VFX Blog

When designing the Balloon Festival project, I wanted to focus on integrating the balloon with the background and creating a multi-layered matte painting. I wanted to try to add different elements and learn new techniques. I achieved my goal, but I also see that the criticism is valid and I overcrowded with the actual video, not creating a coherent story.

Furthermore, I made the mistake of rotoscoping the entire mountain in one piece at first, so I had to roto it again in several parts.

Feedback: I am lacking storytelling in my Balloon Festival project. I should probably add defocus and blend the moons more. Too much going on and no clear concept. I need to refine the idea and focus on one thing.

Tips:

Instead of a Primate node (in case of problems) use a Keyer (luminance key) to adjust the luminance for the flat alpha sky (to mute the colours) – operation Luminance Key.

If there are any white areas in the foreground – roto it out (merge>operation screen).

If the roto is on the bright (white) background then merge it with the operation stencil. I can also use the Keylight node.

The Chroma keyer is for the greenscreen. Play with screen balance to remove the border

Roto with feathering: To gradient this circulatory out, use the Premult node only after the roto (it is the last stage and later connect it with transform through a mask).

Additional resources:

Foundry (2019) How to create Particle Environments in Foundry’s Nuke. Available at: https://www.youtube.com/watch?v=VllMYK_TOnc (Accessed: 05 December 2022).

Foundry (2022) Improve the Look of Your VFX Shots | How to Draw the Audience’s Eye. Available at: https://www.youtube.com/watch?v=CJoFxEH2Xsw (Accessed: 05 December 2022).

Foundry (2018) Skill Up With Nuke | How To Stand Out As A Junior Compositor. Available at: https://www.youtube.com/watch?v=-Em0Wvm8O-I/ (Accessed: 05 December 2022).

LoveVFX (2021) Fantasy CG Environment // Compositing Tutorial. Available at: https://www.youtube.com/watch?v=D3ijPpBvFf4 (Accessed: 05 December 2022).

Ranjith.A (2019) Nuke Tutorial: Disintegration Effect using Particles. Available at: https://www.youtube.com/watch?v=4ic_r9XVptI (Accessed: 05 December 2022).

Ranjith.A (2020) Stranger Things Sky Effect in Nuke. Available at: https://www.youtube.com/watch?v=-KarYnfHO-I (Accessed: 05 December 2022).

Rebelway (2021) Advanced Compositing for VFX | Week 1 Lessons for Nuke Artists. Available at: https://www.youtube.com/watch?v=zD6ZGhfSFdI (Accessed: 05 December 2022).

RileysTutorials (2022) How To Replace a Sky In Nuke. Available at: https://www.youtube.com/watch?v=a6VsBYjVGhI (Accessed: 05 December 2022).

In my version of the high school video, I decided to tell a story (since that was my main problem with the Balloon Festival project). I changed the narration (from the original one) and left the exit sign in post-production. Instead, I cleaned up the text and a piece of paper on the walls because I wanted a cleaner look (no realistic fonts). I made a cartoon story out of it about a fire extinguisher exploding. On top of that, I added visual effects with vivid colours, highlighted exit routes, and added stylized effects to make it look more like an animation/cartoon. I think animating the painted elements would improve the image more, and in the future, I would also diversify the thickness of the drawn lines because currently, the lineart lacks variety

Workshop notes:

Roto Paint:

The RotoPaint node gives you a broader scale of tools to use than Roto, though many of the controls are shared across both nodes. It is used to clean up and clone out unwanted elements from the plate.

Boris FX (2022) Available at: https://borisfx.com/ (Accessed: 29 November 2022).

I chose to reference frame 1032. After the planar tracking I did during the workshop, I corrected the roto frames and added new posters (also resized them). In the end, I blended them with the background (although I had a problem with the left poster and couldn’t fully integrate it). I think there was a problem with my edge blurring, but I decided to leave it and move on to the next task.

Workshop notes:

Filtering Algorithm:

Image filtering algorithms exist to help us define what happens to our pixel values as we transform & process our images. The article below breaks down all the image filters we have available, and what they’re doing to our images in Nuke.

Choosing a Filtering Algorithm (2022) Available at: https://learn.foundry.com/nuke/content/comp_environment/transforming_elements/filtering_algorithm_2d.html (Accessed: 22 November 2022).

Concatenation:

Concatenation is the ability to perform one single mathematical calculation across several tools in the Transform family. This single calculation (or filter) allows us to retain as much detail as possible.

Concatenation of transforms in Nuke (2012) Available at: http://www.nukepedia.com/written-tutorials/concatenation-of-transforms-in-nuke (Accessed: 22 November 2022).

Back to Basics: A Brief Lesson on Image Filtering & Node Concatentation (2019) Available at: https://benmcewan.com/blog/2019/04/22/back-to-basics-a-brief-lesson-on-image-filtering-node-concatentation/ (Accessed: 22 November 2022).

During 2D tracking, I focused on finger movement. I should change the greenscreen and scroll the display even more because the action of the hand initiates a smoother and faster transition. I also designed the screen for the iPhone, photobashing various elements and images in Photoshop.

Workshop notes:

Transform is a super useful node that deals with translation, rotation, and scale as well as tracking, warping, and motion blur.

Animation>Set keys in Transform node.

2D Tracker:

This is a 2D tracker that allows you to extract animation data from the position, rotation, and size of an image. Using expressions, you can apply the data directly to transform and match-move another element. Or you can invert the values of the data and apply them to the original element – again through expressions – to stabilize the image.

This is the general process for tracking an image:

1. Connect a Tracker node to the image you want to track.
2. Use auto-tracking for simple tracks or place tracking anchors on features at keyframes in the image.
3. Calculate the tracking data.
4. Choose the tracking operation you want to perform: stabilize, match-move, etc.

