[GRASS-user] Running canny edge detection on thinned binary image

[Venka]

Hi All,

I have a question about Canny Edge Detection using i.edge

1) I produce a thinned binary image as below

r.thin --overwrite input=line_element output=thinned_line_element

a) the "line_element" represents valleys that are, at places, few pixel
wide

b) the output "thinned_line_element" represents valley lines that are
a single pixel wide

2) I run the Canny edge detector on "thinned_line_element" as below
i.edge --overwrite input=thin_line_element output=edge_map angles_map=angle_map


The resultant "edge_map" produces a monotone (no edges) edge map and the "angle_map" outputs the angles
correctly

3) Running the Canny edge detector on the un-thinned "line_element"

i.edge --overwrite input=line_element at PERMANENT output=edge_map1 angles_map=angle_map1

produces both "edge_map1" and "angles_map1" correctly.

Any idea why the Canny edge detector does not produce edge map on thinned image?

Kind regards,

Venka