Colour Space Fundamentals
Computer monitors emit colour as RGB (red, green, blue) light. Although all colours of the visible spectrum can be produced by merging red, green and blue light, monitors are capable of displaying only a limited gamut (i.e., range) of the visible spectrum.

Whereas monitors emit light, inked paper absorbs or reflects specific wavelengths. Cyan, magenta and yellow pigments serve as filters, subtracting varying degrees of red, green and blue from white light to produce a selective gamut of spectral colours. Like monitors, printing inks also produce a colour gamut that is only a subset of the visible spectrum, although the range is not the same for both. Consequently, the same art displayed on a computer monitor may not match to that printed in a publication. Also, because printing processes such as offset lithography use CMYK (cyan, magenta, yellow, black) inks, digital art must be converted to CMYK colour for print. Many printers now prefer digital art files be supplied in the RGB colour space with ICC profiles attached. Images can then be converted to the CMYK colour space by the printer using colour management methods that honor profiles if present; this helps preserve the best possible detail and vibrancy.

Red, Green, Blue	Cyan, Magenta, Yellow
Additive colour space	Subtractive colour space

CMYK versus RGB Colour Spectrum
Refer to the Instructions for Authors for your journal to determine if files should be supplied as RGB or CMYK. Some printers may prefer your files be delivered in RGB with ICC profiles attached, as this allows the printer to use colour management methods when converting to CMYK. Other printers may prefer your files in the CMYK (Cyan/Magenta/Yellow/Black) mode, as this is the mode required for the printing process. If an RGB (Red/Green/Blue) file is submitted, it must be converted to CMYK for print. When the conversion takes place, colour shifts can occur and TSG will do our best to reproduce as close of a match to your printed output as possible.

It can sometimes be difficult to visualize the reason for colour shift in colour space conversion. The best way to see the colour differences between the CMYK and RGB colour spaces is to look at a colour gamut comparison chart. The chart to the left plots the visible colour spectrum as the large "horse shoe" area, and within this is a plot of the CMYK colours, and the RGB colours. You can see that in some areas the RGB colour space is "outside" that of the CMYK space. It is these colours that will be affected by a conversion from RGB to CMYK

Desktop Scanners and Colour Space
Most desktop scanners, digital cameras, and video capture systems save files as RGB and the conversion of RGB files to CMYK can be done in many ways. RGB converts to only CMY directly. However, when printing, we must add black ink and in doing so must cut back on some colour. The Undercolour Removal (UCR) setup will help control this ratio so that a maximum ink density for the four colours will be 300% when printing on a coated paper stock.

Spot Colours
Digital art that is comprised of spot colours (e.g., special colours: any colours that are not CMYK process colours), generally require conversion to the CMYK colour space to enable file use. Because colour gamut's for spot colour libraries, such as those associated with the PANTONE MATCHING SYSTEM, usually extend beyond the ranges of the CMYK colour gamut, some spot colours may not be represented effectively using CMYK process inks.

Image Halftones
In offset lithography, the density of CMYK inks can not be varied in continuous fashion across an image, so a range is produced by means of halftoning. In halftoning, translucent CMYK ink dots of variable size are printed in overlapping grids. Grids are placed at different angles for each of the ink colours. Smaller halftone dots absorb less light; thus, as a result of an increase in the amount of reflected light, apparent density is decreased and the object appears lighter.

*NOTE: This is NOT an accurate guide due in part to your individual display configuration and as such, iDStyle accepts no responsibility for differences in the colours seen from those chosen from this chart and finished products, no matter what the display medium.