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Lesson#33
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Graphics and Animation
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Graphics & Animation
We will become familiar with the
role that graphics and animations play in computing
We will look at how graphics & animation are displayed
We will look at a few popular formats used for storing graphics and
animation
33.1 Computer Graphics:
Images created with the help of
computers
2-D and 3-D (displayed on a 2-D screen but in such a way that they give
an illusion of depth)
Used for scientific research, artistic expression, or for industrial
applications
Graphics have made the computer interfaces more intuitive by removing
the need to memorize
commands
33.2 Displaying Images:
Most all computer displays consist
of a grid of tiny pixels arranged in a regular grid of rows and
columns
Images are displayed by assigning different colors to the pixels located
in the desired portion of the
computer display
Let’s discuss the pixel a bit more …
Pixel:
The smallest image forming element
on a computer display
The computer display is made up of a regular grid of these pixels
The computer has the capability of assigning any color to any of the
individual pixels on the display
Let’s now see how the computer displays a square
33.3 Pixel Colors :
The color of each pixel is
generally represented in the form a triplet
In a popular scheme – the RGB scheme – each part of the triplet
represents the intensity of one of out of
three primary colors: red, green, blue
Often, the intensity of each color is represented with a byte, resulting
in 256x256x256 (16+ million)
unique color combinations
If this scheme is used to display an image that is equal to the size of
an XGA (1024x768 pixels) display,
the image will require 2.25MB of storage, which is just too much
A number of clever schemes have been invented to reduce the number of
bytes that are required for
storing graphics. 2 popular ones:
Color mapping
Dithering
33.4 Color Mapping :
Instead of letting each pixel
assume one out of 16 million possible colors, only a limited number of
colors – called the platelet – are allowed
For example, the platelet may be restricted to 256 colors (requiring 1
byte/pixel instead of 3)
Each value, from 0 to 255, is mapped to a selected RGB color through a
table, reducing the size of a
2.25MB graphic to 0.75MB
The quality of the displayed image
will not suffer at all if the image only uses colors that are a part of
the platelet
Color Platelet Example:
Color Platelet Code Actual Color
in RGB
1 255, 255, 000 (yellow)
2 255, 000, 000 (red)
3 000, 255, 255 (cyan)
4 255, 153, 051 (orange)
… …
… …
… …
33.5 Dithering:
In this scheme, pixels of
alternating colors are used to simulate a color that is not present in
the platelet
For example, red and green pixels can be alternated to give the
impression of bright yellow
The quality of the displayed image is poorer
33.6 Aliasing:
The computer screen consists of
square-ish pixels arranged in a fixed grid
At times, when a diagonal line is drawn on this grid, it looks more like
a staircase, instead of a straight
line
This effect – called aliasing – can be managed by reducing the size of
pixels
33.7 Anti-Aliasing:
Anti-aliasing is another technique
used for managing the ‘staircase’ effect
Let’s say that we need to draw a white straight-line such that it
overlaps 60% with one pixel, and 40%
with another initially, and near the end, 58%, 41%, and 1%,
respectively, with three pixels
The staircase effect is caused
because the proper drawing of the line requires a pixel that does not
exist
There are three options in this case:
Assign the white color to the pixel corresponding to the largest overlap
Assign the white color to both pixels
Either of these will cause the staircase effect
The 3rd option is to color the pixel with 60% overlap to a 40% gray
color & the other one to 60% gray
Result: A smoother - pleasing to the eye - look
33.8 Graphics File Formats:
The choice of the format generally
depends upon the nature of the image. For example:
An image of natural scenery contains many irregular, non-gemetric
shapes, therefore is stored in bitmap
format
A CAD drawing consists of many geometric shapes like straight lines,
arcs, etc. and therefore is stored
in a vector format
A third situation arises when dealing with graphics that contain both
regular and irregular shapes
33.9 Vector or Object-Oriented Graphics:
Treats everything that is drawn as
an object
Objects retain their identity after they are drawn
These objects can later be easily moved, stretched, duplicated, deleted,
etc
Are resolution independent
Relatively small file size
Examples: swf, svg, wmf, ps
33.10 Bit-Mapped or Raster Graphics:
Treats everything that is drawn as
a bit-map
If an object is drawn on top of another, it is difficult to move just
one of them while leaving the other
untouched
Changing the resolution often requires considerable touch-up work
Relatively large file size
Examples: gif, jpg, bmp
33.11 File Formats Popular on the Web (1):
gif (Graphical Interchange Format)
Bit-map images compressed using the LZW algo.
