This PPT contains overview of Alpha Compositing Computer Technology

1. Guided By: Presented By:
Prof. V. P. Sawalkar Rushikesh A. Welkar
*
Late Purushottam Hari (Ganesh) Patil Shikshan Sanstha’s
Mauli Group of Institutions’,
College of Engineering & Technology, Shegaon. 444002
Department of Computer Science & Engineering.

2. Contents
Introduction
Literature Review
Propose System
 What is alpha?
 What is alpha compositing?
 What is alpha Channel?
 Transparency
Technical Aspect
Advantages & Disadvantages
Conclusion
References

3.  Alpha compositing is the process of combining an
image with a background to create the appearance of
partial transparency.
In this techniques performs pixel by pixel blending of
source and background color of images.
It's a way of mixing the colors of two images together
to form a resultant image.
Pixels are the small elements of the images. In which
each pixels data that is reserved transparency
information of 32 bit.

4. In existing techniques i.e. Image stitching is techniques in
which Combine two or more overlapping images to make
one larger image.
Example
Img1 img2 img3

5. After overlapping 3 images
Resultant images

6. Alpha means transparency
The alpha idea been used to composite billions of
pixels (if not more) to create images for print, video,
film, and probably every other application of computer
graphics.
The alpha values for an image are sometimes referred
to collectively as the "alpha channel" of an image.

7. Alpha compositing is the process of combining an image
with a background to create the appearance of partial
or full transparency of final image.
Compositing is the process by which graphical objects
are combined.

9. The alpha channel is a color component that
represents the degree of transparency or opacity of a
color.
The alpha channel is typically represented by the
letter α i.e.(alpha).
value of alpha

10. The degree foreground color translucency may range from
Completely transparent to completely opaque.
A value of 1 is completely solid and a value of 0 is
completely transparent.
The five rectangles have different alpha values of 0.1,
0.3, 0.5, 0.7 and 0.9 in order, from left to right as shown
in fig.1.Fig1:
* Fig1: Five Green rectangles as foreground and common Red background

11. According to above figure, we can see that when we
give alpha value of 0.1 image is almost transparent and
we cannot see foreground image (Green colour) and
background (Red colour)
α*fgcolor+ (1- α) *bgcolor
Where fgcoloris the colour of the rectangle and bgcolor
is the colour of the background. One can see that
0.1*green+(1-0.1) * red
green(10%)+(90%red)
if a=1, none of the background will be seen, and if a=0
none of the rectangle will be visible.
Example
bgcolor= red
fgcolor= green

12. Alpha compositing is based on the idea of pre-
multiplication. If an alpha channel is used in an
image, it is common to also multiply the color by the
alpha value, to save on additional multiplications
during compositing.
In pre-multiplication process, we store a color's
components (typically red, green, and blue) already
multiplied by alpha compositing.

13. Easy to use
Easy to understand
Pre-multiplication
image quality
Transparency
Disadvantages
Image limitation
Overlapping of background images
Resize single image

14. Alpha compositing is technique in which we can
combine two images and display it as a single image, in
which we resize one image and pixels of that image will
be overlapping pixels of our background image.

15. [1] http://home.comcast.net/~tom_forsyth/blog.wiki.html#Premultiplied alpha
[2] Compositing Digital Images Thomas Porter and Tom Duff, Computer Graphics
Volume 18, Number 3, July 1984.
[3] Porter, T. Duff, SIGGRAPH '84, "Compositing Digital Images", Conference 3.
[Blinn94] Blinn, James F,"Compositing, Part 1: Theory", IEEE Computer Graphics and
Applications, September 1994.
[4] Porter, Thomas, and Duff, Tom, Compositing Digital Images, Computer Graphics,
Vol 18, No 3, Jul 1984, 253-.SIGGRAPH’84.
[5] Smith, Alvy Ray, Color Gamut Transform Pairs, Computer Graphics, Vol 12, No 3,
Jul 1984, 12-19.SIGGRAPH’78 Conference Proceedings
[6] Smith, Alvy Ray, Analysis of the Color-Difference Technique, Tech Memo 30,
Computer Division, Lucasfilm Ltd.,Mar 1982.
[7] Smith, Alvy Ray, Math of Mattings, Tech Memo 32, Computer Division, Lucasfilm
Ltd, Apr 1982. Reissue of techmemo of Dec 30, 1980.
[8] Vlahos, Petro, Composite Color Photography, US Patent 3,158,477, Nov 24, 1964.
The classic color-difference bluescreen compositing technique.
[9] Principles of Color Technology 2nd Edition Billmeyer and Saltzman, John Wiley and
Sons, 198
[10] Thomas Porter and Tom Duff, Compositing Digital Images, Computer Graphics

16. Thank You !!!!!!