Blackmagic Forum

I want to place an image on a whiteboard that is flipped into view, so it needs to have perspective correction. Naturally I should use a Corner Positioning Tracker. However, the entire whiteboard is never visible onscreen. Only the rightmost two corners are ever visible. The leftmost two are off the side of the screen.

I looked at this tutorial () and others, which show using Track Center (Append) to modify a tracker to use a different reference (although I've had problems figuring out how to move the tracker without the corner following), but these assume the corner was onscreen at some point, and you have a track to begin with.

Is there a way to synthesize the corner offscreen and use a different reference from the start (there are words written in the middle of the whiteboard that I can use for reference), before tracking anything, so I can generate the track?

Rick

If you find two points close enough to the offscreen-corners,
you could track those and adjust each Tracker's X-Y-Offset to match the Board.

But aren't those offsets constants? Wouldn't that be a problem as the board flips?

Is there no way to leave the corner trackers offscreen, but move the track point references on screen, like when you use Track Center (Append), except before any rectangle tracking has been done?

Rick

The offset can be accomplished by a LERP (linear extrapolation) and a CornerPositioner.
Please check out this example.

Thanks! I'll take a look when I get back to the workstation.

I did fight with Fusion enough to get something, although far short of what I wanted, performance deadlines being set in stone as they are. The results are at 1:15 in this video, which was used during a high school choir performance of songs from movies (the song accompanies this video, but was sung live for the show):

Rick

Not too shabby that is...

Don't fight Fusion. Rather go with the flow!

OK, thanks so much for the example.

However, this appears to be a completely different way of approaching a solution. I'm not sure I understand:

What are the Trackers tracking? Tracker 1 & Tracker 6 appear to be the upper and lower left corners. But what are Tracker 2 and Tracker 7 tracking?

[I should note here, that unlike the videos I've seen, on my 8.0 build 18 version of Fusion, I do not get proper behavior of the Tracker Control Panel with respect to the Tracker Details. The Pattern Displays do not play (or step frames), and they don't track the current frame in the Timeline. They seem to be stuck on one frame, although it doesn't always appear to be the first frame. -- I also could not get the Track Center (append) to work as it did in the online videos I could find.]

Rick

Eric Westphal wrote:Not too shabby that is...

Don't fight Fusion. Rather go with the flow!

Thanks! It's not as smooth as I'd like, but I didn't realize, until I had done my first pass at tracking, that the actual stand of the whiteboard sways back and forth as it turns. Here is a video comparing the before and after shots:

Moving the trackers manually offscreen is ridiculously complicated. You move in X & Y, but it's actually moving in all three axes, no matter which dial you move. So I was trying to approximate where I thought the corners were at a few key points and interpolate between, using these extremely complicated controls. Then I hand-adjusted the tracking points to keep the image inside the whiteboard frame. Ugh!

If I'd had more time, I would have added some of the whiteboard texture (mostly erased stuff and scratches) back into the brush, but I just didn't. I did add the highlight moving up the board like the one in the original. And I enabled motion blur, but it didn't seem to make much difference.

The school didn't have a decent hi-res logo, so I also had to manufacture that. Thankfully, there are some algorithms for scaling up pixel art, so I was able to take a crappy lo-res version and scale it up. Plus, trying to match the school colors was a challenge.

Color keying her hand was a b!+¢h. The tools don't seem to want to deal with white or flesh as a color key color. I had to just give up on keeping the shadow.

Also, is there an easier way to feather the edges of the brush? The harsh edge is visible if it's not perfectly aligned. And even if it's perfect at the start, it's not later, due to the beveled wooden edge of the board sticking out in front of the board itself. I matched the color of the brush, but even that didn't work. So I had to manually add a transparency to the edge of the brush (in Gimp) to try to make it seamlessly blend with the edges of the original whiteboard (that's why the stripes fade out at the right edge). I tried several ways to add the feathering in Fusion, but nothing seemed to work.

Thanks,
Rick