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Input/Output/Workflow Scanning, printing, color management, and discussing best practices for control and repeatability

RGB to CMYK

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  #1  
Old 01-23-2006, 09:49 PM
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sylvia1065 sylvia1065 is offline
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RGB to CMYK

Hello,
Does anybody know of an efficient way to convert from RGB to CMYK? The colors look so washed out once converted.
Thanks
Sylvia
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Old 01-23-2006, 10:12 PM
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Sylvia, does it looked washed out on your monitor or in print? What S/W are you using and what method are you using to convert it? If you are using Photoshop, it will look exactly the same on screen after conversion unless it is tagged with a strange ICC profile. A little more info or a set of sample images would help us diagnose your problem.
Regardsm Murray
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Old 01-23-2006, 10:31 PM
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Hello Murray,
I use Photoshop 5 (I know, it's a really old version, but my boss won't update). To convert, I just go in Image, Mode, CMYK and then I adjust with Levels.
I work for a newspaper, so of course, the printed pictures are not fantastic. I just wish there was a way to have beautiful colors like in RGB.
Thanks for your suggestions/help.
Sylvia
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Old 01-24-2006, 12:22 AM
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Doug Nelson Doug Nelson is offline
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CMYK is a much smaller space than RGB, so the "washing out" is very real. Your best bet is to use CMYK as your working space, then do your retouching and adjusting. Then there will be no conversion.
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Old 01-24-2006, 01:17 PM
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Hello Doug,
I can't start from scratch with CMYK, since the pictures the reporters give me are always on RGB. I always increase the saturation a bit, but my problem is that the red becomes magenta and so on, which is a problem for logos and stuff like that.
I thought maybe somebody knows of a way to get back some of the colors...
Thanks anyway,
Sylvia
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Old 01-24-2006, 01:44 PM
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Hi Sylvia.

My attached picture shows the difference you should get.
Using the eyedropper.

yellow in the RGB is 255, 255, 7
yellow in the CMYK is 246, 235, 23

red in the RGB is 254, 69, 59
red in the CMYK is 240, 73, 63

It sounds like you are getting a very big difference for some reason.



Ken
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File Type: jpg Ken_253955_6684.jpg (97.3 KB, 15 views)
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  #7  
Old 01-24-2006, 03:49 PM
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A big consideration is the medium you are eventually going to print on. Since you mentioned reporters I'll mention newsprint which requires a very low TAC and has probably the smallest color gamut after BW. In this case there are calibration methods and GCR techniques that can increase your color choices. Even if you're not printing to newsprint though there are TAC and Dot Gain considerations that can significantly change your colors. I would recommend finding out the ICC profile of your output device. That way you can edit in the colorspace of your choice and then when you're done you can duplicate your file and bring it to spec. In order to do this you can either have photoshop convert it or you can use the out of gamut feature and work with the photo yourself.

As Doug mentioned though you are going from a large gamut to a smaller one so your color choices are going to become significantly more limited. The good news is that if you develope a good workflow you can counteract quite a bit of the problems. (If you take a look at any good newspaper there are very good quality photos considering the medium)

Also remember that color perception is relative so to make something redder you sometimes need to make everything else less red. The human eye will adjust to your change as long as it's subtle.
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Old 01-24-2006, 04:05 PM
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Hello again,
Thanks for all the information.
I have no control over the printing process, it's all done by a big company somewhere in Alberta.
In fact, I did try to convert pictures from RGB to CMYK from home on Photoshop CS, the result was pretty good, so I think the problems come from that version of Photoshop we are using that is soooooo old. I suppose the conversion is not done the same way as it is with newer softwares. So until my boss upgrades to a decent version of Photoshop, I suppose we'll be stuck with these ugly colors.
Thanks again,
Sylvia
PS: My colors on Photoshop CS are very close to what you got, Ken, so it's definitively a problem with Photoshop 5.
Goose, what are TAC and GCR?
Quote:
Also remember that color perception is relative so to make something redder you sometimes need to make everything else less red. The human eye will adjust to your change as long as it's subtle.
That's a good point!!!
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  #9  
Old 01-24-2006, 04:45 PM
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TAC is Total Area Coverage also called Total Ink Coverage. It's the amount of ink needed to print a specific color. For example if you're printing a pure red you would use 100 magenta and 100 yellow giving you a TAC of 200 for that color. Most magazines print in the high 200s to the low 300s. Newspapers on the other hand can work at 240 and lower. This is because the paper is thinner so it can only accept a certain amount of ink without bleed-through or drying problems.

GCR is Gray Component Replacement in which equal levels of CM and Y in a given color are replaced with the same percentage of K. This way the TAC drops and there are less printing problems. Heavy GCR can cause problems especially between subtle shadow transitions and rich blacks.

This is a very very simple explanation for both TAC and GCR. I'm sure there are threads here with more information on the subject. There are also a plethora of books on these subjects and I would recommend looking into them as it will give you greater control over your images no matter where they art printed.
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  #10  
Old 01-26-2006, 08:10 PM
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Thanks for all the technical information, Goose.
You sure know what you're talking about!
Thanks again,
Sylvia
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