How to replace the background walls in this shot?

Hi There,

I have difficulties trying to find the right solutions replacing the wall attributes and machine in the background. Can someone pointing me in the right direction? The trains passes by with a lot of motion blur. I need to solve this today actually.



Is the camera moving?
What host are you working with?
do you mean where you can see through the train windows?

Hi ,

The camera is panning just a bit but its moving.
I work in After Effects. The first part without the train should be not to difficult.

This is what the final shot should look like

This is the incoming train with motion blur

That looks hard, you can easily mask out & reposition the background/train & platform but i don’t think you’ll have much choice then to go frame by frame & create masks for where you can see through the windows, if it’s moving that fast you’re not going to be able to track those windows :open_mouth:
Maybe Mary will have a simple solution :grin:

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Well I hope so. I dont have alot of experience with Mocha so I try to figure out how to track the position of those walls as I can only track the tiles in the front and the roof :frowning:

Thanx for your help!

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Yeah, i don’t think i could explain it, I think i would try keep the train & the platform in front as one layer tho, because of the lights flashing on it as the train goes by, a bit like this, reverse this mask then overlay or as an insert using tracking of the back wall, then deal with the windows

Or the other way around might be easier, painstakingly mask the train windows & drop the wall behind, but as you say it’s which part do you track to be able to apply the wall as an insert or background

it’ll be interesting to see what suggestions you get, :+1:

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Hi, would you share a copy of the train clip, put it in a zipped folder & drag it into Google Drive, set the Share to Anyone with the link, Copy link & post it on here using the chain icon at the top of a new comment,
I’m really curious about this now :thinking::face_with_monocle::grin:

Don’t track the wall, track the ceiling and the floor with translation, scale, and rotation only, use adjust track at the beginning of the shot and at the end to manage any parallax problems with the wall and correct them. Then, I am sorry to say, you are going to have to rotoscope windows and likely by hand, but for the train shape, it likely can just be blocked out, linked to the floor and ceiling track, and quickly hand animated. Remember, the train shape just has to encompass the train as it moves through the station, not follow it except for at the beginning and end of the shot, and it’s going so fast that can easily be hand animated.

You can try to track the train, but you’re better off hand animating one window well for both the back wall of the train and the front wall of the train, and then duplicating them, and using Uber Key to offset the duplicates to match the windows on either wall of the train.

I hope that helps.


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Hi Mary thank you so much. I finally had to do a lot of work manually.
I did track the movement of the train and attached all the window shapelayers to that layer. I changed the shape of the window layers during the motion. Finally I imported them ask masks in AE and used a still image of the background as background layer, to make it look like you looking trough it.

The wall logos in the back are tracked during the times when there is no train.
Combining alot of methods and a lot of patience I came to this result:

Also Ive added a logo and grafitti on the train.

That is a lot of tracking! I am glad you got it done!