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Photoshop color help…
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Yochanan
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Join Date: May 2005
 
2005-12-06, 11:57

I have two identical .tif images, one is in RGB the other in CMYK. I'm going to add an adjustment layer (threshold) to one and determine what my brightest and darkest points are. After I finish the adjustment with curves, I'd like to apply those same settings to the other picture.

Is that possible?

Did any of that make any sense to anyone else?
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Ebby
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Join Date: May 2004
Location: Over Yander
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2005-12-06, 15:48

Yes you can. When you make your adjustments in curves, you can save your curve and import it into the other file. I don't think there are any RGB/CMYK differences to worry about, but I never actually use CMYK.

^^ One more quality post from the desk of Ebby. ^^
SSBA | SmockBogger | SporkNET
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709
¡Damned!
 
Join Date: May 2004
Location: Purgatory
 
2005-12-06, 16:55

When working with Curves you can't apply a CMYK setting to an RGB image as they're two completely different colour spaces. It simply won't work.

The best way to go about it is to adjust your CMYK image, flatten it, then convert it to RGB. This is better than going from RGB to CMYK because CMYK has a smaller colour range than RGB. Going from RGB to CMYK requires a bit more tweaking.

Even simple Adjustment Layers (like Brightness and Contrast, for example) that can be swapped between RGB and CMYK images give slightly different results on each.

So it goes.
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Yochanan
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Join Date: May 2005
 
2005-12-07, 06:33

Dear Diary,

Perhaps this mucks up my situation a bit. I started with a 62MB .tif scan, and it (the scanner) created it in the RGB color space. I imported the RGB file into PSCS, and commenced to create a copy and close the original .tif file. I cleaned the copy file of all dust, scratches, and fibers/hair. At that point I had one clean, RGB, .tif file. I have to convert this to CMYK to send to the printers. I create a copy of the clean, RGB, .tif file and convert the copy to CMYK. A little bit of the color info lost to gamut limitations, but not too bad.

At this point I wish to start my adjustments for shadow/highlight, black/white/grey points, and then use the channel mixer for anything else that might come to mind. The important file is the CMYK one. I find it much easier to adjust my RGB file to resemble my master print, but I'd like the CMYK file to match it or come damn close.

From Ebby's input I gather that I can save my curve adjustments, and then port those adjustments to the other file. He doesn't think that there are any color space differences to worry about, but 709 disagrees. 709 says that adjustments to one file in a specific color space cannot be simply ported over to another file in another color space, without giving different results.

Though I'm inclined to go with 709 on this, (as Ebby by his own admission never actually uses CMYK) I'm still in a spot as my important adjustments are to my CMYK file, and his advice seems to be designed to produce a fine RGB file. My starting point is my clean, RGB, .tif file and from that I must produce a good CMYK one. I only concern myself with the RGB file as it's easier to adjust the colors to my liking. Knowing I have a fine RGB color adjusted file, I imagined being able to lift the settings that make it a fine RGB color adjusted file and stamp them onto a CMYK file.

I'm starting to think this might not be possible to get exactly right. Does this mean I'll have to adjust by eye?

Thanks for listening to my ramblings.
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curiousuburb
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Join Date: May 2004
Location: that interweb thing
 
2005-12-07, 07:33

If the Print will be the most important and must be the most accurate, you'll not only want to spend your energies on the CMYK version rather than the RGB, but you'll also be concerned about the colour accuracy of your monitor. Add to that the fact that you're working on an RGB device trying to simulate a CMYK colour space while you correct, and you'll understand why proofs on the actual device are often the only way to know if you've tweaked correctly.

So 709 is more correct...CMYK is the place you need to be if your print takes primacy. But you're taking a bit of a leap of faith in trying to correct CMYK on an RGB device (without even addressing the issue of monitor calibration yet). So if your client is a fanatic about colour on the final print, you'll want to run some proofs and re-tweak.

plink plink
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709
¡Damned!
 
Join Date: May 2004
Location: Purgatory
 
2005-12-07, 09:06

Quote:
Originally Posted by Yochanan
...I'm still in a spot as my important adjustments are to my CMYK file, and his advice seems to be designed to produce a fine RGB file.
No, sorry, I should have explained that a little better. My assumption was (and after re-reading your OP I might've been mistaken) that you'd still like to have two 'identical looking' files in RGB and CMYK after you make your colour adjustments. I was just stating that you'd have to start with your CMYK file to get this to happen, as a CMYK file can be turned to RGB without any noticeable colour change, not the other way around.
Quote:
Originally Posted by Yochanan
I only concern myself with the RGB file as it's easier to adjust the colors to my liking. Knowing I have a fine RGB color adjusted file, I imagined being able to lift the settings that make it a fine RGB color adjusted file and stamp them onto a CMYK file.
Yes, the RGB image is much easier to adjust and can produce results much more vibrant and immediately pleasing than a CMYK image. And no, you're not going to able to get those settings to work on your CMYK file.

As curiousuburb mentions, it's very difficult to get an accurately adjusted CMYK image on an RGB device (ie: computer monitor). Unless you've got buttloads of money to spend on a Barco and some colour-calibration hardware you're going to have to go with the 'print-n-tweak' method.

Out of curiousity, what kind of printing will this image ultimately be reproduced by?

So it goes.
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Yochanan
Member
 
Join Date: May 2005
 
2005-12-07, 12:56

It'll probably get printed on a heidelberg, I'm handing these images over to be printed in a magazine.
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Yochanan
Member
 
Join Date: May 2005
 
2005-12-07, 12:57

I've calibrated my iMac monitor as best I can with the built in tools. I'll try to buy that One-Eye (or is it Blue-Eye?) when I get paid.
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709
¡Damned!
 
Join Date: May 2004
Location: Purgatory
 
2005-12-07, 13:04

It's Eye-One, the Blue-Eye only works with LaCie monitors iirc. MacWorld had a review of hardware/software calibrators earlier this year. It might be worth a look.

I wish Moogs would get in here, he knows far more about this stuff than I do.

So it goes.
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Yochanan
Member
 
Join Date: May 2005
 
2005-12-07, 13:26

All right I just adjusted my CMYK file by eye, it looks great (*yay me*). I used a threshold adjustment layer, the color sampler tool, and the curves. I'm gonna have to get on with all of the other scans (that I'll have to do, man I hate scanning), cleaning, and adjusting. This is probably the last week to put all this stuff off.

/time to get to work
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