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Multimedia Communications EG 371 and EE 348

Multimedia Communications EG 371 and EE 348. Dr Matthew Roach Dr.matthew.roach@googlemail.com Lecture 1 Overview. Recommended texts. F. Fluckiger, Understanding Networked Multimedia , Prentice Hall, 1995.

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Multimedia Communications EG 371 and EE 348

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  1. Multimedia CommunicationsEG 371 and EE 348 Dr Matthew Roach Dr.matthew.roach@googlemail.com Lecture 1 Overview Multimedia communications EG-371 & EE348 Dr Matt Roach

  2. Recommended texts • F. Fluckiger, Understanding Networked Multimedia, Prentice Hall, 1995. • R.A. Earnshaw and J.A. Vince, Multimedia Systems and Applications, Academic Press 1995. • J. Ozer, Video Compression for Multimedia, AP Professional, 1995. • F. Halsall Multimedia communications applications, networks, protocols and standards, Addison-Wesley, 2001. Multimedia communications EG-371 Dr Matt Roach

  3. Course • Course notes online • Read up • Make own notes • http://galilee.swan.ac.uk/ • Publications – teaching – EE371 • 10 lectures • Engineering E, 11:00 • 2 + Tutorials • Worksheets, last years exam questions Multimedia communications EG-371 Dr Matt Roach

  4. Course overview • Visual signals • Image definitions • Image formats • Video formats • image information • image compression Multimedia communications EG-371 Dr Matt Roach

  5. Overview of multimedia Multimedia communications EG-371 Dr Matt Roach

  6. What is multimedia • Media transferred over the net • Text • Formatted, unformatted • Images • Computer generated, digitised photographs • Audio • Speech, sound • Video • All of the above Multimedia communications EG-371 Dr Matt Roach

  7. Multimedia - video • Digital Video • Visual signal • Number of frames per second • A frame is a static image • Spatial resolution • Colour resolution • Acoustic signal • Sampling rate • Quantisation of the amplitude • Meta-data • Text descriptions Multimedia communications EG-371 Dr Matt Roach

  8. Digital video signals • What is a signal • Functions • Scalar • Vector • Video capture • Video storage Multimedia communications EG-371 Dr Matt Roach

  9. Fundamentals of compression • Data information • Redundancy • Compression ratio • Types of redundancy • Coding • Inter-pixel • Psyco-visual • Data compression Multimedia communications EG-371 Dr Matt Roach

  10. Fundamentals of compression • Design concerns • Trade-off • quality loss V’s c compression ratio • Measuring quality loss • Fidelity Criteria Multimedia communications EG-371 Dr Matt Roach

  11. Coding compression • Histograms • Entropy encoding • Run length encoding • Huffman encoding • Differential encoding Multimedia communications EG-371 Dr Matt Roach

  12. JPEG • Static image compression standard • Image/block preparation • Forward DCT • Quantisation • Entropy encoding • Frame building Multimedia communications EG-371 Dr Matt Roach

  13. Tutorials & Exam questions Any questions? Multimedia communications EG-371 Dr Matt Roach

  14. Signals and Functions • What is a signal • Signal = function (variable with physical meaning) • one-dimensional (e.g. dependent on time) • two-dimensional (e.g. images dependent on two co-ordinates in a plane) • three-dimensional (e.g. describing an object in space) • higher-dimensional • Scalar functions • sufficient to describe a monochromatic visual signals – black white video and sound. • Vector functions • represent colour images - three component colours Multimedia communications EG-371 Dr Matt Roach

  15. Visual Functions • image - continuous function of a number of variables • Co-ordinates x, y in a spatial plane • for image sequences - variable (time) t • Image function value = brightness at image points • other physical quantities • temperature, pressure distribution, distance from the observer • Image on the human eye retina / TV camera sensor - intrinsically 2D • 2D image using brightness points = intensity image • Mapping 3D real world -> 2D image • 2D intensity image = perspective projection of the 3D scene • information lost - transformation is not one-to-one • geometric problem - information recovery • understanding brightness info Multimedia communications EG-371 Dr Matt Roach

  16. Visual Acquisition & Manipulation • Analogue camera • frame grabber • video capture card • Digital camera / video recorder • Capture rate  30 frames / second • Human Visual system (HVS) persistence of vision • Computer, digitised image, software (example c) • f(x,y)  #define M 128 #define N 128 unsigned char f[N][M] • 2D array of size N*M • Each element contains an intensity value Multimedia communications EG-371 Dr Matt Roach

  17. Image definition • Image definition: • A 2D function obtained by sensing a scene • F(x,y), F(x1,x2), F(x) • F - intensity, grey level • x,y - spatial co-ordinates • No. of grey levels, L = 2B • B = no. of bits Why? Multimedia communications EG-371 Dr Matt Roach

  18. Brightness and 2D images • Brightness dependent several factors • object surface reflectance properties • surface material, microstructure and marking • illumination properties • object surface orientation with respect to a viewer and light source • Some Scientific / technical disciplines work with 2D images directly • image of flat specimen viewed by a microscope with transparent illumination • character drawn on a sheet of paper • image of a fingerprint Multimedia communications EG-371 Dr Matt Roach

  19. Monochromatic images • Image processing - static images - time t is constant • Monochromatic static image - continuous image function f(x,y) • arguments - two co-ordinates (x,y) • Digital image functions - represented by matrices • co-ordinates = integer numbers • Cartesian (horizontal x axis, vertical y axis) • OR (row, column) matrices • Monochromatic image function range • lowest value - black • highest value - white • Limited brightness values = gray levels Multimedia communications EG-371 Dr Matt Roach

  20. Chromatic images • Colour • Represented by vector not scalar • Red, Green, Blue (RGB) • Hue, Saturation, Value (HSV) • luminance, chrominance (Yuv , Luv) S=0 Green Hue degrees: Red, 0 deg Green 120 deg Blue 240 deg Red Green V=0 Multimedia communications EG-371 Dr Matt Roach

  21. Use of colour space Multimedia communications EG-371 Dr Matt Roach

  22. Visual signal quality • Quality of digital visual signal proportional to: • spatial resolution • proximity of image samples in image plane • spectral resolution • bandwidth of light frequencies captured by sensor • radiometric resolution • number of distinguishable gray levels • time resolution • interval between time samples at which images captured Multimedia communications EG-371 Dr Matt Roach

  23. Image summary • F(xi,yj) • i = 0 --> N-1 • j = 0 --> M-1 • N*M = spatial resolution, size of image • L = intensity levels, grey levels • B = no. of bits Multimedia communications EG-371 Dr Matt Roach

  24. Digital Image Storage • Stored in two parts • header • width, height … cookie. • Cookie is an indicator of what type of image file • data • uncompressed, compressed, ascii, binary. • File types • JPEG, BMP, PPM. Multimedia communications EG-371 Dr Matt Roach

  25. PPM, Portable Pixel Map • Cookie • Px • Where x is: • 1 - (ascii) binary image (black & white, 0 & 1) • 2 - (ascii) grey-scale image (monochromic) • 3 - (ascii) colour (RGB) • 4 - (binary) binary image • 5 - (binary) grey-scale image (monochromatic) • 6 - (binary) colour (RGB) Multimedia communications EG-371 Dr Matt Roach

  26. PPM example • PPM colour file RGB P3 # feep.ppm 4 4 15 0 0 0 0 0 0 0 0 0 15 0 15 0 0 0 0 15 7 0 0 0 0 0 0 0 0 0 0 0 0 0 15 7 0 0 0 15 0 15 0 0 0 0 0 0 0 0 0 Multimedia communications EG-371 Dr Matt Roach

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