Convering from RGB to CMYK

Leo · #1 11-30-2007, 03:55 PM

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 can´t do anything with it in SMYK to renew the color

Can anyone give an advice, please

Thank you

mistermonday · #2 11-30-2007, 04:38 PM

Leo, welcome to RetouchPRO. 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

Leo · #3 11-30-2007, 05:05 PM

I will print it in the printing office. Don´t know now where. It is a large fomat printing. I don´t 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 don´t know what to do. I don´t want to loose a quality of colors. I use Photoshop CS3 and Adobe RGB 1998.
Thank you

Leo · #4 11-30-2007, 05:07 PM

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?

Leo · #5 11-30-2007, 06:13 PM

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

Damo77 · #6 12-01-2007, 04:23 AM

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 ...

Leo · #7 12-01-2007, 08:19 AM

Sory, I´m new to this things. Thank you for your patience. I don´t want to send RGB because than I can´t 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 don´t 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.

theboyk · #8 12-02-2007, 08:36 AM

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.

pixelzombie · #9 12-02-2007, 10:59 AM

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...

theboyk · #10 12-02-2007, 11:10 AM

Quote:

Originally Posted by pixelzombie

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?

pixelzombie · #11 12-02-2007, 11:11 AM

Quote:

Originally Posted by Leo

Sory, I´m new to this things. Thank you for your patience. I don´t want to send RGB because than I can´t 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 don´t 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.

check the Gamut Warning in photoshop of your rgb file, chances are they may be beyond the gamut of a typical inkjet printer and having the right profile would get somewhat pleasing results..i would suggest that you desaturate the reds by blending some of the information from another channel so the reds don't move very far once you make the conversion...

pixelzombie · #12 12-02-2007, 11:16 AM

Quote:

Originally Posted by theboyk

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?

you could send the printer a RGB file, but somewhere along the line it will get converted to cmyk and there is no guarantee that they will use or even have the right profile for your needs...

theboyk · #13 12-02-2007, 11:30 AM

Quote:

Originally Posted by pixelzombie

you could send the printer a RGB file, but somewhere along the line it will get converted to cmyk and there is no guarantee that they will use or even have the right profile for your needs...

Well, I'd find a printer who knows what they're doing then.
Any decent printer outputting to canvas (we're talking about canvas, right?) would be outputting to some sort of Epson or other inkjet that handles canvas. They would much rather get the files as RGB and they would NOT print/convert to CMYK (if they wanted to simulate a CMYK output device, even then they'd just set the output simulation profile to the CMYK device you're proofing for and the original image you submit would never be converted from RGB to CMYK — but, that would be for proofing a print going to a CMYK device and that's not what we're talking about here, we're talking about outputting an image to canvas, most likely a very limited run). They'd use the RGB file you sent them (if anything, I'd get the RGB profile of the printer's RGB working space), the RIP would use the working space RGB profile (thus why I'd get their RGB working space profile so at least you can supply your RGB image in their working space) and the output profile would be set to the profile of the paper (in this case, canvas) you're printing on. This will give you your best possible print.
If you want to limit your colors (which is why you're saturated reds are loosing their brilliance — true CMYK can't replicate these brilliant saturations) then go ahead and convert to CMYK. But, if you want a nice, brilliant print on canvas using the full colors possible, then leave your image as RGB.
k.

Leo · #14 12-06-2007, 09:44 AM

Thank you everyone for help!

pixelzombie · #15 12-06-2007, 02:42 PM

Quote:

Originally Posted by theboyk

Well, I'd find a printer who knows what they're doing then.

If you want to limit your colors (which is why you're saturated reds are loosing their brilliance — true CMYK can't replicate these brilliant saturations) then go ahead and convert to CMYK. But, if you want a nice, brilliant print on canvas using the full colors possible, then leave your image as RGB.
k.

so let me get this straight, you'd rather send a RGB file to the rip instead of a cmyk file?