Session 4 LIS 7008 Information Technologies Multimedia LSU/SLIS.

Session 4

LIS 7008

Information Technologies

Multimedia

LSU/SLIS

Agenda

• HW2

• Quiz

• Images

• Video

• Audio

• Streaming

• SMILe

HW2

• Good work– Your webpage is well rendered in a browser.

• Should use paragraphs

– Findings based on each approach are addressed.– A correct (or partially correct) conclusion is drawn by

pulling together all the findings. An attempt to draw a conclusion of who owns the website is obviously present.

– Some good Examples (although not perfect):• Distributed on Moodle

Quiz• Open book (text, slides, Internet)• Posted on Moodle• Scope: covers Session 1-3

– Readings, slides, homework

• Purposes– Measure your learning progress– Preview what the midterm exam will be like

• Time: 20 minutes from opening to closing• Due:

– See instructions on Moodle– Read the instructions BEFORE opening the quiz!!!– You can download the quiz any time, but do not open it

until you are ready to take it.

The Gullibility of Human Senses

• Three simple tricks for producing– Images

– Video

– Audio

• But how do you move the bits around fast enough?– Remove redundancy – apply compression!

– Throw away stuff that doesn’t matter (b/c eyes cannot see)

• Synchronizing different media to create multimedia

A lighthouse picture

Specify color• Additive colors and subtractive colors.

– Primary colors: RGB: produce secondary colors– http://en.wikipedia.org/wiki/Primary_color

• Red+Green+Blue = White

– Subtractive colors: MCY: absorb colors. – http://en.wikipedia.org/wiki/Subtractive_color

• Magenta+Cyan+Yellow = Black

• Guess the size of that picture on the previous slide?– Typical projector/monitor: 1024x768 = 786,432 pixels.

• Horizontal dimension: 1024 pixels, vertical dimension: 768 pixels

RGB (Red, Green, Blue) are primary colors, which can be combined to produce secondary colors. RGB are used by computer monitors/screens. MCY (Magenta, Cyan, Yellow) are subtractive colors. MCY + K (black) are used by colorful printers.

Basic Image Coding• An image = Collection of picture elements (pixels)

– Each pixel has a “color”• Black/white image: each pixel has 1 color: use 1 bit (either 1 or 0) to

code a color • Grayscale image: each pixel has 1 color: use 8 bits to code a color• Colorful image: each pixel has 3 colors - RGB, each color is coded

with 8 bits (or 1 byte), so each pixel has 24 bits (or 3 bytes, 1 byte=8 bits)

– So, 3 bytes per pixel for colorful images

• Screen– Typical projector resolution: 1024x768 pixels– A 1024x768 image requires 2.4 MB (=1024x768x3)

• So a picture is worth 400,000 words (1 word = 6 bytes)!

• Compression: do not use 3 bytes/pixel– remove some unimportant colors that human eyes cannot see

Look closely

Georges Seurat, A Sunday Afternoon on the Island of La Grande Jatte

Nothing new (color the pixels)

Visual Perception

• Closely spaced dots appear solid– But irregularities in diagonal lines can stand out

• Any color can be produced from just three– Red, Blue and Green: “additive” primary colors

• High frame rates produce apparent motion– Smooth motion picture movie requires about 24

frames/second

• Visual acuity varies markedly across features– Discontinuities of features easily seen, absolute difference

is less crucial

Monitor Characteristics• Technology

– Cathode-Ray Tube (CRT): RGB 3 guns– Flat panel (LCD liquid crystal)

• Size (15, 17, 19, 21 inch)– Measured diagonally– For CRT, key figure is “viewable area”

• Resolution– 640x480 (VGR video card), 800x600 (old laptop), 1024x768 (popular

now or near future), 1280x1024…

• Layout (three dot pixel, by lines)• Dot pitch (0.26mm, 0.28mm)

– Distance between pixels on a monitor screen

• Color Refresh rate (60, 72, 80 Hz)– light flick rate: 60 Hz

Some Questions

• How many images can a 1 GB flash card store?– But mine holds about 500 images. How?

• How long will it take to send an image at 128KB/s?– But my image-intensive Web page loads faster than that. How?

You should be able to answer these questions by the end of this session; otherwise, come to Moodle to discuss.

