Suspected CMYK file would not open in PWP7

[mark_hay]

Hi Kiril
I was sent a jpeg file which I was unable to open in PWP7. It then sits in the Browser bar saying "Error2.
It did open with MS Paint.

Am I right in thinking that this is a deliberate limitation of PWP?

Once opened in Paint and saved as TIFF, I can open in PWP with profile conversion showing it had a profile of "US Web Coated SWOP v2" which relates to CMYK icc profile I believe.

Probably a low priority issue as I can work around it, but I would like to understand more please,
thanks, Mark

[Dieter Mayr]

I have some CMYK JPEG images, too, but they show as "Error" in PWP's Browser, not "Error2", as you described.
I tried your way with Paint, and it's obviously not a very "clean" way to save a TIFF file in RGB and keep a CMYK ICC-Profile in it ("US Web Coated SWOP v2" is, as you suspected, a CMYK profile as is "Euroscale Coated v2"in my images).
Of course Kiril or Jonathan can tell more about it, but just my thoughts: PWP was not designed to work with CMYK files, and without proper implementation of the CMYK to RGB conversion process i don't think it meets the image quality standards that Jonathan has defined for PWP. So I personally doubt there will be full CMYK support, as it is not really nedded for photographers, thats a thing for the guys at the print preparation, as the proper CMYK setings are higly device (= Printing Press, used colors, used paper ...) and process dependant.

[jsachs]

PWP does not support JPEG CMYK files. There is some built-in support for CMYK TIFF files which are converted to RGB on input by the LeadTools libraries using some kind of default conversion method, but if you need to do any kind of serious work with CMYK files you should probably be using Photoshop which is geared for prepress work.

[mjdl]

For what a quick Internet search is worth, LittleCMS (which is the color management library used in PWP) has some extra utilities at http://www.littlecms.com/1/newutils.htm which do various conversions such as RGB<-->CMYK for TIFF and JPEG files. Maybe worth a try--there are win32 binaries listed for all of them, although no information if they are using an up-to-date version of the library.

[jsachs]

The issue is that JPEG files are read by the LeadTools DLLs which, as far as I know, do not support CMYK JPEG files. If we had the CMYK data we could try to use lcms to convert to RGB. CYMK JPEG is also pretty rare - I never even knew there was such a thing as CMYK JPEG until I saw this thread.

[mjdl]

I was trying to be helpful to point to some ready-made color management aware format conversion utilities that might prepare CMYK files to be opened in PWP--in any case, as Dieter mentions above, with CMYK colors are process dependent and I don't know anything about how to deal with that...

[Dieter Mayr]

Jonathan, just to satisfy my curiosity, what is the difference between "Error" and "Error2" that I resp. Mark got for our CMYK images?

I have created my CMYK Jpegs with that old Photoshop version I have around, just a simple Mode conversion and as colorspace the European standard profile as I mentioned above.
The reason I did this was that I had printed calendars at a local digital print studio closeto my home, using a color laser printer and after some testing the CMYK images gave better results then a RGB image.
Don't ask me why, I did not dig into this, we just made a test with all the images on one page like a contact sheet, and printed it both from a RGB and CMYK file, and the CMYK undoubtly looked better.
Other then this I have no other use for CMYK.

[jsachs]

To be honest, without digging into it fairly deeply, I don't know the difference. My assumption is that it is an error generated by the interaction of PWP's file reading code and the LeadTools DLLs.