Computer Graphics Alpha Composting

1. ALPHA COMPOSTING
Farhanullah and Mujahid ur Rehman

2. Contents
 Introduction
 What is Alpha Composting
 What is Digital Composting
 History
 Architecture
 Advantages
 Applications
 Conclusion

3. What Is Alpha Composting.
The process of using the transparency value,
alpha, to combine two images together.

4. •Alpha composting is the process of combining an image with another
image as its background.
•It is mostly used in 2D graphics. Composting is also used to combine
images and live footage.
• This is a very useful process as it is widely used in many fields. It is
a simple process.
INTRODUCTION

5. •Additional information is stored regarding each pixel in the alpha
channel with a value between zero and one.
•The technique is used in many applications. It also has support in
many graphical user interfaces (GUI) and widgets.
INTRODUCTION CONT…

6. •The concept of an alpha channel was introduced by Alvy Ray Smith in the late
1970s, and fully developed in a 1984 paper by Thomas Porter and Tom Duff.
•In a 2D image element, which stores a color for each pixel, additional data is stored
in the alpha channel with a value between 0 and 1.
• A value of 0 means that the pixel does not have any coverage information and is
transparent.
• There was no color contribution from any geometry because the geometry did not
overlap this pixel.
• A value of 1 means that the pixel is opaque because the geometry completely
overlapped the pixel.
History

8. Transparency
• Alpha is a pixel’s transparency
– from 0.0 (transparent) to 1.0 (opaque)
– 32-bit RGBA pixels: each pixel has red, green,
blue, and alpha values
• Uses for alpha
– Antialiasing
In many graphics toolkits, the pixel model includes
a fourth channel in addition to red, green, and blue:
the pixel’s alpha value, which represents its degree
of transparency

9. Antialiasing

10. Alpha channel
• Image(R,G,B,alpha)
Encodes transparency (or pixel coverage):
• Alpha = 1: opaque object
• Alpha = 0: transparent object
• 0<Alpha<1: semi-transparent

11. • Compositing rules control how source and
destination pixels are combined
• Source
– Image
–• Destination
– Drawing surface
When pixels include alpha values, drawing gets
more interesting. When you draw on a drawing
This process is called alpha compositing.
Alpha Compositing

12. • 2D Video Pass Through Compositing
• Image quailty
• Easy to use and easy to understand
• Texture and Render Processing
• Fast 3D Texture Transfer
Advantages

13. • To create special effects in visual arts
• To help us connecting real images with artificially created ones
• To correct photographic mismatches (e.g. color)
Application

14. Film Composting
King Kong (1933)
Superman(1978)

15. Digital Composting
is the process of digitally assembling multiple images to make a final image, typically for
print, motion picture or screen display
Digital Compositing Tools
Some of the software tools we'll be discussing include:
Paint Programs
Color Correction
Matte-Extraction software
General-purpose compositing packages

16. Conclusion:
Compositing is the combining of visual elements from
separate sources into single images, often to create the illusion that
all those elements are parts of the same scene.