Previews of CMYK files

[Stephen]

The previews for CMYK files *without* embedded ICC profiles look wrong -- too bright, oversaturated. I've read through many threads here (some no longer applicable) but fail to get it working.

I have set $icc_extraction = true; which helps files *with* embedded profiles -- but not those *without* profiles.

I have tried setting $default_icc_file to each of the ICC profiles in the iccprofiles directory, but no luck. And have tried uploading different ICC profiles. Again no luck.

Can anyone suggest how to make the CMYK previews look correct?

I'm running r6800 on CentOs with ImageMagick 6.5.4 (RGB).

Thanks!
Stephen

[TimC]

I'm afraid to say that unfortunately there is no way to correctly convert CMYK back to the correct RGB values it had prior to conversion. That ultimately is the purpose of having profiles. CMYK files should never be created and saved without a profile if ever you intend them for anything other than print as you cannot get back the RGB or original LAB values once they have been thrown away. You need some baseline from which to start and without that ImageMagick is just plucking numbers from the air.

The only effective method we have found is to open them in Photoshop add or convert to profile and save them with that profile. Since most CMYK gets converted in Photohop, Photoshop is the only way to get a half decent profile back in the files. 

Having done this, if you re-upload them they should look OK in preview.

I recall sometime back someone in the group looked into embedding a profile in the original file if it was without one prior to the conversion but I'm not sure what became of that experiment. 

[Stephen]

Thanks Tim.

I'm working with a client that has several different levels of users, with several different work flows, on several different continents, so while I can and will push for RGB files, ideally, or at least CMYK files with profiles, unfortunately there are probably a number of legacy un-profiled CMYK files that will be uploaded as-is once the project gets rolling.

I spent the day on what was mostly a fool's errand, I'm sure -- and went on several time-wasting wild goose chases -- but have made a little progress. I now have it checking for CMYK images on upload and applying a generic CMYK profile before converting to the other sizes in RGB. Not ideal, I bet -- still a slight color shift -- and I know I've only tested a handful of images. But, looking much more acceptable (although I hear you about not knowing even what the target I'm shooting for is -- and properly profiled files is the correct answer, short of RGB source files) -- but at least it's a step or two or three away from the neon images -- which were either caused by unprofiled conversions or simply CMYK files displaying as they do in the browser.

At the moment, though, it all falls apart when you use the Transform plugin to save to RGB formats, though... So, short of someone with a magic bullet, let's see where this goes.

Thanks again,
Stephen

[Stephen]

Quick follow up. I disabled the Transform plugin from activating for CMYK files by capturing the color mode as metadata during upload and checking for it before displaying the transform link. Seemed like a more sane (and budget-friendly) solution than opening the color profile can of worms for the plugin.

So, based on the previous post, [1] CMYK files without profiles create acceptable (acceptable for me) previews, and [2] also now avoid off-color transformed images by avoiding Transform altogether.

Let me know if either part of this is interesting to anyone. I personally would find the first part to be a good addition to RS.

[Jeff Nova]

The best solution would be to specify a default CMYK profile for untagged images that is used for transforming previews.

We did this work with a community member a couple years ago and will revisit it. It wasn't totally finished. 

Best,

Jeff

--

Jeff Nova

Chief Executive Officer

Colorhythm LLC

http://www.colorhythm.com

Main Office:  +1 415-399-9921

Fax: +1 415-399-9928

Mobile:  +1 510-710-9590

jn...@colorhythm.com

--
ResourceSpace: Open Source Digital Asset Management
http://www.resourcespace.org
---
You received this message because you are subscribed to the Google Groups "ResourceSpace" group.
To unsubscribe from this group and stop receiving emails from it, send an email to resourcespac...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.