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

  • From: Nikolay Pokhilchenko <nikolay_po@xxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Fri, 06 May 2011 15:38:45 +0400

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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