Unit 4:Video and Animation

▪ Video signal representation ▪ Methods of controlling Animation

▪ Computer Video Format ▪ Display of Animation
▪ Computer- Based animation ▪ Transmission of Animation
▪ Animation Language
Video
• Video is a visual multimedia application that combines a sequence of
images to form moving pictures and sound.
• These images are shown one after the other quickly. How fast they
show up is called "frame rate," measured in frames per second (fps).
• If displayed fast enough our eye cannot distinguish the individual
frames, This makes it seem like things are moving smoothly.
• The frame rate should range between 20 and 30 for perceiving
smooth realistic motion.
• Audio is added and synchronized with the apparent movement of
images.
Video Signal Representation
• In traditional black-and-white TVs, the video signal is displayed on a
CRT (Cathode Ray Tube).
• The electron beam in the CRT carries the information about the
image, such as its brightness.
• To understand how video and animation work, we need to
understand the signals that they use, not the specific cameras or
monitors that they use.
• We analyse the video signal coming from camera and the resulting
pictures (using USA standards).
Video Signal Representation
• Video signal representation includes three aspects:
▪ Visual representation
▪ Transmission
▪ Digitalization
Visual Representation
• The goal of video is to create a sense of presence and participation.
• To achieve this goal, the video should accurately convey the spatial
(location of objects) and temporal (movement of objects) information
of the scene.
• Important measures are:

