The different between this piece and that piece is that in this there is moving footage. This means that tracker nodes will need to be used in order to keep the car in place. The footage pans from the sky down to the beginning of the pavement. This means that the car isn't in the view for a lot of the footage.
The footage for this piece can be seen using the link below:
To begin with, open Nuke and read in the pan footage of the background.
Next the car needs to be read in. Since the car doesn't move or change in anyway in the duration of its footage, one can save themselves a lot of work by simply reading in a single still rather than the whole footage. For example, in this picture the still shot 170 has been used.
The next step is rotoing the car. The same rotos cannot be used from the car colour correction piece because they will not work properly with the trackers.
Unlike the last piece, this time the shadow and wheels have been roto'd along with the body of the car. Also this time the boot lid of the car is closed, which means there is less to roto.
Next we need to merge the car and the new background together. So a merge node needs to be read in.
The A goes into the roto which is still attached to the car footage, and the the B goes into the new background.
Now the background footage needs to have the trackers put in place. This requires at least two stand out points in the footage. One of which is a white stone which can be seen in the picture below:
Attach a tracker node to the background and track this stone.
Make sure the track is clean and straight. Next a transform node needs to be read in and attached to the roto node for the car. The tracking information from the tracker needs to be copied across to the transform node.
The information from the tracker can be found in the transform section of the tracker node.
The information that is needed is the center. Copy this across to the translate section of the transform node.
This should place the car roto on the tracker. A way to tell if the transform and the tracker have linked properly is represented by the green line between the two.
If the car hasn't moved onto the track properly, then it will have to be moved manually. This can be done by right clicking on the translate section of the tranform and selecting edit expression. From here points can be changed and the car moved to the right place.
The next step is the second tracker, this one will keep the car ground whilst the footage plays with the sky frames. A second tracker and transform needs to be read in and attached on the node tree as shown below:
In the picture above the tracking information has already been carried across to the second transform (as represented by the green line.
For this one, one of the green poles has been used as the tracking point, the tracker point was placed on on the first frame where the top of the fence pole comes into view.
After making sure that a clean track has been accomplished, the trackers must be checked to make sure that they do not overlap. The trackers route can be seen on the timeline. It is represented by blue points.
An easy way to make sure that the trackers do not overlap is to find on the timeline where one starts and the over should begin and do a clear forward on one and a clear backward on the over. This means that they should follow on from each other without incident.
Now it is time for the colour correcting. This is the easy part. Copy the colour correct nodes from the car colour correct piece and place them on the node tree.
The colour corrects may been altering slightly. In this piece the car and background looks a lot less saturated than in the car colour correct piece. The piece can be altered in any way, for example, this one could be made to look like it is at a different time in the day to the car colour correct piece.
Now the tricky bit, the windows. In the car colour correct this was an irritating bit to work out. A way has been found that makes it really simple. This involves using the rotopaint node rather than a roto node. Read in the rotopaint node and place it on the tree.
Using the reveal tool (shown below), draw around the windows like in a roto. The main difference is that the winodw must be completely filled in. The easiest may to do is is to is to view the rotopaint and click the A key whilst hovering the mouse over the image to view the alpha channel. This way one can see what is being revealed more easily. It is best to draw around around the edge of the windows before viewing the alpha channel.
The black areas of the windows in the picture above show what has been revealed. When using the reveal tool it is important to get the areas as black as possibly, to reduce spill and get a clearer image. A picture of the icon for the reveal tool is below (the mouse icon for the reveal tool is the same as the picture below):
If a mistake is made, then there are over tools, like an eraser, that can be used to fix the mistake.
Within these icons there are also other tools that can be useful. Like a blur tool, with will work in the same way as the reveal tool. A blur would be useful with this piece to try and give the windows the appearance that they are being viewed through the first set of windows.
The reveal basically allows some to select what they want to get rid of in a shot. Using this node on the car, one can take out the image of the grassy plain and reveal the fence from the new background behind it (since the car was placed on top of the background, the original background is still behind it). By placing the rotopaint onto the node tree on the same branch as the roto, it means that the tracking information that was applied earlier, applies to the rotopaint as well. So the windows will follow the car perfectly.
The picture above shows that the windows now reveal the right background. Sadly the colour correct will not effect the windows for some reason, so the best thing to do is to go to the rotopaint node in the properties bin and change the output and the premultiplier to alpha (for some reason this gives the windows a more glossier appearance).
Then use the blur tool withing the rotopaint and add a slight blur to the windows. This will give the windows a more realistic look.
A picture of the node tree so far is below:
Below is a video of the car pan so far is below:
Upon reviewing the footage, it is clear that another tracker is made. The footage shows that as the camera moves down, the car is supposed to go out of shot. Instead of this happening, the bottom of the car lingers and gets dragged down with the camera. A third tracker can be used to keep the car in place.
That is the end of this blog post, in the next one it will reveal how to use the third tracker to sort this recent problem.
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