Compression• Goal: Send the same information using fewer bits• Technology originally developed for fax transmission

– Send high quality documents in short calls

• Two types of compression:– Lossless compression: can reconstruct the original image exactly after decompression

• File size reduced, but no information is lost

– Lossy: can’t reconstruct the original image after compression, but the compressed image looks the same as the original

• Two compression strategies:– Reduce redundancy– Throw away stuff that doesn’t matter (because human eyes/ears cannot see/hear)

• Whether to compress? Depends on:– Computer speed– Network transmission speed

Palette Selection• Opportunity:

– No picture uses all 16 million colors

– Human eye does not see small differences between colors

• Approach: – Select a palette of 256 colors– Indicate which palette entry to use for each pixel– Look up each color in the palette

……

“The rain in Spain falls mainly in the plain”

→ [*=ain,^=in] “The r* ^ Sp* falls m*ly ^ the pl*”

1 pixel = 3 colors

Compression Using Run-Length Encoding (RLE)

• Pixels are organized into lines• Opportunity:

– Large regions of a single color are common

– Most pixels are the same as the one before• As you can see from the lighthouse image

• Approach:– Record # of consecutive pixels for each color

• An example of lossless encodingSheep go baaaaaaaaaa and cows go moooooooooo→ Sheep go ba<10> and cows go mo<10>

Graphic Interchange Format (GIF)• Do palette selection first , then do lossless compression• Opportunity:

– Common colors are sent more often

• Approach: Huffman Encoding– Use fewer bits to represent common colors– Encoding Color % color in image #Bits vs. #Bits if using regular 2 bits/color

• 1 Blue 75% 75x1= 75 vs. 75x2=150• 01 White 20% 20x2= 40 vs. 20x2= 40• 001 Red 5% 5x3= 15 vs. 5x2= 10 Total: 130 bits vs. 200 bits

What is 10100101? Can you interpret the colors? If you have no idea, come to Moodle to discuss this.

PNG (Portable Network Graphics): replacement for GIF (PNG has no patent restrictions, GIF is owned by Compuserv.)

Joint Photographic Experts Group (JPEG)

• Opportunity:– Eye sees sharp lines better than subtle shading– Eye more sensitive to small changes in brightness than in color

• Approach:– Retain detail only for the most important parts (by human eyes)– Approximate changes in image with mathematical curves: accomplished

with Discrete Cosine Transform• Allows user-selectable fidelity (allow users to select compression rate)• Efficiently captures smooth transitions and shading• Not as good at capturing sharp edges

• Results:– Typical compression rate is 20:1

Variable Compression Rate in JPEG

37 KB (20% rate) 4 KB (95% rate)

Vector Graphics

Line drawing using math functions. Re-scalable without loss of resolution

Raseter vs. Vector Graphics

• Raster images (“bitmap graphics”)– Actually describe the contents of the image– Good for natural scenes

• Vector images– Mathematically describe how to draw the image– Rescalable without loss of resolution

Discussion Point:Selecting an Image Format

• Should I use GIF, JPEG, or vector graphics for …• Color photos?• Scanned black & white text? (Transcript, itinerary)• Line drawings?

These are important practical questions to archivists and digital librarians. Please come to Moodle to discuss this.

Hands-On Exercise: Convert Between Formats

• Download and save two images– http://www.csc.lsu.edu/~wuyj/Teaching/7008/fa14/Images/image1.jpg

– http://www.csc.lsu.edu/~wuyj/Teaching/7008/fa14/Images/image2.gif

• Use Microsoft Paint (on Windows: All Programs AccessoriesPaint) to convert each to the other format, and compare quality and the file size– Observe the difference

– Why the difference?

Basic Video Coding

• Display a sequence of images– Fast enough for smooth motion and no flicker– Motion picture film: smooth show at 24 pictures/second

• NTSC Video– National Television System Committee (analog TV system)– 60 “interlaced” half-frames/second, 512x486 pixel images

• HDTV– 30 “progressive” full-frames/second, 1280x720 pixel images

Video Data Rates• “NTSC” Quality Computer Display

– 640 x 480 pixel image– 3 bytes per pixel (red, green, blue)– 30 Frames per second

• Bandwidth requirement – 26.4 MB/second– That exceeds the bandwidth of most disk drives!

