cosc1078 introduction to information technology lecture 4 images
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Lecture 4: Images Intro to IT
COSC1078 Introduction to Information Technology
Lecture 4
ImagesJames Harland
james.harland@rmit.edu.au
Lecture 4: Images Intro to IT
Introduction to IT
1 Introduction
2 Images
3 Audio
4 Video
5 Binary Representation WebTest 1, Assignment 1
6 Data Storage
7 Machine Processing
8 Operating Systems WebLearn Test 1
9 Processes Assignment 2
10 Internet
11 Internet Security WebLearn Test 3
12 Future of IT Assignment 3, Peer and Self Assessment
Lecture 4: Images Intro to IT
Overview
Questions?
Images
Assignment 1
Lab classes
Questions?
Lecture 3: Images Intro to IT
Introduction
James Harland• Email: james.harland@rmit.edu.au• URL: www.cs.rmit.edu.au/~jah• Phone: 9925 2045• Office: 14.10.1 (Building 14, level 10, room 1)• Consultation: Mon 2.00-3.00, Thu 12.30-1.30
What is the view like from my office?
Lecture 4: Images Intro to IT
Representing Colours
01010100001010101010100110100010101001101001010010100011100010101010100101111001001010…
PixelR
GB
Lecture 4: Images Intro to IT
Representing Colours
There are various different schemes for representing colours
RGB CMYK HSB HSL CIE XYZ
01010100001…
Lecture 4: Images Intro to IT
RGB
Human eye uses red, green, blue sensors Additive --- more colours means lighter colour
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yellow
cyan
magenta
+ +Other colours by varying amounts of R, G, B
Lecture 4: Images Intro to IT
RGB
Often represented as (#R, #G, #B) where #R, #G, #B in range 0, 1, …, 255 (ie 28 -1)
This means 8 bits per channel, or bit depth 24
Gives 2563 = 16,777,216 colours overall
Note that RGB is a scheme, not a particular set of numbers
Lecture 4: Images Intro to IT
RGB 8 bits per channel
Colour #R #G #B
White 255 255 255
Black 0 0 0
Red 255 0 0
Green 0 255 0
Blue 0 0 255
Yellow 255 255 0
Cyan 0 255 255
Magenta 255 0 255
“Light orange”
255 166 38
??? 142 223 177
Lecture 4: Images Intro to IT
CMYK
Based on 4 colours Subtractive – more colours means less light
YellowCyan Magenta blacK
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red
green
blue
Lecture 4: Images Intro to IT
CMYK Why Black? Why not CMY?
Used mainly in printing (“4-colour print”) In practice, doesn’t look “black” “There is no colour with more shades than black”Too much ink to make black soaks the paper too much Text is traditionally black (and lots more text than pictures in colour) Black ink is cheaper than coloured
+ +
Lecture 4: Images Intro to IT
Representing Colours
There are various different schemes for representing colours
RGB CMYK HSB HSL CIE XYZ
01010100001…
Lecture 4: Images Intro to IT
HSB (or HSV)
How do humans describe colour?“rich dark green”
Hue: basic colour (red, green, blue, yellow, …)Saturation: amount of colour (intensity, purity)Brightness: light or dark or in-between …
Can be thought of as a cone or cylinder or hexacone
Lecture 4: Images Intro to IT
HSB and HSV and HSL
Hue is represented on a circle, and hence as a bearing (like on a compass)
Saturation and Brightness/Value are percentages
HSL is similar, except that 100% luminance is always white (just as 0% brightness is black)
Lecture 4: Images Intro to IT
CIE XYZ
Standard derived from work in 1931 to identify all colours visible to humans Colours divided into brightness and chromacity Humans can see more colours than a typical monitor can display RGB produces more colours than CMYK
Lecture 4: Images Intro to IT
File Formats
Colour schemes are not the same thing as file formats!
Joint Photographic Experts Group (JPEG)
Uses RGB idea Encodes RGB data into more compressed form before storage Has `lossy’ compression Human eye more sensitive to brightness than colour …
Lecture 3: Images Intro to IT
Assignment 1
Use GIMP (or a similar tool) to perform some manipulations on an image
Use Audacity to perform some manipulations on sound
Address three issues in relation to this
Lab classes 2 and 3 will be based around GIMP
Lab class 4 based on Audacity
Main emphasis is on process, not result!
Will be released this week
Lecture 3: Images Intro to IT
Lab Classes
Start in week 2 (this week)
Work on practical exercises and sometimes assignment materials
Lab assists present to help and an answer questions
Details will be in the Learning Hub
Lecture 4: Images Intro to IT
Conclusion
Go to laboratory classes (and tutorials) this week!
Lab notes in the Learning Hubub
Check details in Course Guide
Start reading (notes, problems, report topic)
GET THE BOOK!
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