Detecting crosses in an image

Question

I am working on a program to detect the tips of a probing device and analyze the color change during probing. The input/output mechanisms are more or less in place. What I need

Answer 1

How about simply determining the autocorrelation as you have a nice periodic pattern in your images.

Let say you have your target image:

And a template image to synchronize to

You can determine the Autocorrelation of both:

In both you can detect the ACF peaks, as in this example

These peaks you can match against each other using the Hungarian algorithm. Here a match is indicated by a white line.

This gives you a set of matching 2D coordinates, which hopefully satisfy the relationship:

x = Ax'

Where A is tranformation matrix with scaling and rotation. Solving it thus gives you the rotation and the scaling between your template and your target image. Translation can then be ascertained via normal cross-correlation with the partly rectified/corrected image and the template image.