Should RGB or CMYK colour space be used for canvas prints?...

Many people ask us this question and it is our recommendation to work and save your files in RGB colour space. The reason for using RGB as opposed to CMYK for editing images is because it has a wider colour gamut. If you edit images in CMYK you may be constraining the amount of colours you can use simply by having the default settings applied in Photoshop. When you work and edit images in RGB, they need converting to CMYK for printing your canvas prints. This is best left to us as we use a very complex RIP to do the conversion. What is a RIP? Simply put, it is a piece of software or hardware that converts RGB colour data into a language that is readable by the printer. It also applies pre defined colour parameters to the canvas print prior to printing so that there are no surprises when the canvas is complete.
So, our conclusions are:-
Always work in RGB for editing canvas prints as this will give us the best chance of achieving all the colours in your picture.
For more information read the following article-
Color Space Fundamentals
Computer monitor screens emit colour in RGB colour space (red, green, blue) light. Although all colours of the visible colour spectrum can be produced by mixing red, green and blue, computer monitors are capable of showing only a limited colour gamut. Colour gamut is the visible spectrum.

Where monitors emit light, printed paper absorbs or reflects specific wavelengths of light. Cyan, magenta, yellow inks act as filters, subtracting varying degrees of red, green and blue from white light to produce a selective gamut of spectral colour. 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 honour profiles if present; this helps preserve the best possible detail and vibrancy.

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

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 Under colour Removal (UCR) setup will help control this ratio so that a maximum ink density for the four colours will be 280-300% when printing on a coated paper printing stock.

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 colors may not be represented effectively using CMYK process inks.