# A-level Graphic Products/Edexcel/Unit 3 :Designing for the Future/Industrial and commercial practice/Digital special effects
## Compositing using blue screen and green screen / Chroma key

This is a way for actors to be imposed onto a separate piece of film. This can be used if the real event would have been too dangerous, or would need a large budget.
This effect is created by having two separated pieces of film. One where there is an actor in the foreground standing in front of a green/blue back ground, the other piece of film will be filmed or computer generated. Software then removes the green/blue background from the foreground image, reveling the background behind.
It consists of four layers:
* Background
* Foreground
* White silhouette
* Black silhouette
The white and black silhouettes act as a layer mask for the foreground, one colour will represent the area of the foreground to keep, the other colour will represent the area of the foreground to delete.
One problem with green screen is that you can't have green on the actor, similarly, actors can't wear blue in front of blue screen. This is why there are two main colours of back drop, but it does mean people can't wear blue and green without getting another backdrop colour.

## Computer-generated graphics (CGI)

Computer-generated graphics are now common in most films; they are used to create effect that would have otherwise been impossible. CGI can be combined with film footage (most likely through the use of a Chroma key) to create extreme special effects which makes for an excellent piece of final footage.
Computer-generated graphic animation are created through the following steps:
* A wire-frame of model is created; this is a series of lines that connect up the points/corners of a model.
* Faces are then added that lie in-between the connected points of the wire-frame.
* Colour and textures are then added to the faces of the model.
* A skeleton can then be added inside the model, this will warp the points of the geometry making for easier animation.
* Lighting is then added to the scene which affects the look of the geometry/model.
* A camera is then added to the scene as a way to view the scene from.
* Key-framing is then used; this where you place things in the scene and you save the state and time, you then move the object and the time and save again, the computer will then add a smooth transition from the first state to the last state over the given time.
| Advantages | Disadvantages |
| The director of the footage can choose the angle in which it is shot from, where as in reality, there would be certain angles that would be difficult. | Costs a lot of money to buy good enough hardware for the computer that will be good enough to render and process the data. |
| Many possibilities come from the fact that objects can be rotated. | Requires highly skilled staff that know how to use the software and create a good animation. |
| Can eliminate the need for green-screen in certain cases which would save a lot of time. | The software and hardware will become out of date quickly, which requires you the company to spend more money. |
| Features of a person can be changed digitally: costumes, make-up, body size and age. | |
| People can blend into the background | |
| Lighting can be added to the scene | |

### Motion Capture

Motion capture is when people where camera can track their location as they move; this is achieved by them standing in a room full of sensors that pick up tracking nodes in their suit. This is useful for obtaining a digital accurate representation of reality in an animation. Sportsmen and women have found this useful for tracking their movements in their sport and observing their technique to look for problem in their technique.

### Rotoscoping

Rotoscoping is where film is recorded, and then it is then traced over, frame by frame to create a pictorial representation of the footage. Previously, this would have been done by hand, but more recently computer graphics have replace the tedious task. Rotoscoping can be used to give the newly created footage a distinct look to it.

## References

* ↑ https://en.wikipedia.org/wiki/Motion_capture#Methods_and_systems
* ↑ https://en.wikipedia.org/wiki/Rotoscoping