Participant

Question

Converting CMYK to RGB - How to?

Forum|Forum|16 years ago
March 23, 2009
3 replies
144613 views

Posted on Acrobat for Windows Forum this morning - then found this group
- Hope someone can help us...

We are a small non-profit working with adults with developmental disabilities ramping up a very short run color printing service for other non-profits. We print/mail newsletters and brochures and give our adults work to do in our workshop setting.

So we have purchased Acrobat Pro 9.0 - and all we want to do is be a printer of "print ready" pdf'S...

Our knowledge of graphic arts and/or acrobat is very limited - we are just users and again, we want to print out submitted PDF's to our HP high end laser (HP CP6015dn) and give our clients great color printing.

Most PDF files we receive work fine and we output what we see and that is what they get but now one client has sent us a file in CMYK and the color is off. I sent him some other PDF's we have used and he tells us our other files are all RGB so...

Can we take his CMYK file and convert it to RGB and then print it out?

If yes, can you explain it to us very simply?

Thanks

Bob

This topic has been closed for replies.

M

Mander123

Participant

And can I ask a question as I am very new to Adobe Acrobat 9?

So it would appear that you cannot convert an RGB pdf to CMYK in Acrobat 9? You need one of the other programs you are speaking about?

thanks

Tai_Lao

Inspiring

Does this help?

http://help.adobe.com/en_US/Acrobat/9.0/Professional/WS58a04a822e3e50102bd615109794195ff-7b94.w.html

Never underestimate the power of the Help files in the Help menu of Acrobat.

Participant

Participant

I openly confess to being a beginner (who is seriously trying to learn more) when it comes to color management so I ask you to please be kind.

I am a photographer and I work mainly with stock photo agencies who offer images to photo users. Even though almost of the photo uses are for magazine and book publishers who use offset printers, stock agencies all require RGB files. I recently discovered the "gamut warning" button in PS CS4 and it has changed the way I think about digital photography. When the gamut warning is activated, virtually every photo that I take contains large amounts of out-of-gamut colors, especially in the yellow-green range. If I were over-saturating or over-manipulating my images then I could understand it, but even photos straight out of the camera with no tweaking or correction of any kind have huge areas of unprintable colors. I'm using pretty standard Color Settings in Photoshop.

According to a popular book that deals with Photoshop for photographers, the only way of dealing with this situation is to Select> Color Range> Out of Gamut and then use Hue/Saturation to de-saturate the offending pixels until the gray gamut warning overlay disappears. This is easy to do, but I have to de-saturate the image until the yellows-greens are almost gray. The overall effect on the image is disastrous.

I've found that converting my RGB file to CMYK (using the Relative Colorimetric setting) and then back to RGB produces a much better looking image (only slightly unsaturated, but not objectionably so) but this seems like the wrong way to correct the situation and even though the resulting colors look smooth when viewed on my monitor at 100% I can't help but wonder if some sort of image degradation must occur.

Does anyone have any suggestions or hints? Thanks in advance.

P

Printer_Rick

Inspiring

I would not throw in an extra conversion to CMYK and go back to RGB. A few points to consider:

1. There are many different CMYK color spaces. Some are much larger than others. The gamut warning hinges on your Proof Setup CMYK space – if you are in U.S., this would default to US Web Coated SWOP v2. Just be certain that the CMYK is appropriate for your project (check with your printer).

2. Use Proof Setup. Then you can view the conversion and preserve the source RGB.

3. If possible avoid converting the image in Photoshop. Most document layout programs (such as InDesign) support color management of source RGB images. By preserving source color you can use the same image and repurpose it for a variety of outputs.

4. The color truncation as you move from source RGB to CMYK is quite normal, and it is also normal to see a lot of gray with Gamut Warning. The key is to modify the source image so that the damage moving to CMYK is acceptable. Do not try to eliminate all the grays you see in Gamut Warning. Just make certain that the spirit of the source color is somewhat preserved. Use adjustment layers which are non-destructive. For example, you may see blues shifting to purple. In such case you could add a hue shift layer to move it towards cyan.

5. Many times extremely saturated RGB areas will lose detail on conversion. In such cases the desaturation you mentioned may be warranted, but use an adjustment layer.

6. I recommend Adobe RGB as a source space for print. It is a very large color space. It was designed to contain almost all printable colors. Unfortunately, in order for it to contain almost every conceivable print color, it has fringe colors that extend way beyond print. If your image has these fringe colors, don't try to force them all into your destination CMYK while you are still in RGB. It is normal for the image to take a hit when the move happens, your goal should be making the damage something you can live with.

