Corner Pin severely distorts even with accurate tracks


#1

Hi. Another issue I’m having is with the corner pin transformation. I’m attempting to superimpose a monitor shot so I put trackers on each corner. Once I have four of them I review the track error and each one is sub pixel in accuracy (we’re talking 0.01 error per track on average). When I set up a corner pin and attach my footage, the first and last frames match up. In between the corner pin distorts wildly, and the corner pin transform error jumps to over 8 pretty regularly. How is this happening when the individual tracks have such a low error? Blender had no problem doing a plane deform with the same track locations.


#2

Please indicate the steps you take in order to produce those results. You do not necessarily need to put tracks in the corners, just where there’s texture. Then in the Transform tab you can set the CornerPin from points to wherever you’d like them to be.
Natron tracker works differently than Blender’s one, even though they share the same internal tracking algorithm, in Natron you could refine a CornerPin by tracking any number of markers (the more the merrier), not necessarily 4.

See the following tutorial which covers it partially: https://www.youtube.com/watch?v=hCP5472a2o8


#3

After the 4 tracks are placed I set the transformation to match move and export a linked transform node. I attach the monitor image to that node and then set the ‘from’ points to the corners of the image and the ‘to’ points where I want it on the base footage (also in the transform node). I do the initial alignment on the first frame. I also set that frame as the reference in the tracker node. The first frame aligns perfectly, as well as the last frame. Its all the in between frames that are distorting and generating the high corner pin errors.


#4

Hmm have you tried exporting with the CornerPin instead of Transform node ? If the motion you track is really perspective a simple transform node cannot properly lock onto it.
There may be a possibility that there’s a bug with the Transform export, I must admit the CornerPin is more tested.


#5

I think I am exporting a corner pin. I select that from the Transform Type in the tracker node before I hit the export button.


#6

A video indicating the steps you perform as well as showing parameters and your node graph would help figure out what’s wrong. Have you looked at the tutorial I linked above ?


#7

Yes I’m doing those steps. I’m going to analyze the tracks to see if maybe something is going on that is throwing the plane solution off.


#8

Okay it was my mistake. I wasn’t aware that I had to use two corner pin modes for the screen footage. That’s not the most intuitive method but after following that video it works now.