• Storage– CD-ROM would hold 25 seconds worth of NTSC video

• What is the capacity of CD-ROM? 650-900MB

– 30 minutes would require 46.3 GB– About 100GB/hr: too big!– Compression! Multimedia is big! Compress harder!

Video Compression• Opportunity:

– One frame looks very much like the next

• Approach: – Record only the pixels that change (trace the difference)

• Standards:– MPEG-1: for Web video (download then play)

– MPEG-2: for HDTV and DVD (commercial quality)

– MPEG-4: for Web video (streaming)– Next?

MPEG Encoding

FrameTypes:

• • • • • •

I1 B1 B2 B3 P1 B4 B5 B6 P2 B7 B8 B9 I2

I Intra (JPEG) Encode complete image, similar to JPEGP Forward Predicted Motion relative to previous I and P’sB Backward Predicted Motion relative to previous & future I’s & P’s

MPEG1 Frame Reconstruction

• • •• • •

I1

P1 P2

I2

updates

I1+P1 I1+P1+P2

I frames provide complete image

P frames provide series of updates to most recent I frame

What if drop an I frame? Bad!

Frame Reconstruction

• • •• • •

I1 I2I1+P1 I1+P1+P2

B1 B2 B3 B4 B5 B6 B7 B8 B9

Interpolations

B frames interpolate between frames represented by I’s & P’s

Basic Audio Encoding (Digitizing)• Sample at twice the highest frequency (22KHz)

– 8 or 16 bits per sample, sample rate: X samples/second

• Speech (0-4 kHz) requires 8 kB/s – Standard telephone channel (1-byte samples)

• Music (0-22 kHz) requires 172 kB/s (uncompressed)– Standard for CD-quality audio (2-byte samples)

• Pitch range: – http://www.youtube.com/watch?v=zESbrwRvMyM– Caution! Extremely high pitch: the following can hurt your

ears! Stop playing when feel uncomfortable! http://www.youtube.com/watch?v=BX7Ar3Z-oTo

Sampler

Music Compression• Opportunity:

– The human ear cannot hear all frequencies at once

• Approach:– Don’t represent “masked” frequencies

• Standard: MPEG-1 Layer 3 (.mp3)

loudness

frequency

Loudness: http://www.tlc-direct.co.uk/Technical/Sounds/Decibles.htm

Temporal MaskingIf we hear a loud sound, then it stops, it takes a while until we can hear a soft tone at about the same frequency.

“Psychoacoustic compression”– Eliminate sounds below threshold of hearing – Eliminate sounds that are frequency masked – Eliminate sounds that are temporally masked – Eliminate stereo information for low frequencies

Compact Disk (CD) Recording• Parameters

– 44,100 samples per second• Sufficient for frequency response of 22KHz

– Each sample takes 16 bits• 48 dB (decibel) range

– Two independent channels: stereo sound• Dolby surround-sound uses tricks to pack 5 sound channels + subwoofer effects

• Bit Rate– 44.1K samples/sec x 2 channels x 2 bytes/sample = 172 KB/sec

• Typical Capacity– 74 Minutes maximum playing time– 747 MB total

Speech Compression

• Opportunity:– Human voices vary in predictable ways

• Approach:– Predict what’s next, then send only any corrections/changes

• Standards:– Real audio can code speech in 6.5 kb/sec

• Demo at http://www.data-compression.com/speech.html– Scroll down to near the bottom: “VII. Demonstration”– Listen to the original and LPC10U (2400bps) to understand

speech effect with different compression rate.

Narrated PowerPoint

• Create your slides using PowerPoint

• Slide Show Record Narration– Set microphone level

• Record the narration– Slide transitions are automatically captured

• Narration plays automatically when displayed– Synchronized between slide flipping and narration

Adding Video to PowerPoint

• InsertMovies and Sounds– Movies from file (a .mpg file)

• Decide whether you want “autostart”– If not, it starts when you click on it

The “Last Mile”: bandwidth to your desk

• Traditional modems– “56” kb/sec modems really move data at ~3 kB/sec– Maximumly 56 kb/s theoretically

• Digital Subscriber Lines (DSL)– 384 kb/sec downloads (~38 kB/sec)– 128 kb/sec uploads (~12 kB/sec)

• Cable modems– 10 Mb/sec downloads (~1 MB/sec)– 256 kb/sec uploads (~25kB/sec)

Multimedia on a Web Server

• Object stored in a file• File transferred as an HTTP object:

– Received entirely at the client– Passed to media player for play– This seems stupid because downloading is slow

WebBrowser

MediaPlayer

WebServer

Streaming

• Browser gets a portion of media file over HTTP– Launches media player to interpret that media file

• Media player contacts streaming server

WebBrowser

MediaPlayer

WebServer

StreamingServerbuffering Can be downloaded

and installed

Streaming Audio and Video

• Begin to play after only a portion received • Buffer provides time to recover lost packets• Interrupts replay when “rebuffering”• Data not saved to hard drive.

