Commit c3b1c982 authored by Igor Filatov's avatar Igor Filatov Committed by Bastien Nocera

elan: Set max frame height to 50, add note about performance

Frame height is a loosely experience-backed guesstimation. 50 seems to be
a good middle ground between swipe speed and quality.
parent b098399b
......@@ -19,6 +19,23 @@
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/*
* The algorithm which libfprint uses to match fingerprints doesn't like small
* images like the ones these drivers produce. There's just not enough minutiae
* (recognizable print-specific points) on them for a reliable match. This means
* that unless another matching algo is found/implemented, these readers will
* not work as good with libfprint as they do with vendor drivers.
*
* To get bigger images the driver expects you to swipe the finger over the
* reader. This works quite well for readers with a rectangular 144x64 sensor.
* Worse than real swipe readers but good enough for day-to-day use. It needs
* a steady and relatively slow swipe. There are also square 96x96 sensors and
* I don't know whether they are in fact usable or not because I don't have one.
* I imagine they'd be less reliable because the resulting image is even
* smaller. If they can't be made usable with libfprint, I might end up dropping
* them because it's better than saying they work when they don't.
*/
#define FP_COMPONENT "elan"
#include "drivers_api.h"
......
......@@ -48,7 +48,7 @@
#define ELAN_MAX_FRAMES 30
/* crop frames to this height to improve stitching */
#define ELAN_MAX_FRAME_HEIGHT 30
#define ELAN_MAX_FRAME_HEIGHT 50
/* number of frames to drop at the end of capture because frames captured
* while the finger is being lifted can be bad */
......
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