[sane-devel] sanei_magic

[Simon Matter]

> Historically, many of us (myself included) have advocated for software
> features like deskew, despeckle and auto-crop to be done in the
> front-end. This has obvious advantages for code reuse and
> maintainability, since there appear to be fewer front-ends than
> backends. But, I think the biggest reason is more selfish. These
> features are hard to write, and I, for one, would rather that it was
> someone else's problem :)
>
> However, many current brands of scanner can do various image
> processing steps in hardware, but only on the medium & high cost
> machines. Users of the low cost machines get these features via
> software in the vendor's proprietary drivers, and don't see any
> difference. Also, the number of front-ends is a bit of a red herring,
> since the most popular ones by far are scanimage, scanadf, and Xsane,
> none of which has yet provided these features. Besides, the first two
> of these are produced by us, so much for passing the workload to
> someone else :)
>
> So, in the interest of consistency for all users, I have undertaken to
> provide these features somewhere in sane. I considered adding this
> type of code to scanimage, but then the users of Xsane cannot reach
> it. Then I started writing a 'middle-end', but after I got done
> replicating much of the logic in the dll backend in order to load
> lower layers backends, I switched to adding the code to the backends
> directly. Such code has been in the canon_dr backend for a few weeks.
> Though simplistic, it is fairly well tested, and does work reasonably.
>
> Now, to improve reusability, I have spun a more generic version of
> that code into sanei_magic, updated sane-fujitsu to use it, and
> committed both to git.
>
> Details:
> 1. Deskew, autocrop and despeckle
> 2. Deskew and autocrop are each divided into two functions, one to
> find the appropriate boundaries/angles, and one to correct the image
> based on those parameters. This gives the caller a chance to inspect
> and/or change the outcome of the operation.
> 3. Despeckle takes a maximum diameter to remove, and fills the area
> with average surrounding color
> 4. Deskew uses a simplified iterative 'original' Hough transform which
> searches for the top and left edges of the media inside the image.
> This is less sensitive to false positives than looking at content, but
> does not function well if no media edge is visible. I continue to
> search for alternative mechanisms.
>
> With all this code I am certainly open to modifications and
> adjustments (even renaming, sanei_magic was the best I could do). I
> will even accept criticism for even including it in the first place,
> though I think once users take notice of it, these will become popular
> features.

As a user of the fujitsu backend I'm happy to hear about the new features.
I have missed such features in the past.

Regards,
Simon