Hello Makarena.osorio good afternoon,
Thanks for contacting us at forum support, based on the information that was provided I would recommend that you can try to use the Express VIs for the acquire and assistant to create protoypes and it would be easier to modify all of the settings for the detection of the edges. The vision acquisition module would determine if you are going to use the camera or a folder where you can have all of your images for testing. The vision assistant would help you perform the tests you need and determine which settings to modify.
NI Vision Assistant Tutorial
http://www.ni.com/pdf/manuals/372228m.pdf
Since they are VI express they would guide you for the implementation and if you need to have the code of the VI you can select the option by right clicking and selecting the option open front panel, keep in mind that this would change the VI express into a regular code and you cannot go back to the Assistant.
Hope this information is helpful.
Best Regards,
CaEnOs.