25/05/2012  | by: Shaun Cleary



For those in the printing business understanding the basics of RGB vs CMYK is essential. However, what do you know about the two? We run you through the basics.





The pixels or dots on your page make up the image and the dot concentration of a colour make up the specific colour. In CMYK, there are three shades - cyan, magenta and yellow and of each of these three there are 100. This means that CMY has (100x100x100) - 1Million colours. The K part of CMYK is black. Essentially black is 100 per cent of CMY and is the subtraction of colour on white paper.


On the other hand, white is all the colours together, essentially like light is. This is the opposite of black which is the absence of colour. So, when we begin with white paper it has all the colours on the paper. In CMYK by adding varying ink we are subtracting and creating specific colours from those blends. This subtractive method is one of the things people never realise about the printing process.


The CMYK model masks colours on a lighter backing. This ink then reduces the amount of light that would usually be reflected and so by subtracting brightness creates colours.


Black as a part of CMYK


Why do we have K? Why then not use 100 per cent CMY to make it? Well, imagine the amount of ink it would take to create black through CMY - a lot - which would increase the price of printing significantly. Also CMY black is quite muddy. Though, you may not expect it, a CMY black is not very crisp. Finally, K - black is also better for creating greys.


Paper Matters


The paper in CMYK is also important. Obviously the default colour is white. However, use colour paper and watch the difference. Cream paper will create a warmer colour, whereas blue is colder. Some printers often show up their colour combinations on coloured paper. Blacks with a hint of cyan can come through. However, a good printer will remove magenta from black and create the rich, deep colour you desire.



RGB - Red, Green, Blue





So, what's RGB? Well, it's the complete opposite, an additive colour. When you turn off your computer screen it's black. RGB adds colours to that screen. However, unlike CMYK which is made of dots, RGB is made of electronic signals and levels of brightness created by either a cathode ray or liquid crystal diode.  RGB also has 255 shades of brightness for each of its red, green and blue. This makes for (256x256x256)16,777,216 colour possibilities. In the case of RGB the 255 colour is white and 0 is black.




On screen colour is RGB and print is CMYK. One is subtractive and one is additive. This is why computers use RGB to create images and they then have to be converted to CMYK.


In essence, printer companies appreciate the colour being converted before it is sent for printing so the buyer can see and amend any colour shifts. Conversions are not perfect, especially due to the absence of black in RGB.


So, now you know why, the next time you print, convert to CMYK, check the file and send it.  



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