R

Rikka_chan

Participant

Thank you Rick for taking the time to provide this very useful information.

I've made the adjustments that you suggested and I think I'm on the right track now. Especially useful were the suggestions to use Proof Setup and to not try to eliminate all the gray areas in Gamut Warning. I've since learned that the gray areas only show which colors are out of gamut, but without any indication of how much or how little. Proof Setup is a much better indicator of how the final image will look in CMYK.

Thanks again for your help!

G

Gernot_Hoffmann

Participating Frequently

Bob,

the conversion of CMYK to any RGB isn't recommended,
but in your case it's perhaps not bad, because you'll
have then the same printing workflow for all PDFs:

Acrobat Pro (tested for 7) > Tools > Print Production >
Convert Colors:
1. Device CMYK > Convert > to Profile sRGB
2. Calibrated CMYK > Convert > to Profile sRGB
3. Grayscale > Convert > to Profile Gamma=2.2
4. Lab > Convert > to Profile sRGB
x Embed Profile as Output Intent
Execute for all pages
Save As by new name

Device CMYK is CMYK without a profile.
Calibrated CMYK is CMYK with a profile.
The CMYK PDF can contain one of them or both.
Grayscale is doubtful.
There is most likely no Lab in the PDFs.
RGB destination space is for simplicity sRGB.

Use eventually p.4 and 5 of this doc for printer
tests:
http://www.fho-emden.de/~hoffmann/a3gencolorhigh.pdf

Best regards --Gernot Hoffmann

P

Paula LA

Participating Frequently

I am in a similar situation. I've just started using InDesign to create a bi-monthly newspaper. The first issue seemed fine -- it printed well. But the printer told me he had to do something to convert all my JPG images to TIFF prior to publication -- because JPG is RGB and TIFF is CMYK, which is what he said his print shop required.

(I should add that I am using ID CS4, and this print shop's clients seem to pretty much exclusively rely on Quark. I did read in the ID book I purchased that you don't need to save to CMYK for print, so perhaps there is something about ID that this printer doesn't know about).

Anyway, the second go-round I saved the file of 36 tabloid-sized pages using TIFF images and CMYK settings, then PDFed that. The printer said there were still formatting issues, but that is not my main issue, since the paper printed fine. My problem is, when I now go to save the document in the "lowest resolution possible" for web display, it keeps giving me an error reading and says my transparency settings aren't compatible with the output selection.

I've tried to go in manually and change the settings back to RGB/JPG, but when I try to PDF it that way it tells me InDesign has encountered a problem and has to close (and needless to say the PDF doesn't produce).

I'd like to know if there's a way to PDF this document at the lowest resolution possible without having to go in and replace every photo with a jpg (and I'm not even sure that would work).

Should I just follow the same directions outlined above? Since it's for web display and not high rez print out put I thought it might be different.

Thank you.

P

Printer_Rick

Inspiring

Paula LA wrote:
I am in a similar situation. I've just started using InDesign to create a bi-monthly newspaper. The first issue seemed fine -- it printed well. But the printer told me he had to do something to convert all my JPG images to TIFF prior to publication -- because JPG is RGB and TIFF is CMYK, which is what he said his print shop required.

Not to be mean, but your printer is not very knowledgeable. JPG and TIFF are image formats. You can have a CMYK JPEG, and an RGB TIFF.

(I should add that I am using ID CS4, and this print shop's clients seem to pretty much exclusively rely on Quark. I did read in the ID book I purchased that you don't need to save to CMYK for print, so perhaps there is something about ID that this printer doesn't know about).

Yes if your printer relies solely on Quark, he's definitely behind the times. You should be able to leave all images jpeg RGB, and output a print ready CMYK PDF, and give that to the printer instead of native files

Anyway, the second go-round I saved the file of 36 tabloid-sized pages using TIFF images and CMYK settings, then PDFed that. The printer said there were still formatting issues, but that is not my main issue, since the paper printed fine. My problem is, when I now go to save the document in the "lowest resolution possible" for web display, it keeps giving me an error reading and says my transparency settings aren't compatible with the output selection.

This may be caused by transparency blend space setting in ID. Try changing that to RGB if you output PDF for web

I'd like to know if there's a way to PDF this document at the lowest resolution possible without having to go in and replace every photo with a jpg (and I'm not even sure that would work).

It is fine to leave links as TIFF. When you output PDF, the images in the PDF result will be JPEG, you don't have to change them in Photoshop.

Hope this helps...

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