The number of colors is first reduced to 256 and then consecutive pixels
having the same color are
encoded in a [color, numberOfPixels] format
Works well with computer-generated graphics (e.g. CAD, block diagrams,
cartoons) but not with
natural, realistic images
Loss-less for images having 256 colors or less
1 2 3 4 5
jpg (JPEG – Joint Photographic
Experts Group)
Compressed, full-color and gray-scale bit-map images of natural,
real-world scenes, where most every
pixel differs in color from its neighbor
It does not work as well as gif with non-realistic images, such as
cartoons or line drawings
Does not handle compression of B&W images
Lossy
swf (Shockwave Flash)
Designed for 2-D animations, but can also be used for storing static
vector images as well
A special program (called a plug-in) is required to view swf files in a
Web browser
svg (Structured Vector Graphics)
New format; may become more popular than swf
33.12 Image Processing:
A branch of computer science
concerned with manipulating and enhancing computer graphics
Examples:
Converting 2-D satellite imagery into a 3-D model of a terrain
Restoring old, faded photographs into something closer to the original
Determining the amount of silting in Tarbela lake from a satellite image
33.13-D Graphics:
Flat images enhanced to impart the
illusion of depth
We perceive the world and the objects in it in 3-D - breadth, width,
depth - although the images formed
on the retinas of our eyes are 2-D
The secret of 3-D perception: stereo vision
The two eyes are spaced a few cm apart
Result: The images formed on the two retinas are slightly different
The brain combines these two into a single 3-D image, enabling us to
perceive depth
3-D Graphics: Applications:
Games
Medical images
3-D CAD
3-D Rendering:
The process of converting
information about 3-D objects into a bit-map that can be displayed on a
2-D
computer display
Computationally, very expensive!
Steps:
Draw the wire-frame (skeleton, made with thin lines)
Fill with colors, textures, patterns
Add lighting effects (reflections, shadows)
33.14 Animation:
Graphics in motion, e.g. cartoons
Illusion of motion is created by showing the viewer a sequence of still
images, rapidly
Drawing those images - each slightly different from the previous one -
used to be quite tedious work
Computers have helped in cutting down some of the tediousness
See next slides
Computer Animation: Examples
Games
Cartoons, movies
Visualization of processes, e.g the IM process
Displaying the results of scientific experiments, e.g. nuclear fusion
Tweening:
Creating a reasonable illusion of
motion requires the drawing of 14-30 images per second of animation
– very tedious!
In practice, only 4-5 images (called key images) instead of 14-30 are
drawn, and then the computer is
asked to create the remaining in-between images
This process of creating these in-between images from key images is
called in-betweening (or tweening
for short)
The simplest algorithm for tweening calculates the position of a
particular segment of an image by
calculating the average of the positions of that same image segment
belonging to adjacent key images
The Future of Graphics & Animation:
New graphic-file storage formats
will appear with better compression efficiencies
3-D animation will become more popular as computers become faster and
algorithms become smarter
More realistic games; better realism in movies – may, one day, make the
human actors extinct
Today’s Goal:Graphics & Animation
We became familiar with the role
that graphics and animations play in computing
We discussed how graphics & animation are displayed
We also looked at several formats used for storing graphics and
animation
Next Lecture:(Intelligent Systems)
To become familiar with the
distinguishing features of intelligent systems with respect to other
software
systems
To become able to appreciate the role of intelligent systems in
scientific, business and consumer
applications
To look at several techniques for designing intelligent systems
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