Offer FairScan as a library to be included in other apps

[PhilLab]

This app is already great plus has great potential!
Following the recent addition of an intent system to facilitate interplay with other apps, #81, could the app also be offered as a library to be fully immersed in another app, with all the CV and UI it offers?

Specifically, I am currently looking at the document scanner functionality of the Nextcloud Android App, which is built on a very old library, https://github.com/Hazzatur/Document-Scanning-Android-SDK.

It would be great to give it a complete rework, and FairScan would be a perfect fit.

• This would instantly increase FairScan's distribution drastically.
• Nextcloud's F-Droid build currently excludes the whole document scanning feature, because it is not built from source. Using FairScan would resolve this.
• The Nextcloud team would be generally interested in a face lift: Build scanner binary component (for F-Droid/etc scanning support) nextcloud/android#12624 (comment).
• The licensing (AGPL) is also compatible with FairScan.

I am not yet sure what all requirements might be, but this is what came to mind:

1. x86 and x86_64 support would also be needed
2. A way of adjusting the color scheme
3. F-Droid compatible build (which is what Nextcloud's current scanner lacks)
4. As small as possible 3rdparty library artifacts (looking at you, OpenCV)
   • The whole issue of not being built from source comes from them using build pre-built artifacts of a custom, tiny OpenCV build, https://github.com/Hazzatur/Tiny-OpenCV/blob/master/how_to.md. So the library size is of a concern.

[pynicolas]

@PhilLab Thanks for your interest in FairScan.

FairScan is intentionally developed as a standalone application, not as a library or SDK. Turning it into a reusable component would introduce significant constraints and maintenance costs, and is outside the scope of the project.

As you already mentioned, FairScan exposes an intent that allows other applications to invoke it. If an application such as Nextcloud wants to rely on FairScan's scanning capabilities, this is the intended integration path.

[PhilLab]

@pynicolas I see, what a pity. I don't know whether Nextcloud will accept the dependency on another app, but nevertheless do you have a rough idea when the Intent feature will leave the experimental state so one can build on it? Is this already on the horizon or completely unclear right now?

[pynicolas]

@PhilLab At this stage, the intent API is still experimental, and I don't have a clear timeline for when (or if) it will be considered stable.

I added it recently and prefer to keep some flexibility until it has been used in real-world scenarios and I'm more confident about the contract.

More generally, FairScan is a relatively young project (first public release was about 4 months ago), and it's my first Android app as well as my first experience with image processing and with machine learning. Because of that, I'm intentionally cautious about committing to long-term API guarantees too early.

[PhilLab]

@pynicolas FYI, see my current state of the Nextcloud -> FairScan integration, based on the Intent, here: nextcloud/android@4a29962

Let me know your thoughts. One shortcoming I need to address: the file is currently uploaded with the same filename as provided by FairScan. Which is just a long number. I'd like to change it to yyyy-MM-dd_HHmmss, so I need to find a way to manipulate it before the Nextcloud upload.

[pynicolas]

@PhilLab Thanks for sharing the integration, it looks good.

Regarding the filename: FairScan intentionally keeps things simple and just generates a timestamp-based name for the produced PDF. From FairScan's point of view, the calling app is free to copy the returned file/URI and rename it locally before doing anything else (upload, move, etc.).

Let me know if you run into any limitations with the Intent or the returned data.

[PhilLab]

@pynicolas yes, sure. I now added the file renaming as well, here is the Nextcloud PR if you are interested in following: nextcloud/android#16427