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RGB vs CMYK
RGB is a colour profile used in devices such as computer monitors or TV screens to display pictures. Tiny dots of Red, Green and Blue in different combintions can create just about any colour imaginable.The RGB spectrum of colours extends further than the CMYK spectrum. Red, Green and Blue are additive colours
CMYK is a colour profile used for commercial printing worldwide. Similar to the RGB profile, CMYK uses combinations of dots, in this case Cyan, Magenta, Yellow and Black (Key ) to display a range of different colours including photographic images. The CMYK spectrum is somewhat limited compared to the RGB spectrum, lacking some of the more vibrant colours but can be enhanced by adding PMS colours, sometimes referred to as 'Spot' colours; see article on PMS or 'Spot' Colours. The CMYK printing process alone, also known as Full Colour printing.uses four printing units. Cyan, Magenta and Yellow are subtractive colours.
To the right is a colour gamut comparison chart showing the significant differences between the CMYK, PMS (Pantone) and the RGB colour spectrums. From this chart it is pretty obvious that extremely vibrant colours cannot be reproduced in CMYK. The colours outside the CMYK area and within the RGB area will be the most affected by the conversion from RGB to CMYK.
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__________RGB Image_______________________________CMYK Image
The above comparison may shock you but most photographic images convert pretty well.
Images to be used as part of a website for example are usually optimised for this purpose using the RGB colour spectrum, ideal for computer monitors but would print poorly even when converted to CMYK. These images are often referred to as 'Low Res' since the optimum resolution for online viewing is only 72 dpi (dots per inch) as opposed to the 300 dpi optimum for imaging devices outputting at 150 lpi (lines per inch).
Please refer to the article Halftones, image resolution (DPI) and LPI for further reference on this subject.
When using RGB images in your artwork you should convert them to CMYK as early in the process as possible using your image editing software (refer to your software's help file for instructions). If you do not have the facilities to convert to CMYK yourself please contact us as any artwork supplied in RGB will automatically be converted to CMYK using default conversion settings during the final output to the imaging device.
Written by A. S. Bergant, © Samberg PTY LTD, 2007
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