Re: Hysteresis step in Canny edge detection

Subject: Re: Hysteresis step in Canny edge detection
From: Mateusz Loskot (mateusz_at_[hidden])
Date: 2019-03-20 17:32:01

On Sun, 17 Mar 2019 at 00:20, Olzhas Zhumabek
<anonymous.from.applecity_at_[hidden]> wrote:
> I had a look at it, and it seems like it has the same problem as I had in
> the beginning: applying hysteresis as I go, not at once in the end. From
> what I understand, hysteresis makes transition from weak edge to strong
> edge only when strong edge is in immediate vicinity,
> [...]
> E.g. relative position of weak edges to strong edges matters in code of the
> linked pull request.

The goal of hysteresis thresholding (HT) is to take connectedness into
account, isn't it?
That is, to preserve pixels that belong to continuation of curves
(edges) and filters
pixels that belong background/noise. AFAIR/AFAIU, the HT is a thresholding
that specifically takes spatial proximity into account.
So, the relative position of pixels/edges does matter, doesn't it?

> I wanted to verify if I'm right before contacting the
> author, because I've seen various interpretations on the internet.

Please, feel free to ask related questions as comments to the PR
https://github.com/boostorg/gil/pull/258
This way, we can share our findings in common space.

Unfortunately, I didn't have time to look at either of the
implementations in details.
I will let you know if I have.

Best regards,
-- 
Mateusz Loskot, http://mateusz.loskot.net