Pre-tracking treating:

Sometimes we should treat the original plate to obtain better tracks. We usually at least denoise the plate before tracking.

1. Denoise plate (denoise node – median node).
2. Increase contrast with grade node.
3. Lapalachian node can help in certain case to lock better tracks.

It is a good idea to denoise footage to improve track.

Stabilise footage:

It is essential to denoise your plate before tracking. After this: call denoise node; select area of sample noise across the image; make sure to select an area with even colors (possibly mid greys); control amount of denoise and smoothness; write out the denoise plate and read it back in.

At first, I tried to match the colour, but I wasn’t satisfied with the result. It was too white and too far from the source. So I decided to do it manually because I generally like to adjust colours in Photoshop. When doing colour correction, I first used the Grade node to quickly alter the gain, multiply and gamma of the plane shot. Then I tried ColorLookup, where I focused on the blue channel (to enhance the colour and match it better with the background) and the alpha channel (which helped me blend the end of the plane and add some warmth there). I adjusted almost all the channels in the HueCorrect node. Finally, I added some minor adjustments to the mid-tones and shadows in the ColorCorrect node. I still think the front part of the aircraft is too bright and doesn’t blend in with the surroundings, but patching it up with colour nodes messed up other parts of the plane, so I left it as it is.

Workshop notes:

Premultiplication:

By default, Premult multiplies the input’s rgb channels by its alpha (in other words, premultiplies the input image). You may need this node when merging unpremultiplied (without alpha) images. Because Merge nodes in Nuke expect premultiplied images, you should use this node before any Merge operations if your input images are unpremultiplied. This avoids unwanted artifacts, such as fringing around masked objects.

Colour correcting premultiplied images:

When you colour correct a premultiplied image, you should first connect an Unpremult node to the image to turn the image into an unpremultiplied one. Then, perform the colour correction. Finally, add a Premult node to return the image to its original premultiplied state for Merge operations. Typically, most 3D rendered images are premultiplied. As a rule of thumb, if the background is black or even just very dark, the image may be premultiplied.

Other:

1. Reformat lets you resize and reposition your image sequences to a different format (width and height). This also allows you to use plates of varying image resolution on a single script without running into issues when combining them.
2. Merge nodes deal with layering multiple images together. The default mode is over, which simply places one image on top of another. You can choose from a variety of operations that change how merged layers interact.
3. Keymix (all) is similar to Merge but accepts unpremult assets. Often used for merging masks.
4. The ColorCorrect node is used to make quick adjustments to contrast, gamma, gain, and offset. You can apply these to a clip’s master (entire tonal range), shadows, midtones, or highlights. You can control the range of the image that is considered to be in the shadows, midtones, and highlights using the lookup curves on the Ranges tab. However, do not adjust the midtone curve – midtones are always equal to 1 minus the other two curves. You can also create this node by pressing C on the Node Graph.

Colorspace and Linearization:

Colorspace defines how the footage was captured or exported. Most files are non-linear, and knowing the correct colorspace is critical for proper linearization.

Linearization is the process of converting footage into linear space. All the tools inside nuke are built around linear math. This also allows the mixing of media types. We need to know what colorspace of the file was before starting to work on the file!

You can work in LOG/RAW or Linear.

LUTs, CDLs, and Grades:

1. LUTs can be used for creatively or technically, i.e. converting from log to lin, or adding a “look”.
2. CDLs are creative, i.e. adding a “look” to a clip.
3. Graded footage means colored to it’s “final” look.

Two most commonly used nodes are Grade and ColorCorrect. Both gives us the chance to grade H, M, S of the shot. In the Nuke to grade highlights we use either gain or multiply. For shadows we use lift and to grade, midtones we use gamma. In the ColorCorrect the lift is called offset.

White-balancing in the Nuke (can be useful at times to white balance an asset before grade it to match the backgroung):

1. Push all the way up the gain in the viewer and use the eyedrop in the Grade Node to select the darkest point in the images.
2. Push the gain in the viewer low and select with the eyedrop from grade node the bright/white point.
3. Match luminosity by manipulating multiply in the Grade Node.
4. Exposure adjust in stops!

While doing the rotoscoping of the man, I initially had a problem with choosing the mainframes for the roto. This prompted me to spend a lot of time fixing the individual head and arm frames. However, after practising it a few times, I started to see movement patterns and it greatly improved the speed of my workflow. Still, I had to check it frame by frame because I added too many points in the Roto nodes and overall it slowed things down more than helped with the details. I think with the Blur node I would still achieve precision even without such a detailed roto. Additionally, I wasn’t sure if I should roto closer to the edge (I shouldn’t as that would be adjusted later via the Blur node and motion blur options. I changed the parts of the roto between Bezier and B-Spline. I don’t think I initially chose the right tools for the right body parts, but again, after the task is done, I would say the head, feet and torso should be done with B-Spline and the arms and legs with Bezier.

Unfortunately, I ran into node Tracker issues and couldn’t export the video. It tracked the front parts of the bridge well, but the left-back one moved up and down at times. I think the problem with the export was connecting the previous Roto part.

Workshop notes:

Rotoscoping is the technique of manually creating a matte for an element on a live-action plate so it may be composited over another background. Via rotoscoping we can creating animated alpha channels “matte” to match the footage motion.

Rotoscoping is a core skill for a digital compositor. You need to be proficient and quick at it in order to be be a good compositor. Rotoscoping requires attention to details, patience and precision. It is most of the time a frame by frame job. Occasionally tracking can be used to speed the roto process.

Remember to use motion blur while rotoscoping.