Wednesday 10 May 2006 — This is over 18 years old. Be careful.
For work (which I’ll be saying much more about very shortly), I’ve been having to consider color calibration with a printer. By printer I don’t mean a thing the size of a bread box that sits on my desk and squirts ink onto paper. I mean a person who runs a printing shop using room-sized machines like an HP Indigo 5000.
I send him PDF files, and sometimes they look fabulous, and sometimes they look like someone dipped them in a yellow wash. I know a bit about printing technology, for example, I was Digital’s PostScript expert for a while. I can even throw around terms like tristimulus values and color gamut without completely faking it.
But he and I don’t see eye-to-eye on this problem. My PDF files are RGB, mostly because it was the simplest thing to do. He wants CMYK, but my understanding is that the mapping from RGB to CMYK is a very fluid thing, depending a great deal on the actual printing technology and printing machine used. How could I convert the colors into CMYK better than the HP Indigo’s RIP could itself?
Does anyone have any insight or good pointers for me? I took a look at the International Color Consortium site (you know, the ICC in ICC profiles), but man, that’s one thick site.
How does one make a PDF file that can be confirmed correct once it is printed?
Comments
http://www.planetpdf.com/creative/learningcenter.asp?ContainerID=1516
You could also post to Python's image-sig mailing list; some regulars know a lot about stuff like this.
They're kind of analogous to charset encodings. To properly display a string you have to have the character data *and* its encoding. To properly display/print an image you need the pixel data *and* its working color profile. (To complicate things, we also have variance across devices -- this is where calibration and device profiles come in. But device profiles don't need to travel with the image as long as proper calibration is being done by both parties.)
In short, if you want to see the closest possible thing to what's going to come out of the press, you need to 1) Make sure you're working with software that understands color profiles, 2) calibrate your monitor, and 3) agree with your printer on a working color profile ("Adobe RGB 1998" is widely used).
I worked in the magazine business for many years. I always consoled myself with the fact that since exact mapping between transmissive color (monitor) and reflective color (print) is impossible, the fact that we get as close as we do is pretty amazing and something to be thankful for.
Fred (if that is your real name!): we are generating our own PDFs with PDFlib, effectively, it's like spitting out straight PostScript. The good thing about this is that I have tight control over what's in the PDF. The bad thing is that I have to do everything "manually" in the code.
Paul is right about the color profiles. You might put your PDF file into Illustrator or Photoshop to take advantage of the color calibration therein.
I suspect you are using an LCD monitor, so calibration is going to be blunt at best. That is one thing that CRTs still do better....
regards
Steve
Basic color calibration of your system, then color profile choice
are critical. IIRC yellow washout may be the out of gaumut color for when you've chosen colors that can't be represented in CMYK space.
HTH,
William.
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