Aleksei Guzev …
Are you sure that this will happen if the files are already in CMYK ? IMO the conversion is already done and specific curves for the imagesetter
should just compensate minor machine errors.
Why do we have the option to embed Transfer Functions ?
Just to show e.g. UCR /GCR ?
A customer said that a printer made wrong reproductions from his files. His files were Photoshop PSD in CMYK. I opened the files. The first impression was that the pictures were desturated very much. I saved Photoshop PDF. PDF looks just like PSD. Then the customer told he is sure that saturation is lost due to "all Adobe’s programs have an error for years". He stated his files contain pictures with good saturation. He asked me to export a picture to EPS. I had done this, and, of course, I had turned OFF the option "Include Transfer Function". Then a had distilled the EPS. The second PDF had about 90% of cyan at the point, where source PSD had only about 50%. It’s surely a kind of color correction, but I did not embed any profiles. Then I exported the picture to EPS with the option turned on. The third PDF was equal to the source PSD and the first PDF. I think the option should be turned on to get good results. But what function does Photoshop embed I do not know.
What the customer had done to alter the functions? And what functions had he altered?
Aleksei Guzev
Aleksei,
perhaps this issue can be clarified with help by others.
1. If the CMYK image looks bleached in PhS then it´s probably spoiled.
2. PDFs should be made generally by
"Input file None",
"Leave Colors unchanged",
"Rendering Intent Default".
This guarantees an unmodified transport of colors by original numbers.
3. After reading the PostScript Language Reference Manual: A transfer function is a tone reproduction curve for an output device, here a CMYK printer.
This would make sense for an uncalibratated laser printer – the output values are tweaked for compensating dot gain or for better appearance. In this case "PostScript Color Management" should be checked (On). If the file is already in CMYK, generated from an RGB image by an appropriate CMYK profile (Euroscale Coated) then a further transfer function would be quite useless.
I would use "Don´t embed transfer functions" and for Export as EPS "Don´t use PostScript Color Management".
Everything "IMO", can be corrected.
Best regards –Gernot Hoffmann