Lecture 4: Images Intro to IT

COSC1078 Introduction to Information Technology

Lecture 4

ImagesJames Harland

james.harland@rmit.edu.au

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 4.30-5.30, Thu 11.30-

12.30What is the view like from

my office?

Lecture 4: Images Intro to IT

Overview Questions?

Images

Assignment 1

Lab classes

Questions?

Lecture 4: Images Intro to IT

Introduction to IT1 Introduction 2 Images3 Audio4 Video WebLearnTest 1 5 Binary Representation Assignment 16 Data Storage7 Machine Processing8 Operating Systems WebLearn Test 19 Processes Assignment 210 Internet11 Internet Security   WebLearn Test 312 Future of IT Assignment 3, Peer and Self Assessment

Lecture 4: Images Intro to IT

Assessment Process Submit all assignments via Blackboard in the

Learning Hub Assignment 1 due 11.59pm Sunday 1st April Assignment 2 due 11.59pm Sunday 6th May Assignment 3 due 11.59pm Sunday 27th May Late assignments attract a penalty of 10% per

day late, up to a maximum of 50%

Lecture 4: Images Intro to IT

Assignment Assignment will be in three parts Overall task is to produce a video Groups of up to 3 Assessed by final video and group blog Part 1: images and audio (end of week 5) Part2: hardware (end of week 9) Part 3: reflection, research (end of week 12)

Lecture 4: 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

Use a movie making tool to produce something like (and much better than!) ‘Lord of the Controllers’

Email me your group and its name so that I can set up a blog on the Learning Hub

Lecture 4: Images Intro to IT

Representing Colours01010100001010101010100110100010101001101001010010100011100010101010100101111001001010…

Pixel RGB

Lecture 4: Images Intro to IT

Representing ColoursThere 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

+++

yellowcyanmagenta

+ +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 #BWhite 255 255 255Black 0 0 0Red 255 0 0Green 0 255 0Blue 0 0 255Yellow 255 255 0Cyan 0 255 255Magenta 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

+++

redgreenblue

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 ColoursThere 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 FormatsColour 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 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!