Computer Science 1033 Topic 2 Notes

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Western University
Computer Science
Computer Science 1033A/B
Vivi Tryphonopolous

Topic 2 Images  Images: We rely on images for information, entertainment, and visual appeals.  Origins of images: o Non-digital mediums (Paper copy of a photo) o Photography (Images uploaded to a file on the computer) o Clip art images (Images created and saved to a file on the computer) Graphics  Numbering systems: o Binary: A numerical system containing only 0s and 1s o Octal: A numerical system containing 8 digits o Decimal: A numerical system containing 10 digits o Hexadecimal: A numerical system containing 16 digits (including alphabets A – F)  Bit: Fundamental unit of information in a computer system that uses binary. This is because computers are electronic devices that have only two possible states: on – high voltage or off – low voltage.  Digitization: Process of translating piece of information into binary bits o The information takes a series of values that equal either ‘0’ or ‘1’  More bits used to encode colors mean more colors available to assign to a picture (y = 2f)bits  1 bit can take on 2 value (colors)  2 bit can take on 4 values (colors)  3 bits can take on 8 values (colors) o Conversion from analog to digital: A two-step process with:  Sampling: How many pixels will I break up the image into?  Pixel: Smallest image component with 1 color assigned to it  When images are taken from scanners or cameras, they are represented in pixels.  The more samples are taken, the clearer the picture becomes.  Quantizing: How many discrete values will I use to represent each pixel?  Each pixel is given a numerical value that represents the corresponding color  Using 8 bits (1 byte), it is possible to obtain 256 values of colors Color Models  Subtractive Model (CMYK) o Primary colors are cyan, magenta, yellow, and black o Used for printing (commercial plates and inks) o Uses printer ink. When applied to paper, removes colors from a white background.  Additive model (RGB): o Primary colors are red, green, an blue o Adds ‘light’ to a black background (monitor) o Used for web. This is because cathode ray devices display colors with red green and blue light. RGB can also represent a large portion of the color spectrum by mixing the three colors on a monitor. o Brighter than CMYK  Coding: o True color: Uses 24 bit color representation (~16 million colors) o RGB code: 8  Each pixel is represented by 3 numbers of 2 bits  Total of approximately 16 million colors available.  Each value ranges from 0 (no amount) to 255 (max amount)  Red: <255, 0, 0>  Green: <0, 255, 0>  Blue: <0, 0, 255>
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