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