I'm using Blender 2.75a. I'm fixing the lens distortion using Grease Pencil and a checker image as guide, but the lines do...

I'm using Blender 2.75a. I'm fixing the lens distortion using Grease Pencil and a checker image as guide, but the lines doesn't seem to distort moving the K1, K2 and K3 sliders. What I did was import the image, create the guide lines with grease pencil and move the sliders, like in the video, and nothing happens. What am I doing wrong?