Elements of Multimedia Colors, Images and Sound

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Elements of MultimediaColors, Images and Sound

• Sohaib A Khan
• CS101 Week 2, Lecture 1

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RGB Images
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RGB Color

• 256 colors in each channel
• Total Colors
• 256x256x25616,777,216
• True Color or 24 bit color
• Based on Additive Color Model
• Valid for light beams and displays (monitors,
  LCDs)

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RGB ColorAdditive Color Model
153,0,255
255,102,0
153,153,153
0,0,102
0,0,0
255,255,255
White
Black
255,0,0
0,255,0
255,255,0
0,255,255
0,0,255
255,0,255
Cyan
Yellow
Red
Green
Blue
Magenta
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CMY Color Printing

• Subtractive Color Model
• Pigments reflect only the component of light
  which matches their color

Paint
Paint
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RGB and CMY Color
Printing is done using CMYK colors Cyan, Magenta,
Yellow, Black
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Issues with Color

• Color matching is a very difficult aspect of
  desktop publishing
• Conversion from RGB to CMYK has problems
• Sometimes printed material looks very different
  from what you had designed on a monitor

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Pixels

• The number of dots (pixels) on your monitor are
  limited
• Causes problems at the edges when zoomed

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Image Resolution and Size

• Resolution gt How sharp (detailed) is the image

256 x 192
128 x 96
64 x 48
32 x 24
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Screen Resolution
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Print Resolution

• In printing, image size is measured in inches
  rather than pixels
• Print resolution is measured in dpi (dots per
  inch)
• A 300 dpi image will appear crisper in printing
  than a 50 dpi image, even though both may appear
  the same size on paper

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Screen vs Print Resolution

• Screen
• Image size in pixels
• Image size varies with resolution
• Image size is modified by resampling
• Image is displayed as one pixel at each location
• Color at one location is specified using RGB
  values

• Print
• Image size in inches
• Image size remains same with resolution
• Image size is modified by scaling
• Image pixels are placed according to given
  resolution
• Several pixel dots specify color at one location

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Example

• For the Orientation, CS Departments Poster had
  to be designed
• It was to be printed in 4 x 2 size
• Press people demanded that the resolution be at
  least 300 dpi for good results
• Question What is the size of the poster in
  pixels?
• Answer
• 4 x 12 x 300 14,400 pixels
• 2 x 12 x 300 7,200 pixels
• Low resolution pictures are okay for display on
  monitors, but not for printing

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Photo Editing Brightness and Contrast
Brightness
Contrast
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Sound
Chimes.wav

• Sound is sampled and is represented as a series
  of numbers
• Same discretization concept as images

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Sound

• Quality of sound depends on number of samples
  taken in a fixed time interval
• Example Telephone quality sound is sampled at
  8kHz, i.e. 8000 values in one second
• CD quality sound is sampled at 44 kHz
• There is no need to try for better-than-CD-quality
  sampling, because the human ear cannot discern
  the difference