2. Session 4 LIS 7008 Information Technologies Multimedia LSU/SLIS

3. Agenda HW2 Quiz Images Video Audio Streaming SMILe

4. 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

5. 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.

6. 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

7. A lighthouse picture

8. Specify color Additive colors and subtractive colors. –Primary colors: RGB: produce secondary colors –http://en.wikipedia.org/wiki/Primary_colorhttp://en.wikipedia.org/wiki/Primary_color Red+Green+Blue = White –Subtractive colors: MCY: absorb colors. –http://en.wikipedia.org/wiki/Subtractive_colorhttp://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.

9. 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

10. Look closely

11. Georges Seurat, A Sunday Afternoon on the Island of La Grande Jatte Nothing new (color the pixels)

12. 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

13. 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

14. 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.

15. 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

16. 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

17. 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 encoding Sheep go baaaaaaaaaa and cows go moooooooooo → Sheep go ba and cows go mo

18. 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 1Blue 75% 75x1= 75 vs. 75x2=150 01White 20% 20x2= 40 vs. 20x2= 40 001Red 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.)

19. 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

20. Variable Compression Rate in JPEG 37 KB (20% rate)4 KB (95% rate)

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

22. 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

23. 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.

24. Hands-On Exercise: Convert Between Formats Download and save two images –http://www.csc.lsu.edu/~wuyj/Teaching/7008/fa14/Images/image1.jpghttp://www.csc.lsu.edu/~wuyj/Teaching/7008/fa14/Images/image1.jpg –http://www.csc.lsu.edu/~wuyj/Teaching/7008/fa14/Images/image2.gifhttp://www.csc.lsu.edu/~wuyj/Teaching/7008/fa14/Images/image2.gif Use Microsoft Paint (on Windows: All Programs  Accessories  Paint) to convert each to the other format, and compare quality and the file size –Observe the difference –Why the difference?

25. 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

26. 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!

27. 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?

28. MPEG Encoding FrameTypes: I1I1 B1B1 B2B2 B3B3 P1P1 B4B4 B5B5 B6B6 P2P2 B7B7 B8B8 B9B9 I2I2 IIntra (JPEG)Encode complete image, similar to JPEG PForward PredictedMotion relative to previous I and P’s BBackward PredictedMotion relative to previous & future I’s & P’s

29. MPEG1 Frame Reconstruction I1I1 P1P1 P2P2 I2I2 updates I 1 +P 1 I 1 +P 1 +P 2 I frames provide complete image P frames provide series of updates to most recent I frame What if drop an I frame? Bad!

30. Frame Reconstruction I1I1 I2I2 I 1 +P 1 I 1 +P 1 +P 2 B1B1 B2B2 B3B3 B4B4 B5B5 B6B6 B7B7 B8B8 B9B9 Interpolations B frames interpolate between frames represented by I’s & P’s

31. 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=zESbrwRvMyMhttp://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 http://www.youtube.com/watch?v=BX7Ar3Z-oTo Sampler

32. 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.htmhttp://www.tlc-direct.co.uk/Technical/Sounds/Decibles.htm

33. Temporal Masking If 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

34. 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

35. 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 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.

36. 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

37. Adding Video to PowerPoint Insert  Movies and Sounds –Movies from file (a.mpg file) Decide whether you want “autostart” –If not, it starts when you click on it

38. 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)

39. 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 Web Browser Media Player Web Server

40. Streaming Browser gets a portion of media file over HTTP –Launches media player to interpret that media file Media player contacts streaming server Web Browser Media Player Web Server Streaming Server buffering Can be downloaded and installed

41. 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

42. 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

43. 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

44. 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

45. 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)

46. SMILe Follows W3C standard –Player-specific extensions are common –Real Player implements SMIL (or SMILe) It is XML, with a structure similar to HTML …

47. Elements in SMIL Window controls (in ) –Controlling layout:, Timeline controls (in ) –Sequence control:,, –Timing control:,, Content types (in ) –,,,

48. 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.

49. SMIL Example <region id="AnimChannel1" title="AnimChannel1" left="0" top="0" height="265" width="280" fit="hidden"/> <animation src="otscompfin.swf" id="Animation" region="AnimChannel1" title="Animation" fill="freeze"/> Slide from http://www.umiacs.umd.edu/~jimmylin/LBSC690-2007-Spring/content.html (Session 5) Synchronizing audio, animation, and text.

50. 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

51. Discussion Point: When is Lossless Compression Important? For images? For text? For sound? For video? Please Come to Moodle to discuss.