Presentation on theme: "Introduction to Digital Libraries Digital Data (2)"— Presentation transcript:
Introduction to Digital Libraries Digital Data (2)
Why digitize audio? 100 years of data on a Wide variety of unstable media Wide variety of playback mechanism
Analog to Digital Recording Chain ADC Continuously varying electrical energy is an analog of the sound pressure wave. Microphone converts acoustic to electrical energy. Its a transducer. ADC (Analog to Digital Converter) converts analog to digital electrical signal. Digital signal transmits binary numbers. DAC (Digital to Analog Converter) converts digital signal in computer to analog for your headphones.
Wire Recordings Time Frame – The 1930s and '40s Technology – Magnetized wire Use – Field correspondents used portable versions in World War Two. Their repair kits included extra wire, grips and a soldering iron.
Acetate tape Time Frame – Introduced in the early 1950s – Widely in use during 1960s Technology – Magnetic signal on acetate tape – curls, shrinks and loses mass over time. – Does not stretch or deform but breaks easily Uses – Home recording – Archiving older recording – Broadcast radio recording
Polyester tape Time Frame – 1970s Technology – Magnetic signal on polyester tape – Excellent sound fidelity – Polyester tape deforms (stretches) easily – Restored by gentle heating in the so- called "easy bake" oven Uses – Home recording – Archiving older recording – Broadcast radio recording
Digital Audio Basics Bit Depth Bit Rate Sampling Rate Frequency Equalization Sound Scrubbing
Bit Depth In digital audio, bit depth describes the potential accuracy of a particular piece of hardware or software that processes audio data.
Binary representation 16 bits can represent 65,536 possible speaker cone or microphone diaphragm positions (possible levels). This is enough for very high quality audio The current maximum resolution used is 24 bits. This equates to 16,777,216 positions. nobody has manufactured a converter accurate to more than 24 bits.
Bit Rate In general, describes the data transfer rate In digital audio, describes the kilobits per second (kbs) in your file Standard MP3 file has 128 kbs Very high quality audio has 320 kbs
Frequency The number of vibrations in a sound wave per unit of time (Spectrum of sound). Measured in hertz (Hz)
Equalization In audio processing, equalization (EQ) is the process of modifying the frequency envelope of a sound. The frequencies are controlled by bands (ranges of frequencies) Controls the overall quality of the sound
Sampling Rate The number of times per second the program converting the analog to digital records the sound. CD sampling rate is 44.1 kHz Higher rates kHz, 96 kHz, and 192 kHz. Telephone speech is sampled at 8 kHz.
Synthesis Audio synthesis is the art and science of generating audio signals. A synthesiser is an electronic instrument capable of producing musical sounds
Audio Formats Emerging Archival Standards – AIFF – Audio Interchange File FormatAudio Interchange File Format – BWF – Broadcast Wave FormatBroadcast Wave Format Delivery formats – Real – proprietary streaming protocol – MP3 – the standard – MPEG4 – multimedia streaming standard
Data GIS and Maps
GIS Defined In the strictest sense, a GIS is a computer system capable of assembling, storing, manipulating, and displaying geographically referenced information, i.e. data identified according to their locations. Practitioners also regard the total GIS as including operating personnel and the data that go into the system.
Data for a GIS comes in three basic forms: Spatial data -What Maps are Made Of Spatial data, made up of points, lines, and areas, is at the heart of every GIS. Spatial data forms the locations and shapes of map features such as buildings, streets, or cities. Tabular dataadding information to maps Tabular data is information describing a map feature. For example, a map of customer locations may be linked to demographic information about those customers. Image datausing images to build maps Image data includes such diverse elements as satellite images, aerial photographs, and scanned
Is it 'spatial' or 'geographic'? 'geographic' has to do with the Earth – its two-dimensional surface – its three-dimensional atmosphere, oceans, sub- surface 'spatial' has to do with any multi-dimensional frame – medical images are referenced to the human body – engineering drawings are referenced to a mechanical object – architectural drawings are referenced to a building
Enter GIS A computer-based tool for holding, displaying, and manipulating huge amounts of spatial data.
