What Is 3D Rendering?

What is 3D rendering?

3D rendering is the step that creates the picture. A 3D scene is a description: shapes in space, materials on those shapes, lights and a camera. A renderer reads that description and works out the colour of every pixel. Wikipedia defines rendering as the process of producing an image from the description of a 3D scene, and the result is what people call a 3D render.

Everything you see in a CGI ad, a product image on a web shop or a rendered film frame went through this step. It is the last stage of the 3D work and the moment where weak decisions upstream become visible, which is why CGI projects spend more time on look development and lighting than on the render itself.

How does 3D rendering work?

A renderer answers one question for each pixel: what light arrives here? To answer it, it follows light through the scene.

1. Rays leave the camera. For every pixel, a ray goes out into the scene.
2. The ray hits a surface. The material decides what happens: it can absorb, scatter, reflect or let light through.
3. Light is gathered. The renderer checks which lights, and which bright surfaces, reach that point.
4. The bounce repeats. Light that reflects from one surface onto another adds colour and softness. This indirect light is a big part of why a render looks real.
5. Many samples are averaged. The first result is noisy, so more samples are added until the noise is low enough to be clean, often finished by a denoiser.

Tracing light this way is called ray tracing. A version of it, path tracing, is according to Wikipedia currently the most common technique for photorealistic rendering. The renderer I use for commercial work is Redshift, an offline renderer.

What is the difference between 3D modelling and 3D rendering?

Modelling builds the geometry. Rendering photographs it. Between those two sit the steps that actually create realism.

Stage	What happens	Who spends the time
Modelling	Shapes are built or cleaned up from CAD	The artist
Look development	Materials, textures and surface detail are set	The artist
Lighting and camera	Lights, reflections and lens are arranged	The artist
Animation	Movement is defined, if there is any	The artist
Rendering	Pixels are calculated	The computer
Compositing	Layers are combined and graded	The artist, see what is compositing

The practical consequence is that the render button is the cheapest minute of the job. Changes are cheap before it and expensive after it, which is why the stages are reviewed in order in my 3D product visualization process.

What is the difference between real-time and offline rendering?

Both turn a scene into an image. They answer different problems.

	Offline rendering	Real-time rendering
Time per frame	Seconds to hours, as long as the quality needs	Fractions of a second
Light accuracy	High, close to physical behaviour	Approximated, with tricks
Typical use	Commercials, film VFX, product images	Games, configurators, live previews
Interactivity	None, the output is a file	Yes, the viewer can move
Example tools	Redshift, Arnold, V-Ray, Cycles	Unreal Engine, Unity

Wikipedia puts the same split plainly: interactive applications such as games must primarily use real-time rendering, while offline rendering can use a slower, higher-quality renderer. For a fixed commercial or a product image, I use offline rendering. If your product needs a viewer that rotates it live in a browser, that is a different build and I would say so before quoting.

What files do you get from a 3D render?

This is the question most explainers leave out, and it decides how useful the work is to you. A render is not always one picture.

Deliverable	What it is	Who needs it
Final image or video	A graded, finished file in the agreed format	Most clients
Image with transparency	The subject with an alpha channel, no background	Web shops, layouts, ad variants
Multi-pass EXR	Separate layers for diffuse, reflection, shadow, depth	Teams with their own compositor
Resolution and format set	Print size, web size, vertical and square crops	Campaigns across several channels
Turntable or reference render	A quick angle check of the final asset	Approval and internal review

Tell me which of these you need at the start. Passes change how the scene is built, and a transparent product image changes how the shadow is handled. For the handover of layers, see Houdini FX and the compositing side in what is compositing.

What makes a 3D render take longer?

Render time is not random. Six things move it:

1. Resolution. Double the width and height and there are four times the pixels.
2. Duration. An animation is rendered frame by frame, so seconds of film multiply every other cost. My guide to CGI commercial costs says it as: duration is render time, shot count is human time.
3. Materials. Glass, liquids, skin and metal that reflects other things cost more than a matte plastic.
4. Lighting. Many soft lights and light bouncing through interiors need more samples to look clean.
5. Hair, fur, particles, fluids. Each adds geometry or volumetric calculation.
6. Quality target. A preview that is good enough for a review round is cheaper than a final frame with no visible noise.

That last point is how a project stays affordable. Early review rounds run on fast previews, and only approved frames go to a final render. There are no invented hours here because they depend on the scene.

What have I rendered for client work?

The facts below come from my project pages, not from a template.

Project	What was rendered	Why the render mattered
Trainline Tap That App (2025)	Hyperreal CG hands for a music video, social cutdowns and out-of-home key visuals	Look development for skin, nails and the app button had to hold up in close-up
Hyperreal portrait studies (2021 to 2025)	A personal series of photoreal heads, built in Houdini, ZBrush and Redshift	A test bed for skin, hair and fabric looks before they go into client work
adidas ZK 2K Boost (2020)	Three animated product videos for the sneaker's cushioning	Playful, physics-driven animation, one of the videos passed 3 million views on adidas' Instagram

The portrait series is where new render settings and materials get tested without a client deadline, as the about page explains.

Which software is used for 3D rendering?

Offline: Redshift, Arnold, V-Ray, Cycles, Octane. Real-time: Unreal Engine and Unity. Most 3D tools ship with one or more of these or connect to them. I model and simulate in Houdini, render in Redshift and composite in Nuke. The renderer matters less than the person setting it up: the same scene can look flat or expensive depending on the light and the materials. The wider process around the render is in what is computer animation.

How do you commission a 3D render?

Start with what the image is for. A hero visual for a landing page, a set of product shots for a shop and a 20 second ad are three different jobs. Send the product files or references, the target formats, where it will run and the deadline.

For single products and image sets, 3D product visualization shows what is included and what drives the cost. For films and campaigns, see CGI commercials. Or write to me with a few lines, and you will get a straight answer on scope.

Written by Marco Mori, 3D artist and creative director in Lindau at Lake Constance, Germany, working with brands and agencies worldwide.