1. Vertical Detail and 4. Perception of Depth 7. Continuity of motion

Viewing Distance 5. Luminance and 8. Flicker
2. Horizontal Detail and Chrominance 9. Temporal Aspect of
Picture Width 6. Temporal Aspects of Video Bandwidth
3. Total Detail Content of Illumination
the Image
Vertical Detail and Viewing Distance
• The geometry of the field occupied by the television image is based on the
ratio of the picture width W to height H. It is called aspect ratio. The
conventional aspect ratio is 4/3=1.33.
• When a television image is scanned, the scanning lines are spaced evenly
apart. However, the smallest detail that can be reproduced in an image is a
pixel, which is a square. This means that some details in the scene may fall
between the scanning lines. In order to reproduce these details, two
scanning lines may be required. This means that some vertical resolution is
lost.
• The Kell factor is a measure of how much vertical resolution is lost due to
the scanning process. It is typically about 70%, which means that about
30% of the vertical resolution is lost.
Horizontal Detail and Picture Width
• The picture width chosen for conventional television service is 4/3*picture
height.
• Using the aspect ratio, we can determine the horizontal field of view from
the horizontal angle.
• The horizontal field of view is the width of the area that can be seen in the
picture. It can be determined from the horizontal angle, which is the angle
between the left and right edges of the picture.
• If the height of a conventional television picture is 100 pixels and the
horizontal angle of the picture is 60 degrees, then the horizontal field of
view is 57.735 pixels.
• HFOV = 100 * tan(60/2) = 100 * tan(30) = 100 * 0.57735 = 57.735 pixel
Total Detail Content of the Image
• The vertical resolution is equal to the number of picture elements
separately presented in the picture height, while the number of
elements in the picture width is equal to the horizontal resolution
times the aspect ratio.
• The product of the number of elements vertically and horizontally
equals the total number of picture elements in the image.
Perception of Depth
• When we look at an object, each eye sees a slightly different image of
the object. This is because our eyes are slightly separated, and the
object is not directly in front of us. The brain combines these two
images to create a single image with depth perception.
• In TV pictures, things seem to have depth because they look closer or
farther away based on how they're shown.
• The focal length of the lens and the depth of focus of the camera also
affect the depth perception of a flat image.
Luminance and Chrominance
• Luminance is like the overall brightness of an image. It's the signal that tells how
light or dark something is.
• Chrominance is about the specific colors and how they differ from each other. It's
the signal that holds the details about the colors in the image. Instead of telling
how bright or dark something is, it tells the TV how to make colors look right.
• Color vision is achieved by combining three signals: red, green, and blue (RGB).
• The three signals are sent to different parts of the TV screen, and this makes sure
the TV shows the right amounts of red, green, and blue colors in each spot, just
like the camera saw them.
• During the transmission of the signals from the camera to the receiver (display), a
different division of signals in comparison to the RGB division is often used.
• The color encoding during transmission uses luminance and two chrominance
signals.
Temporal Aspects of Illumination
• Our eyes also have a special way to see things that are moving, called
motion resolution.
• Human vision can perceive a rapid succession of slightly different still
pictures as a continuous sequence.
• This property is used in television and motion pictures.
• To represent visual reality, two conditions must be met:
▪ The rate of repetition of the images must be high enough to guarantee
smooth motion from frame to frame.
▪ The rate must be high enough so that the persistence of vision extends over
the interval between flashes.
Continuity of motion
• Human eye can perceive continuous motion at any frame rate faster than
15 frames per second.
• Video motion seems smooth and is achieved at 30 frames per second.
• Movies are typically shot at 24 frames per second.
• The new Show scan technology involves making and showing movies at 60
frames per second.
• This produces a bigger picture and smoother motion.
• There are several standards for motion video signals, each with its own
frame rate.
• The NTSC standard in the United States uses a frame rate of 29.97 Hz.
• The PAL (Phase Alternating Line) standard in Europe uses a frame rate of 25
Hz.
Flicker
• When things move slowly on screen, we might see a blinking effect
due to changes in brightness. This is called flicker.
• The marginal value to avoid flicker is at least 50 refresh cycles/s.
• To achieve continuous flicker-free motion, we need a relatively high
refresh frequency.
• Movies, as well as television, apply some technical measures to work
with lower motion frequencies.
Temporal Aspect of Video Bandwidth
• The bandwidth required to transmit motion video depends on its temporal
specification.
• Temporal specification is the rate at which the video is scanned, which is
determined by the visual system and the human eye.
• For example, a regular TV device scans lines and frames in microseconds,
while an HDTV device scans pixels in less than a millionth of a second.
• The human eye can perceive smooth motion at a frame rate of 1/25 second
or higher.
• This means that the bandwidth required to transmit motion video must be
high enough to support a frame rate of 1/25 second or higher.
Transmission
• Video signals are transmitted to receivers through a single television
channel. The NTSC (National Television Standards Committee)
channel is shown in Figure below:
Transmission
• To encode color, a video signal is a composite of three signals. For transmission
purposes, a video signal consists of one luminance and two chrominance signals.
• Luminance is the brightness of the image, while chrominance is the color of the
image.
• The subcarrier is a signal that is used to carry the chrominance information.
• In NTSC systems, the way colors are sent in the TV signal follows a special pattern
that matches how the screen is scanned. This pattern helps the colors appear
correctly on the screen. It's like having a rhythm that makes sure the colors look
right when you watch TV.
• This means that the chrominance signals are combined with the luminance
signals.
• The goal is to separate the two sets of components in the receiver and avoid
interference between them before the recovery of the primary color signals for
display.
Digitalization
• To process a picture or motion video by a computer or transmit it over a
computer network, it needs to be converted from analog to digital
representation. This process is called digitization.
• In digitization, the gray (color) level in the picture is sampled at a regular array of
points. The gray level at each point is then quantized, which means that it is
divided into a finite number of levels.
• The number of quantization levels determines the quality of the digital image.
• A higher number of quantization levels produces a higher quality image, but it
also requires more storage space.
• The next step in the creation of digital motion video is to digitize the pictures in
time.
• This means that the pictures are taken at regular intervals, such as 30 frames per
second.
• The sequence of digital images is then used to create the illusion of motion.
Computer Video Format
AVI (Audio Video Interleave):
• Windows format, plays in Windows Media Player
• Very good quality, even at smaller resolutions
• Large file size – not recommended for delivering video over the Internet.
• Popular format for videos stored on a computer.
MOV (Movie):
• Apple format, plays in the QuickTime Player
• Very good quality
• Popular format for videos downloaded from the Internet.
Computer Video Format
MPEG (Moving Pictures Expert Group):
• The standard for compression and storage of audio and motion video for use on
the World Wide Web.
• Creates video small file sizes.
• Popular format for videos downloaded from the Internet.
• Its biggest advantage is that it will play in many different media players.
RM (RealMedia):
• Plays in the RealPlayer player.
• Typically contains a movie clip.
• Popular format for streaming video viewed over the Internet.
• Real Player is generally supported by many different computers and operating
systems.
Computer Video Format
WMV (Windows Media Video):
• Proprietary video format developed by Microsoft.
• Plays in Windows Media Player.
• Popular format for streaming video viewed over the Internet.
FLV (Flash Video):
• New file format widely used on the Internet.
• Plays in Adobe Flash Player.
• Very small file size.
• Popular format for streaming video viewed over the Internet
Computer Based Animation
• Animation means giving life to any object in computer graphics.
• It has the power of injecting energy and emotions into the most seemingly
inanimate objects.
• Computer-assisted animation and computer-generated animation are two
categories of computer animation. It can be presented via film or video.
• An animation covers all changes that have a visual effect. Visual effects can
be of different nature. They might include time-varying positions (motion
dynamics), shape, color, transparency, structure and texture of an object
(update dynamics), and changes in lighting, camera position, orientation
and focus.
• A computer-based animation is an animation performed by a computer
using graphical tools to provide visual effects.
Processes of computer based animation
i. Input Process
ii. Composition stage
iii. In-between process
iv. Changing colors
Processes of computer based animation
i. Input process:
• It is the first stage before the animation.
• The image of object must be digitized or drawing should be completed before the
animation process.
• These can be done by optical scanning or tracing the drawing with a data tablet or
producing the drawings by the use of drawing application or programs.
• Optical scanning: using a scanner to convert a physical image into a digital format.