GIS Basics Points Lines Polygons Layers Features Attributes Basic Set math – Unions – Intersections
Different Maps for Different Functions U.S. Geological Survey (USGS) digital line graph (DLG) data of roads. USGS DLG of rivers. USGS DLG of contour lines (hypsography). USGS digital elevation (DEM).
GIS Basics Builds relationships between data by geographic location x, y and z coordinates Latitude, Longitude ZIP code Highway marker Other control identifiers
Global Positioning Systems GPS is a constellation of 27 satellites (31+/- Satellites orbiting the earth) orbiting the earth which send signals to GPS receiver on earth. The receiver measures the travel time of signals transmitted from at least three satellites. The receiver calculates its distance from the satellite.
H OW T O G ET A P OSITION Need signal from at least four SVs for 3D position One SV provides a time reference Distance to three remaining SVs is determined by observing the GPS signal travel time from SV to the receiver With three known points, and distances to each, we can determine the GPS receivers position (trilateration)
Real World Vector Representation Raster Representation Concept of Vector and Raster line polygon point
Representing Data using Raster Model area is covered by grid with (usually) equal-sized cells location of each cell calculated from origin of grid: – two down, three over cells often called pixels (picture elements); raster data often called image data attributes are recorded by assigning each cell a single value based on the majority feature (attribute) in the cell, such as land use type. easy to do overlays/analyses, just by combining corresponding cell values: yield= rainfall + fertilizer (why raster is faster, at least for some things) simple data structure: – directly store each layer as a single table (basically, each is analagous to a spreadsheet) – computer data base management system not required (although many raster GIS systems incorporate them) corn wheat fruit clover fruit oats
Raster Data Structures Runlength Compression (for single layer) Full Matrix--162 bytes ,7,2,17,3,18 1,7,2,16,3,18 1,7,2,15,3,18 1,6,2,14,3,18 1,5,3,18 1,3,3,18 Run Length (row)--44 bytes Value thru column coding. 1st number is value, 2nd is last column with that value. Now, GIS packages generally rely on commercial compression routines. Pkzip is the most common, general purpose routine. MrSid (from Lizard Technology)and ECW (from ER Mapper) are used for images. All these essentially use the same concept. Occasionally, data is still delivered to you in run-length compression, especially in remote sensing applications. This is a lossless compression, as opposed to lossy, since the original data can be exactly reproduced.
Applications Military (DoD) – civilian uses now exceed military Space Travel (NASA) Survey, Mapping & GIS Resource and Asset Management Environmental & Forestry Mining, Oil & Gas Agriculture Utilities & Construction Transportation Vehicle Security (Fleet Management) Public Safety Emergency Management, Search & Rescue Crime Prevention Timing & Synchronization (banking, telecommunications) LBS - Location Based Services (cell phones, wireless web) Solar GPS Cattle Herder (noise or electric shock) Precision Construction & Agriculture
Other Applications… Tracking Systems - Pet Collar - Teddy Bears, Backpacks - Implants… Nano GPS tracker ($200 + $45/month), panic button, for people or nativity scenes… Xega injectable GPS chip ($4,000 + $350/month) Mexico (requires additional wearable accessory) GTX Ambulator (Alzheimers GPS Shoes) (tracking and geo-fence) Garmin Astro Pet Tracker (communicates with base unit) Pet collars Web or cell connection Virtual/Geo-Fence
The Future… Does GPS make a dumber…? Bus driver follows GPS directions, ignores signs, plows into overpass… GPS directions send Mercedes downstream… Trucker drives past sign, becomes wedged in small farm lane… Driver follows GPS directions onto train tracks…
GIS Metadata FGDC – the Metadata Standard for GIS Federal Geographic Data Committee Under the auspices of the U.S. Geological Survey They refer to the standard as Content Standard for Digital Geospatial Metadata (CSDGM) Spatial Data Transfer Standard (SDTS) is for transferring digital spatial data sets between spatial data software.
Video Video comes from a camera, which records what it sees as a sequence of images Image frames comprise the video Frame rate = presentation of successive frames minimal image change between frames Frequency of frames is measured in frames per second [fps]. Sequencing of still images creates the illusion of movement > 16 fps is smooth Standards: is NTSC, 24 for movies, 25 is PAL, 60 is HDTV
ODU CS 751/851 Fall 2006 Michael L. Nelson Mechanical Television
The Video Data Firehose To play one SECOND of uncompressed 16-bit color, 640 X 480 resolution, digital video requires approximately 18 MB of storage. One minute would require about 1 GB. Without compression, digital video would not be possible with current storage technology.
