Help Me With a Digital-To-Print CMYK Conversion Problem
August 31, 2007 8:10 PM   Subscribe

I'm having problems converting digital photos to CMYK for print. Please help.

(Asking this question for a friend, and TIA.) I shot some images for a lighting design firm with a Canon 30-D digital in the highest quality raw file. I'm prepping them for print and, in converting them to CMYK color, I am noticing the images are drained of their vibrancy and depth and are also becoming grainy. Is there something I should have done pre-production in the camera, or is there a post-production fix I can do in the computer that will help to match the original appearance of my images?
posted by theperfectcrime to Media & Arts (8 answers total) 4 users marked this as a favorite
what are you using to convert to CMYK? The CMYK gamut is much smaller than the RGB gamut, especially in certain colors.

Many desktop printers expect an RGB input. Your friend knows this, right?
posted by notsnot at 8:17 PM on August 31, 2007

Dan Margulis is the guy you're looking for.

There are LOTS of post-production fixes. The first thing to do would be to color correct it, setting proper range. That can be found in this pdf. This will often bring back a lot of saturation.

Another thing is, if you genuinely ARE losing color when you go to CMYK, you might want to try Converting to a different RGB profile to reign in some colors before converting to CMYK (Photoshop Edit > Convert to Profile or Image > Mode > Convert depending on the version)
sRGB is pretty desaturated, AdobeRGB is more saturated. If it's in Adobe, convert to sRGB then to CMYK.

Poke around that site more. There's TONS of useful stuff.
posted by Brainy at 8:30 PM on August 31, 2007 [1 favorite]

If you're using Photoshop you can do a preview (VIEW>PROOF SET-UP) and choose cmyk for print or on-screen, then adjust the colors in RGB with the cmyk preview for viewing. This gives you more of a range to work with than converting to cmyk immediately.
Keep a copy of your original up onscreen to match colors to the rgb.
Usually the conversion flattens all contrast (fix with levels) and distorts the blues and reds(and other colors) which can be fixed with selective color.
posted by beckish at 8:49 PM on August 31, 2007 [1 favorite]

Why dont you let the printer do it? They probably haveprofiles built for their presses
posted by nathan_teske at 8:58 PM on August 31, 2007

(notsnot: It sounds like they're using an actual printing firm with printing presses; these places usually require files in CMYK.)
posted by lisa g at 9:18 PM on August 31, 2007

I am noticing the images are drained of their vibrancy and depth

Sadly, that's fairly common, due to CMYK's limited palette relative to RGB.

One trick may be to convert from RGB to LUT, then LUT to CMYK. LUT has a higher palette than either RGB or CMYK, and tends to convert to CMYK very cleanly. Some printers* may even accept files in the LUT colorspace - they will use the RIP software to do the conversion, which may (no promises) retain some of the vibrancy.

*for example, I can theoretically do this, but I've never been given the opportunity to try.
posted by lekvar at 9:54 PM on August 31, 2007

i don't understand the "grainy" comment, and i'm also not sure if you're talking about how things look on the screen, or how they look when printed.

rgb to cmyk conversion has two parts: changing the colours (in very simple terms, replace red with magenta+yellow, etc) and adding black (the "k"). i wonder if what you're calling "grain" is the black component, and, if you're talking about how this looks on a screen, then it may be that it will not look so bad when actually printed.

(a screen is rgb, so it doesn't really make sense to display a cmyk image on a computer screen - it has to be reconverted back to rgb. i imagine decent software will attempt to do this in a way that tries to emulate what a printed product will look like, but it can't be perfect, because it's trying to show you apples using oranges).

disclaimer: i have written cmyk conversion software, but don't use actually use it as part of my job (i'm a software engineer, not a designer). sorry if this confuses rather than helps.
posted by andrew cooke at 8:00 AM on September 1, 2007

Yep, I'm pretty sure the "grain" is the K showing through, which it will on a bad conversion.

I used to work on a desk of people who did hand RGB->CMYK conversions for pre-press all day, and I've no idea how to condense that into some tips! I mean, not only do you need to think about everything above, but you really need to know the profile of the press you're printing on, what inks they use and what paper stock will be used -- Photoshop takes all these things into consideration when converting, so if your settings are wrong, so too will the results be.

It's a pretty specialised bit of work, to be honest. If you have a paying client and this is an important job, you may want to outsource the work to a specialist house. I've got a couple of recommendations if that's a route you want to try -- email's in profile.
posted by bonaldi at 9:04 AM on September 1, 2007

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