Multimedia Sheet

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Modern University For Technology & Information
Faculty of Computer Science
CS 371 Multimedia
Prof. Dr. \ Alaa Abd El-Rahim
2018 Fall CS 371Multimedia Final Review Sheet
Question
Discuss the different image formats: TIF, JPG, PNG, and EXIF.
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BMP, Bit Map - Developed by Microsoft. A bit-map representation stores the graphic/image
data in the same manner that the computer monitor contents are stored in video memory
(Video Card).
JPEG (JPG), Joint Photographic Experts Group - A standard with several different image
representations. The transform-based lossless compression method can create very small files.
GIF, Graphic Interchange Format - Originally, developed by CompuServe, GIF uses indexed
color and LZW (Lempel-Ziv Welch compression algorithm).
TIFF (TIF), Tagged Image File Format - A standard with lossless compression.
PNG, Portable Network Graphics - Developed as non-proprietary alternative for GIF
EXIF Exchange Image File: is an image format for digital cameras.
Question
Explain how the dithering technique is used with the binary image to increase the gray
levels.
Dithering is an intentionally applied form of noise used to randomize quantization error,
preventing large-scale patterns such as color banding in images. Dither is routinely used in
processing of both digital audio and digital video data, and is often one of the last stages of audio
production to compact disc
Dithering is used for displaying monochrome images
Also, For printing on a 1-bit printer, dithering is used to calculate larger patterns of dots, such that
values from 0 to 255 corresponding to pleasing patterns that correctly represent darker and
brighter pixel.
The main strategy is to replace a pixel value by a larger pattern, say 2 x 2 or 4 x 4 , such that the
number of printed dots approximates the varying sized disks of ink used in halftone printing.
Half-tone printing is an analog process uses smaller or larger filled circles of black ink to
represent shading, for newspaper printing say.
Question
Explain the multimedia authoring and describe briefly the most common three metaphors.
Multimedia Authoring
Multimedia authoring is the creation of multimedia productions, sometimes called “movies” or
“presentations”.
An Authoring System is a program which has pre-programmed elements for the development of
interactive multimedia software titles. Authoring systems vary widely in orientation, capabilities, and
learning curve. There is no such thing (at this time) as a completely point-and-click automated authoring
system; some knowledge of heuristic thinking and algorithm design is necessary.
Iconic/Flow Control: - This tends to be the speediest (in development time) authoring style; it is best suited for
rapid prototyping and short-development time projects. Many of these tools are also optimized for developing
Computer-Based Training (CBT). The core of the paradigm is the Icon Palette, containing the possible
functions/interactions of a program, and the Flow Line, which shows the actual links between the icons.
Frame: The Frame paradigm is similar to the Iconic/Flow Control paradigm in that it usually incorporates an icon
palette; however, the links drawn between icons are conceptual and do not always represent the actual flow of
the program.
Card/Scripting: The Card/Scripting paradigm provides a great deal of power (via the incorporated scripting
language) but suffers from the index-card structure. It is excellently suited for Hypertext applications, and
supremely suited for navigation intensive (a la Cyan's "MYST" game) applications.
Question
Explain the Color Look-Up Tables (LUTs) algorithm used with the GIF image.
Answer
Question
Calculate the image storage required for image resolution 640 X 480
for the following image types: Binary Image, True Gray-Level Image,
GIF Color Image, BMP Color Image.
The Binary image each pixel store in one bit, so the image resolution
640 X 480 required
Storage size = 640 X 480 = 307200 Bits
= 640 X 480 / 8 = 38400 Bytes
= 640 X 480 / (8 * 1024) = 37.5 KB
The True Gray image each pixel store in one byte, so the image
resolution 640 X 480 required
Storage size = 640 X 480 = 307200 Bytes
= 640 X 480 / (1024) = 300 KB
The GIF Color image each pixel store in one byte, so the image
resolution 640 X 480 required
Storage size = 640 X 480 = 307200 Bytes
= 640 X 480 / (1024) = 300 KB
The BMP Color image each pixel store in 3 bytes(24 Bits),
( pixel R G B ) , so the image resolution 640 X 480 required
Storage size = 640 X 480 X 3 = 921600 Bytes
= 640 X 480 / ( 1024) = 900 KB
Question
Discuss what is meant by the terms static media and dynamic media. Give some examples
of static media and dynamic media.
