Detected Edges: Offset from Image

[Breslov]

Hello Robert!
Thanks for a nicely-structured implementation of the Canny algorithm.

I try to utilize your code to identify the borders of an A4 page pictured over a wooden table (picture is attached).

• I use your hardcoded defaults for GAUSSIAN_RADIUS (7) and GAUSSIAN_INTENSITY (1.5).
• I call the JCanny.CannyEdges method passing-in the parameters used in your test code (within Tester.java), i.e. numberDeviations=1 and fract=0.2.

The result image is attached. It includes the source-image, after being gray-scaled, and on top of it - the detected edge-points, in red.

You could see that (A4) page-borders are not appropriately marked.
The detected edges are shifted a bit in relation to page's actual location.

Could you please advise - how to fix this offset? It would be much appreciated.

Source:

Result:

Result - Zoom: