[sane-devel] Digital ICE support

[Jonathan Buzzard]

andras at users.sourceforge.net said:
> You can either do IR cleaning during scanning, in which case the user
> can maybe set a few parameters and then gets a cleaned RGB image. This
> approach would be possible with SANE1, provided the backend cleans the
> image. Or you can scan the RGBI image, and then the frontend (or an
> external application) does the cleaning. In this case, you can of
> course give a lot of feedback to the user, but since cleaning is done
> after the information has gone through the SANE API, there's no need
> to extend the API at all. 

I think that IR cleaning is a front end task personally. For starters
you can tweek the IR cleaning parameters after the image has been
scanned if you are not happy with the default ones, without having
to scan the image again.

Also there is need to change the SANE API, we need a consistent way to
get the IR data back from the scanner, which SANE I, simply does not
support. I hope you are right and SANE II, does indeed support this
feature.

> I think if a user has the image cleaned during scanning, they accept
> that the result can be sub-optimal, and the last thing they want to do
> is to scan the same frame over and over again with the same exposure/
> focus settings when the only thing that changes is the post-processing
> of the data. If the user wants more control, they have to scan first,
> then post-process separately. 

Which is why IR cleaning should be a front end operation, with a set of
default parameters for the most common scenario. I note that Vuescan
only provides light, medium and heavy options in the front end for
this. Clearly there is not a lot of need to twiddle parameters.

> That's right. It's possible with Kodachrome, but a lot harder because
> the IR channel isn't as well-separated from the rest of the channels. 

I suspect that you are reading to much into what your particular scanner
is doing. Infra-Red is a broad term describing a wide range of wavelengths.
It starts just above the visible at 730nm or so and extends well
over a 1000nm. I imagine what you see on a particular film depends
heavily on the wavelength used which is likely to vary between scanners.

I note in the release notes for Vuescan there are often notes to the
effect that the IR cleaning on a particular model has been changed/improved
which would tend to hold this out as being the case. If IR scanning
was all the same this would surely not be the case.

This might complicate doing IR in the frontend somewhat. However I suspect
as long as the backend can communicate some parameters to the front end,
then this can be taken care of.

I also note that IR cleaning is going to become a less specialised
interest. Canon for one have started adding this to their flatbed
scanners. As it cannot cost very much, one imagines that it will
spread down the ranges to the cheaper models. Let's face it scanners
are extremely cheap these days, and it is a way of differentiating
your product in the market place.

I suspect that IR cleaning is useful for normal flatbed scanning. I
certainly get dust and spot marks on normal scanning.


JAB.

-- 
Jonathan A. Buzzard                 Email: jonathan (at) buzzard.me.uk
Northumberland, United Kingdom.       Tel: +44 1661-832195