VIDEO ELEMENT Flashcards
is the element of
multimedia that can hold the
interest of viewers in a
presentation
Motion video
The visual effect of motion is due to a biological phenomenon known as
persistence of vision
An object seen by the human eye remains mapped on the eye’s ___ for a
brief time after viewing (approximately 25ms)
retina
Another phenomenon contributing to the vision of motion is known as
phi
phenomenon
Due to the above two phenomena of our vision system, a discrete sequence
of individual pictures can be perceived as a
continuous sequence
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
Temporal aspect of Illumination
The frequency at which the flicking light source
must be repeated before it appears continuous is
known as the
fusion frequency
It is known that we perceive a continuous motion to
happen at any frame rate faster than 15 frames per
second
VISUAL REPRESENTATION
has a frame rate of 25
frames/s
PAL television system
occurs due to a
periodic fluctuation of brightness perception
flicker
A technique known as ____ improves the
view by
* dividing a frame into two fields, each
contains the alternative scan lines, and
* displaying the field in twice of the frames
rate
interleaving
three conventional broadcast
television systems
NTSC(National Television Systems Committee)
SECAM(SEquential Couleur Avec Memoire)
PAL (Phase Alternating Line)
A picture consists of 525 lines and frame rate is
approximately 30Hz
NTSC(National Television Systems Committee)
A picture consists of 625 lines and frame rate is
25Hz
SECAM(SEquential Couleur Avec Memoire)
A picture consists of 625 lines and all current
television broadcasting system are analog in nature
PAL (Phase Alternating Line)
The smallest detail that can be reproduced in the
image is a
pixel
Only about __% of the vertical detail is presented
by the scanning lines.
70
Conventional video systems have relative __ ___ compare to computer screens: typical resolution of 640 x 480, even up to 1024 x 768
low resolution
Hardware required to capture video:
- Video sources:
- Video capture card
- Storage space: large hard disk
The common features in these cards are:
- Can accept composite video or S-VHS in NTSC or PAL
- Video input mixer and ADC—
- Video frame buffer
- Video processor
- Compressor/encoder
- Interface
to
select/combine video sources, to convert
analog video signal to digital samples
Video input mixer and ADC
temporary storage for
video frame
Video frame buffer
to filter or enhance the
video frame, e.g., reduce noise, adjust
brightness, contrast and color
Video processor
to compress and
encode the digital video into a required format
Compressor/encoder
was defined by Microsoft for its Video for
Windows systems
* It supports video playback at up to 30 frames per second on a small window
(typical size 300 x 200 with 8 or 16 bit color)
* It is a software-only system
* It supports a number of compression algorithms
AVI (Audio Video Interleaved)
was originally developed by Apple for storing audio and video in
Macintosh systems
* It supports video playback at up to 30 frames per second on a small window
(typical size 300 x 200 with 8 or 16 bit color)
* It is a software-only system
* It supports a number of compression algorithms
QuickTime
is a working group under ISO
* There are several versions of mpeg standard. The most commonly used now is
mpeg-1
* It requires hardware support for encoding and decoding (on slow systems)
* The maximum data rate is 1.5Megabit/sec
* The next generation mpeg-2 is now getting popular
* Mpeg-2 improves mpeg-1 by increasing the maximum data rate to 15Mbit/sec
* It can interleave audio and video
MPEG (Motion Picture Expect Group)
