Posted by Marko Trebušak on November 10, 2006 at 9:10 AM
Can any kind soul explain to me, how to translate my RGB colures to CMYK colour space for my greeting cards to be printed. I saw some tables on net, but don't have a slightest idea what to do. I guess that Photoshop action of convert profile to CMYK will not be optimal engine.
Cheers,
Marko
Posted by Robert Fisher on November 10, 2006 at 10:37 AM
Are you printing the cards yourself? If so then you don't need to do a conversion, nor should you. The printer software will do the necessary conversion of RGB values to CMY values for you. If you're using a printing service then check with them what format they want the files in. In all probability, they will want the files in RGB and will do any necessary conversion themselves.
The CMYK color spectrum is not continuous as is the case with RGB, so simply pressing a button in Photoshop will not necessarily give you a perfect color match. That's why the printer wants you to do the conversion, since you know what the adjusted colors are supposed to look like.
The best source we have found is Professional Photoshop by Dan Margulis. That's the 4th Edition, and there's a new 5th edition to be released Nov 22. I'm a bit confused by Amazon on this link because retail for our book was $49.95, while the link says $194. It's worth asking them about the difference!
In our experience you need to know which inks and papers the printer is using (they will tell you), and enter that info when making your CMYK conversion. Do this as a first step before processing an image if at all possible. Processing an image first in RGB and converting to CMYK as a last step is always more challenging than doing the CMYK conversion first. We're by no means facile CMYK users, so take this as a "duffers" account.
Get the book, and I think Margulis will help you immensely.
The printing company should hopefully take care of this for you if you ask them and provide a sample 'proof' print - they might charge a fee though. Otherwise, you need to ask them which CMYK colour space they're using (Euroscale coated or something else?, Dot Gain % they use and so on). once you have that info, you can start to use PS to check the image for out-of-gammut (non-printable) colours - go to View->Proof Setup and choose the target CMYK colour space. Then turn on 'soft' colour proofing in PS by checking View->Proof Colours. This should make the screen display the image using the colour pallete available to the chosen proofing profile - you may or may not see some of the colours on-screen change. You can then make PS show you the colours that willl not print (out-of-gamut) by selecting View->Gamut Warning - this will show non-printable colours in grey. Out-of-gammut colours will appear on the print run as blocks of uniform colour with no detail. If you've not too much grey on-screen, then you should be OK, but if you've got a lot of grey, or grey'ed out detail, then you need to start playing around with the colour controls and adjusting things like saturation and so on - you can also try replacing individual problem colours if you're feeling brave! It's a long process and you need to keep checking back by turning the soft proofing on/off.
Like I said, ask the press people nicely and see if you can get their graphics people to do it for you!
If you're printing them on your own inkjet/laser then you don't need to do anything as the printer driver/RIP handles the RGB/CMYK conversion itself.
Posted by Marko Trebušak on November 10, 2006 at 6:07 PM
Thank you for replys. Well, I know that when printing on desktop, I can use RGB. I'm sending my cards to press, and that's why I'm asking.
Discussion
4 repliesCheers,
Marko
The best source we have found is Professional Photoshop by Dan Margulis. That's the 4th Edition, and there's a new 5th edition to be released Nov 22. I'm a bit confused by Amazon on this link because retail for our book was $49.95, while the link says $194. It's worth asking them about the difference!
In our experience you need to know which inks and papers the printer is using (they will tell you), and enter that info when making your CMYK conversion. Do this as a first step before processing an image if at all possible. Processing an image first in RGB and converting to CMYK as a last step is always more challenging than doing the CMYK conversion first. We're by no means facile CMYK users, so take this as a "duffers" account.
Get the book, and I think Margulis will help you immensely.
The printing company should hopefully take care of this for you if you ask them and provide a sample 'proof' print - they might charge a fee though. Otherwise, you need to ask them which CMYK colour space they're using (Euroscale coated or something else?, Dot Gain % they use and so on). once you have that info, you can start to use PS to check the image for out-of-gammut (non-printable) colours - go to View->Proof Setup and choose the target CMYK colour space. Then turn on 'soft' colour proofing in PS by checking View->Proof Colours. This should make the screen display the image using the colour pallete available to the chosen proofing profile - you may or may not see some of the colours on-screen change. You can then make PS show you the colours that willl not print (out-of-gamut) by selecting View->Gamut Warning - this will show non-printable colours in grey. Out-of-gammut colours will appear on the print run as blocks of uniform colour with no detail. If you've not too much grey on-screen, then you should be OK, but if you've got a lot of grey, or grey'ed out detail, then you need to start playing around with the colour controls and adjusting things like saturation and so on - you can also try replacing individual problem colours if you're feeling brave! It's a long process and you need to keep checking back by turning the soft proofing on/off.
Like I said, ask the press people nicely and see if you can get their graphics people to do it for you!
If you're printing them on your own inkjet/laser then you don't need to do anything as the printer driver/RIP handles the RGB/CMYK conversion itself.
Cheers,
Marko