Exploring 8 Essential VFX Compositing Techniques

By: Rebelway

In this article, we’ll take a look at 8 essential compositing techniques inside Nuke.

Compositing is one of the most essential components of professional FX pipelines. In fact, compositing is often the difference between a scene that looks world-class and a scene that looks laughably bad.

As a result, we thought it’d be helpful to take a look at 8 of the most essential compositing techniques for FX artists to understand. These tips come to you from Nick Chamberlain’s webinar on essential compositing techniques. If you haven’t seen it, here is the full two-hour presentation.

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8 Essential VFX Compositing Techniques

Here is our list of essential compositing techniques for FX artists.

1. Tracking

One of the best ways to create a camera track is to simply help yourself before you get started by stabilizing the camera during production. Nevertheless, Tracking is an essential part of the compositing process. As you may know, there are essentially three distinct types of tracks: 2D Tracking, 2.5D Tracking, and 3D Tracking.

Let’s take a look at a few essential camera tracking methods.

2D Tracking

2D tracking is great if the camera is moving around, but there is very little parallaxing. Think of a single camera person standing in a single location.

2.5D Tracking

2.5D tracking is typically best on compositing projects like monitor burn-ins or screen replacements. Typically artists will use tools such as corner pin trackers or planer trackers for this.

Motion Blur in Tracking

In order to ensure that your track looks as convincing as possible, you should try to get your Motion Blur to match your scene. Many times, you will need to figure out the exact shutter speed of the camera that shot the footage in order to get it right.

2. Levels

Levels is an incredibly important aspect of compositing as it allows your scene to blend color, luminance, and saturation. Without good leveling, your assets will feel like they don’t belong to your scene. This process is called Color Balancing. Let’s take a look at the three most important components of levels.

Luminance

Luminance is important as it is ideal for making sure your white and black levels are aligned. You wouldn’t want an asset with dark grey blacks to be composited into a video with deep blacks. In short, Luminance is all about matching the overall contrast level of your assets. In the example above the luminance is way off.

Color Tone

Color Tone is simply the process of matching the various levels of different colors in your scene. Just like luminance, the levels of your RGB should all match in Mids, Highlights, and Darks. Notice how the green tones in the spaceship above don’t allow it to sit well in the scene.

Saturation

In a similar vein, the overall intensity of the saturation of your given assets should also be matched. It doesn’t make sense for a dull asset to be comped into a brightly colored scene. Be mindful of spot saturation in your scene where certain parts are more saturated than others.

3. Grain

All footage, no matter the camera, has a specific type of grain inside them. While traditional film cameras have more grain, even modern cameras have a specific grain pattern that must be analyzed and replicated if you want your scenes to look convincing. Some projects will require grain addition and others will need to remove the grain.

The example below shows just how much grain is visible in a seemingly ‘clear’ video.

Here are 5 simple characteristics and steps to match the grain in your scene.

5 Characteristics to Match Grain

Match Intensity – The overall amount of grain in your scene.
Match Luminance Curves – Digital cameras typically have heavy grain in blacks and blue channels with light grain in highlights.
Match Size – How big are your grain specs?
Match Sharpness and Softness – Is the grain rigid or soft around the edges?
Irregularity & Shape – What are the unique qualities of the grain?

4. Edge Detail

One of the most important components of keying is simply getting the edges right. If you’ve traditionally used the built-in tools in a program like After Effects or Premiere, then you know that edge detail isn’t something that you can simply ignore.

In the image below you can see a poor edge that is too fuzzy to be believable.

Here are a few key steps for dealing with edge details.

Steps for Detailing Edges

Step 1: Extract the edges so they match the original footage in detail and shape.
Step 2: Modify the edge color to fit with the new background.
Step 3. Modify the edge position and softness to fit within the new background (if necessary)

5. Focus

All lenses have a focus area in which some things are sharp and some things are blurry. This means you need to match the focus to help your composited scene look realistic.

When it comes to matching focus, you should really try to consider two key things, Focus Amount and Bokeh Shape.

Focus Amount is simply matching the sharpness or softness of a given area in your shot based on the footage. Macro shots have a very shallow depth of field. Whereas establishing shots have a wide depth of field.

