Transcript CM613 - Multimedia storage and retrieval lecture: Colour

CM613 Multimedia storage and retrieval
Lecture: Colour
CM613 Multimedia storage and retrieval
Colour
D.Miller
Slide 1
CM613 Multimedia storage and retrieval
Lecture: Colour
What is colour?
Slide 2
CM613 Multimedia storage and retrieval
Lecture: Colour
Perception of colour
Sir Isaac Newton (1643-1727)
Source: http://ccrs.nrcan.gc.ca/resource/tutor/stereo/chap2/chapter2_4_e.php
Slide 3
CM613 Multimedia storage and retrieval
Lecture: Colour
Colour Physics
Source: http://www.mic-d.com/curriculum/lightandcolor/electromagnetic.html
Slide 4
CM613 Multimedia storage and retrieval
Lecture: Colour
Colour Physics
Slide 5
CM613 Multimedia storage and retrieval
Lecture: Colour
Evolution of the eye
(source [3])
Slide 6
CM613 Multimedia storage and retrieval
Lecture: Colour
Diagram of human eye
Containing specialised cells:
“rods” – sensitive to light and dark
“cones” – sensitive to colour
Slide 7
CM613 Multimedia storage and retrieval
Lecture: Colour
Rods and cones
Source: [2]
Slide 8
CM613 Multimedia storage and retrieval
Lecture: Colour
Colour (in)constancy
Slide 9
CM613 Multimedia storage and retrieval
Lecture: Colour
Colour (in)constancy
Slide 10
CM613 Multimedia storage and retrieval
Lecture: Colour
Colour (In)constancy
• Colour perception is influenced by surrounding colours:
– http://www.echalk.co.uk/amusements/OpticalIllusions/colourPerception/colourPerception.html
Slide 11
CM613 Multimedia storage and retrieval
Lecture: Colour
Colour after-image
Slide 12
CM613 Multimedia storage and retrieval
Lecture: Colour
Colour after-image
Slide 13
CM613 Multimedia storage and retrieval
Lecture: Colour
http://www.psych.ucalgary.ca/PACE/VA-Lab/colourperceptionweb/theories.htm
Slide 14
CM613 Multimedia storage and retrieval
Lecture: Colour
Colour Spaces: Colour Wheel
Purest (spectral) colours
on perimeter
A
Combining pure colours at
A and B produces a result along this line
B
Slide 15
CM613 Multimedia storage and retrieval
Lecture: Colour
Colour mixing
Subtractive colour mixing
Additive colour mixing
Source 1
http://home.att.net/~B-P.TRUSCIO/COLORSYS.htm
http://konicaminolta.com/yourcolours/colour_knowlege_seminar/c_knowlege_seminar001.html
Slide 16
CM613 Multimedia storage and retrieval
Lecture: Colour
CIE 1931 colour space chromaticity diagram
Imaginary GREEN primary
Actual perceivable colours
X value represents proportion of red,
Y represents proportion of green
1-(X+Y) represents proportion of blue
http://www.cs.bham.ac.uk/~mer/colour/cie.html
http://hyperphysics.phy-astr.gsu.edu/hbase/vision/cie.html
Imaginary BLUE primary
Imaginary RED primary
Slide 17
CM613 Multimedia storage and retrieval
Lecture: Colour
Gamut (“range”)
http://en.wikipedia.org/wiki/Gamut
http://www.luminous-landscape.com/tutorials/prophoto-rgb.shtml
http://www.naturephotographers.net/articles1203/mh1203-1.html
http://www.drycreekphoto.com/Learn/color_spaces.htm
Slide 18
CM613 Multimedia storage and retrieval
Lecture: Colour
RGB colour space
http://www.cs.bham.ac.uk/~mer/colour/hsv.html
Slide 19
CM613 Multimedia storage and retrieval
Lecture: Colour
CIE L*A*B* model
Commision Internationale de L'Eclairage (CIE)
Source 1
Colour solid
Slide 20
CM613 Multimedia storage and retrieval
Lecture: Colour
Digital data representation of colour
Picture element – (pixel, pel) smallest discrete component of an image.
Perceived as a coloured dot.
more pixels per square cm = “higher” resolution.
Bitmap
Bitmaps are defined as a regular rectangular mesh of cells called pixels, each pixel
containing a colour value. They are characterised by only two parameters, the number
of pixels and the information content (colour depth) per pixel
1 bit image (binary image, 1 bit monochrome image)
Smallest possible information content for a pixel?
Black and white only?
Storage requirements?
Use for?
http://astronomy.swin.edu.au/~pbourke/dataformats/bitmaps/
Slide 21
CM613 Multimedia storage and retrieval
Lecture: Colour
Digital data representation of colour
8-bit grey-level image
how many shades of grey?
8-bit colour image
how many different colours?
which colours?
why lookup tables?
Slide 22
CM613 Multimedia storage and retrieval
Lecture: Colour
Digital data representation of colour
24-bit colour image
how many different colours?
storage penalty?
32-bit colour image
What is the extra byte used for?
Slide 23
CM613 Multimedia storage and retrieval
Lecture: Colour
Colour printing
Detail of colour wheel photographic plate in [2].
Scanned at 300 dpi.
Scanned at 1200 dpi.
http://en.wikipedia.org/wiki/Four-color_printing#Color_separation_process
Slide 24
CM613 Multimedia storage and retrieval
Lecture: Colour
Pixels and halftoning
Detail of colour wheel photographic plate in [2].
Scanned at 300 dpi.
Scanned at 1200 dpi.
Slide 25
CM613 Multimedia storage and retrieval
Lecture: Colour
As you might wish it to be
Because colour data can be stored
and retrieved consistently, colour will
be perceived consistently
The reality
Retrieved colour data is perceived
differently when it is presented on
different media, and perception is also
affected by other factors such as the
presence of other colours or the level
of ambient lighting.
Slide 26
CM613 Multimedia storage and retrieval
Lecture: Colour
References
[1] Coren, Ward and Enns (1999) Sensation and Perception (5th Ed). Harcourt Brace College
Publishers
[2] Li and Drew (2004) Fundamentals of Multimedia. Pearson
[3] Rosenzweig, Breedlove and Leiman (2002) Biological Psychology. Sinauer.
Slide 27