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Images, Sound,and Multimedia
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No Surprises
• Images, Sound, Music, and Movies– It’s all numbers– Binary Numbers
• Today we’ll discuss how multimedia is converted to and from numbers, and processed on a computer
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Colors
• In a computer’s memory colors are represented as a combination of three-additive primary colors
(red, green, blue)• Nearly every color that you
perceive can be generatedby combining these colors
• Under normal conditions,humans can discern about100 shades of a color(Just noticeable differences)
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Visual Sensitivity
A light sensitive organ; the highest bandwidth
channel into the brain.
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Trichromatic Sensitivity
• Two kinds of cells,rods and cones
• Three types of conesred, green, and blue
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Computer Colors
• Combining what we know– Only 3 colors are needed to stimulate the
perception of nearly all others– Roughly 100 shades of each are perceivable
• Three one-byte channels (r, g, b) each with 256 levels
• Alternatives: 15-bit color, 5-bits per r, g, b(banding is sometimes noticeable)
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Some Preliminaries
• Download the Python Imaging Library fromhttp://www.pythonware.com/products/pil
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Image Compression
• There are 2 common types of image compression– Lossy - (.jpg)– Higher compression rate (fewer bits/pixel)
• Good for “Natural images”– Lossless - (.bmp, .png)– Lower compression rate (more bits/pixel– Best for “Graphics Arts Images”– Preserves Sharp lines
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Image Compression Example
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Sound by Numbers
• Sound is a result of pressure waves propagatingthrough the air
• You perceive soundas the intensity andfrequency of thesepressure waves
• How are these“waves” representedin a computer
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Sound Perception
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Some Quick and Dirty Sound
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Audio Sampling
• The sampling rate, definesthe number of samples persecond taken from acontinuous signal to make adiscrete (digital) signal.
• It is measured in hertz (Hz)• The inverse of the sampling
frequency is the samplingperiod or sampling interval,which is the time betweensamples.
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Common Sampling Rates
• The table above gives the common sampling rates used in many audio applications
• The highest reproducible audible frequency by any format is 1/2 of its sampling rate
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Making a Sound
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A Square Wave Tone
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Noise
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More to Come…
• Digital Sound and other• Graphics, images, etc