OpenCv Template Matching - Unexpected masking result

Question

I am trying to match a template with transparency in a scene with OpenCv v3.3.0 I am using the Java example code from the official documentation.

My test case looks like this:

Scene:

Template with transparency:

Template mask (masked the transparency layer to black):

Matching result (red border marks the match):

Expected result (red border marks the expected match):

For the matching I am using CV_TM_CCORR_NORMED. The matching itself works fine with the mask (without the mask I get a wrong possition). But the found region is the same size as the template and it's mask. I expected it to be the size of the masks colored content.

How can I get the expected results (see image)?

Answer 1

Transparent region means that it can match any pixels as long as those pixels are present. So to make OpenCV find only non-transparent pixels, you need to crop the transparent region on your "query image" first.