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CMYK vs. RGB (long winded)

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Old 04-07-2003, 11:55 AM
dtrayers dtrayers is offline
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Question CMYK vs. RGB (long winded)

First, I want to thank Richard for a great book and tools. I'm a relative newbie to digital photography but I'm learning a lot.

Over the weekend, I was calibrating my printer (Canon S820) to match the output on my monitor. I've calibrated the monitor (actually, an LCD panel) with Adobe Gamma and everything looks good. Images downloaded from my camera look pretty good for color balance and brightness.

I then printed a number of test pages to try to closely match the output from the printer to the LCD monitor.

I used this for a test image: a3gencolorhigh.pdf Actually, I used the first page. It has several CMYK color patches, several grayscale bars, and some rich color images. After several pages and changing settings, I was able to nail the colors and black levels. I can hold the print to the LCD and it's almost spot on.

So what's my question? In a minute...

So all was well with printing from Acrobat, but I wanted to make sure Photoshop Elements would also match, so I opened the a3gencolorhigh.pdf in Elements and printed it again. In PE, the imaged looke the same as in Acrobat (I had both programs open, and put the windows side-by-side), and the print output matched the LCD. Again, all is well.

(As the late great Archie Bunker was known to say, "Get to the pernt, Edith!")

What I noticed was that the CMY color samples don't match a CMY color created in PSE. For example, Cyan is created in PSE by Green and Blue, and no Red (RGB= 0/255/255). However, the color picker for the a3gencolorhigh.pdf file says that the cyan is 0/172/239. And the CMYK.pdf on the HP disk exactly matches the pdf I downloaded. But the cmyk.psd on the CD has Cyan as 0/255/255, the way I could create cyan.

So maybe this is just academic, since my monitor matches the print output, but what if I were to have some of my photos professionally printed? Since the colors in the pdf's don't match PSE, will I get drastic changes in color? Or is this just the way PSE imports an PDF file? I wouldn't think so, since in the side-by-side window comparison (PSE to Acrobat) showed the colors to be exactly the same, and there were no color shifts in the image part of the a3gencolorhigh.pdf.

By the way, I have color management set to "No color management".

I think that I'm missing something here, but I'm not sure what, and I don't know if it matters.

I would appreciate it if someone could explain to me what I'm observing and if it matters.

If you made it this far in the message, thanks for reading...

-Dave.
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Old 04-07-2003, 04:23 PM
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Richard_Lynch Richard_Lynch is offline
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I've read it all a few times and don't know that I am getting the exact problem. You are trying to evaluate your output and seem to be going with it toward reasonable success (you say the screen matches output, which is an accomplishment in itself).

Have you read the section of the book that deals with this subject? You need to keep in mind that CMYK (the ink the printer uses) is different than the RGB used for the display. The difference between these is discussed in more depth in the section that shows how to make custom CMYK separations.

It is a lot to digest, and for the most part, you don't have to. What is probably a little more confounding is that while I can have you make a CMYK file from Elements, it really doesn't handle CMYK directly (which is why you have to go through the work-around with the DCS file).

One GOOD thing about that is more and more output devices are handling RGB. That is, there are LED and cathode ray devices that will develop images using light and exposure -- essentially photographic process and RGB -- so CMYK never even comes into the picture...ahem. If I output photographs for friends or clients that I plan to frame as is, I go to one of these processes and they are AMAZINGLY cheap for what they do.

SO, please review what I have in the book on calibration and CMYK. If you still have questions, let me know again...but it seems like you are getting the results you need to. I've been a little dense recently, so you might try rewording the problem...I'll take another stab.
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Old 04-07-2003, 11:56 PM
kudbegud kudbegud is offline
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i would also be interested in what you did as i have canon s820 enroute as we speak. i'll read the section in you book Richard, so i'll be ahead when the printer arives.
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Old 04-08-2003, 01:26 PM
dtrayers dtrayers is offline
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Thanks for the reply, Richard!

Well, I had just typed another long post rephrasing the issue when I finally got it.

My problem was I was assuming that when PSE displayed a cyan (RGB=0/255/255), the printer would print with just the cyan ink. That is not true. However, when printing the CMYK.pdf, the cyan patch will use just the cyan ink (or it's supposed to). RGB cyan has nothing to do with CMYK cyan.

Anyway, it's just academic, since I can get good results on the screen and match them with the printer.

Thanks again.

kudbegud,

Here are my printer settings. I am using WinXP, so if you have a Mac the settings may be named different. Your manual has both a Mac and Windows section, so you should be able to figure these out. Also, I use Canon ink, and print with Kodak Premium Paper Satin. Also make sure to calibrate your monitor with Adobe Gamma Utility.

Paper Type: Photo Paper Pro

Print Quality: Custom - Quality = 1 (fine), Halftone = Diffusion

Color Adj: Manual - Color Balance and Intensity all zeros, ICM not checked, Print Type = Photo, Brightness = Normal

Effects: Vivid not checked, no optimizations

You can save these settings as a profile and quickly load them for future print sessions.

Good luck.

Dave.
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Old 04-08-2003, 02:04 PM
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Richard_Lynch Richard_Lynch is offline
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Oh, I see...You were thinking the RGB equivalent to the CMY values would turn up after the conversion of CMY into Elements...and you are getting like 0, 173, 239 instead. That happens due to how CMYK is interpreted in RGB, which is not a 1 to 1 relationship.

I'm glad you figured it out. Sorry I didn't locate the question.
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Old 04-08-2003, 10:28 PM
kudbegud kudbegud is offline
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thanks for the info....now if the printer will just show up! aaarrgg!
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