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Elements of Elements of MultimediaMultimedia
Colors, Images and SoundColors, Images and Sound
Sohaib A KhanSohaib A Khan
CS101: Week 2, Lecture 1CS101: Week 2, Lecture 1
RGB Images
RGB ColorRGB Color
256 colors in each 256 colors in each channelchannel
Total Colors:Total Colors:256x256x256=16,777,216256x256x256=16,777,216
‘‘True Color’ or ‘24 bit color’True Color’ or ‘24 bit color’ Based on Based on Additive Additive
Color ModelColor Model Valid for light beams Valid for light beams
and displays (monitors, and displays (monitors, LCDs)LCDs)
RGB ColorRGB ColorAdditive Color ModelAdditive Color Model
WhiteBlack
Red Green Blue Magenta Cyan Yellow
[255,0,0] [0,255,0] [0,0,255]
[0,0,0] [255,255,255]
[255,255,0][0,255,255][255,0,255]
[153,0,255] [255,102,0] [0,0,102][153,153,153]
CMY Color: PrintingCMY Color: Printing
Subtractive Color Subtractive Color ModelModel
Pigments reflect Pigments reflect only the only the component of component of light which light which matches their matches their colorcolor
PaintPa
int
RGB and CMY ColorRGB and CMY Color
Printing is done using CMYK colorsCyan, Magenta, Yellow, Black
Issues with ColorIssues with Color
Color matching is a very difficult Color matching is a very difficult aspect of desktop publishingaspect of desktop publishing
Conversion from RGB to CMYK has Conversion from RGB to CMYK has problemsproblems
Sometimes printed material looks Sometimes printed material looks very different from what you had very different from what you had designed on a monitordesigned on a monitor
PixelsPixels
The number of dots (‘pixels’) on your The number of dots (‘pixels’) on your monitor are limitedmonitor are limited
Causes problems at the edges when Causes problems at the edges when zoomedzoomed
Image Resolution and SizeImage Resolution and Size
Resolution => How sharp (detailed) is the Resolution => How sharp (detailed) is the imageimage
256 x 192
128 x 96
64 x 48
32 x 24
Screen ResolutionScreen Resolution
Print ResolutionPrint Resolution
In printing, image size is measured in In printing, image size is measured in inchesinches rather than rather than pixelspixels
Print resolution is measured in Print resolution is measured in dpi dpi ((ddots ots pper er iinch)nch)
A 300 dpi image will appear crisper A 300 dpi image will appear crisper in printing than a 50 dpi image, even in printing than a 50 dpi image, even though both may appear the same though both may appear the same size on papersize on paper
Screen vs Print ResolutionScreen vs Print Resolution
ScreenScreen Image size in pixelsImage size in pixels Image size varies with Image size varies with
resolutionresolution Image size is modified Image size is modified
by resamplingby resampling Image is displayed as Image is displayed as
one pixel at each one pixel at each locationlocation
Color at one location is Color at one location is specified using RGB specified using RGB valuesvalues
PrintPrint Image size in inchesImage size in inches Image size remains same Image size remains same
with resolutionwith resolution Image size is modified by Image size is modified by
scalingscaling Image pixels are placed Image pixels are placed
according to given according to given resolutionresolution
Several pixel dots specify Several pixel dots specify color at one locationcolor at one location
ExampleExample For the Orientation, CS For the Orientation, CS
Department’s Poster had to be Department’s Poster had to be designeddesigned
It was to be printed in 4’ x 2’ sizeIt was to be printed in 4’ x 2’ size Press people demanded that the Press people demanded that the
resolution be at least 300 dpi for resolution be at least 300 dpi for good resultsgood results
Question: What is the size of the Question: What is the size of the poster in pixels?poster in pixels?
Answer: Answer: – 4’ x 12 x 300 = 14,400 pixels4’ x 12 x 300 = 14,400 pixels– 2’ x 12 x 300 = 7,200 pixels2’ x 12 x 300 = 7,200 pixels
Low resolution pictures are okay Low resolution pictures are okay for display on monitors, but not for display on monitors, but not for printingfor printing
Photo Editing: Brightness and Photo Editing: Brightness and ContrastContrast
Brightness
Contrast
SoundSound
Sound is sampled and is Sound is sampled and is represented as a series of represented as a series of numbersnumbers
Same ‘discretization’ concept as Same ‘discretization’ concept as imagesimages
Chimes.wav
SoundSound
Quality of sound depends on number of Quality of sound depends on number of samples taken in a fixed time intervalsamples taken in a fixed time interval
Example: Telephone quality sound is Example: Telephone quality sound is sampled at 8kHz, i.e. 8000 values in one sampled at 8kHz, i.e. 8000 values in one secondsecond
CD quality sound is sampled at 44 kHzCD quality sound is sampled at 44 kHz There is no need to try for better-than-There is no need to try for better-than-
CD-quality sampling, because the human CD-quality sampling, because the human ear cannot discern the differenceear cannot discern the difference