Grip Image processing

[hadarsi320]

I'm trying to learn how to use Grip. I'm using the sample images from the wpilib website of the 2016 frc to get the outline of the tape.

I encounter some problem in the images that include a side shot of the goal that includes two sides of equal size, this is how it looks: http://imgur.com/a/ilKUe

Does anyone have any idea what should I change in the filters?
I tried changing it specifically for certain types of images but it ends up ruining images that are closer/further away.