What is CMYK colour mode in printing? The difference between RGB and CMYK colour spaces



Officeworks CMYK requirement

Have you ever wondered why some print shops ask for your document to be in CMYK? What does that even mean? If there’s one thing that you should remember when it comes to printing, it is that the colours on the printed item will never look exactly like it does on screen. Your monitor can never be trusted. This is because our computers use a different colour spectrum from printers. All computer and digital screens including scanners and digital cameras use RGB (red, green, blue) whereas printers and presses use CMYK (cyan, magenta, yellow and black). Therefore almost any image that you can see digitally is in RGB.
RGB vs CMYK diagram | The Hello Bureau Blog
The main difference between the two colour spaces is that RGB refers to the different colours of light and CMYK refers to the different colours of pigment. RGB is additive meaning our screens emits light and CMYK is subtractive because paper absorbs light. The spectrum of colours that digital images use is entirely different from physical inks which is why the colours vary so much from onscreen to physical. Thus when the printer tries to mix inks to match the RGB spectrum it comes out with completely unexpected results.
When it comes to printing a document at the print shop, most printers will ask for it to be in CMYK. When a document is created with CMYK colours, the results are more likely to be accurate. If you have a document that is in RGB, you will need to find a designer to convert the file to the correct mode (or perhaps the print shop can convert it for you for a fee). If you have access to the Adobe Creative Suite you can manually convert the colour mode using Photoshop or InDesign. Although many digital printers now use RGB because it is easier for file formats, most printing presses still use CMYK. It is best to check with your print shop or supplier about what the print specifications are before starting your design and sending it to print.
Fun fact: Did you wonder why ‘K’ stood for black in CMYK? Our brains are wired to follow patterns so surely it would’ve made sense to be ‘B’ instead. Well the ‘K’ actually stands for ‘Key’ because in traditional printing, the key plate is the plate that holds all the image details and is usually done with black ink. 


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