Telecommunications Networking IInformation and SignalsCapturing SoundSlide 4Capturing Sound (cont’d)Slide 6Representing SpeechRepresenting Speech (cont’d)Slide 9Slide 10Representing AudioSlide 12Slide 13Slide 14Character Mapped ImagesRepresenting ImagesScanned ImagesSlide 18Bit-mapped ImagesBit Mapped Image ExampleSlide 21Transform Image RepresentationTransformsVideoVideo (continued)InterlacingSlide 27Slide 28NTSC VideoVideo Compression CodingCopyright 1998, S.D. Personick. All Rights Reserved 1Telecommunications Networking ILectures 2 & 3Representing Information as a SignalCopyright 1998, S.D. Personick. All Rights Reserved 2 Information and Signals•Sound: speech, audio•Images: character mapped, scanned, bit mapped, transform representations•Video: frame-by-frame, compressionCopyright 1998, S.D. Personick. All Rights Reserved 3Capturing SoundCopyright 1998, S.D. Personick. All Rights Reserved 4Capturing Sound•Sound takes the physical form of an acoustic wave... variations in pressure vs time and space... that travels through a compressible physical medium such as air•A microphone (transducer) converts locally received pressure variations into a varying voltage/current that represents the soundCopyright 1998, S.D. Personick. All Rights Reserved 5Capturing Sound (cont’d)•The varying voltage waveform that represents the captured sound is communicated to another location using one of many possible communication system technologies •The received varying voltage waveform is not an exact replica of the transmitted voltage waveformCopyright 1998, S.D. Personick. All Rights Reserved 6Capturing Sound (cont’d)•The received varying voltage waveform is used to “drive” a speaker (transducer) which produces a new acoustic wave (sound) that is perceived as an approximation of the original sound•Does the reproduced acoustic wave “sound” like the original acoustic wave? The answer depends upon the applicationCopyright 1998, S.D. Personick. All Rights Reserved 7Representing SpeechCopyright 1998, S.D. Personick. All Rights Reserved 8Representing Speech (cont’d)•Speech is one of the most important analog signals•Representation qualities include:-Intelligibility: Can I understand what you are saying? Can I build a machine that responds properly to what you are saying?-Naturalness: Does it sound like face-to-face communication? -Comfort: Is it pleasant to listen to?Copyright 1998, S.D. Personick. All Rights Reserved 9Representing Speech (cont’d)•Traditional telephone quality speech: 3 kHz high frequency cutoff small amounts of noise and echo•AM radio quality speech: 5 kHz high frequency cutoff varying amounts of noise and interference•FM radio, TV, other high quality speech: 10 kHz+ high frequency cutoffCopyright 1998, S.D. Personick. All Rights Reserved 10Representing Speech (cont’d)•Compressed speech-Uses digital signal processing to remove redundancies in the original speech signal. -This typically impacts on the naturalness and comfort associated with the speech signal produced at the receiving end of a link, but (hopefully) still provides intelligibilityCopyright 1998, S.D. Personick. All Rights Reserved 11Representing Audio•Audio signals, like music, typically demand a high accuracy of representation to meet users’ expectations >10 kHz high frequency cutoff <100 Hz low frequency cutoff low noise and distortion•A typical audio system specification includes a 20-20,000 Hz “frequency response”Copyright 1998, S.D. Personick. All Rights Reserved 12Capturing Analog Images•Use a camera or scanner (transducer) to produce a signal or a set of data which represents the image•Communicate this signal or data to a receiving location•Use the received signal or data, which is not necessarily identical to the transmitted signal or data, to reconstruct a new imageCopyright 1998, S.D. Personick. All Rights Reserved 13Representing ImagesCopyright 1998, S.D. Personick. All Rights Reserved 14Representing Images•Character-mapped Images-The image consists of a number of “characters” or objects selected from a data base-To capture the image, one must obtain or derive its description in the form of: data that represents each character or object used; data representing its location on the image; data describing colors used, fonts, object sizes, object and character overlaps, etc.-The set of data is communicated to the receiving location and used to recreate the imageCopyright 1998, S.D. Personick. All Rights Reserved 15Character Mapped ImagesFigure 1Figure 1Copyright 1998, S.D. Personick. All Rights Reserved 16Representing Images•Scanned images-Scan the image …e.g., left-to-right, and top-to-bottom-Represent the scanned brightness and color (e.g., red, green, and blue color brightness) by a set of signals which change in time as the scanning point moves-Communicate these signals to the receiving location; and use them to “paint” a new image with a complementary scanning processCopyright 1998, S.D. Personick. All Rights Reserved 17Scanned ImagesScanCopyright 1998, S.D. Personick. All Rights Reserved 18Representing Images•Bit-mapped Images -Divide the image into an n x m array of “pixels” (e.g., 800 x 600)-Represent the brightness and color of each pixel (e.g., red, green, and blue color intensities) by a set of numbers-Communicate these numbers to the receiving end, and use them to recreate the imageCopyright 1998, S.D. Personick. All Rights Reserved 19Bit-mapped ImagesCopyright 1998, S.D. Personick. All Rights Reserved 20Bit Mapped Image ExampleAn image contains 800 x 600 = 480,000 pixels3 bytes of information are required to represent the intensity and color of each pixelTo store this image you would require 480,000 x 3 bytes of memoryTo transmit this image in 1 second, you must transmit at a data rate of 480,000 (pixels) x 3 (bytes per pixel) x 8 (bits per byte) bits per secondCopyright 1998, S.D. Personick. All Rights Reserved 21Representing Images•Transforms-Example: Hadamard transform (for a single color) What is the average brightness across the entire image? What is the difference in the brightness of the upper left quadrant vs the upper right quadrant? Upper left vs lower left? Upper right vs lower right? Etc., …Copyright 1998, S.D. Personick. All Rights Reserved 22Transform Image RepresentationCopyright 1998, S.D. Personick. All Rights Reserved 23Transforms•Creative use of transform coding