Static Media – does not change over time, e.g. text, graphics
Dynamic Media --- Time dependent (Temporal), e.g. Video, sound, animation.
Question
What is meant by MIDI? How is a basic MIDI message structured?
MIDI is a protocol that enables computers, synthesizers, keyboards, and other
musical devices to communicate with each other. It is a set of instructions how a
computer should play musical instruments.
MIDI Message structure:
MIDI message includes a status byte and up to two data bytes.
Status byte
The most significant bit of status byte is set to 1.
The 4 low-order bits identify which channel it belongs to (four bits produce 16
possible channels).
The 3 remaining bits identify the message.
The most significant bit of data byte is set to 0.
Question
Explain how can MIDI be used effectively in multimedia musical applications?
Multimedia Application:
-Low Bandwidth/(Low Quality?) Music on Web, Quicktime etc supports
Midi musical instrument set
-Sound Effects --- Low Bandwidth alternative to audio samples, Sound Set
part of GM sound set
Control of external devices --- e.g Synchronization of Video and Audio
(SMPTE), Midi System Exclusive, AUDIO RECORDERS, SAMPLERS
Control of synthesis --- envelope control etc
-MPEG 4 Compression control --Digital Audio
Question
What is the purpose of using "Chroma" sub-sampling with the digital video?
Why is it feasible?
Human vision has less acuity in colour vision than it has in black and white—one can distinguish close
black lines more easily than colour lines, which soon are perceived just a mass without texture as the lines
move close to each other. Therefore, it is acceptable perceptually to remove a good deal of colour
information.
In analog, this is accomplished in broadcast TV by simply assigning a smaller frequency bandwidth to colour
than to black and white information. In digital, we “decimate” the colour signal by subsampling (typically,
averaging nearby pixels). The purpose is to have less information to transmit or store.
Question
How many signals are used in S-Video? And what are the signals used in S-Video?
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S-Video is used 4 signals
The signals used in S-Video are :
 Luminance
 Chrominance
 Audio
 Sync
Question
What are the advantages of using digital video?
The advantages of using digital video are:
i) Video can be stored on digital devices or in memory, ready to be processed (noise removal, cut and
paste, etc.), and integrated to various multimedia applications;
ii) Direct access is possible, which makes nonlinear video editing achievable as a simple, rather than a
complex, task;
iii) Repeated recording does not degrade image quality;
iv) Ease of encryption and better tolerance to channel noise.
Q Discuss the audio quality versus the audio data rate.
Quality
Sample
Rate(KHz)
Telephone 8
AM Radio
FM Radio
11.025
22.050
CD
44.1
DAT
48
DVD
Audio
192
Bits
Data Rate
Mono /
Frequency
per
(if
Stereo
Band
Sample
Uncompressed)
200-3,400
8
Mono 8 KBytes/sec
Hz
8
Mono 11.0 KBytes/sec 16
Stereo 88.2 KBytes/sec 176.4
20-20,000
16
Stereo
KBytes/sec
Hz
192.0
20-20,000
16
Stereo
KBytes/sec
Hz
1,152.0
20-20,000
24
Stereo
KBytes/sec
Hz
Question
Calculate the space required for recording sound with duration of 15 minutes for the telephone
conversation.
The Telephone sample rate is 8 KHZ and Bits per sample is 8 Bits
8 x 103 x 8 x (15 x 60) / (8 * 2^20) =
MB
Question
Calculate the space required for recording sound with duration of 15 minutes for the CD mono and
the CD stereo.
