RE: Laminate profile - Abstract profile?
RE: Laminate profile - Abstract profile?
- Subject: RE: Laminate profile - Abstract profile?
- From: Nils Johansson <email@hidden>
- Date: Mon, 3 Aug 2009 23:01:42 +0200
- Importance: Normal
Hi
again,
I don't believe that it will be necessary to use the press' ICC-profile as an
intermediate conversion step – I just think that it could reduce the picture's
gamut in an undesired way, preventing some colours from being reproduced
correctly in the lamination gamut. Instead I think the best idea would be to convert directly to the
laminate-profile, trying to keep the original picture's colours unchanged as
far as possible (our results showed that it appears that some parts of the
gamut actually gets slightly widened post (glossy) lamination, when viewed in
the a*–b*-plane – see diagram on p. 17 in the report).
Concerning delta Eab, it appears to be slightly more complicated. Let's say
that the press operator gets a proof which he tries to match – take for
instance that the actual colour should be patch nr 7 but he matches it to patch
nr 8 in the report (see Table on page 36, where the left columns show the
L*a*b*-values pre matte lamination, and the right columns show the values post
matte lamination).
Prior to lamination this is a colour difference of about 28 delta Eab, but
after lamination the difference between two such laminated patches would be
about 17. And when comparing patches 23 and 28 on that same page, it's about
6,5 before and 4,0 delta Eab after lamination...
This would actually mean that the colour difference should be smaller than 3
delta Eab in your case (if the difference is also in the chroma)... But we have
not discussed this further in the report, and I actually don't know if this is
a general result.
I still think that the best match would be obtained if using as an accurate
press-profile and as a stable process as possible. Please let me know if your
plain, vanilla profile works for you :)
Another way of possibly simulating the colour changes would be to use a special
transformation which translated the unlaminated L*a*b*-values to laminated
L*a*b*-values. I don't know if there is a good way of doing this. Perhaps one
could make an Abstract profile (as specified by ICC - http://www.color.org/faqs.xalter#p5)
performing this? (I've never used one, or really know exactly what it's capable
of doing) :S Anyone out here knowing if this would be possible?
Also, I don't know how spot colours are affected. As it said in the report, lamination
seems to cause an optical dot gain. Perhaps the fact that one is using
half-tone dots is the reason for these colour changes (however not the only
reason, as also the solid colours (where no dot gain can occur) are affected).
If there is anyone else who would like to share their experiences with
simulating lamination, please post a message :)
Nils
> From: email@hidden
> To: email@hidden; email@hidden
> Subject: Laminate profile
> Date: Mon, 3 Aug 2009 12:39:52 -0400
>
> Thank you Nils Johansson,
>
> I think I follow your reasoning. The only step I was forgetting about, which
> you so kindly suggested, was to make a proof of how ugly the original
> client's separations would look, once laminated.
>
> So, your steps are:
>
> > 1) Make an ICC-profile based upon a colour chart not being laminated
> > (this would be the printing press' ICC-profile)
>
> I wonder to what extent I am shooting myself in the foot by *not* using the
> custom press profile as opposed to plain, vanilla GRACoL2006_C1 profile?
> There is an average 3.5 deltaEab difference between the actual press profile
> and GRACoL2006_C1. Maybe I could make a first conversion from GRACoL2006_C1
> to myCustomPress profile, and then make a conversion from myCustomPress
> profile to myLaminateProfile?
>
> > 2) Laminate the test chart from step 1 and make another ICC-profile (we
> > call this the laminate-profile).
>
> Got that step right.
>
> > 3) Use the laminate-profile as a destination (target) profile when
> > converting your pictures and when producing your plates.
>
> Yes, this make sense as this is the final color space into which the
> original imagery will be viewed in.
>
> > Perhaps this sounds
> > strange, but
> > this should produce the best colour match between the digital colour
> > data and
> > the final, laminated result. Converting to this ICC-profile should
> > eliminate
> > the change in colour when the prints are laminated.
>
> I agree there should be a close match between the client's original and the
> final laminated results. And it's also good to convince us that the whole
> procedure will actually produced the expected results.
>
> > 4) However, to show the printer operator which colours he/she should
> > aim for,
> > you cannot give him/her a proof based upon the laminated-profile as the
> > produced prints have not undergone any lamination yet.
>
> Right. That wouldn't be smart.
>
> > Instead you must print a proof where you show how the colours should
> > look when
> > unlaminated. This you do by assigning the press' ICC-profile to your
> > already separated pictures in step 3, and then make a proof.
>
> You seem, this traces back to my first comment, above. If I proof using the
> GRACoL2006_C1 profile then, knowing that the press is already 3.5 deltaE off
> GRACoL2006_C1, maybe once laminated, the sheets will be off my 3.5 deltaE
> also?
>
> What do you think?
>
> > Similarly, if you want to simulate how the laminated result would be
> > when using
> > the press' profile as the destination profile (which I believe most
> > printing
> > houses do), you should assign the laminate-profile to your separation
> > and proof that.
>
> Yes, that will show what kind of color shift will occur as a consequence of
> lamination.
>
> > I hope you could follow my reasoning. As I said, we haven't had the
> > opportunity
> > to test this in practice, but we believe this should work pretty well,
> > at least
> > theoretically, for CMYK-data.
>
> Yes, I concur with your reasoning.
>
> > If you want, you can download our report as a draft from
> > http://www.hej.st/Laminate_draft.pdf. It is written in Swedish, but has
> > an
> > English summary. I will try to post an English translation in a very
> > near future.
>
> I still need to brush up on my Swedish :-)
>
> > Try to contact the library at Dalarna University (http://www.du.se) and
> > ask for the report, if the link doesn't work.
>
> OK. I won't hesitate.
>
> > Nils Johansson
> > Student at Graphic Technology Dept., Dalarna University, Sweden
>
> Thank's / Roger
>
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