david wrote:
Excuse my ignorance, but isn't this roughly what colour management (http://www.argyllcms.com/?) is supposed to do?
The main purpose of colour management is that the colour you use on one device is accurately displayed on another device. For example, if you scan an object and display that object on the screen, then when holding the object against the screen you can see no differences of colour between the object on the screen and the original object in your hand. The way we do that is to give each device a "colour profile" which describes adjustments which need to be made against a theoretical colour space for a given colour to come out "right". A problem is that there are multiple theoretical colour spaces -- as differing technologies can show a wider or narrower range of colours. So a computer screen (RGB), a three-colour plus black (CMYK) and spot printing (mixes of inks, but those mixes cannot overlap) all form differing colour spaces. And you can see from the mixed-ink case that the spaces can have internal gaps too. There are also other colour spaces not used at all in printing, but in other fields. Some colour management systems attempt to translate between the differing colour spaces. This is moderately successful, but also fails when the gamuts of the two spaces do not overlap. For example, there is no way to accurately represent a mirrored finish as opposed to a flat finish ink on CMYK or RGB. Even CMYK/RGB is problematic -- RGB colour are a light box, whereas CMYK colours are printed. So at equivalent resolutions photographs look much better on RGB screens (which goes back to the old-time serious photographer's preference for slides over paper). Going the other way, the black ink in CMYK allows much better control over dark shades than with RGB. Colour is a complicated field. I hope this gives you the flavour of it. To answer your question, there is a PANTONE colour space. In theory a CMS could convert between devices using PANTONE (actually a no-operation, since all PANTONE printers are pre-calibrated to be identical). In theory, a space-converting CMS could handle spot printing technologies such as PANTONE. In practice, the whole point of spot printing is precise control of printed colour and a designer isn't going to leave it to some subsystem to convert an RGB pixel to the exact shade they have in mind. They want to enter that exact shade into the application. With PANTONE spot printing in particular, there's perhaps some legal questions. Which Andrew mentioned in a previous post. Having written all of the above, it is well worth the hassle to get the DPI of your screen correct (so that 1inch in the application is one inch on the display) and to colour calibrate the screen, printer and scanner. Increasingly manufacturers are releasing nominal values for these calibrations for each model, and in the long run the hope is that some calibration good enough for all but the most fussy will occur out of the box. -- Glen Turner -- SLUG - Sydney Linux User's Group Mailing List - http://slug.org.au/ Subscription info and FAQs: http://slug.org.au/faq/mailinglists.html
