Chance's "Visual Effects" Lecture

VISUAL EFFECTS PRIMER

COMPUTER GENERATED IMAGES - CGI

Visual Efx Primer-Film

Vis.Efx. Are obvious in certain genres, like Sci-Fi films

Reality is most films in any genre use some form of Vis. Efx.

What is the process?

Understanding Digital Efx

Typical Efx team includes:

Artists

Technicians

Producers

Managers

“ Digital” should tell you it primarily involves computers and software

Vs. Older forms

Miniatures, models, etc.

Thus “CG” or “CGI”

What do you need?

3D Software--Maya, 3Ds Max, XSI

Blue/Green Screen

Matte Painter--Photoshop

Compositor--Shake, After Effects

Advantages of CGI?

Realism

Flexibility

Relatively Low

Cost (compared

to alternatives)

Safe

The CGI Team is involved in entire

Preproduction,

Production, and

Post-production

process…

2 Basic Terms:

2D Animation

Done only on

two axes, the length

and breadth axes

3D Animation:

Adds depth perspective

Object moving away

from or to you

Generally, 3D more

costly, time consuming,

Complex, longer renders, larger file sizes

Overview of the Process

Typical Movie has around

1,000-1,500 shots, ranging from 2 seconds to 60 seconds in length.

A given scene might be filmed w/ a # of cameras -- wide vistas, close-ups, changes of perspective, etc.

In the final movie, these different viewpoints are mixed together to create the scene. Therefore a single scene might contain dozens of individual shots.

The first step of the visual effects process is deciding which of the shots need to have visual effects applied to them.

The rolls of film for these shots are sent to be scanned and used by post houses

HI-RES.

SCANNING

AND

PRINTING

Up to

12,750,000

Dots per frame

(4,096 X 3,112 dots

per frame)

Once Digitized…

Creation / Integration of 3-D models and characters.

3D Modeling

Create a wireframe model by adjusting a series of nodes (or Nurbs)

This step is frequently eliminated by using motion capture systems .

Ex: Polar Express

Sculpting/Modeling

3D Modeling

Add a rough skin to the model--simple color layers

This is a rough version of the final model

Skinning

3D Modeling

Add a final, realistic texture to the model.

This texture often comes from actual photos of textures.

Ex: wood, metals, etc

Texturing

3-D modeling: A collection of shapes (polygons) that form the outside of the object.

Soldiers in "The Patriot" are formed from of spheres, cylinders and other shapes.

3-D setup - Process of adding a "skeleton" of bones and joints to a 3-D model

--Often called “ rigging ”

SO THAT the different shapes in the model move correctly with respect to one another.

Bring it to life

3-D setup cont’d

In some cases the bones and joints are created by hand.

In other cases they come from motion capture (MOCAP) or performance capture .

To gather Motion Capture data,

--Actor fitted with suit that has reflective markers or lights at every joint.

--Actor moves on special stage

--3-D cameras watch the actor from a number of different angles.

--Computer software tracks all of the markers

--With help of technicians, binds them together into a stick figure that accurately duplicates the motion of the actor.

Stick figure is the bones and joints that then control and animate a 3-D model.

A variety of different poses and activities are captured to provide variety

3-D Tracking (Motion Tracking) - after scanned in, markers added to the scene to create (in computer)

--a 3-D model made of the scene AND then

--a 3-D camera.

http://www.adobe.com/tips/aft65cornerpin/main.html

http://www.apple.com/shake/quicktours/tracking.html

GOAL -- 3-D camera to exactly mimic motion of the real camera SO THAT the 3-D elements added look and move as the REAL camera moves in the actual scene.

The Alpha

The alpha channel is possibly the most important invention for modern visual effects

EX: Older Disney cartoons

Originally people worked w/ just RGB channels…now RGB + A

Created by former Pixar animator

Like transparency sheets for projectors

Background does not exist…usually represented w/ checkerboard

Alpha continued

Important Feature**--alpha channel allows for multiple layers on the same frame

Same concepts used in programs like Photoshop

ROTOSCOPING

Process of outlining and "lifting" elements of a filmed scene off the frame

SO THAT other elements can be added to the frame either in front of or behind the rotoscoped elements.

ROTOSCOPING: To create this town in THE PATRIOT…

CGI Artists combined these 2 elements

Bottom element is the rotoscoped item

ROTOSCOPING: The final image - elements combined, or COMPOSITED

Compositing is another technique used in the creation of visual effects

Compositing

Basically a layering of video and background elements onto a single output.

+ + +

Mattes

PAINTING or

MATTE PAINTING

The creation of imaginary scenery.

Once called "airbrushing" -- the process of adding or removing things from a scene.

Matte Painting-Use of Glass Panel: 3D and 2D combined with perspective

Required painting with emphasis on realism

Techniques vary: rear projection, front projection, Latent image projection

Images from Hitchcock’s The Paradine Case

Latent Image Matte Painting

Photographic tech. of combining 2 scenes

Runs film through twice, once with a portion blacked out and unexposed

Can use it now with stills and paintings

Latent Image, cont.

Pros

Original stock quality (highest)

Matching of hues easy

Cons

Hard to estimate needed footage with live action

Mistakes are expensive

Latent image projection used with Matte Painting in Return of the Jedi

Rear Projection

Movie projector placed behind glass with painting

Window covered with frosted plastic

Camera films from front

Rear Projection, cont.

Pros

Easiest

Cons

Loss of image quality

Least sharp image of all techniques

EX: Star Wars dog fight scenes

Digital Mattes

Mattes can also be CG.

The cowboys were created separately from the environment. Thus, the BG is a 3D matte.

Digital Painting

Examples

Advantages ( LOTRings)

Ability to move camera

No more limitations of pan

As in Empire Strikes Back

Reflections and moving animations can be combined easily

Digital editing is cost efficient and easier

Truman Show : Digital Matte goes 3D A “camera” is tracked w/ image in the exact motion and perspective of the actual camera.

2D Compositing: Putting all the layers Together

Example 1 - The Patriot

Original Shot -- Making it Digital. First the shot’s scanned frame by frame (24 frames per second-20 sec. shot), then each frame is stored as an individual full-color image with a resolution of 2,048 by 1,556 pixels.

Rotoscoping : Artist at a computer outlines frame by frame the portion of original shot that’ll be used in the final version -- in this case, a portion of the field and several of the running soldiers.

ADD WATER -- 2nd camera crew creates an ocean shot --

In this case -- the ocean near Hollywood.

Once ocean shot is cleaned up & color-corrected, it and the rotoscoped scene can be integrated.

Creating The Town -- Another artist creates a Matte Painting of the town.

This is high-res. digital image was created using a computer painting/illustration package.

ADDING THE TOWN -- Once the town is added in, the scene looks like this.

Adding boats encircling the town and firing on it. The boats are all CGI-computer generated .

Each is modeled, then added to the shot. Above is the boat “Mask” - you mask out areas where you want boats to be.

Cannon fire for the boats is its own stand-alone effect, created separately, then added.

Practical EFX added - smoke over the town, people in the town, a large explosion on the right, etc.

FINAL STEP, Compositing the different components (rotoscoped foreground, water, town, people in the town, boats, cannon fire, smoke, explosion, birds flying overhead,etc.) LAYER BY LAYER to create the final shot as it appears in the movie. Once digitally composited, the shot is “written back” to film so that it can be spliced into the movie

Even though the shot only appears on screen for 20 seconds , hundreds of hours went into the visual effects to create a rich, convincing visual image.