• The drawing may need to be post processed (filtered) to clean up any glitches arising
from the input process.
• The digitize image should be kept in the key frames at extreme or characteristics
position which has to be animated.
Processes of computer based animation
ii. Composition stage:
• Foreground and background figures and colors are combined to generate the
individual frames for the final animation in this stage.
• Several low resolution frames are place in a rectangular array to generate a
trial film using pan zoom, features available in frame buffers.
• The frame buffer can take a particular portion of such an image (pan) and
then enlarge it the entire screen (zoom).
• This process can be repeated on several frames of animation stored in the
single image.
• If it is done fast enough, it gives the effect of continuity for animation.
Processes of computer based animation
iii. In-between process:
• This step in animation is all about making things move smoothly from one place to
another. It's like filling in the gaps between important moments.
• For example, imagine a ball thrown in the air. We know where it starts, where it
ends, and where it is in the middle. In-betweening helps us figure out how it moves
in those moments in between.
• The easiest interpolation method is linear Interpolation called leaping, which is like
taking big jumps.
• it has some limitations. For instance, if we're trying to figure out how the ball moves
between three key points (start, middle, and end), leaping might not work well.
• In such situation splines are used. Splines can be used to vary any parameter
smoothly as a function of time. It can make an individual point move smoothly in
space and time, in-between process also involves interpolation of objects shape in
immediate frames.
Processes of computer based animation
iv. Changing colors:
• For changing color, computer based animation, usages CLUT (color lookup
table) in a frame buffer and the process of double buffering.
• The LUT animation is generated by manipulating the color lookup table. The
simplest method is to cycle the colors in the LUT.
• Thus changing the color of various pieces of the image, using LUT animation is
faster than sending an entire new pixmap to the frame buffer or each frame.
• For example 8 color bits per pixel in 640*512 frame buffer, a single image
contains 320 kilobytes of information. Transferring a new image in every
1/30th second to the buffer required a bandwidth of 9mbps where as LUT
needs a few hundred to few thousands bytes.
Computer Animation Languages
• There are many different languages for describing animation, and
new ones are constantly being developed. They fall into three
categories:
a. Linear-list Notations Language
b. General-purpose Languages
c. Graphical Languages
Linear-list Notations Language
• It is the specially animation supporting language. Each event in the
animation is described by start and ending frame number and an
action that is to take place (event). The example of this type of
languages is SCEFO (scene format).
• For example: 42, 53, B, rotate, “palm”, 1, 30
Here,
42 => start frame no.
53 => ending frame no.
B => table.
Rotate => action.
Palm => object.
1 => start angle.
30 => end angle.
General-purpose Languages
• The high level computer languages which are developed for the
normal application software development also have the animation
supporting features along with graphics drawing.
• For example QBASIC, C, C++, java etc.
Graphical language
• It is also computer high level language and especially develop for
graphics drawing and animation has been already develop for e.g.
AutoCAD.
• Graphical animation languages describe animation in a more visual
way. These languages are used for expressing, editing and
comprehending the simultaneous changes taking place in an
animation.
Methods of Controlling Animation
• Controlling animation is independent of the language used for
describing it.
• There are different ways of controlling animation in multimedia. They
are:
a. Full Explicit Control
b. Procedural Control
c. Constraint-based Systems
d. Tracking Live Action
e. Kinematics and Dynamics
Full Explicit Control
• Simplest way of animation control
• Animator provides a description of everything that occurs in the
animation, either by specifying simple changes, such as scaling,
translation, and rotation, or by providing key frame information and
interpolation methods to use between key frames.
• This interpolation may be given explicitly or (in an interactive system)
by direct manipulation with a mouse, joystick, data glove or other
input device.
Full Explicit Control
Procedural Control
• It is based on communication between various objects to determine
their properties.
• Procedural control is a significant part of several other control
mechanisms.
• In physically-based systems, the position of one object may influence
the motion of another (e.g., balls cannot pass through walls)
• In actor based systems, the individual actors may pass their positions
to other actors to affect the other actors' behaviors.
Constraint-based Systems
• Although some objects in the real world move along a straight lines,
this is not always the case.
• Many object’s movements are determined by another objects with
which they come into contact.
• E.g. presence of strong wind or fast moving large objects
• This includes objects to stop, changing directions etc.
Tracking Live Action
• Control is achieved by examining the motions of objects in the real world.
• Rotoscoping: is a technique where animators trace live action movement,
frame by frame, for use in animated films.
• Originally, pre-recorded live-film images were projected onto a frosted
glass panel and redrawn by an animator.
• This projection equipment is called a Rotoscope.
• Another way is to attach indicators to key points on the body of a human
actor.
• For example the data glove [gesture language for hearing-impaired people]
Rotoscoping
Rotoscoping
Kinematics and Dynamics
• Kinematics refers to the position and velocity of points. A kinematic
description of a scene, for example, might say, "The cube is at the origin at
time t =0. It moves with a constant acceleration in the direction (1, 1, 5)
thereafter.
• dynamics takes into account the physical laws that govern kinematics (e.g.
Newton's laws of motion for large bodies, the Euler-Lagrange equations for
fluids, etc.).
• A dynamic description of a scene might be, "At time t =0 seconds, the cube
is at position (0 meters, 100 meters, 0 meters). The cube has a mass of 100
grams. The force of gravity acts on the cube." Naturally, the result of a
dynamic simulation of such a model is that the cube falls
Kinematics and Dynamics
Display of Animation
• It basically deals with how animated pictures can be displayed on the
screen there are different ways to accomplish this like random scan,
raster scan.

