[argyllcms] Re: Determining proper error value for -r
- From: Ben Goren <ben@xxxxxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Wed, 24 May 2006 22:30:43 -0700
On 2006 May 24, at 9:31 PM, Graeme Gill wrote:
> Ben Goren wrote:
>
>> Before I go any further, the only really important part. What
>> ``average deviation as a percentage'' does the following sample
>> of values represent? These partial readings are of the same
>> color (paper white, in this case) in different patches on the
>> same sheet of paper, and the last line is the standard
>> deviation.
>>
>> LAB_L LAB_A LAB_B 400 410 420 430 440
>> 94.69 2.28 -9.05 27.72 49.83 84.45 104.77 109.47
>> 95.23 2.32 -9.36 27.92 50.59 86.03 106.81 111.64
>> 95.37 2.32 -9.29 28.09 50.88 86.36 107.08 111.88
>> 95.3 2.29 -9.35 27.62 50.39 86.09 107 111.85
>> 95.22 2.31 -9.21 28.2 50.71 85.86 106.5 111.29
>> 95.2 2.34 -9.25 27.45 50.21 85.82 106.61 111.38
>> 95.37 2.28 -9.35 27.92 50.73 86.4 107.23 112.02
>> 95.23 2.31 -9.3 27.88 50.41 85.84 106.69 111.54
>> 0.22 0.02 0.11 0.25 0.34 0.61 0.77 0.81
>>
>> (That's the readings of but one ``color'' patch from a chart
>> with a few dozen such. If you need the full set of the spectrum
>> readings, just give a holler.)
>
> Well, the whole thing is a little "loose", because it's not
> actually that critical in the scheme of things. I calculate the
> average deviation (absolute) as 0.08, 0.02, 0.05 for L, a and b
> respectively. Since the range of L is 0 to 100, this translates
> roughly into a percentage.
Um...I guess what I'm /really/ asking for: what does that mean for
-r? Would it be -r 1, or -r 0.5, or -r 2...?
Put another way, how does -r relate to standard deviation? Given
the one, how would you convert to the other? Or is that the worng
way to go about it entirely?
> In the 0.53 release, if you set -r to 1.3 or so, it should be
> fine for 99% of all situations too.
I'll try that as a starting point for my parents' LaserJet the
next time I'm there. Thanks!
>> What I'm envisioning for the future is a two-pass profiling
>> process, not noticeably different for the end user from what's
>> currently used for high-end profiling. I think it has a chance
>> at giving better results for high-end profiling, and I'm almost
>> certain it'll make profiling poorly-behaved devices pretty much
>> straightforward.
>
> Sorry, I don't agree. While there may be some merit in a
> more complicated approach for high end profiling (still to
> be proven), I can't see how it is relevant to low end
> devices. There's no point trying to get that extra 1 delta E
> accuracy somewhere in the colorspace, if the device is banding,
> has inks that change by 3 delta E in the first 24 hours, or has
> a repeatability of +/- 2-6 delta E.
With that perspective, I completely agree with you.
What I'm looking at, however, is the case where you've got a
device that needs more leeway than the default (assuming that -r
1.3 won't cut it for, for example, my parents' LaserJet) but don't
want to spend lots of time experimenting to find out what the
optimal value is.
But if a higher default value will work for them and won't
(significantly) hurt everybody else, it's obviously a moot point.
> I'm sure these sorts of issues can be improved on, with
> sufficient knowledge, ingenuity and persistence, but it's the
> sort of project that would normally take some time and
> resources.
Would that be time and resources that us non-C-hackers could help
with? If it means, for example, some grunt work of creating and
measuring charts or hacking together Perl programs or spreadsheets
to analyze them, I'd be more than happy to volunteer. And I won't
complain if it turns out that it's a dead end. Well, not very
loudly, at least.
Cheers,
b&
Other related posts:
