Lecture 4: ImagesIntro to IT COSC1078 Introduction to Information Technology Lecture 4 Images James Harland

Lecture 4: ImagesIntro to IT Introduction to IT 1 Introduction 2 Images 3 Audio 4 Video WebLearn Test 1 5 Computer Fundamentals Assignment 1 6 Computer Fundamentals 7 Computer Fundamentals 8 Operating Systems WebLearn Test 1 9 Operating Systems Assignment 2 10 Internet 11 Internet Security WebLearn Test 3 12 Future of ITAssignment 3, Peer and Self Assessment

Lecture 4: ImagesIntro to IT Overview  Questions?  Images  Assignment 1  Lab classes  Questions?

Lecture 4: ImagesIntro to IT Introduction James Harland URL: Phone: Office: (Building 14, level 8, room 13) Consultation: Wed , Thu What colour is my office door? Carpet? Chair?

Lecture 4: ImagesIntro to IT Representing Colours … Pixel R G B

Lecture 4: ImagesIntro to IT Representing Colours There are various different schemes for representing colours  RGB  CMYK  HSB  HSL  CIE XYZ …

Lecture 4: ImagesIntro to IT RGB  Human eye uses red, green, blue sensors  Additive --- more colours means lighter colour yellow cyan magenta ++ Other colours by varying amounts of R, G, B

Lecture 4: ImagesIntro to IT RGB  Often represented as (#R, #G, #B) where #R, #G, #B in range 0, 1, …, 255 (ie )  This means 8 bits per channel, or bit depth 24  Gives = 16,777,216 colours overall  Note that RGB is a scheme, not a particular set of numbers

Lecture 4: ImagesIntro to IT RGB 8 bits per channel Colour#R#G#B White255 Black000 Red25500 Green02550 Blue00255 Yellow255 0 Cyan0255 Magenta2550 “Light orange” ???

Lecture 4: ImagesIntro to IT CMYK  Based on 4 colours  Subtractive – more colours means less light YellowCyanMagentablacK yellow cyan magenta

Lecture 4: ImagesIntro 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: ImagesIntro to IT Representing Colours There are various different schemes for representing colours  RGB  CMYK  HSB  HSL  CIE XYZ …

Lecture 4: ImagesIntro 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: ImagesIntro 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: ImagesIntro 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: ImagesIntro to IT Assignment 1  Use GIMP (or a similar tool) to perform some manipulations on an image  Address two issues in relation to this  Lab classes 2 and 3 will be based around GIMP  Main emphasis is on process, not result!  Will be released (on the Learning Hub) by Wednesday 10 th March (later today)

Lecture 4: ImagesIntro 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: ImagesIntro 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!