CP1030 : Multimedia
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Transcript CP1030 : Multimedia
Multimedia
Contents
Multimedia
Graphics / Pictures
Audio / Sound
Video
Multimedia
Multimedia is:
Sound
Graphics
Videos
Multimedia applications
Office documents
Webpage content
Movies
Music
Pictures
Multimedia
Multimedia files are quite large
Use compression to reduce file sizes
Lossless Compression – algorithms reduce
size of files
○ No information is lost
Lossy Compression – algorithm reduces
size of files
○ Some information is lost
Multimedia
Trade offs between lossless and lossy
compression
Lossy can reduce file sizes much more
Example: File compression like 7-zip
Uses lossless compression
If some data is lost, then file becomes
corrupted
Lossy compression is used in multimedia
Multimedia
Example: 38.56666666
Lossless compression
38.56(7)
Lossy compression
38.6
Pictures / Graphics
Graphics
Bitmap (BMP) - windows
Graphics Interchange Format (GIF)
Joint Photographic Experts Group (JPEG)
Tagged Image File Format (TIFF)
Portable Network Graphics (PNG)
Note – the abbreviations are the file
extensions
Pictures / Graphics
Digitizing Images
Bit Map – each image is laid out in a grid
pattern
Pixel - each cell in the image
Pixel could be black or white
Grey scale value
Color
The more pixels, the better the image quality
Digital cameras – megapixels
My camera is 14.1 megapixels
Each picture has 14.1 million cells that compose the
pictures
Pictures / Graphics
Grey Scale Bit Map Image
The snowman face is a 7x7
bitmap
Composed of 15, 15, 0, 0, 0,
15, 15, 15, 15, 0, 0, 0, 15, 15,
15, 0, 0, 0, 0, 0, 15, 7, 15, 3,
15, 3, 15, 7, 7, 15, 15, 7, 15,
15, 7, 7, 15, 3, 3, 3, 15, 7, 15,
7, 7, 7, 7, 7, 15
The file also contains a
header containing the size of
the bitmap which is 7 x 7
Bitmap of a snowman
Pictures / Graphics
Color Bit Map Image
The top photograph is a
picture with birds flying in the
sky
The bottom picture is one bird
blown up to show pixels
Pictures / Graphics
RGB (Red-Green-Blue)
All digital images are composed of red, green and
blue
Usually represented by hexadecimal numbers
24 = 16;
Numbers – 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, and F
Example: HTML command
bgcolor =“#0F69F3”
bgcolor is background color
Red = 0F, Green = 69, and Blue = F3
Pictures / Graphics
Each color has two
hexademical digits or 00
– FF, which ranges from
0 to 255
Each color is 28 and
three colors 28 28 28 =224
24-bit true color
We also have 32-bit
color
RBG can make the other
colors
Pictures / Graphics
Windows BitMap
Bitmaps do not use compression
Bitmaps have very large file sizes
Easy to calculate the file size
Image is 800 x 600 with 8 bit (1 byte)
color
256 color values
Pictures / Graphics
Calculating
Image File Size (BitMap)
Number of pixels = 800 x 600 = 480,000
pixels
Image size = number of pixels x
number of bits
Image size = 480,000 pixels x 1 byte =
480,000 bytes
Image size = 480,000 / 1024 = 468.75
KBytes
Pictures / Graphics
Graphics Interchange Format (GIF)
Moderately compresses images
Lossless compression (simple pictures)
Good for simple pictures and graphics
Displays 256 colours or 8 bit
Palette – it chooses the best 256 colors out of 24bit color
Common for websites
Animated GIFs – images can display simple
animation, especially for websites
Pictures / Graphics
The animated GIF
shows a four cycle
gasoline engine
Requires special
software to create
animated GIFs
File size 369 kb
Pictures / Graphics
Joint Picture Experts Group (JPEG)
JPEG uses complex mathematical compression
Reduces file size up to ten times that of GIF
Causes lossy compression
Supports True Color - 24 bit color
JPEG is great for photographs
Used on websites
Pictures / Graphics
Note
If the same JPEG image is re-edited, then the image can
degrade
If you have photos that are never edited, then leave them
in JPEG
If you re-edit the same photographs, then keep photo in
another format
○ PNG is good; file compression
○ BMP is okay if you have the space; no compression
Pictures / Graphics
Picture is 858x643
True color, 32 bit or 4
bytes
Bitmap = 2.2 MB
I converted this to BMP
and it was 2.1 MB
Tuzla, Bosnia
Pictures / Graphics
JPEG (20%) – very small
file size; 34 k
JPEG (95%) – medium
size; 212 k
Pictures / Graphics
Portable Network Graphics (PNG)
Uses loseless data compression
Uses 24-bit or 32-bit color
Can be used for webpages
Note: 32-bit color is RBGA
○ A is for alpha
○ Alpha allows translucent pictures
○ 50% alpha – can see images behind the picture
Windows Aero effects
Pictures / Graphics
Creating digital pictures
Scanning – digitizing an image using a
scanner
Digital cameras
Paint programs
Screen capture – use prtsc to capture a
screen
Pictures / Graphics
Software
Create pictures by hand
Microsoft Paint – comes with Windows
Paint,net - free
Enhance photographs
Microsoft Picture Editor
Google Picasso
Paint.net
Professional Software
Adobe Photoshop
Adobe Illustrator
Adobe Pagemaker
Pictures / Graphics
Conclusion
For websites
○ JPEG
○ GIF
○ PNG
○ Cannot use BMP or TIFF; too large
Pictures / Graphics
Conclusion
No compression
○ BMP
○ TIFF
Lossless compression
○ GIF
○ PNG
Lossy compression
○ JPEG
Audio / Sound
Data is processed in two ways: analog or
digital
People generally process analog data that
is continuous wave patterns.
