ELAN image sensors - poor upstream behaviour (USB 04f3:0c28 and the 0c0x/0c1x/0c2x family)

Status: Claimed upstream, but frequently unusable. Two open MRs improve it.

The in-tree elan driver claims a long list of ELAN image sensors (04f3:0c01 through 04f3:0c4x, including 04f3:0c28). Being on libfprint's supported list is misleading here: on many of these readers enrollment fails at every second capture, or never completes at all.

If your ELAN reader is recognised by libfprint but you cannot finish an enrollment, this entry is for you. If it is not recognised at all, you want a different entry: see the ELAN entries for 0c4c, 0c6c, 0c8e, 0c9c, 310d.

What is broken

Reported by the MR authors and matching a long tail of user bug reports:

Too few calibration loops, so every second capture fails.
Result code 0xaf from CAPTURE_READ_DATA is unhandled, and it occurs often.
bz3_threshold is too high for these low-resolution, low-quality images.
Captures are treated as swipe images to give NBIS enough pixels, which fits the hardware poorly - these are press sensors.

What the fixes do

libfprint MR !217 ("elan: Add support for touch devices", Piotr Piastucki / @ppiastucki), based in part on iafilatov's elan-touch branch: more calibration loops, handling for 0xaf, a lower bz3_threshold, image resize plus a sharpening convolution to roughly double extracted minutiae.

libfprint MR !530 ("add sigfm algorithm implementation (rebased and enabled Elan sensors)", @Tooniis, continuing @418's work): brings the OpenCV-based sigfm matcher into libfprint and switches ELAN sensors to it, so they can be used as the press sensors they are instead of being faked as swipe devices.

The two are independent; !530 is the more fundamental change and is actively rebased on master.

How to try them

git clone https://gitlab.freedesktop.org/libfprint/libfprint.git
cd libfprint
git fetch origin merge-requests/530/head:mr-530   # or 217
git checkout mr-530

!530 needs OpenCV (and doctest for its tests) on top of the usual build dependencies. Then build per docs/BUILD.md.

Tested on

MR !217: the author's 04f3:0c28 reader, where stock libfprint could not complete an enrollment.
MR !530: the author's ELAN sensors, using sigfm in press mode.
If you have any 04f3:0c0x-0c4x reader, a before/after report is valuable - this family is large and under-reported.

License

Part of libfprint (LGPL-2.1).