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Elements of Multimedia Colors, Images and Sound

Elements of Multimedia Colors, Images and Sound. Sohaib A Khan CS101: Week 2, Lecture 1. RGB Images. RGB Color. 256 colors in each channel Total Colors: 256x256x256=16,777,216 ‘True Color’ or ‘24 bit color’ Based on Additive Color Model

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Elements of Multimedia Colors, Images and Sound

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  1. Elements of MultimediaColors, Images and Sound Sohaib A Khan CS101: Week 2, Lecture 1

  2. RGB Images

  3. RGB Color • 256 colors in each channel • Total Colors: 256x256x256=16,777,216 ‘True Color’ or ‘24 bit color’ • Based on Additive Color Model • Valid for light beams and displays (monitors, LCDs)

  4. RGB ColorAdditive Color Model [153,0,255] [255,102,0] [153,153,153] [0,0,102] [255,255,255] [0,0,0] Black White [255,0,0] [0,255,0] [0,255,255] [255,255,0] [0,0,255] [255,0,255] Cyan Yellow Red Green Blue Magenta

  5. CMY Color: Printing • Subtractive Color Model • Pigments reflect only the component of light which matches their color Paint Paint

  6. RGB and CMY Color Printing is done using CMYK colors Cyan, Magenta, Yellow, Black

  7. 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

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

  9. Image Resolution and Size • Resolution => How sharp (detailed) is the image 256 x 192 128 x 96 64 x 48 32 x 24

  10. Screen Resolution

  11. 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

  12. 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 Screen vs Print Resolution

  13. Example • For the Orientation, CS Department’s 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

  14. Photo Editing: Brightness and Contrast Brightness Contrast

  15. Sound Chimes.wav • Sound is sampled and is represented as a series of numbers • Same ‘discretization’ concept as images

  16. 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

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