How to get well-defined edges regardless of the color

Question

I am trying to develop an App that detects cards \"master cards, visa, cutomer cards, etc\" using Android Camera, for that purpose i used OpenCV4Android version 3.0.0. To achiev

Answer 1

You can use Structured Edge Detection.

I got these results running the C++ code in this my other answer. This seems like a good and robust result to me.

To use this in Java, you should know that Structured Edge Detection is in contrib module ximgproc. You probably need to recompile OpenCV to use it: Build OpenCV with contrib modules and Java wrapper