Image correlation

[Workaholic]

Hi,

I try to write a program which makes use of the image correlation VI to obtain the correlation coefficient over the two attached images. The file 200 is the template, and 201 is the sub-image with a narrow mark by pen on it. However when I swept over the sub-image and compare it with the template, the output 2D correlation coefficient does not change even when the sub-image enters into the pen mark zone. Therefore it does not make sense to me. Any advice on this? Thanks.

Wallace Lai

[Eric_R]

Hi Wallace

Unfortunately the code you linked contained subVI's that did not open. From looking at this code you will need to specify a rectangle smaller than the image you are correlating over. As a problem solving strategy try placing probes on the input and output of your correlation. Use this to confirm that the output is what you intend it to be before transforming the data into an array. Also please see chapter 6 of the Vision Concepts Manual for more information on image comparison and the algorithms used.

[Workaholic]

Sorry I forget to attach the subVI. Here they are.

Wallace

[rpursley8]

The maximum value of the correlation seems to change only by one.  I don't think you have enough of a change in the two images to detect the change.  The images and the correlation are 8-bit and that may not be enough resolution to detect the change in maximum correlation value.

[Workaholic]

In other words, the program itself is fine?

Wallace

[rpursley8]

Seems to be to me.