Can I control rotation on IMAQ find Edge?

[NIDave]

Hi all,
Im using the IMAQ tools in LabView including the "IMAQ Find Horizontal Edge" but sometimes it picks up on erroneous edges especially when I get more specular back in my image (yeah I could do image processing to get rid of it but I want to eliminate the possibility of it occuring regardless).  So my question is there any way to control it so that it will only search for edges that are perfectly horizontal or +/- a few degrees.  I cant seem to find any settings for that.  They have edge strength and contrast and what not but nothing for rotation.  Im sure there has to be a way.  Any help would be really apreciated.
Thanks,
Dave

[Scott_R]

Hello,

While there is not any way to search for an edge at a particular angle of rotation, there are several settings for the Find Horizontal Edge function that could be used to improve its accuracy.  I would suggest starting with modifying the contrast and subsampling ratio settings.  The contrast determines what pixel intensity change will constitute an edge (increasing this value will require a greater change in pixel values for an edge to be detected) and the subsampling ratio determines the number of rake lines that will be used to detect the edge.

In addition to those parameters, you can also fine-tune the steepness to help determine the size (in pixels) of the transition area.  A steeper angle will require a faster transition from one intensity to another to register as an edge.  You can also modify the filter width to specify the number of pixels on either side of the edge that are averaged to determine the contrast of the transition.

Take a look at the IMAQ Vision for LabVIEW VI Reference Help for more information about the different parameters that are available with this function.  This help file can be loaded by turning on the Context Help for LabVIEW, hovering over the IMAQ Find Horizontal Edge function, and selecting "Click here for More Help."

Regards,
Scott R.
Applications Engineer
National Instruments