ICC profiles - the point

[rtwwpad]

I cant find a definitive answer on teh rest of the web so am posting here to see if i can get an answer as to what icc profiles are really for.

I am a keen amateur photographer, looking to produce some prints of my work for sale in a local gallery on Canons new i9100 A3 printer from my Canon EOS10D or my Nikon 4000 scanner with slide film using Photoshop 7 on my monitor.

1. Monitors, Scanners, Digital Cameras. Use light, so must belong to Adobe RGB or sRGB.
2. Printers, presses, anything with ink requires CMYK.
3. Colour gamuts between all 3 are different, greater range and more greens in Adobe RGB than sRGB, CMYK ranges outside sRGB, most of CMYK inside Adobe RGB.

From what I read on the web and ICC website. ICC profiles allow the colours which fall inside all the gamuts to be translated to the same effect on all devices. Colours outside the gamut are shifted to their closest approximation.

Whats the point, why dont I just print out a copy of my file as the printer will do a best guess, transforming colours anyway and I can tweak this by doing another print. Are ICC profiles more suited to the arena of multiple monitors and multiple hardware? For example a BMW designer sees that the porsche red on his system, matches the porsche red on the designer next doors screen. Or is it just to ensure that the colours which fall inside the RGB and CMYK gamuts are clearly defined so you end up with everything within the intersection of the two gamuts reproduced, as you see on screen, on paper. Anything outside the gamuts, well you just get a best match.

I hope someone can demystify this for me and put me onto the path of reproducing fine quality prints. Thanks for your help

Phil Thomas

[dn7elson]

Take a look here and you should find just about everything you want.

http://www.color.org/

[Roger_Cavanagh]

rtwwpad wrote:

1. Monitors, Scanners, Digital Cameras. Use light, so must belong to Adobe RGB or sRGB.

Sorry, that's completely untrue. Real world colours do have a much wider range than can be represented on any device currently available (AFAIK), but there are many that have a wider gamut than Adobe RGB, let alone sRGB, which is quite small. There are many colour spaces other than Adobe RGB and sRGB.

2. Printers, presses, anything with ink requires CMYK.

Just because a printer has CMYK inks does not mean that it is not an RGB printer. It is common error to think that you have to convert to CMYK to print on a desktop printer like the Epson 1290 or 2100/2200.

Check this link for some examples of gamut comparisons:

http://www.digitalmastery.com/color/

3. Colour gamuts between all 3 are different, greater range and more greens in Adobe RGB than sRGB, CMYK ranges outside sRGB, most of CMYK inside Adobe RGB.

Also not entirely true. Yes, Adobe RGB does extend more into green than sRGB. Not every printer gamut (which depends on both ink and paper) fits inside Adobe RGB.

From what I read on the web and ICC website. ICC profiles allow the colours which fall inside all the gamuts to be translated to the same effect on all devices. Colours outside the gamut are shifted to their closest approximation.

Colour outside the gamut of a device profile will not be captured accurately. Different devices capture colour different. It is a bad idea to edit images in a device colour space. Images should be converted to a working space. Adobe RGB is probably to most popular, but not the only working space. Personally, I use ProPhoto RGB.

Colour management is about about consistent colour between devices.

Whats the point, why dont I just print out a copy of my file as the printer will do a best guess, transforming colours anyway and I can tweak this by doing another print.

You could do this if you want to work in a closed loop system. but you'll waste a lot of paper and ink. Chances are, if you send a file to someone else or post a picture on the web, it will look completely different on another system.

Are ICC profiles more suited to the arena of multiple monitors and multiple hardware? For example a BMW designer sees that the porsche red on his system, matches the porsche red on the designer next doors screen.

Yes to multiple hardware in that you have input and output device profiles and working spaces, but that doesn't necessarily mean multiple monitors or multiple systems, although proper colour management and system calibration will ensure colour consistency across systems. A single system - input device (camera, etc.), output devices (monitor, printer) - will benefit from correct colour management.

Or is it just to ensure that the colours which fall inside the RGB and CMYK gamuts are clearly defined so you end up with everything within the intersection of the two gamuts reproduced, as you see on screen, on paper. Anything outside the gamuts, well you just get a best match.

This certainly is part of what colour management will achieve, although there are different "rules" that can be used during conversion. Some conversions from colour space a to colour b use rules that mean the colour that overlap will be made identical and those that do not will get the closest match. Another option uses rules that means all colour may change so that the perception of colour in the new space is as close as possible to what it was in the old space.

I hope someone can demystify this for me and put me onto the path of reproducing fine quality prints. Thanks for your help

I'm afraid there is no easy path to colour management enlightenment. I am a long way from knowing all that I should, but I have collected some links that have been helpful to me:

http://www.rogercavanagh.com/helpinfo/10_colourmanagement.htm

Regards,

[Kevin Connery]

Roger's answer was very good.

One other--somewhat simplified--way to think of it is that an RGB or CMYK file is like a color negative: you don't know how it SHOULD look based on just that frame.

Knowing what light the photo was shot in, what film it is, and so-on will let you 'decode' the negative. That knowledge is akin to what goes into the profile: how the file should be interpreted visually.

An RGB file without a profile is just a set of numbers, and there's no way to KNOW how it's supposed to look. Dark, light, contrast, saturation--all of those are in the profile "recipe".

[rtwwpad]

Roger, thanks for the excellent answer. Will browse the links mentioned and hopefully understand more.