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Animating transform center based on a tracker

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StathisSideris

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Animating transform center based on a tracker

PostWed Jan 25, 2017 3:25 pm

I'm trying to replace the sky of a shot with camera panning (1920x1080). I've keyed out the original sky, and I found a photo with enough resolution to become the replacement and have enough sky for the whole pan (3072x2048). I also found a very clear feature of the original footage that appears in all the frames which gave me good tracking for one tracker.

I'm transforming and then cropping the replacement sky photo so that it matches the dimensions of the footage. My plan was to "connect to" the center of the transform tool of the replacement sky to the "tracker path/position" property of the tracker tool of the original footage so that their movement matches. That resulted in the sky moving in the right direction, but the movement was exaggerated, as if the movement of the tracker was being multiplied by some unknown factor. I figured that this could be because of the relative coordinates used for the center of the transform, so I enabled "Use Frame Format Settings" under "Reference size", but that didn't help.

Is there a way to match the tracker position when the resolution of the two sources differs so much? I also tried animating the offset of the crop tool instead, but it wasn't very obvious what I should connect the X and Y sliders to.

This is for practice (and it may be that I'm out of my depth) but it seems like it should be a relatively easy thing to do.

Many thanks,

Stathis
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Chad Capeland

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Re: Animating transform center based on a tracker

PostWed Jan 25, 2017 5:27 pm

Did you match the pixel sizes?
Chad Capeland
Indicated, LLC
www.floweffects.com
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StathisSideris

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Re: Animating transform center based on a tracker

PostWed Jan 25, 2017 8:34 pm

I didn't match pixel sizes at the point of animating, I needed the photo at its original size so that I had enough of it to allow panning, so it has to be larger than the foreground footage. I can see how this can be a problem, but I'm not sure how to solve it. I have attached an annotated version of my flow to make it clearer.
Attachments
Screen Shot 2017-01-25 at 22.28.51.png
annotated flow
Screen Shot 2017-01-25 at 22.28.51.png (190.62 KiB) Viewed 311 times
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Sander de Regt

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Re: Animating transform center based on a tracker

PostWed Jan 25, 2017 9:38 pm

From the screenshot it's hard to tell what you did exaxtly. It does seem to be the wrong way to approach this. For example I see two stabilizers and something called 'movement' - what is that?

And you're merging the footage over a still frame that you moved with a transform tool (probably connected to the tracker) That would explain why there is a discrepancy in the amount of movement between foreground and background. The crop isn't helping either.

Since this is for practice, would you mind sharing the footage so I could do a QnD (Quick 'n Dirty) tutorial to show you (and other new users in Fusion) a more efficient way to approach this?
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StathisSideris

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Re: Animating transform center based on a tracker

PostWed Jan 25, 2017 10:43 pm

Sorry, you're right, the custom naming of the tools doesn't help! I've zipped the comp with the footage (which I got from an website with royalty free footage) and the image of the sky:

https://www.dropbox.com/s/uke95xqs2t76e ... m.zip?dl=0

(zip file is 14MB)

I still don't know how to do relative filenames in loaders, so you may need to point the loaders to the files after you open it. Also, please excuse the horrific keying, I'm only playing.

A tutorial is way more help than I hoped to get, many thanks!
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Steve Iskenderian

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Re: Animating transform center based on a tracker

PostMon Apr 17, 2017 12:25 pm

I have the exact same problem and the tutorial would be much appreciated.
Is it available somewhere?
Thank you for helping.
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Sander de Regt

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Re: Animating transform center based on a tracker

PostMon Apr 17, 2017 8:17 pm

I haven't gotten around to doing it completely, since the original footage was pretty difficult to work with.
I did make a start to demonstrate the tracking part, but I didn't finish the whole thing yet.
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Adelson Munhoz

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Re: Animating transform center based on a tracker

PostMon Apr 17, 2017 8:54 pm

Tracking has some tricky things.

In your shot, obviously the sky replacement image is bigger than the pan shot.

If you change the sky replacement size in order to match the pan shot, it will no longer be big enough to cover all the movement. But if I don't do that the tracking doesn't work because the same percentage shift in two images of different sizes result in different pixel shifts. That's your "unknown factor".

That's the tricky part: You don't have to scale your sky image down. Just put it in a frame whose size matches your pan shot. The exceeding image will still be used by the tracker tool, even if it's off the frame.

That's because any transform tool in Fusion concatenate, i.e. they sum all their transformations and act as one single transform node. The transform node itself, the merge node, the crop and the tracker behave like tranform nodes.

The only condition for this is that you cannot put any bitmap-based tool between them (for example a Blur or Grid Warp). In this case, the transformation of the previous node will be "flatten" and, for tools that does not have a "Clipping Mode" option (like Grid Warp), the information off the screen will be lost.

To put your big image inside a frame that matches your pan shot, you can use either:

- a merge over a transparent background with the same size of your pan shot

- a crop with the same size of your pan shot. Set the Clipping Mode to "None" to preserve the pixels outside the frame. By doing so, the information off the frame is still "usable" by other transform tools downstream, including the Tracker.

In both cases you can ajust the offset of the sky inside the tool itself (merge or crop) since both offer transform / offset adjustments.
Last edited by Adelson Munhoz on Tue Apr 18, 2017 12:38 am, edited 2 times in total.
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Kel Philm

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Re: Animating transform center based on a tracker

PostMon Apr 17, 2017 9:21 pm

Great post, I had the exact problem with a blur that kept cropping my BG plate and now I know why.
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Bryan Ray

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Re: Animating transform center based on a tracker

PostMon Apr 17, 2017 11:13 pm

Much of the time, if you turn the Clipping Mode to "None" or "Domain" in a tool like Blur, it will preserve the Domain of Definition, allowing you to keep those pixels that are off-screen.

Likewise, the Crop node will clip outside of the crop region unless Clipping Mode is set to "None."
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Adelson Munhoz

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Re: Animating transform center based on a tracker

PostTue Apr 18, 2017 12:26 am

Much of the time, if you turn the Clipping Mode to "None" or "Domain" in a tool like Blur, it will preserve the Domain of Definition, allowing you to keep those pixels that are off-screen.

Indeed but:
- the default Clipping Mode setting of the Blur tool is "Frame"
- there are many tools that work at bitmap level that does not have this setting (like Grid Warp)
- whatever "Clipping Mode" you choose, the transform concatenation is broken by the Blur tool (or any bitmap-based node).

For example: if you take a full HD image and connect it to a transform node that reduces it to just one pixel and, in the sequence, connect another transform node that brings the image back to its original size, all the information is preserved.

On the other hand, if you place any bitmap-based node between them (even a Blur set to zero), the concatenation is broken and all the image information is lost.

But I corrected the post regarding to the outside pixels to be more precise.

Likewise, the Crop node will clip outside of the crop region unless Clipping Mode is set to "None."

You are right. I set my crop tool default to "none" long ago. I corrected this.
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Steve Iskenderian

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Re: Animating transform center based on a tracker

PostThu Apr 20, 2017 5:17 pm

Thank you very much for these infos, it's so useful.
I managed to make the bg and it follows quite well, but only "quite" sadly, and while it doesn't slide anymore, it jitters, as if there was a missing coordinate.
Should I add more than one tracking point?

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