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TIPS, converting RGB to CMYK.

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  #11  
Old 09-24-2011, 04:16 PM
P_fuzz P_fuzz is offline
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Re: TIPS, converting RGB to CMYK.

thanks for all the tips... a bit nervous, buut it should work out well!
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  #12  
Old 09-24-2011, 04:47 PM
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Re: TIPS, converting RGB to CMYK.

I recommend you do all your edits in RGB, and convert a copy to CMYK at the end using Edit>Convert to profile... Ask what CMYK profile they need the image to be in.
If they require images delivered in CMYK there is a possibility they are ignoring colour profiles (not doing any conversion, just printing the numbers), making it extra important to use the correct one.

Soft-proofing (and gamut warning) as someone mentioned is very useful to see what colours can't be reproduced in CMYK (a typical problem could be a saturated red/pink/blue dress).

Personally I think a magazine should recieve nice tagged RGB images, and do the final CMYK-conversion themselves when they export for print. That makes sure they have control of the colour, and also allows them to keep all/more of the colours if they cross-publish (e.g. to web or ipad). And they have more to work with if they need to adjust the images. But, unfortunately, many use outdated workflows.
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Old 09-24-2011, 07:13 PM
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Re: TIPS, converting RGB to CMYK.

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Originally Posted by Flashtones View Post
Andrew, I'm curious. if a printer requests a SWOP file and person gives them a file converted to and tagged or identified as SWOP, how many can't hit it? And why would they request it if they can't
Its miss if the press conditions are not aimed at an actual specification for a SWOP press behavior like TR001. SWOP just means a sheetfed press. It says nothing else about the specifics of the paper, the inks, TAC, Dot Gain, GCR or UCR etc. I’ve even seen people with sheetfed presses tell customers to convert for SWOP! That’s just a big lie.
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Old 09-24-2011, 07:49 PM
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Re: TIPS, converting RGB to CMYK.

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Originally Posted by andrewrodney View Post
SWOP just means a sheetfed press. .
Wait what? Typo maybe? (specifications for web offset publications)


That aside the guys that just provide generic conversion information like that are something you deal with at times. The problem is an exact profile would generally be good but if they just give you generic information like that and you tell them it isn't good enough, they'll probably just go ahead and covert it to this exact profile themselves if they receive it in RGB. If this is a truly great concern at the very least you should ensure that all areas can produce detail within a generic SWOP profile.

Make sure gamut warning and black point compensation are checked and set the proof colors for relative colorimetric. It'll indicate any areas that would clip detail in one or more channels. You can then make any necessary adjustments. If something is too saturated to reproduce this way, you can at least ensure it won't suffer a detail loss even if you aren't comfortable doing this conversion yourself.

If you send it to a magazine without checking, you don't have any way of knowing what will happen.
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Old 09-24-2011, 09:24 PM
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Re: TIPS, converting RGB to CMYK.

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Originally Posted by kav View Post
Wait what? Typo maybe? (specifications for web offset publications)
Typo-brain fart. Yes, Web press (not sheetfed). None the less, I’ve seen shops that do use Sheetfed presses recommend users convert using the SWOP V2 profile. That’s a red flag!

So you can find someone with a Web press that confirms to SWOP and a good SWOP profile can work. Or you can find someone with a Web press that’s a mile from that condition and they can tell you to use SWOP V2 or similar, not ideal at all.

If at all possible, aim for a contract proof, one that the press will contractually match closely.
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Old 09-25-2011, 02:47 AM
kav kav is offline
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Re: TIPS, converting RGB to CMYK.

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Originally Posted by andrewrodney View Post

So you can find someone with a Web press that confirms to SWOP and a good SWOP profile can work. Or you can find someone with a Web press that’s a mile from that condition and they can tell you to use SWOP V2 or similar, not ideal at all.

If at all possible, aim for a contract proof, one that the press will contractually match closely.
I agree with you on the contract proof part. The problem that I'm trying to mention here is if it's something like a magazine interior page where they're going through this stuff rather quickly. I'm saying regardless of if it's a generic spec that may not work, I would in fact ensure that the colors in the image would all fit within this spec anyway. That way if they convert over to the profile mentioned (generic or not) the resulting image won't have clipped channels. How this behaves when proofed out or on press is a different matter, but if they're converting to a SWOP V2 and you have say a really saturated red garment or something that you know would block up in such a space, it should be dealt with before sending it over to them. Otherwise they're likely to just mess it up in conversion.


Edit: I'm not saying the hypothetical situation there is a good one, but it's not that uncommon.
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Old 09-25-2011, 10:45 AM
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Re: TIPS, converting RGB to CMYK.

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Originally Posted by kav View Post
I agree with you on the contract proof part. The problem that I'm trying to mention here is if it's something like a magazine interior page where they're going through this stuff rather quickly. I'm saying regardless of if it's a generic spec that may not work, I would in fact ensure that the colors in the image would all fit within this spec anyway.
That’s why I’d either send them RGB (the ColorMatch trick of Jeff’s or sRGB) OR if they demand a generic CMYK conversion, some delivery notice that has a contractual note that I would have no responsibility in how the CMYK prints on press. Its just too dangerous and expensive otherwise.
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  #18  
Old 09-25-2011, 06:16 PM
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Re: TIPS, converting RGB to CMYK.

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Originally Posted by andrewrodney View Post
the ColorMatch trick of Jeff’s

Can't seem to find that. What is it? I haven't heard of anyone using ColorMatch in years.

Edit: Even if you're sending them an RGB file, you should still pay attention to saturated primary colors. Letting them do the conversion is no guarantee that they won't mess up the detail.
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Old 09-25-2011, 09:23 PM
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Re: TIPS, converting RGB to CMYK.

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Originally Posted by kav View Post
Can't seem to find that. What is it? I haven't heard of anyone using ColorMatch in years.
Convert working space to SWOP or suggested CMYK, then convert back to ColorMatch RGB and let em separate from there. You’ve funneled the RGB data into a gamut which they can’t screw up. But they have to convert to CMYK from that RGB gamut.
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  #20  
Old 09-25-2011, 10:24 PM
kav kav is offline
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Re: TIPS, converting RGB to CMYK.

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Originally Posted by andrewrodney View Post
Convert working space to SWOP or suggested CMYK, then convert back to ColorMatch RGB and let em separate from there. You’ve funneled the RGB data into a gamut which they can’t screw up. But they have to convert to CMYK from that RGB gamut.
*Sigh* don't take this the wrong way (I've seen your site I know how much time you put into color management solutions) but I don't buy that argument entirely. If you make that first conversion with default settings and no regard for what colors are present in the data, it can screw it up. They can't screw up the data then because you've essentially butchered it for them.

Either perceptual or relative colorimetric conversions can produce clipping and weird effects. If you just did a straight conversion without regard for saturated colors, it will find a way to get them into a reproducible range for the profile. Say it's a red object. If the saturation pushes cyan to 0, or yellow and/or magenta to 100%, the result is a loss of detail in these areas. I get that if you converted it back to colormatch the resulting rgb values could all be within gamut, but this doesn't reverse the detail loss that has occurred.

Had you adjusted to get them in range, your image would not take the same detail loss. Anyway yeah you could do the round trip to cmyk back to colormatch if you want, but without making adjustments before the first conversion, the problem remains.
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