Discussion :

[Javeria Malik]

Hi all
Can any one tell me how to find zero crossing from the laplacian image
Kindly help
Best regards
Javeria

[hunta_kirua]

Hello,

I have some difficulties to understand your problem. You only have to find pixels whose value is equal to zero.
To acces pixel value, you can use the cvGet2D function. Take care of the depth of your destination image (signed/unsigned value, try IPL_DEPTH_16S for example).

I hope it can help,

Hunta

[Javeria Malik]

hi
The zero crossing detector looks for places in the Laplacian of an image where the value of the Laplacian passes through zero --- i.e. points where the Laplacian changes sign. Such points often occur at `edges' in images --- i.e. points where the intensity of the image changes rapidly, but they also occur at places that are not as easy to associate with edges.

so its not only the point in image where value is zero
Kindly reply
regards

[hunta_kirua]

Perhaps is it possible to use absolute values and search for extrema and in a second time verify that there is a zero crossing? Or use a threshold at zero to have a binary image and look for black pixels in the neighbourhood of white ones (or the inverse).

I don't know if it is the correct way of thinking.

Hunta