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What Is Compositing?
Compositing is the step where separate image layers are combined into one final image. In VFX and animation those layers are rendered 3D passes, filmed footage, mattes, particles and graphics. The compositor matches colour, light, grain, blur and depth so that all of it looks like it was captured by one camera, then grades the result. It is the last place a shot can still be changed cheaply, because adjusting a layer in comp takes minutes while a re-render can take hours. Below: how compositing works, what layers go into a comp, what you can fix in comp and what needs a re-render, which software is used, and who composited which of my own projects.
Written by Marco Mori, 3D artist, Lindau, Germany · Updated 2026-11-02
What is compositing?
Compositing is the process of combining several images into one final image. Wikipedia describes digital compositing as digitally assembling multiple images to make a final image, and as the digital version of optical film compositing. It is one of the core jobs inside VFX, and the one every VFX shot ends with.
The word covers more than green screens. A compositor can put a rendered product on a filmed table, add a glow to a CG object, remove a cable, build a sky from three photographs or merge twenty render layers into one animated frame. What stays the same is the aim: the viewer should not be able to tell where one layer ends and the next begins.
How does compositing work?
Each layer carries colour and an alpha channel. Alpha is a value from 0 to 1 per pixel, where 0 is fully transparent and 1 is fully solid. Stacking layers means blending them according to that value, from the back layer to the front.
That is the mechanism. The craft is in making layers that were created separately behave like one capture:
- Set the order. Background, midground, subject, effects, overlays.
- Cut or key. Separate the subject with a matte, drawn by rotoscoping or pulled from a green screen.
- Match the colour. Black level, white level, saturation and colour cast of the added layer follow the plate.
- Match the camera. Grain, sharpness, lens blur, depth of field, motion blur, chromatic fringing.
- Add contact. Shadows, bounce light and reflections where the added object touches the real world.
- Grade. Set the final look across the whole image.
Steps three to five are where most amateur composites fail. A perfect cutout with the wrong black level still looks pasted.
What layers go into a composite?
A 3D render does not have to leave the renderer as one flat picture. It can leave as a stack of passes, each holding one part of the image, so the compositor can change them separately.
| Layer or pass | What it holds | What the compositor does with it |
|---|---|---|
| Beauty | The finished render | Base of the composite |
| Diffuse and reflection | Colour and mirror-like light, separately | Balance how matte or glossy the object feels |
| Shadow and ambient occlusion | Where light is blocked | Strengthen or soften contact with the ground |
| Depth (Z) | Distance from the camera per pixel | Add depth of field or fog in comp |
| Alpha or object masks | Transparency and per-object cutouts | Isolate parts for separate colour work |
| Plate | The filmed footage | Reference for colour, grain and light |
| Effects and elements | Smoke, sparks, dust, glow | Layer on top, tuned to the shot |
I render in passes by default for this reason, and it is also how I hand over work to other teams. The Houdini FX service covers delivering multi-pass EXRs for a client's own compositor.
Should you fix it in comp or re-render?
This is the practical question behind most review rounds, and it is the part generic explainers skip. The rule: anything that is a property of the image can be fixed in comp, and anything that is a property of the scene needs a re-render.
| Change request | Fix in comp? | Why |
|---|---|---|
| Warmer or cooler overall colour | Yes | Pure colour adjustment |
| Product slightly too glossy or too matte | Usually | Reflection pass can be balanced |
| Stronger or softer shadow | Usually | Shadow pass exists, within limits |
| More or less depth of field | Often | Depth pass drives a fake blur, with edge limits |
| Glow, flare, grain, vignette | Yes | Added as layers |
| Move the product in frame by a little | Often | If the layer has a clean alpha |
| Different camera angle | No | The whole perspective changes |
| Change the product shape or logo | No | Model change, new render |
| Change the lighting direction | No | Every highlight and shadow moves |
| Change the animation timing | No | New animation, new render |
The edge cases are why a clear brief matters. "Make the light warmer" is a minute in comp. "Make the light come from the left" reopens the scene. Saying which one you mean on the review round saves a day, and it is the reason my CGI cost guide asks for approvals in stages.
What is the difference between compositing and editing?
