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Convering from RGB to CMYK

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  #1  
Old 11-30-2007, 04:55 PM
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Leo Leo is offline
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Convering from RGB to CMYK

Hi!

I have have a question. I have made some changes in RGB file. Now I want to print it on canvas. I tried to convert to SMYK to have better results when printing. But the image has lost its color (it has very intense red). And I canīt do anything with it in SMYK to renew the color

Can anyone give an advice, please

Thank you
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Old 11-30-2007, 05:38 PM
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mistermonday mistermonday is offline
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Re: Convering from RGB to SMYK

Leo, welcome to RP. What kind of printer are you printing on? If it is a standard ink jet printer, they need RGB color as the they are not designed to work from CMYK output (even though the actual process uses CMYK inks). Conversions from RGB to CMYK are destructive. Hopefully you have the original file.
If you tried to print from an RGB file and got poor results it was most likely to to your Color Management process. What type of color management are you using? What software are you using?
Regards, Murray
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Old 11-30-2007, 06:05 PM
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Re: Convering from RGB to SMYK

I will print it in the printing office. Donīt know now where. It is a large fomat printing. I donīt have pinter for this job. It will be 170 cm x 90 cm. I want to make it look like a picture and I will print it on canvas. I have RGB. I read that CMYK is better to use. So I donīt know what to do. I donīt want to loose a quality of colors. I use Photoshop CS3 and Adobe RGB 1998.
Thank you
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Old 11-30-2007, 06:07 PM
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Re: Convering from RGB to SMYK

May be I have made conversion in a wrong way? I only choose in Photoshop change mode to CMYK. May be I should do by another way?
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Old 11-30-2007, 07:13 PM
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Re: Convering from RGB to SMYK

It looks that I have just resolved the problem. At least on the screen the files look identical. I have find an interesting article and have changed color space for CMYK.

http://designer-info.com/Writing/rgb_to_cmyk.htm
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Old 12-01-2007, 05:23 AM
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Re: Convering from RGB to CMYK

Leo, you haven't told us what your CMYK Working Space is set to in Photoshop's Color Settings. This is critical.

Tell us, has your canvas printer specifically TOLD you to send them a CMYK file? If not, you're much better off just sending them your RGB file. However, you should ask them for a profile with which to soft-proof your file.

I know what you're saying about reds. Very bright reds which look fantastic in RGB simply CAN'T be reproduced on canvas. Don't be too disappointed when you get the print ...
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Old 12-01-2007, 09:19 AM
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Re: Convering from RGB to CMYK

Sory, Iīm new to this things. Thank you for your patience. I donīt want to send RGB because than I canīt conrol the rusults of convertin. Am I right? Well the first colorspace was Euroscale coated v2. The results were bad. Than I have changed the profile to Toyo Inks uncoated, and this works very goog and only this profile. The problem is that I donīt know which profile will be used in the printing offece. I will investigate it today. And the main problem that my picture has 90% of reds.
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Old 12-02-2007, 09:36 AM
theboyk theboyk is offline
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Re: Convering from RGB to CMYK

Leo,
If you're going to be outputting (printing) to canvas, more than likely your printer will be outputting your image from RGB as it won't be printing to a traditional CMYK-based ink press, but rather something like a wide-format Epson, etc. This being the case, you would not want to restrict your color gamut by randomly converting from your RGB color space (such as Adobe RGB (1998), which has a very wide gamut) to a CMYK color space (any of which, almost always have much smaller gamuts than most RGB).
So, I would highly suggest leaving your image as RGB for printing unless your printer tells you otherwise (in which case they'll have to provide you with a CMYK profile for accurately converting your image from RGB to CMYK).
Providing it in RGB will allow them to output the widest range of colors in your image. If anything, you'll want to find out what their RGB working space is and what the output device profile is (most likely the canvas brand they'll be printing on) so you can accurately soft-proof on screen (if you have calibrated monitors, etc.).
But again, I would highly suggest against converting to CMYK for this job as there is no need to restrict your color gamut. And remember, if you *do* convert to CMYK, make sure you keep an original, untouched copy of your RGB file incase you ever want to print it again to a different device.
Regards,
Kristin.
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Old 12-02-2007, 11:59 AM
pixelzombie pixelzombie is offline
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Re: Convering from RGB to CMYK

all inkjets use cmyk inks/pigments, the only device i know of that is a true RGB output device is a Lambda and that requires E-6 chemistry...
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Old 12-02-2007, 12:10 PM
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Re: Convering from RGB to CMYK

Quote:
Originally Posted by pixelzombie View Post
all inkjets use cmyk inks/pigments, the only device i know of that is a true RGB output device is a Lambda and that requires E-6 chemistry...
True, they use a CMYK inkset (typically CMYK, then depending on the printer/manufacturer, light cyan, light magenta, photo or matte black, light black, light light black, etc.) but they use these inks (typically with a minimum of 5 inks for lower end inkjets, and up to 12+ for pro machines, plus sometimes a gloss ink coating, such as in the Epson R1800) to output the RGB gamut on the paper. But, when you send the job to print, unless you run it through a RIP (or, direct from Photoshop w/ proof options) and have it set to simulate a CMYK output device (which, you would never want to do, because of the loss of color gamut, unless you were outputting proofs for going to a true CMYK press) then you're printing from RGB as your source file. There is no good reason (expect for proofing) that I know of where you'd want to print CMYK when you have the option to print RGB. Why would you not want to output the full gamut of colors of RGB?
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