For (a random) example, what is the process behind thinking ‘I want two people sword fighting on top of a moving train in the mountains’ and seeing that formed on the screen. How are those images generated, is it purely animation, does it involve prop actors with green screens, etc.
In: Technology
There is a youtube channel Corridor Crew where bunch of cgi artists do videos about everytthing CGI, check them out
It can be entirely in camera, entirely CG or (most commonly) some combination of both. Exactly how will vary based on many, many things – without a more specific question, it’s difficult to give a more detailed answer!
(I’ve been doing this professionally for about 14 years).
As u/CyclopsRock said: it depends. Actors may be put in front of a green screen with certain other elements covered in the same green, which will all be replaced with other imagery (potentially computer generated). The specific green is chosen because it’s generally not a color people naturally wear/have and can be edited out with video editing tools. Such as in your example, a green platform in the general shape of the train (or a train car itself) could be placed on a stage in front of a green screen with fans blowing gusts of air at the actors to simulate movement. Other props could be digitally added later. Say, for example, a sign fast approaches and the hero needs to duck underneath it. The actor could act out ducking in alarm, then a crossbar with a sign on it could be edited into the shot to simulate a real sign flying past him at speed. Of course, they could also be Jackie Chan and actually have the actor on a train duck under a rapidly approaching sign.
Actual graphics, ie a T-rex chasing characters across a field, is made up of polygons that are generated in a 3d modeling program like Blender. Those polygons can be manipulated and given additional complexity and attached to each other, then coordinated and animated so that they all move in a believable fashion. A picture can then be painted on the polygons via texture mapping where images that give the illusion of texture are wrapped over the polygons.
In movies it’s usually green-screen and a lot of FX blending. Except in fully CG movies, where everything is rendered using imported or modeled assets and FX.
Doesn’t happen too often these days but there’s also practical FX, where they play with scale models and high FPS or tilt-shift capture to make small things look enormous.
If you look through “the making of” videos for many movies or shows they’ll show you the green screen sets and blending passes that are done in post-processing to get the final shot.
If you want to know the absolute most basic concepts of modeling/rendering, grab a download of blender and follow some beginner videos for making a character, or making fire/smoke effects. You’ll gain an appreciation for exactly how meticulous the workflows are and how much dedication goes into the craft.
Ex 3D animator here:
1. Everything gets modeled. The process is somewhat similar to making a sculpture out of toothpicks and marshmallows (connecting points and lines to form triangle and square polygons), and modern tools make this process a lot more fluid by allowing the artist to manipulate many points at once, automatically generate symmetrical models from one half of a model, and even allowing them to sculpt high-detail models like they would clay. For your example of 2 people fighting, the model (AKA a **mesh**) would be modeled to look like the characters who were fighting.
2. Texturing. **Textures** are the 2D images that are pasted onto 3D models sort of like wallpaper, giving them their color as well as things like small bumps and such that are easier to do in textures rather than in geometry. First, the model is “unwrapped,” where the 3D geometry is flattened out onto a 2D plane, and then the textures are made either in a traditional 2D painting application, or by painting them onto the model directly.
3. Rigging. “Bones,” are added to the model that allow it to be posed and animated.
4. Animation. The bones are posed, and multiple **keyframes** are made that allow for “tweening,” where the animator basically says “I want the model to be in this pose on frame #10, and this other pose on frame #27,” and the software automatically blends between them. When animating living things, **motion capture** can also be used to match the model’s animation to the captured motion of a real life person or animal. Either of these techniques could be used to animate a fight scene, it just depends on what style they’re going for.
5. Rendering. Computers don’t actually “see,” the model, all they see is a big list of points similar to [<0, 3, 2>, <3, 4, 9>, <20, 1, 68>…], and so at some point the computer has to turn those points into an image. There are 2 main ways to do it: **Raster Rendering** which is fast and used for most video games, and **Raytracing/Pathtracing Rendering** which is used for almost all movies, looks absolutely amazing, but takes a long time and involves the computer simulating millions of light rays bouncing around the scene similar to how light behaves in real life. Each frame would be rendered out individually (takes literal weeks or months to render an entire scene depending on size of the production), and then combined into a video.
6. Compositing. Think of it as sort of “video photoshop.” You’re taking the rendered out 3D elements, and combining them together with other 3D elements, 2D photo elements, as well as 2D video footage to make the final product.
Usually on a professional film, most of these steps are going to be done by separate people, and in the end it all comes together to form your finished scene. Here’s a great timelapse video showing all steps of the process where they make a dinosaur: [https://youtu.be/YsLt6lSl5ZM?si=_YAKMf0WtR8c-9ZU](https://youtu.be/YsLt6lSl5ZM?si=_YAKMf0WtR8c-9ZU)
The simple version is you make a 3D scene or character, like something out of a video game, and superimpose it over actual footage.
In order for it to not look like you just pasted an image over actual footage, you need to get the lighting just right. They’ll generally recreate the scene in 3D, including the positions of the lights, and then do their best to match the lighting intensity/color/quality so that the 3D elements don’t pop out against the background. To get them looking realistic they’ll simulate actual light and the ways it interacts with different materials in an expensive process that can take months of computing.
Once you get the 3D portion looking like it fits with the rest of the scene, you start to edit out the stuff you’re pasting it over. This is why green screens are so useful, they’re a clear indicator of what you’re absolutely removing from the scene and replacing with CGI.
There’s always little details that need to be edited too, like removing wires or putting things on different layers to make sure that a CGI character in the background doesn’t overlap something real in the foreground. In big budget productions this might mean a small army of VFX people literally going frame by frame and editing things out using Photoshop.
After all that you’ve got a realistic 3D render superimposed over the actual footage that has been combed through by a bunch of artists to remove anything that doesn’t look right.
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