Editing arranges complete shots in time. Compositing builds the picture inside each shot. A commercial of 20 shots is composited 20 times, then edited into one film. Some editing software can do simple compositing, but the layer control in a dedicated compositing tool is deeper.
A related point: mixed reality video production is compositing-heavy by definition, because a rendered element has to sit inside filmed footage. Camera tracking supplies the movement, and compositing supplies the integration.
Who composited my own projects?
Compositing is often split between people, and agencies sometimes finish a shot after the 3D artist hands it over. These are the facts for my own listed work, taken from the project pages.
| Project | My part | Compositing |
|---|---|---|
| Samsung Galaxy Z Flip 7 (2025) | 3D animation in real footage: camera tracking, lighting and clean compositing | Part of the job, a tracked CG element had to sit in a filmed outdoor scene |
| Trainline Tap That App (2025, via Wieden+Kennedy Amsterdam) | All of the CG side: hands, look development, animation, lighting, rendering | Included in my CG scope, with sound and final edit by the agency's partners |
| PUMA Be the Spark (2020) | Modelling, layout, dynamics and timing of the shot | Not mine: final compositing was handled by Nuderobot |
| Hyperreal portrait studies (2021 to 2025) | Personal series, full build | Glitch, particle erosion and layered effects are composited, as part of the series |
The PUMA row is the useful one. When another studio composites, the 3D side has to deliver clean passes and a clear handover, which is exactly the setup compositing teams ask for.
What software is used for compositing?
Nuke is the standard in film VFX and high-end commercials. It is node-based, so every operation is a visible, editable step in a graph. After Effects is layer-based and is the usual choice in motion graphics. Blackmagic Fusion is another node-based tool and ships inside DaVinci Resolve.
I composite in Nuke, build the 3D in Houdini and render in Redshift. The choice of tool matters less than the habit of keeping each fix a separate, removable step, so a client note three days later does not mean starting over. The same logic applies to the 3D side, compared in Houdini vs Blender for commercial VFX.
How do you get a shot composited?
Decide what you are sending. If you have footage and need a 3D element inside it, mixed reality production covers tracking, rendering and compositing in one job. If your own team composites, ask for multi-pass EXRs, the camera, and a reference render, and say so before the scene is built, because it changes how the 3D is set up.
Send the original clips, not a social media export, plus the delivery format and any reference you like. Write to me with a few lines and you will get a straight answer, including when a simple fix in your editor is all you need.
Written by Marco Mori, 3D artist and creative director in Lindau at Lake Constance, Germany, working with brands and agencies worldwide.
Frequently asked questions
What is compositing in simple terms?
Compositing means stacking several images into one. Each layer has its own transparency, and the compositor blends them, matches their colour and light, and grades the result so the viewer sees a single picture.
What is compositing in animation?
In animation, compositing assembles the rendered layers of a scene, such as characters, background, effects and shadows, into the final frame. Rendering in separate layers lets the compositor adjust each one without rendering the whole scene again.
What is the difference between compositing and editing?
Editing arranges whole shots in time, deciding which shot comes next and how long it runs. Compositing works inside a single shot, stacking layers within each frame. A film is composited shot by shot and then edited together.
What is the difference between compositing and VFX?
VFX is the purpose, changing or adding to a shot. Compositing is one of the VFX jobs, and the one that every VFX shot ends with, because all the separate pieces have to be merged into the final image.
What software is used for compositing?
Nuke is the node-based standard in film and high-end commercials. After Effects is common for motion graphics and layer-based work. Blackmagic Fusion, part of DaVinci Resolve, is another node-based option. I composite in Nuke.
Is compositing the same as colour grading?
No, but they touch. Compositing makes the layers belong to one image. Grading sets the overall colour and mood of the finished image. In practice both happen at the end of a shot, often by the same person.
Can a compositor fix a bad render?
Often yes for colour, contrast, shadows, glow, blur and small errors. Not for a wrong model, wrong camera move or broken animation. Those need the 3D scene reopened and rendered again.
Why does compositing matter for product ads?
Because the product has to look real next to real things. Matching grain, blur, shadows and colour between a render and a photographed plate is what separates a believable shot from a visible cutout.