RE SUB PIXEL Estimation

Calvin asks about sub-pixel measuring.

Yes its possible.
The key to doing this reliably is to understand the shape of the transition
between the edge of the object and the background.
A useful first approximation is to use a gaussian to model the shape of the
transition. A paper by Kurt Benke some years ago explores this. (I am
currently moving my office so I can't get an anything, so chasing the
reference is left as an exercise).
Essentially, the process will involve taking an image under controlled
conditions of a well known object (standard).
Producing an enlargement using either interpolation or not, try both.
Plot the transition from black to white across the edges and choose the
point which gives the correct answer.
You the know where on the transition, for your conditions of lighting,
contrast, camera etc, where the edge falls.
The keeping everything the same, repeat the process with your unknowns.
And it might sound easy but it is very difficult to keep everything the
same.
Best wishes
Noel Goldsmith

Noel Goldsmith
Aircraft Forensic Engineering
Air Vehicles Division
DSTO
506 Lorimer Street
Port Melbourne
Vic 3207
AUSTRALIA
Phone (613) 96267538
FAX (613) 96267089
Email noel.goldsmith@xxxxxxxxxxxxxxxxxxx



>
> 
> Date:    Tue, 28 Mar 2006 07:20:04 -0800
> From:    calope14 <calope14@xxxxxxx>
> Subject: Sub-Pixel Edge detection plugin?
> 
> Hello to all,
> I am doing an intensive project over the next couple weeks that is concerned
> with computer vision dimensional guaging. I was planning to use ImageJ for
> the image editing software as there are possibilities of needing to write a
> plugin to gather and store data about a picture.
> 
> But what I really need is a plugin that can find edges to a sub-pixel
> standard. All I will be doing is finding the diameter of a circular object
> to a sub-pixel standard. Does any one knnow of a plugin that does this. I
> would gladly make one but this is an area that I know little about and dont
> have time to do a lot of background learning. So if anyone could even let me
> know the steps in the procedure of sub-pixel edge detection and the names of
> some algorithms or processes used for them it would be a tremendous help, I
> have searched the internet thouroughly and there are no real clear
> insrtuctions for what I'm doing that doesnt cost money. I am sorry to bother
> you all but time is really an issue so if anyone could give me a shove in
> the right direction I would be most grateful.
> Thank you for you time, and I wish you all luck on your current work
> projects.
> 
> Calvin Slope
> --
> View this message in context:
> http://www.nabble.com/Sub-Pixel-Edge-detection-plugin--t1356294.html#a3631519
> Sent from the ImageJ forum at Nabble.com.
>