Media Sever

Internet

Buffer

Lost Packets (IP Phone)

• Network loss – Packets completely lost (e.g., due to collisions)

• Delay loss– Packets arrives too late for playout

• Due to: queueing; sender and receiver processing delays• IP Phone: Typical maximum tolerable delay: 400 ms

• Loss tolerance– 1% to 10% packet loss may be tolerable

• Some encoding schemes are more tolerant than others

Multiple Client Rates

Q: how to handle different client receiving rate capabilities?

– 28.8 Kbps dialup

– 128 Kbps to 3 Mbps (residential DSL service)

– 100Mbps Ethernet

A: server stores, transmits multiple copies of video, encoded at different rates, for different users

1.5 Mbps encoding

28.8 Kbps encoding

Synchronizing Multiple Media

• Scripting Languages for synchronizing multiple media:– Synchronized Multimedia Integration Language (SMIL)

• Custom applications for this:– Macromedia Flash

• Content representation standards for this:– MPEG 4

SMIL

• Synchronized Multimedia Integration Language

• Integration of multimedia with text, audio, video

• Supported in RealPlayer

Slide from http://www.umiacs.umd.edu/~jimmylin/LBSC690-2007-Spring/content.html (Session 5)

SMILe

• Follows W3C standard– Player-specific extensions are common

– Real Player implements SMIL (or SMILe)

• It is XML, with a structure similar to HTML<smil>

<head> … </head>

<body> … </body>

</smil>

Elements in SMIL

• Window controls (in <head>)– Controlling layout: <region>, <root-layout>

• Timeline controls (in <body>)– Sequence control: <seq>, <excl>, <par>

– Timing control: <begin>, <end>, <dur>

• Content types (in <body>)– <audio>, <video>, <img>, <ref>

SMIL Examples

• Implemented in RealOne Player• You need to install RealOne Player (or Real Player) to run the following

examples

• Demo: http://www.csc.lsu.edu/~wuyj/Teaching/7008/fa14/SMIL-demo/index.htm

There are 3 sets of executable and text files, at least run/read the last set:

– First, run the smildemo.smil (executable)– Then, view smildemo.smil (xml) file

• Question: can you make sense of smildemo.smil?

– You are welcome to play with the first 2 sets.

SMIL Example<smil> <head> <meta name="title" content="Online Teaching Services promo" /> <meta name="author" content="Jay Moonah, CAT" /> <layout type="text/smil-basic-layout"> <root-layout width="280" height="316" background-color="white"/> <region id="AnimChannel1" title="AnimChannel1" left="0" top="0" height="265" width="280" fit="hidden"/> </layout></head><body> <par title="Online Teaching Services promo" author="Jay Moonah, CAT" > <audio src="final.rm" id="Soundtrack" title="Soundtrack"/> <animation src="otscompfin.swf" id="Animation" region="AnimChannel1" title="Animation" fill="freeze"/> <text src="cc.rt" id="caption" region="cc" title="cc" fill="freeze"/> </par></body></smil>

Slide from http://www.umiacs.umd.edu/~jimmylin/LBSC690-2007-Spring/content.html (Session 5)

Synchronizing audio, animation, and text.

From Media to Multimedia…

• Tricking the human senses:– Blending pixels into a seamless image– Rapidly cycling through images to create motion (video)– Sampling analog waveforms to create digital recordings

• Lots of information required to encode images, movies, and sounds– Result: you get a bulky digital file, not handy for online

distribution and access.– The Key is compression!

• Synchronization of different media sources leads to multimedia applications

Discussion Point: When is Lossless Compression Important?

• For images?

• For text?

• For sound?

• For video?

Please Come to Moodle to discuss.