The CD sample rate is 44.1 KHz and Bits per sample is 16 Bits
Mono
44.1 x 103 x 16 x (15 x 60) / (8 * 2^20) = MB
Stereo (left/right) channels, the amount of Mono is doubled:
x 2 = MB
Question
Calculate the space required for recording sound with duration of 15 minutes for The DVD mono
and the DVD stereo.
The DVD sample rate is 192 KHZ and Bits per sample is 24 Bits
Mono
192 x 103 x 24 x (15 x 60) / (8 * 2^20) = MB
Stereo (left/right) channel, the amount is doubled:
x 2 =
MB
Question
Calculate the space required for recording sound with duration of 15 minutes for the Radio FM.
The Radio FM sample rate is 22.050 KHZ and Bits per sample is 16 Bits
Radio FM is Stero
22.050 x 103 x 16 x (15 x 60) /(8 * 2^20) =
MB
Question
Calculate the space required for recording sound with duration of 15 minutes for the Radio AM.
Radio AM is Mono only
The Radio AM sample rate is 11.025 KHZ and Bits per sample is 8 Bits
11.025 x 103 x 8 x (15 x 60) / 8 (bits) * 2^20 = MB
Question
Discuss the distinction between lossless and lossy compression algorithms.
Lossless Compression
-- where data is compressed and can be reconstituted (uncompressed)
without loss of detail or information. These are referred to as bit-preserving
or reversible compression systems also.
Lossy Compression
-- where the aim is to obtain the best possible fidelity for a given bit-rate
or minimizing the bit-rate to achieve a given fidelity measure. Video and
audio compression techniques are most suited to this form of compression.
Question
Briefly explain, the entropy coding and transform coding techniques. Illustrate your answer with a
simple example of each type.
ENTROPY METHODS:
The entropy of an information source S is defined as:
H(S) = SUMI (PI Log2 (1/PI)
Where PI is the probability that symbol SI in S will occur.
Log2 (1/PI) indicates the amount of information contained in SI,
i.e., The number of bits needed to code SI.
Question
Suppose the dynamic range of speech in telephony implies ratio Vmax/Vmin of about 256.
Using uniform quantization, how many bits should we use to encode speech to make the
quantization noise at least an order of magnitude less than the smallest detectable telephonic
sound?
The Telephone sample store in 8 Bits -- 8 ^ 2 = 256
So Sound range will be 0 .. 256,
We will use something like the Median Cut Algorithm but on gray scale level,
as picking a value between 0 and half of the range. Pick the intensity level of gray scale most near
to the rate.
Q Explain how to handling the stored sampled audio (Synthetic Sounds
Q Discuss the main steps in JPEG image compression.
JPEG is a lossy image compression method. The effectiveness of the DCT
transform coding method in JPEG relies on three major observations:
Observation 1. Useful image contents change relatively slowly across the image—
that is, it is unusual for intensity values to vary widely several times
in a small area—for example, in an 8 × 8 image block. Spatial
frequency indicates how many times pixel values change across an
image block. The DCT formalizes this notion with a measure of
how much the image contents change in relation to the number of
cycles of a cosine wave per block.
Observation 2. Psychophysical experiments suggest that humans are much less
likely to notice the loss of very high-spatial frequency components
than lower frequency components.
JPEG’s approach to the use of DCT is basically to reduce high-frequency contents
and then efficiently code the result into a bitstring
Observation 3. Visual acuity (accuracy in distinguishing closely spaced lines) is
much greater for gray (“black and white”) than for color. We simply
cannot see much change in color if it occurs in close proximity—
think of the blobby ink used in comic books. This works simply
because our eye sees the black lines best, and our brain just pushes
the color into place. In fact, ordinary broadcast TV makes use of
this phenomenon to transmit much less color information than gray
information.
When the JPEG image is needed for viewing, the three compressed component
images can be decoded independently and eventually combined.
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