In this lesson, we checked further nodes in Nuke and we learnt how to use a planar track to add a flat image to a sequence.
We reviewed nodes such as ‘Reformat’ (to change sequence format to match main plate), ‘Crop’ (to crop an image or a video as required), ‘Merge’ (we saw how to use it to fix the size of the bounding box of a sequence to the Alpha layer or the Background layer), and ‘Shuffle’ (to add or remove channels – R, G, B, Alpha, and Depth).
We also learnt how important is the concatenation in a Nuke comp. Concatenation is the process of moving pictures/frames in a sequence. Nuke does calculations that need to follow a logic and if this logic is broken, the final result will not work. Following on this, we analysed several ways to organise the nodes in Nuke so they follow an order and, therefore, we achieve the desired result without any error.
Finally, we also studied how to use the ‘Planar trackers’ to add a 2D image to a 3D space and how to make it follow the movement of the sequence. First we added the ‘Planar tracker’ node, select the area we want with tracking points and track like we do with a regular ‘Tracker’ node. Then we turn on and align the grid to the tracking points to create the perspective desired, and finally, we create a ‘CornerPin2D (absolute) to create the tracker node that we are going to link to the image that we want to add. We can track translation, scale, and rotation together or separately if desired. When there is an object in front of the area that we want to track, we can track the object separately with another ‘bezier’ in the same ‘Planar tracker’ node, so Nuke recognises that object as an area of exclusion (so it does not take it in consideration when tracking the area that we want to).
As a homework, this week we were asked to add an image to the following sequence using what we learnt today in class.
I added both posters using a ‘planar track’ node to track the plane where I wanted to add the poster. For the left poster I just tracked it, adjusted the grid lines to the perspective plane I wanted, and then created a ‘corner pin 2D (relative)’ that will be linked to the poster. This node will let the poster or image added to follow the movement of the shot that we have tracked.
For the second poster, it was necessary to add second bezier that tracks the pole that passes in front of the poster so the programme understands that the area of the second bezier does not have to be taking in consideration when tracking the first bezier area (it is excluded). The roto of the pole was already added in the comp by the professor so I just had to ‘merge’ the second poster ‘corner pin 2D’ to the main comp. I also adjusted the ‘grade’ and ‘saturation’ of the posters, skewed them a little bit with ‘transform’ node to fit 100% the perspective, and added some ‘blur’ to remove the sharp edges from the posters and blend them in to the comp.
This practice seemed pretty easy to me compared with other assignments as ‘Planar tracking’ is a straight forward tool. However, at the beginning I had a problem with the middle poster that has the pole obstructing part of the view in front of it. The ‘Planar tracker’ was not reading the area properly as the tracking points were jumping from the area selected to a completely different area and was not keeping the perspective I wanted to keep. I solved this making the tracking area bigger so the programme had more information to create the track along the frames. I also colour corrected the posters to blend them with the scene and make it more realistic. Overall, I am very happy with the result.