Data Reduction through Scaling The easiest way to save memory is to store less, e.g. through size scaling. Original digital video standards only stored a video window of 160 X 120 pixels. A reduction of 1/16th the size of a 640 X 480 window. A 320 X 240 digital video window size is currently about standard, yielding a 4 to 1 data reduction. A further scaling application involves time instead of space. In temporal scaling the number of frames per second (fps), is reduced from 30 to 24.
Frame Compaction The individual frames (intraframe compression) is a sequence of three standard text file compression schemes. Run-length encoding (RLE), Huffman coding, and arithmetic coding. – RLE replaces sequences of identical values with the number of times the value occurs followed by the value (e.g., ==>> ). – Huffman coding replaces the most frequently occurring values|strings with the smallest codes.
Interframe Compression (MPEG style) Interframe compression takes advantage of minimal changes from one frame to the next to achieve dramatic compression. Instead of storing complete information about each frame only the difference information between frames is stored.
MPEG: Motion Picture Experts Group MPEG-1 (1992) Compression for Storage 1.5Mbps Frame-based Compression MPEG-2 (1994) Digital TV 6.0 Mbps Frame-based Compression MPEG-4 (1998) Multimedia Applications, digital TV, synthetic graphics Lower bit rate Object based compression MPEG-7 Multimedia Content Description Interface, XML-based MPEG-21 Digital identification, IP rights management
HDTV 2x horizontal and vertical resolution SDTV: 480 line, 720 pixels per line, frames per second x 16 bits/pixel = 168 Mbits/sec uncompressed HDTV: expanded to 1080 lines, 1920 pixels per line, 60 fps x 16 bits/pixel = 1990 Mbits/sec uncompressed HDTV Audio Compression is based on the Dolby AC- 3 system with sampling rate 48kHz and perceptually coded
Comparison Current TV HDTV
Original Timeline of HDTV First began in 60s at NHK, the Japan Broadcasting Corporation. In 1993, FCC suggested an alliance that could create the best possible system November 1998: HDTV transmissions begin at 27 stations in the top 10 markets November 1999: digital broadcasts in the next 20 largest markets May 2002: remaining commercial stations must convert 2003: public stations must convert to digital broadcasts 2004: stations must simulcast at least 75% of their analog programming on HDTV 2005: stations must simulcast 100% of their analog programming 2006: stations relinquish their current analog spectrum NTSC TV sets will no longer be able to pick up broadcast signals
45 Interleaver Stream Graph
46 Trellis Encoding In HDTV, the trellis encoder is a convolution encoder followed by a symbol mapper. This provides good noise immunity (somehow) HDTV encoder uses 12 trellis coders in parallel
47 Convolution Encoding Input is an m bit symbol Output is an n bit symbol m/n is the rate (HDTV uses 2/3) K is the reach: the number of output symbols that each input symbol affects (HDTV has K=3)
48 Trellis Encoding (cont.) Trellis Encoder used in HDTV ungerboeck encoder pre-coder Source: ATSC standard A53, revision b
49 Trellis Encoding (cont.) 12 Trellis Encoders Source: ATSC standard A53, revision b
Comparison (current TV)
HDTV and NTSC Specifications
MPEG-7 Data + Multimedia Content Description Scheme Description Definition Language (XML-based) Still not final, but close Does not deal with data, but meta-data transmission Description Scheme + Content Description, e.g: Table of content Still Images Summaries links etc. How does the Description data get generated? How is it used?
Mpeg-7 Examples T0:0:0:0 PT6S CNN World News World Today PT01N30F PT2S
Compression Schemes Quicktime (Apple), Video for Windows – Open architecture allowing different codecs Motion JPEG – no interframe compression Cinepak is an asymmetric codec designed for 24- bit video in a 320 X 240 window for single-speed CD-ROM drives. Compression typically takes 300 times longer than decompression. Indeo asymmetric codec (Intel). Playback can take place on a Intel 486 processor without any hardware assistance. Less efficient than Cinepak DVI Digital Video Interactive requires off-line supercomputer processing power for the compression.