RGB. Any colour we see that’s based on light is based on RGB. That includes projectors, computer displays, digital cameras, scanners, televisions, etc. When all three colours are projected together, out comes white. So it is called an additive space. The absence of light is black. The absence of ink (CMYK) is white. So they are opposite in how they work.
Each colour (RGB) goes from 0 to 255, so there are over 16.5 million colours possible. It is a bigger gamut than CMYK. There are more colours than your display can show. So, there are versions of RGB that have different gamuts, but most people choose to work in sRGB as it most closely aligns to what your monitor can display.
In practice, you’ll want to receive files in RGB. Save your work in RGB as this preserves as much range of colour as is possible. You can try printing an RGB file, but if you are unhappy with the results, convert it to CMYK and make any adjustments necessary, and print again. But remember, always go back to your RGB master file to make any additional edits. Another CMYK version can be created from the updated master file if needed.
Just imagine you and your Crayola-rich friend enter a colouring contest. When each of you is done, you look at your work, then their work and notice, you only had 2 purples to choose from and they had 200. Had you worked with 2,000 colours in the first place, think what your image would look like! Now think about what happens when you have a beautiful image of spring flowers and the first thing you do is convert it to CMYK. Think of all the colours that just got flushed down the sink. Converting back to RGB will not bring back the colours. They are gone forever.
So get out your big colour box and always work in RGB!