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I'm working with an artist to create a comic, which will be printed eventually, but which is currently being serialized online. The artist is working in CMYK in Photoshop, on the theory that it's better to convert CMYK to RGB than vice versa, and we'll need both.

We'd like to generate a master PDF file for each page which can be rendered into a suitable image for the web and can be used for a print run. That is, rather than export multiple versions from Photoshop, we'd like to export a single file that can be converted to anything we'll need (using a tool like ImageMagick). But I can't seem to get the color to work.

(I can't reveal the whole page yet, so I'll use a piece that shows off the problem.)

  • Here's an sRGB JPEG he exported from Photoshop. This one looks the best to me, and I believe accurately represents the colors he wants.

    sRGB JPEG from Photoshop

  • Here's what I see (a screenshot) when I open his (CMYK) PDF in Preview.app on my Mac. (The artist exported it using Photoshop's "High Quality Print" export setting.) It looks all washed out and flat. This is not what he sees on his Windows machine; there the PDF looks like the JPEG.

    PDF in Preview

  • Here's the same PDF, rendered in Chrome (another screenshot). My theory here was that Preview is funky, and a different renderer would help. It looks better, but it's not the same as the JPEG file.

    PDF in Chrome

  • Here's the PDF exported to sRGB through Affinity Designer (the closest thing I have to Photoshop). The colors are still wrong; they're basically the same as Chrome displays.

    Converted with Affinity Designer

  • Lastly, here's one that I converted from the PDF to sRGB JPEG with ImageMagick. This is the workflow I'd like to use in the end, to automate everything. This one is wrong in a different way: it's all greenish.

    Converted with ImageMagick

Oddly, I accidentally created a CMYK JPEG in my first attempts to use ImageMagick, and it came out similarly greenish in Chrome, but bluish-flat in Preview, rather like the PDF looked in Chrome (but—wait for it—not as washed out as the PDF looked in Preview.)

My head is spinning. Clearly there's enough information in the CMYK pixels in Photoshop to render the colors we want, and clearly they can be represented in the sRGB gamut, because we have a JPEG that does exactly that. But to save our artist from exporting multiple files (and potentially getting them out of sync), all I want to know is:

How can I render an sRGB JPEG with the same colors as his, starting with his CMYK PDF?

Or, if that won't work, is there a variation on this workflow that would? Or, if this is all folly, what am I misunderstanding?

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    ... and if you open the CMYK PDF with Photoshop and save for web???? Preview and Browser plug-ins are horrible where PDF rendering is concerned. You can't have a "single file" which is usable on the web and in print if color is a concern. They are two different technologies. – Scott Dec 2 '14 at 23:05
  • I know, I'm not looking for a single format which will work on the web and in print. I'm looking for a format which I can transform into a web version and a print version. – Peeja Dec 3 '14 at 1:47
  • I don't understand. The CMYK PDF for print, open it in Photoshop, save for web and you have a web version. – Scott Dec 3 '14 at 2:10
  • Ah, yes, there's where I wasn't clear. I need to do this without Photoshop, in some automated fashion, preferably using ImageMagick. (Sorry, I'm literally feverish at the moment, and not thinking quite straight.) – Peeja Dec 3 '14 at 3:16
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Oh, do not worry. That is a never-ending color management horror.

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I recommend you to use the following settings on all Photoshop instances you using (and also in all Adobe programs)

In Edit > Color Settings chose those two profiles:

RGB: Adobe RGB (1998) CMYK: Coated GRACoL 2006 (ISO 12647-2:2004)

Management Policies should be all "Convert to xxxx" and all tick boxes should be selected.

That is the pretty much good way to preserve consistency trough out the project.

Then he should be converting his files to that GRACol CMYK profile, send it to you and then you can convert it to RGB.

Try that and show us results.

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Another way is just simply to go to Edit > Assign Color Profile and to select "Do not color manage this document" But it can produce real mess depending on different monitor color profiles.

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Third way is to use LAB color mode, and then to convert it to CMYK or RGB as necessary.

P.S. DO NOT use any photo viewers since they can use different color profiles and enchance the picture. Use only Photoshop. When opening PDF via Chrome it can be using it's own color profile. Also, this can be the issue of your own monitor profile. There is a lot of things to go wrong. I advise you to try my settings and if that do not work, then read about color management.

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