2. Introduction
What is Alpha Composting
History
Architecture
Advantages
Disadvantages
Applications
Conclusion
Bibliography
Contents
3. What Is Alpha Composting Technology?
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.
•This creates the appearance of full or partial transparency of the
resulting image.
•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 and vital process.
•To combine these images in an effective manner, it is essential to keep
the matte of each element.
INTRODUCTION
5. • The information is regarding the shape of each element. Alpha
channel is the concept designed to store information.
•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
7. Date Notes
2011-10-12 Added to iOS Developer
Library and updated for iOS
5.0.
2011-06-06
Added additional constants for
OS X v10.7.
New document that describes
the programming interface for
high-performance alpha
compositing operations.
2007-07-12 The content in this document
was formerly part of Optimizing
Image Processing With vImage.
History table
9. 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
– Nonrectangular images
– Translucent components
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
10. • Compositing rules control how source and
destination pixels are combined
• Source
– Image
– Stroke drawing calls
• Destination
– Drawing surface
When pixels include alpha values, drawing gets
more interesting. When you draw on a drawing
surface – whether it’s using stroke calls such as
drawRect(), or pixel copying like drawImage(),
there are several ways that the alpha values of your
drawing calls can interact with the alpha of the
destination surface. This process is called alpha
compositing.
Alpha Compositing
14. • Uncompressed 8-, 10-, or 12-Bit SDI Output
• Ancillary Data Support
• 2D Video Pass Through Compositing
• Genlock (House Synchronization)
• 512MB to 1.5GB Ultra-Fast Graphics Frame Buffer Memory
• 8K Texture and Render Processing
• Fast 3D Texture Transfer
Advantages
15. • If a feature is sensitive to that dilution or interference,
it disappears. If that feature would have been relevant to
the user’s task, alpha blending becomes unsuitable.
Hence it introduces visual ambiguity.
•The relationships between features become obscured: it
can be difficult to determine whether two observed
features belong to the same window.
Disadvantages
16. •Alpha value of a pixel governs transparency.
•Instead of overwriting a destination pixel we mix its
color with the source pixel.
Alpha Composting : Blitting + Alpha Blending
17. • To create special effects in visual arts
• To help us connecting real images with artificially created ones
• To correct photographic mismatches (e.g. color)
• To change or substitute backgrounds And foregrounds
• To create illusion of depth.
Application
19. 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.
We have introduced a novel set of composting models and
matting methods which expand the working range of matting and
composting in two directions: eliminating the need for special
setups for acquiring foreground plates in traditional matting, and
moving beyond the limitations of the traditional compositing model.
We also present a novel application of matting and
compositing to animate still pictures.
