Alpha layer transformed to black on grayscaled images with feature detection

[Wharenn]

Hi everybody,

We're using thumbor with feature detection but we have problems when we use grayscaled PNGs having an alpha layer. On these images, the whole alpha layer is transformed into black color.

It seems somehow related to this FIXME:
https://github.com/thumbor/opencv-engine/blob/master/opencv_engine/engine.py#L193

Called by:
https://github.com/thumbor/thumbor/blob/bc52ab6bb8934c08d24c89ef5e52f20744468e58/thumbor/detectors/feature_detector/__init__.py#L23

Did anyone also encountered this problem and have clues to fix it?
Thanks by advance.

[christianjgreen]

Can you upload an existing test case image so I can add it the tests for the current cv2 PR?

[Wharenn]

Hi, this was a long time ago and I can not reproduce the bug anymore on my environment (we made some changes for this). However, I am pretty sure this one triggered an issue: