[argyllcms] Re: Number of patches vs. profile quality

  • From: Roger Breton <graxx@xxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Fri, 06 May 2011 08:02:13 -0400

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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