[Lcms-user] [SPAM] Re: Bug in soft proofing?

[Marti M. <mar...@li...>]

<div dir='auto'><div>Hi, nice to hear from you.</div><div dir="auto"><br></div><div dir="auto">Regarding the issue, I've checked the profile with photoshop and also got weird results, so chances are the a2b1 proof table is not correct in this profile.</div><div dir="auto"><br></div><div dir="auto">Softproofing is performed in lcms by two steps. In first step the image is converted to the target colorspace using the settings the user wish, bpc rendering intent, etc. Once we have the image in the desired colorspace, we measure the lab values of the colors. To do so, we use relative colorimetric (i.e., no gamut remapping) in the reverse direction. This is encoded in the profile as the a2b1 table and is often called the "proofing" table. This is different from using the reverse table of perceptual a2b0, which "undoes" gamut mapping to display the image. So, tables may be diffeent on certain profiles.&nbsp;</div><div dir="auto">This could explain the differences you see.</div><div dir="auto"><br></div><div dir="auto">Regards</div><div dir="auto">Marti</div><div dir="auto"><br></div><div dir="auto"><br><div class="gmail_extra" dir="auto"><br><div class="gmail_quote">On 8 Oct 2019 11:42, Boudewijn Rempt via Lcms-user &lt;lcm...@li...&gt; wrote:<br type="attribution"><blockquote class="quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><p dir="ltr">Hi,
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We recently received this bug report: https://bugs.kde.org/show_bug.cgi?id=412604 "CGATS21_CRPC1.icc has a different rendering between softproofed and converted".
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As its summary says, if you use the profile provided in the bug report for soft-proofing, the rendering is different than when you use it when converting to CMYK. Because GIMP and Scribus have the same behaviour, I'm wondering whether this could be a problem in LCMS?
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Boudewijn Rempt | https://www.valdyas.org | https://www.krita.org</p>
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