Nuke W4. Rotoscoping

Rotoscoping is a technique in animation and visual effects where artists trace over live-action footage frame-by-frame to isolate a character or object. This allows for easier compositing or layering of visual effects. It’s often used in films, commercials, and music videos to blend different visual elements seamlessly.

In real-world settings, fast-moving objects appear blurred to the human eye and camera sensors, so it’s recommended that we use motion blur/blur nodes mimic this natural phenomenon to blend seamlessly into new scenes or with added visual effects.

Calculate motion blur in Nuke:
24 frames per second
1/60 shutter speed
24fps/60=0.4

For this week homework, I was assigned to do the roto of the running man and the bridge in this particular footage, using the given setups below. At first these complex setups were really confusing to me, as I understand the nodes individually but I don’t exactly know why and how they are linked to each other. Therefore I did further research by watching tutorials and observing and playing around with the setup, then it starts to make more sense what the teacher was presenting here.

Reference: Nuke Rotoscoping Tutorial – Introduction to Roto Node. Available at https://www.youtube.com/watch?v=ELg9ncl-0Wo

This is a standard roto setup, where the plate (read) and the (roto) note is connected to a (copy) node, but separated into 2 different branches (A & B). Then the (premult) node is to multiply the alpha channel with the rgb.

The benefit of this setup (using (copy) node) is that it gives us a more broken down workflow of our script, so if there is any further modification added to the alpha channel, it won’t affect the rgb (original footage).

However, the first set up is a simplified one where you will be required to do the roto manually frame by frame. With this second setup, the only difference is that the (roto) nodes are separated into different branches, then got combined using (channelmerge) node. Additionally, we got introduced to the (tracker) node, which can be used to track the movement of a particular area in the shot. It helps speeding up the roto process, and is especially used in tracking very subtle shifts of static objects from camera movement that we might oversee with our own eyes.

Reference: NKE 101- Nuke 101- PART 10: Intro to Tracker Node. Available at https://www.youtube.com/watch?v=ELg9ncl-0Wo

At first, I wanted to try saving time by using tracker node to track the movement of the man. But after a few attempt it didn’t seem to work very well, perhaps because of the drastic movements.

The rotoscope process took me a lot of time, especially at first when I didn’t realize the technique and the movement pattern. I found the arms were the most tricky parts to work with as they don’t stay at the same shapes and placements and it takes really long to modify frame by frame.

Final takeaways:
Eventhough this first attempt at rotoscoping is not perfect, I have learned a lot through this assignment. First of all, the most important thing to remember is to break down the subject into small parts that you can easily track and modify. I separated the head, torso, and then both arms and legs into 3 parts. Additionally, it would help save more time if I have observed the movement pattern, in order to find main keyframes to start with. Thirdly, I initially started the assignment with a mouse, then I found that using a wacom has drastically improve the quality and save much more time on rotoscoping. The result doesn’t satisfy me 100%, yet it reflected exactly where I struggle at first, clearly shown through how the roto of the arms and head were not that good, then I improved much more on the legs after learning the right techniques.