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Perception

Perception. Perception. “The consciousness or awareness of objects or other data through the medium of the senses.”. Perception. In Multimedia Systems 1 we have already covered the physics of sound and its perception Here we will deal with visual perception

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Perception

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  1. Perception

  2. Perception “The consciousness or awareness of objects or other data through the medium of the senses.”

  3. Perception • In Multimedia Systems 1 we have already covered the physics of sound and its perception • Here we will deal with visual perception • It is important when designing multimedia to have a fundamental grasp of visual perception and the physiological aspects of sight

  4. Electromagnetic Spectrum • Visible light is only one component of a wide range of waveforms known as the electromagnetic spectrum

  5. Speed of Light • All electromagnetic waves travel at the speed of light (c) • c = 300,000,000ms-1 • c = f • 300,000,000ms-1 / 900,000,000Hz = 0.333m • 0.333m is the wavelength () of what?

  6. Visible Light • Visible light has a wavelength from 400 – 700 nanometers

  7. Colour Vision

  8. Colour Vision

  9. Measurement of Light • Light is often measured in terms of its: • Radiance (watts)– Total amount of energy emitted • Luminance (lumens) – Light strength that is perceived by the human eye • Brightness – Subjective measure of how bright an object appears to be

  10. Colour Vision • Most colours can be made by combining different amounts of Red, Green and Blue (RGB) light

  11. Colour Vision • There are different models for measuring colour depending on the source • Active sources such as monitors and projectors produce colours by emitting different wavelengths of light • Passive sources such as printed documents produce colours by absorbing wavelengths and reflecting others

  12. Passive Displays • Passive displays have the primary colours Cyan, Magenta and Yellow (CMY) • This known as the subtractive colour system as these colours absorb (subtract) the colours Red, Green and Blue respectively

  13. Passive Displays

  14. Active Displays • Active displays emit combinations of Red, Blue and Green light

  15. Colour Gamut

  16. Colour Sensitivity • The eye is not equally sensitive to all colours • Intensity is the weighted sum of RGB components: • For a particular colour the intensity is: 0.299 x Red + 0.587 x Green + 0.114 x Blue

  17. Psychophysical Colour Models • Based on human perception of colours. • HLS • Hue – The pure dominant colour • Lightness • Saturation - How much the colour is diluted by white light • HSV • Hue • Saturation • Intensity (Value)

  18. Representing DigitalImages • Digital images are composed of pixels (or picture elements) • Picture resolution is the number of pixels or samples used to represent the image

  19. Representing DigitalImages • Digital images are often referred to as as bitmaps

  20. Representing DigitalImages

  21. Representing DigitalImages

  22. True Colour Image Data Model

  23. True Colour

  24. Palette Colour Image Data Model

  25. Palette Colour R G B 165 16 49

  26. True Colour Vs. Palette Colour • True Colour: • High quality • Expensive hardware • Require more memory (normally 3 times) • Palette Colour • Limited number of colours • Cheap hardware • Enables easier implementation of certain techniques

  27. Resolution • Image resolution determines: • the amount of detail • storage requirements • Here is a digitised image with a resolution of: • 300 x 466 • 139,800 pixels

  28. Resolution • Here is the same digitised image, but with a resolution of: • 75 x 115 • 8625 pixels

  29. Resolution • Here is it is again with a resolution of: • 43 x 67 • 2881

  30. Resolution and Digital Cameras • Digital camera resolution ranges from approximately 1 – 6 megapixels • A 2 megapixel camera will have a resolution of 1600x1200 • 1,920,000 pixels

  31. Aspect ratio • Aspect Ratio expresses the resolution of an image as: • number of horizontal pixels x the number of vertical pixels • It is a format attribute • Typical ratios: • 320 x 240, 640 x 480, 800 x 600, and 1024 x 768, 1600 x 1200, 1792 x 1344, 2048 x 1536 – all of which are 4:3 • 1280 x 1024 (5:4) • 768 x 576 (4:3) standard PAL TV format • 1024 x 576 (16:9) wide screen TV

  32. Fin Fin

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