Raster Scan Image Random Scan Image

Display of Animation
• To display animations with raster systems, the animated objects must be
scan-converted and stored as pixmap in the frame buffer. Example: Imagine
taking a car that's moving in a video game and turning it into a picture that
sits on your screen.
• Scan conversion must be done at least 10 times per second to ensure
smooth visual effects. Example: Think of a video game character moving
smoothly, and each step of its movement is updated 10 times in a second.
• The actual scan-conversion must take a small portion of 10 times/second in
order to avoid distracting ghost effect. Example: If you move your mouse
pointer, it shouldn't leave behind a trail or ghost image.
• Double buffering is used to avoid the ghost effect.
Transmission of Animation
• Two forms of transmission:
• Symbolic representation of an animation is transmitted together with
the operations performed on the object.
• The animation is described as a series of instructions, such as "move the ball
to the left" or "scale the triangle up".
• These instructions are sent to the receiver, which then displays the animation.
• This is a fast way to transmit animation because the instructions are much
smaller than the actual animation frames.
• However, it is slower to display the animation because the receiver has to
generate the animation frames from the instructions.
Transmission of Animation
• The pixmap representations are transmitted and displayed.
• Each frame of the animation is sent to the receiver as a bitmap image.
• The receiver can then display the animation immediately, without having to
generate any frames.
• This is a slower way to transmit animation because the bitmap images are
much larger than the instructions.
• However, it is faster to display the animation.