<br><br><div class="gmail_quote">On Thu, Jan 19, 2012 at 4:03 PM, Hadmut Danisch <span dir="ltr"><<a href="mailto:hadmut@danisch.de">hadmut@danisch.de</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Am 19.01.2012 22:49, schrieb Patrick Noffke:<br>
<div class="im">> PDF/X-3 specifically allows the images to be saved in the file as RGB, as<br>
> long as they have a profile associated with them. The profile(s) for RGB<br>
> images define what L*a*b* color you want for each RGB value for that image.<br>
><br>
> Then the output intent tells how to convert from L*a*b* to CMYK.<br>
<br>
</div>So the rendering intent is stored in the PDF/X-3 file?<br>
<br>
I believed the intent is used only locally to convert the given into the<br>
wanted colormodel (i.e. some RGB to some CMYK)<br>
<div class="im"><br>
<br></div></blockquote><div><br></div><div>The output intent (different from the rendering intent) is stored in the PDF/X-3. Apparently, PDF/X-1a allows the file to contain an identifier for a registered output intent characterization data on <a href="http://color.org">color.org</a>. This can only work if the file is 100% CMYK, as it must be for PDF/X-1a. Otherwise, to convert from RGB -> L*a*b* -> CMYK (as with PDF/X-3), you need the output intent ICC profile stored in the PDF file. I'm not sure if the spec for PDF/X-3 allows you to store the identifier if the file is only CMYK. If so, there must be a profile somewhere to go along with that identifier.</div>
<div><br></div><div>The rendering intent for each image is also stored in the PDF/X-3.</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="im">
<br>
<br>
><br>
> Your printer has said Fogra27L should be your output intent. Did they give<br>
> you an ICC profile?<br>
</div>No. They just said they use what all printing service providers use, "4C<br>
Euroskala". On their website they say they're using Fogra27L.<br>
<div class="im"><br></div></blockquote><div><br></div><div>You can get the Fogra27L characterization data from here:</div><div><a href="http://color.org/chardata/fogra27.xalter">http://color.org/chardata/fogra27.xalter</a>
</div><div><br></div><div>But you will need an ICC profile to complete the process. See below.</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="im">
<br>
> Any printer that accepts PDF/X-3 should convert the RGB images to CMYK<br>
> (possibly during their RIP) using first the image profiles to convert to<br>
> L*a*b*, and next the output intent profile to convert to CMYK. This should<br>
> be supported by their RIP software or some step in their process. They may<br>
> add a further step that does ink optimization (i.e. GCR), which is supposed<br>
> to leave the color (L*a*b* value) alone.<br>
<br>
</div>That would make sense.<br>
<br>
But where in that process does the rendering intent (perceptual,...)<br>
play it's role? Do the image profiles depend on it?<br>
<br>
<br></blockquote><div><br></div><div>The basic problem is the gamut for RGB (and L*a*b*) color space is much wider than that for a printer. The rendering intents allow you to "store" different ways of doing the gamut compression, such as when going from L*a*b* to CMYK.</div>
<div><br></div><div>The output intent characterization data (only a subset of what is stored in an ICC profile) only defines what the printer needs to achieve (the L*a*b* that they should achieve for any given CMYK value). This is stored in the "BToA" direction (CMYK to L*a*b*) in the ICC profile. The absolute colorimetric rendering intent tells you what L*a*b* value you should expect to get if you measured your printed page with an instrument capable of measuring L*a*b*. The media-relative (or sometimes just "relative") colorimetric intent is the same as the absolute intent, but divided by the paper color in XYZ space. This intent is how a lot of color tools render images, and has the result of making paper appear the brightest white that your monitor can display. This rendering intent is quite useless in my opinion, and for some reason is the default of many tools that try to "do" L*a*b*. If you want to soft-proof how an image will look when it is printed, you must use the absolute colorimetric rendering intent (and of course have a calibrated monitor). But, I digress.</div>
<div><br></div><div>Because RGB images have such a wide gamut, the absolute/relative rendering intents shouldn't be used to convert to CMYK. Otherwise colors outside the printable gamut will just get clipped to the closest printable color. The perceptual intent is typically used, and there is some secret sauce in the tools that make these profiles as to how they do this gamut compression (so it has a smooth mapping from RGB space to the printable gamut).</div>
<div><br></div><div>I've heard the saturation intent is mostly supposed to be used for things like logos, not images from a camera.</div><div><br></div><div>To get to your issue, you will need to get a Fogra27L ICC profile. I think you can find one at the link below, but don't know how they setup the profile for the "AToB" (L*a*b* to CMYK) direction. Aside from the perceptual and saturation rendering intents, it is also possible to do ink optimization, as I mentioned earlier. Perhaps you can find info on whether that was done.</div>
<div><a href="http://www.fogra.org/en/fogra-standardization/fogra-characterizationdata/a-icc-en.html">http://www.fogra.org/en/fogra-standardization/fogra-characterizationdata/a-icc-en.html</a>
</div><div><br></div><div>Otherwise, does anyone know if there are FLOSS tools for making profiles, with options to customize the perceptual intent, GCR, and so on?</div><div><br></div><div>Pat</div></div>