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Lecture 4

Computer Science 1033A/B Lecture Notes - Lecture 4: Raster Graphics, Display Resolution, Cmyk Color Model


Department
Computer Science
Course Code
COMPSCI 1033A/B
Professor
idk
Lecture
4

Page:
of 2
Sept 30, 2013
Graphics
Images
Common screen resolutions: 640x640, 600x800, 1024x768 (most common), 1280x1024
Less pixels = larger images/textt, less fits on screenMore pixels= smaller text/image, more on
screen
Amount of screen a picture takes up depends on: size of picture, screen resolution, not DPI
Average pixels/dots per inch is 72ppi
-is equal to 100% zoom level, pictures are crisp
When printing an image, ensure that it is at least 300 dpi
More pixels = larger file size, but dpi/ppi does not make a difference in file size
On the web, you want the smallest file size but still have a good size picture
-large file sizes will take a long time to download when on a webpage
Colours
1 bit = 2 colours, 2 bits = 4 colours, 4 bits = 16 colours
Subtractive Model - CMYK
-Used for printing, refers to ink on a page
-Primary colours are Cyan, Magenta, Yellow and Black
-When ink is applied, it removes the white (paper colour)
Additive Model - RGB
-Used on monitors
-"adding" light to a black background (the monitor)
-Primary colours are Red, Green and Blue
True colour:
-can represent 16 million colours (2^24)
-256 shades of red X 256 shades of green X 256 shades of blue
-3 bytes are needed for True Colour (1 for each colour)
Sept 30, 2013
-True Colour can be encoded in two ways:
RGB (3 values, one for each colour)
Hexadecimal Code (using digits 0-F, # then 6 values, 2 per colour)
Bitmapped Images vs Vector Graphics
Bitmapped
Bitmapped graphic images consist of pixels in a grid
When enlarged, bitmapped image adds new pixels to fill space and guesses what colour they
should be, based on surrounding pixels (interpolation), become jagged
Also called raster graphics image
All images from scanners and digital cameras are bitmapped images
Photoshop uses bitmapped images
Vector
Image consists of individual, scalable objects
Objects created by mathematical equations, image consists of lines, curves and shapes
The image is not distorted when enlarged, still crisp
Only can be used for drawings/clip art images, not photographs
File size is usually smaller than the same image as a bitmap
Often used for logos
Images on Webpage
Image needs to be "appropriate size" for our page, while still looking good
Also it needs to download quickly, so the file size needs to be small
To make image smaller:
-Reduce the number of pixels (but image will look smaller on screen)
-Compress image file (do not use True Colour, therefore less bytes are used)