sRGB to CMYK

[tony_black1]

I will print a book soon. All my photos are in sRGB color space. I need to convert them to CMYK for the press.

The press here cannot do the conversion professionally so I have to do it on my own with Photoshop CS3.

 

How can I get the best results in CS3? Thanks.

[ellis_vener_photography]

"The press here cannot do the conversion professionally so I have to do it on my own with Photoshop CS3. "

 

I'd find a better printer.

 

you'll need the press to supply you with a profile for the press they will be printing on and be able to produce match prints to provide them as guides. Also make sure you give them your CMYK images on a DVD-R or CD-r so that way when they screw them up they can't blame you if they messed wit h the color after you gave it to them. .

[tony_wellington]

I've printed two books of photos. I simply convert in CS3 and "save as" so I can open the CMYK version next to the original RGB

version. You will note a few changes. Most significantly, the greens will lose their impact, and the blues will shift a little. Having them

both open on the screen means you can make some tweaks to the CMYK if you wish to. Remember that your book printer (assuming

it's off-set/lithographic) is working in a very different way to your photo printer. You need to know whether the printer is operating a 3

colour, 4 colour, 5 or 6 colour machine too. Also what DPI it is printing. RULE No. 1 - make sure what you provide is in a program that

the printer can work with - that the final layout is in Photoshop or InDesign or a PDF. RULE No. 2 - get reasonable proofs. Ideally have

"wet proofs" done - which are produced on an offset printer, not a digital printer. These will match the real print result. They're very

expensive, so if you can't do the whole book, choose some key pages and have them done. RULE 3 - Get any sort of proofs, even

digital, of every page before you print to check your layout files.

 

It's a complicated business with lots of traps. So get the printer to provide you with examples of their other books. Get them to make

you up a dummy (plain paper) copy using the exact same paper and cover yours will be on. Most importantly, check out the binder's

quality control!

 

Find out what paper will be used for the text and cover pages. Get samples. Work out whether the internals will be machine varnished.

Work out whther the cover will be celloed, and whther gloss or matt cello. If it's a soft cover book, remember that cello can cause

curling, particularly if they print it with the paper grain running the wrong way.

 

Whew, that's probably enough for now. Don't want to scare you. Just remember that off-set lithography does not produce the same

results as quality photo printing. Do your research and look at other books.

 

Good luck!

 

Tony

[tony_black1]

its very interesting that when i convert the srgb images to cmyk , some has very little change which is nice. only the blacks look lighter which i can easily adjust it. but some images have red colors and the reds switches to orange. and i dont know how to get back that red red color again. any advice will be appreciated.

[digitaldog]

In terms of just the question about sRGB to CMYK, shouldn't be a big issue. Yes, having the correct CMYK profile is 99%

of this issue. That said, the sRGB gamut is a tad shy compared to the CMYK gamut (specifically say U.S. Web Coated

(SWOP) v2 or similar CMYK device). ColorMatch RGB would be a better option but the toothpaste is out of the tube, you've

got sRGB so use that for this job.

 

You're bigger and more critical issue is not the current working space but rather the correct output color space for this

process.

[tony_wellington]

Tony, you can only work with the colours available within the colour system. Plainly red/green/blue uses different pigments to

cyan/magenta/yellow/black. So the colours are going to shift. The blue in RGB is quite different to the cyan in CMYK, so sky colours are

going to shift, depending on how much black is included. The red in RGB is also very different to the pinky magenta in CMYK. So

expect changes at that end of the spectrum. Do what you can to minimise the differences (by tweaking your colours), but don't expect to

be able to match your CMYK images to your RGB ones. It's simply not possible. If I want a rich grass green in RGB, the deep blue

pigment mixed with the yellow works a treat. In CMYK however, you're mixing cyan with yellow (and a touch of black) which can never

provide a really rich grassy green. In this case I usually add some more yellow to the greens to get them brighter, but they never match

the RGB. You might find you just have to live with the shifts in the red/orange colours, if you can't alter them in CMYK to suit your liking.

Of course, depending on the printer you use, you can make further tweaks during a press check.