[argyllcms] Re: workflow

Graeme Gill schrieb:

>I'm not sure it matter much, since scanning a screening print with scanin 
>probably has very limited purposes. It's not likely to be for the purposes of 
>characterizing a scanner, so it's probably for the purpose of using it as a 
>low quality colorimeter.
>
Sure, it's only relevant for printer calibration using a scanner.

>In such a case the quality is going to be a compromise, so
>does it matter exactly how the screening is dealt with ?
>
I'm not sure, actually my statement was also rather meant as question - 
I have no clue about the magnitude of the potential error. For fine 
screens (e.g. inkjet in photo mode), if not scanned at too high 
resulution, it's hopefully low. Coarse screens (e.g. 50 lpi) seem to be 
more problematic, also due to the issue you mentioned below. Anyway, the 
major problem with scanner based printer calibration still seems to be 
scanner/obervser metamerism.

>Scanin can trip up on the screening artefacts (it making
>it difficult to register the test square edges), so from
>this point of view it's best to scan at a lower resolution
>(assuming the scanner averages rather than point samples.)
>

>[To be visually correct, averaging would have to be in
>a linear color space, but to compute this the response
>of the scanner would have to be known.]
>
Actually yes. Besides outlier removal, this is another issue where a 
robust mean is IMO helpful. If I assume that noise has a zero mean and 
is normally distributed in linear space (or has at least a symmetric 
probability distribution in linear space), then likely a robust mean in 
non-linear space comes closer to the "true" mean (if it would have been 
computed in linear space) than a simple averaging in non-linear space.

>[...]
>It's a tricky problem. I wanted to avoid having to create a
>user interaction application to register a standard chart
>(Like n IT8.7/2). [...]
>
Basically I like it! Scan, crop roughly, scanin, done :-) And yes, it 
works pretty reliably, but sometimes, it fails. Unfortunately, if it 
fails, one is lost.

>[...]
>I really can't be bothered fiddling with this aspect of the project when there 
>is no good replacement build system currently available, and far too much else 
>to do in Argyll.
>
Please don't misunderstand me. Even if I don't like Jam, I nevertheless 
can live with it as is. Functionality is clearly more important.

>[...]
>I generally take a quick look at an archive before unzipping it, for this 
>reason. Also to make sure it won't overwrite anything unexpected.
>
So do I. Usually. Nevertheless it also happened to me in the past in an 
incautious moment ...

Regards,
Gerhard

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