Bokeh Shape has to do with the way in which the out of focus ‘orbs’ look and feel. Some cameras will blur the background shapes into donuts, while others will be softer orbs. The shape of the bokeh is exactly related to the shape of the iris in the camera that captured the footage.

6. Lens FX

Imperfections in lenses contribute to the way in which footage is captured. Some footage may be incredibly crisp, but normally there will be small characteristics in the lens that give the scene character. Here are a few lens FX to look out for when compositing.

Chromatic Aberration

Chromatic Aberration is an optical effect that happens on contrasted edges in a scene. The most notable is ‘Purple Fringing’ in which a soft purple haze can be seen around the edges. Green and Red shifts are also very common. It is very typical for old lenses to have more Chromatic Aberration than newer lenses.

Notice the purple fringing in the image above.

Lens Distortions

Lenses distort the shape and characteristics of the background and subject based on a variety of factors, from focal length to lens quality. A lens grid is often used as a tool to understand the characteristic of a lens. Furthermore, lens breathing relates to the way in which the background and foreground changes based on the location of the lens.

Notice how the background bends in the image above.

Glows

One of the most popular ways to hide a bad composite is to simply put a glow around your scene. Glows help for your scene to sit together. In short, a glow is a way to cheat. The best way to match your glows is to simply look at your reference footage to match any glows.

Furthermore, Nick Chamberlain (the instructor of Compositing in Nuke) is a champion of The Glowden Rule, which simply states that when you think your glow amount looks correct, cut it in half… now your glow amount should be good.

Lens Flares

Lens Flares are another very popular part of the process of compositing. While it can certainly be taken too far (looking at you JJ), they are still a powerful compositing device that can be used to give your scene character. The most important thing to remember is that you should go beyond presets. Lens flares need to be based in reality to be believable. If you simply through a huge lens flare into a scene without the ambient lighting to suggest such an effect, it will look awkward and out of place.

Light Wrap

Light Wrapping is the spillover of light that happens on the edges of objects that are near a light source. As a compositor, you want to be able to match both the temperature and intensity of a light source as it relates to the other objects in your scene. Dialing a light wrap is essential.

See how the light source in the background bleeds onto the subject above.

Lens Grime

Lenses aren’t always squeaky clean. As a result, you should be mindful to match any lens grime or imperfections that may be present in your scene. Some compositors also like to add grime into a scene. Like Lens Flares, however, lens grime should be used as a storytelling tool and not simply a go-to effect.

Vignette

Our last lens effect is probably the most popular, vignettes. A vignette is simply the darkening of a lens as you approach the edges of a frame. Older lenses are notorious for having a lot of vignetting on the edges which is part of their appeal. As a compositor, it’s important to note the amount of vignetting that your lens has and make sure your elements match accordingly.

7. Perspective

Perspective is another incredibly important aspect of the compositing process. In short, assets in your scene need to fit with the optical perspective of the shot you are working with.

It would be nearly impossible to composite the two assets below due to persepctive.

If you have a shot that features assets shot from above, no amount of warping or adjustments will help your composite look more compelling. In fact, when you are compositing there are two major perspective characteristics you must line up:

Lens Compression – How the background warps in relation to the foreground.
Horizon Line – Where the skyline is in your asset or scene.

Notice how the background compresses and expands based on the focal length in the image below.

Both Lens Compression and Horizon Line are determined by the camera focal length, sensor size, and position.

8. Lighting

Our final compositing technique is simply matching the lighting in your scene.

Assets must always look like they come from the same lighting environment and source. Audiences can quickly pick up on mismatched lighting or shadows.

So when you are lighting try to match three key components.

1. Light Direction – The direction the light is coming from. In the image below you can see how the light source of the statue doesn’t match that of the footage.

2. Light Quality – The softness or harshness of the light source. In the example below the statue light source is too soft compared to the source footage.

3. Light Intensity – The brightness of the light source. The assets simply don’t fit the brightness levels of the source footage below.

Want to learn more about compositing?

Want to learn how to composite realistic VFX scenes in Nuke? Check out our exclusive course, Compositing in Nuke with Nick Chamberlain. The course will show you the essential techniques used by professional compositors on world-class FX projects. Here’s a trailer from the course:

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