2011
Table Of Contents
- Autodesk Composite 2011 User Guide
- Contents
- Preface
- Getting Started
- Reference
- About Reference
- Projects
- Wiretap
- Importing Media
- Getting Familiar with Your Workspace
- The Player
- About the Player
- Player View Default Settings
- Setting the Target
- Setting Context Points
- Playing Back in Multiple Views
- Playback Performance
- Setting the Target for the Player
- Setting the Channels for the Target
- Setting the Mark In and Mark Out Points for Playback
- Setting the Repeat Mode
- Setting the Frame Rate for Playback
- Setting the Real-Time Playback Preference
- Synchronizing or Separating Playback between Views
- Setting the Playback Point when the Player Updates
- Setting the Resolution for a Player
- Setting the Grid in the Player
- Setting a Region of Interest (ROI) in the Player
- Displaying Masks and Guides
- Showing or Hiding Tiles
- Turning Hardware Rendering On or Off
- Setting the Pixel Aspect Ratio of the Player
- Displaying Player Option Information in the Player view
- Displaying Manipulators in the Player
- In-player Pixel Display
- Adjusting the Zoom or Pan
- Applying a LUT or Color Conversion Tool to the Player
- The Mini-Player
- The Fullscreen Player
- Working with Compositions
- Multilayer Compositing and 3D Effects
- Reaction Compositing and Effects
- Compositing Workflow
- Basic Compositing in Reaction
- Working with Maya Pre-Comps
- Working with Layers
- Working with Geometric Surfaces
- Using Parenting Axes
- Working with Materials
- Working with Lights
- Working with Cameras
- Camera Mapping
- 3D Displacement
- Transforming Objects
- Reaction Rendering Effects and Output Results
- Setting up a Stereo Camera Rig
- Pre-Compositing
- Importing FBX Files
- Premultiplication
- 2D Compositing
- Image Processing Tools
- Pixel Expressions
- Warping
- Effects Tools
- Managing Film Grain
- Pulling Keys and Creating Mattes
- Masking
- Raster Paint
- Vector Paint
- Color Correction
- About Color Correcting
- Applying LUTs
- Working with ASC CDLs
- Broadcast Safe Tool
- Transforming Color Space with the Log and Delog Tools
- Color Correcting with CC Basics
- CC Histogram
- Clamp Color Tool
- Color Space Tool
- Processing Images with Photo Lab
- Inverting an Image
- Remap Color
- Set Fill Color
- Solarizing an Image
- Creating a Monochrome Image
- Modifying a Display With the Pass Through Tool
- Setting the Amount of Gray in an Image
- Converting an Image to sRGB
- Animation
- Animation Concepts
- The Animation Tab
- Composition Browser
- Animation Editor
- The Animation Property Area
- Player Controls
- Working with Cue Marks
- Contextual Menus
- Keyframing Workflows
- Marking Attributes for Keyframing
- Setting Keys Manually
- Setting Keyframes Automatically
- Editing Keyframes in the Tool UI
- Editing Keyframes in the Animation Editor
- Adding and Deleting Keyframes
- Modifying Interpolation
- Modifying Extrapolation
- Temporarily Modifying Attribute Values
- Customizing the Layout when Working with Animation Curves
- Global Time vs. Local Time
- Time Offsets, Keyframing, and Instancing
- Time Tools
- Customization Tools
- Vectors
- Expressions
- About Expressions
- Short Expressions
- Expression Input Paths
- Visual Linking
- Visual Linking Methods
- Navigating the Expression String
- Validating and Applying the Expression String
- Viewing the Expression
- Associating Comments with an Expression
- Editing an Expression
- Removing an Expression
- Setting Expressions Examples
- Expression Reference Tables
- Arithmetic Operators
- Comparison Operators
- Operator Precedence
- Math Functions
- Vector Functions
- Random Number Functions
- Rounding Functions
- Trigonometric Functions
- Constants
- Time Functions
- Profile Functions
- Conditional Functions
- Tracking and Stabilizing
- About Tracking and Stabilizing
- Tracking Concepts
- Stabilizing Concepts
- Tracker UI
- Tracking Workflow
- Choosing a Reference Point
- Positioning the Reference Box
- Resizing the Reference and Tracker Boxes
- Resetting the Reference Box
- Resetting the Tracker Box
- Changing the Color of a Tracker
- How the Tracker Works
- Tracking Position
- Tracking the Scale of an Object
- Tracking the Rotation of an Object
- 4-Point Tracking
- Tracking Difficult Shots
- Correcting Errors
- Stabilizing
- 1-point Stabilizing
- 2-point Stabilizing
- Simultaneous Stabilizing and Tracking
- Video Tools
- Utilities
- Hotkeys
- Composite Executables
- Python Scripting
- Initialization Variables and String Substitutions
- Glossary
- Index
Premultiplication
Topics in this chapter:
■
Premultiplied Images on page 337
■
When to Premultiply on page 337
■
Common Problems with Premultiplication on page 338
■
Premultiplication Tools on page 338
Premultiplied Images
A premultiplied image is one where the RGB channels have been multiplied by
the alpha channel. In other words, it is a four-channel image in which the red,
green and blue channels have already been multiplied by the integrated matte
channel.
Typically, images from a 3D renderer are premultiplied, which means that the
transparent areas are black in both the RGB channels and the alpha channel.
As such, in premultiplied images, the RGB channels never have a higher value
than the alpha channel.
When to Premultiply
You should consider premultiplying an image if you have to modify a foreground
element and composite over a background image. Furthermore, you should also
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