Everything we see and hear is transmitted
to our eyes and ears as light and sound
waves.
We are equipped with analog receptors
A computer is digital
Two discrete states: on (or 1) and off (or 0).
Audio / Sound
Computers:
Analog to digital
converters
Convert analog to digital
○ Microphone
Digital to analog
converters
Convert digital to analog
○ CD, MP3, etc.
Analog and digital signals
Audio / Sound
Sound cards and Modems are digitalto-analog and analog-to-digital signal
converters
The Wave file (.wav) – used in PCs.
Windows systems sounds
○ Start up sound
○ Many game sounds
Wave files do not use compression
Files are quite large
Audio / Sound
Wave file is created by
Sampling sound – convertor samples the sound so many
times per second
CD quality is 44,100 samples per second
Less sampling is lower quality
Sound information is stored as bits
Commonly 8, 16, or 32 bit sound file
Sampling – how often a sound file is read
Bitrate – how much information is stored per second
Includes magnitude
Includes how often sound is sampled
Audio / Sound
Audio / Sound
MP3 (MPEG-1 Audio Layer 3)
MP3 compresses sound information
Uses lossy compression
Some information is lost
Example: 128 kbits per second
Reduces the file size of CD sound quality by 11
times
Good for webpages, because file sizes are
small
Note – many audio sound formats exist;
usually for movie files
Audio / Sound
Audio Software
Audio Editing Software lets users modify
audio clips and produce studio quality
sound tracks.
Contains equalizers, controls, etc to modify clips
Rippers – converts audio to different
formats
Windows 7 contains a music CD to MP3
ripper
Videos
More complex
Has RGB color and sound
RGB is Red-Green-Blue
Video has three colors and a sound
Stream – picture and sound change
over time
Requires much more information
Videos
Frame – the dimensions of a video in
pixels
Width x height
Example: 320x120
Each picture has color
24-bit color
Picture changes each second
Called bit rate
Bit rate 25 frames per second
Videos
Our video is one hour (or 3600 seconds)
File size = (frame)(color)(bit rate)(time)
= 320*120*24*25*3600 = 82 Giga bits
= 10.4 GB
Video files are always compressed
Most use lossy compression
○ Use compression to reduce size of the image
of a frame
○ Use compression to reduce the bit rate
Videos
Frame – dimensions of the video
Small videos can be blown up
Bit rate
Important for video quality
The higher the bit rate, the higher the quality
Videos – fast motion requires a higher bit
rate
Example – vastly simplified
Videos
An example of a video compression
Uses three frames
I-frame: The true picture
P-frame: predict which pixels change
B-frame: uses difference between the next
frame and previous frame
Videos
Compressor-decompressor (CODEC) –
a program that encodes or decodes a
streaming file
Streaming file is video and/or audio
Companies hold patents or copyrights
for their codecs
Restrictions apply
Videos
Video files
mp4
Windows (avi)
Windows (wmv)
Flash video (flv)
Matroska (mkv)
Files are containers (not codec)
A variety of codecs are used which are in
the file
MPEG2 is a codec
○ Used for DVDs
Videos
Some codecs are open source
Windows pays for the rights
Some codecs play in MediaPlayer
Users either use
K-lite – a windows program that contains most
codecs
VLC Player – media player that contains most
codecs
Software may be illegal in the United States
Videos
Linux is free
They do not pay for rights to use codecs
Installers have to manually install codecs
Most distributions want to be legal,
especially for businesses
Distribution is a particular Linux operating
system
Most do not come with codecs
Forums teach people how to install codecs
Videos
Ubuntu – install codes as software update
Manually install DVD codec via terminal
Businesses and companies can get into trouble
installing codecs without paying for them
England
Linux Mint – comes with all codecs
including DVD
France
Videos
Video editing software - users can modify a
segment of a video, called a clip.
Users can
Reorder sequence of clips
Reduce length of clip
Add special effects to clips
Add extra tracks to clip (eg. Sound, text captions)
Video Editing Software usually includes audio
editing capabilities.
Videos
Video editing – requires a very fast
computer
Expensive program
VirtualDub.org – free video editing
○ Powerful filters to clean video
○ Had trouble encoding videos
○ Files were much bigger
Videos
DVD ripping – the process of converting a
DVD into a regular video file
Converting may or may not be illegal in the U.S.
Software may or not be illegal in the U.S.
Windows – most programs were terrible
Linux – AcidRip
○ Free simple program
○ Majority of the time produced good quality videos
with good file sizes
○ Linux tends to be faster than Windows