[argyllcms] AW: Re: Number of patches vs. profile quality
- From: "Jens Heermann" <heermann@xxxxxxxx>
- To: <argyllcms@xxxxxxxxxxxxx>
- Date: Fri, 6 May 2011 14:57:54 +0200
Hi Roger
What makes me wonder is, the phenomenon of different visual impression while
measuring the same Lab-values... As Lab is directly related to the visual
perception of the human eye (CIE norm observer XYZ curves), there should be no
visual difference. What is found quite often, is that identical patches (in
terms of their reference values) are perceived differently on two printouts,
but when measured, these patches will also create different Lab-values.
Getting the "same" Lab-measurements on different printers confused me also...
Due to a normal measurement deviation you should get different values in a
range of roundabout dE0,5, depending on the measurement device, even in
measuring the same patch on the same substrate more than one time.
No offense, but maybe you are a little imprecise in describing the problem and
your "workflow", which makes it hard to analyse the cause.
So, I assume you are able to create standard-conformant printouts, but the
visual impression on different printers is also different, even if the average
dE is near to same on both printers. Is that correct?
What is the lighting condition under which you evaluate the printouts? Maybe
this phenomenon is caused by different reactions of the different colorant in
the different inks to the lighting condition (aka metamerism).
On the general topic my option is, that the more patches you measure the more
"support points" you get for the profile creation the more precise your device
is characterized. Also measuring more patches means more time needed, so you
have to find a practical compromise between the number of patches and the time
you like to invest into your profile quality.
The other thing is that, some devices (and/or the combination of printer and
measurement device) do not react completely linear, so you may get in some
areas inhomogeneous measuring data (lots of positive/negative peaks) which may
lead to tearing in gradients, because the behavior is documented to precisely.
For the optimal visual output it may be better, if more interpolation in those
areas is used to smooth the profile data. Especially the i1 pro is quite
unstable with dark patches...
Regards
Jens
-----Ursprüngliche Nachricht-----
Von: argyllcms-bounce@xxxxxxxxxxxxx [mailto:argyllcms-bounce@xxxxxxxxxxxxx] Im
Auftrag von Roger Breton
Gesendet: Freitag, 6. Mai 2011 14:02
An: argyllcms@xxxxxxxxxxxxx
Betreff: [argyllcms] Re: Number of patches vs. profile quality
Hi Nikolay,
I am curious to study the role of colorants in a CMYK printer (could be
applicable to RGB too). But the problem I run into, profiling CMYK printers, is
that, using a constant substrate, depending on the printer model (Epson vs HP),
I get very different visual appearance for the same CIE Lab measurements. I
don't know where to start the study of this "problem", because it is a problem
for me and I'm sure many other users. Is this something I can see in the SPDs
of the "solids", the CMYK primaries and their "overprints", RGB? Or in the way
that the grays are formed? Colorimetrically, these printers will create perfect
match to any reference conditions. Very close to 0.35, 0.5 deltaE. But
visually, it's garbage. So reddish, for instance. I won't mention printer
model. And this is an effect I observe all the time.
I wish I would know where to start...
Best / Roger
-----Original Message-----
From: argyllcms-bounce@xxxxxxxxxxxxx [mailto:argyllcms-bounce@xxxxxxxxxxxxx] On
Behalf Of Nikolay Pokhilchenko
Sent: May-06-11 7:39 AM
To: argyllcms@xxxxxxxxxxxxx
Subject: [argyllcms] Re: Number of patches vs. profile quality
Hello Graeme! Hello list!
It's interesting question.
From my experience, there is not enough 1400 patches for profiling "unknown"
RGB printer (Canon or Epson with non-original inks). The most problems are in
the darks: the printer and paper combination may have an unpredictable behavior
(steepness of device response in dark region) and the 1440 patches of OFPS is
insufficient. With 1440 patches, darks are not well characterized in 50% of
cases. There may be few patches per volume unit of the darks.
My stable workflow for distant profiling of "RGB" inkjets is 2880 patches on 2
pieces of A4 sheets (6x6mm patches). The 2880 patches is enough to profiling
any printer in good condition. In some cases one of 2 sheets is "broken" - by
customer error or for another reason. In such cases I do the profiling only by
1 sheet. It's mostly OK.
There is critical patch R=G=B=0 and if it's absent or misreaded, the profile
may become incorrect in darks - there may be noticeable hue shift in blacks. So
I ask to add more black patches to RGB chart - as many as white patches. As I
understood, the only one black patch is important for determination of device
black point and it's color value is critical. So it will be more correct to
have several black patches on the chart by default.
When I profiling wide format CMYK inkjets, usually the profile with 1200..1400
patches is OK. But the device is linearized previously - by intrinsic RIP or by
printcal.
Wed, 04 May 2011 13:11:45 +1000 Graeme Gill wrote:
>
> I am interested in hearing about peoples experience with profile
> quality vs. number of test patches using Argyll. In particular, I'd
> like to get an impression of what aspect of a profiles quality are
> seen as improving as more patches are used. If this aspect is color
> accuracy, is there a particular area of the color gamut that is seen
> as the critical area ? If so, what area is it ?
>
> [I'm wondering if the profiling efficiency can be improved by some
> simple changes to the patch distribution.]
>
> thanks,
>
> Graeme Gill.
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- » [argyllcms] AW: Re: Number of patches vs. profile quality - Jens Heermann
