colour representation schemes filtering of colour images
TRANSCRIPT
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IE PŁ P. Strumiłło, M. Strzelecki
Processing of colour imagesimages
�Colour representation schemes
� Filtering of colour images
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IE PŁ P. Strumiłło, M. Strzelecki
Electromagnetic spectrum
10181024 1016 1014 1012 1010 108 106 104 1021022 1020
frequency, Hz
gamma rays radio waves
X raysmicrowaves
Infrared wavesultravioletVisibleVisible lightlight
400 500 600 700 [nm]
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IE PŁ P. Strumiłło, M. Strzelecki
Eye sensitivity to colour components
infraredultraviolet
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1µm
00
0.2
0.4
0.6
0.8
1
rods
cones
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IE PŁ P. Strumiłło, M. Strzelecki
Commission Internationale de l’Eclairage (CIE)
Chromaticity Diagram
Point of equalenergy
(saturation zero)
CIE diagrams all colours that can be humanly perceived
(pure colours)
(pure purple)
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IE PŁ P. Strumiłło, M. Strzelecki
R
GB
RGB colour images
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IE PŁ P. Strumiłło, M. Strzelecki
RGB colour images
R
B
G
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IE PŁ P. Strumiłło, M. Strzelecki
RGB colour space
Each colour
compoment (R,G,B) is
registered and digitized
in a separate video
channel
greys
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IE PŁ P. Strumiłło, M. Strzelecki
RGB additive primaries
R B
G
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IE PŁ P. Strumiłło, M. Strzelecki
CMY subtractive primaries
C
YM
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IE PŁ P. Strumiłło, M. Strzelecki
cyan magenta
yellow black
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IE PŁ P. Strumiłło, M. Strzelecki
RGB and CMY colour systems
Subtracting subtractive primariesAdding additive primaries
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IE PŁ P. Strumiłło, M. Strzelecki
RGB and CMYK colour systems
Wikipedia®
K – stands for black, which is used as a
fourth colour to improve
the contrast of prints
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IE PŁ P. Strumiłło, M. Strzelecki
R
G
B
C
M
Y
RGB colours produced by
typical CRT device (RGB
colour gamut) and CMY
colour printers (CMY colour
gamut)
RGB and CMY colour systems
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IE PŁ P. Strumiłło, M. Strzelecki
YIQ (YUV) colour space
Y is a luminance component and is a linear combination of (R,G,B)
(I,Q) are the chrominance (colour)components.
NTSC system
Y – luminance,
I – inphase,
Q – quadrature
YUV ≠≠≠≠ YCbCr
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IE PŁ P. Strumiłło, M. Strzelecki
There exist a one-to-one mapping between
RGB and YIQ systems.
Y=0.299R + 0.587G + 0.114B R=Y + 0.956I + 0.621Q
I = 0.596R - 0.274G - 0.322B G=Y - 0.272I + 0.647Q
Q=0.211R - 0.523G + 0.312B B=Y - 1.106I + 1.703Q
For a human eye perception a better approach is is to code
separately luminance and chrominance components (S-Video)
Equivalence of colour spaces
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IE PŁ P. Strumiłło, M. Strzelecki
I
Y
Q
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IE PŁ P. Strumiłło, M. Strzelecki
YUV and YCbCr
Y=0.299 *R + 0.587*G +0.114 *B
Y
U
V
RGBYUV – used in NTSC TV system
U = 0.49*(B – Y)
V = 0.88*(R – Y)
chrominance
luminance
Wikipedia
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IE PŁ P. Strumiłło, M. Strzelecki
Y
Cb
Cr
RGB
Cr = 0.5 *R - 0.42*G -0.08*B
A standard diffrent from YUV in chrominancecomponents
S-video
Cb = -0.17 *R - 0.5*G +0.5*B
Y=0.299 *R + 0.587*G +0.114 *B
Wikipedia
YUV and YCbCr
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IE PŁ P. Strumiłło, M. Strzelecki
Use of Cr colourcomponent for detectionof skin regions in images(not dependent on skin colour)
RGB Cr
Cr – monochrome Cr - enhanced Cr - binary
PhD work of A. Królak at the Medical Electronics Division
YCbCr
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IE PŁ P. Strumiłło, M. Strzelecki
Filtering of colour images in spatial domain
1. Convert from RGB to YCbCr
2. Filter the Y (luminance) component and
keep the colours (Cb,Cr) unchanged
3. Convert back to RGB
Another possible approach:
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IE PŁ P. Strumiłło, M. Strzelecki
%Matlab
h=fspecial(‘unsharp’);
ys=filter2(h,y);
High pass
filtering of the
Y component
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IE PŁ P. Strumiłło, M. Strzelecki
H - hue, S - saturation, I - intensity
Useful in designing
colour graphics
HSI (HSV) colour system
Wikipedia
black
white
S
H
V V
RGB ↔ HSI
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IE PŁ P. Strumiłło, M. Strzelecki
Hue
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IE PŁ P. Strumiłło, M. Strzelecki
Saturation
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IE PŁ P. Strumiłło, M. Strzelecki
Intensity (Value)
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IE PŁ P. Strumiłło, M. Strzelecki
Colour coding in SVGA graphics cards
7 0 7 0 7 0R BG
Digital to Analog Converter (DAC) 3 x 8 bits
screen
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IE PŁ P. Strumiłło, M. Strzelecki
Colour resolutions in PC computers
• True-colour: 224 colours -> 16777216
• High-colour: 216 colours -> 65536 (R5, G6, B5)
• 256 colours (indexed colours from look-up-table)
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IE PŁ P. Strumiłło, M. Strzelecki
RGB to indexed image
RG
B
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IE PŁ P. Strumiłło, M. Strzelecki
Colour palette
Indexed images in thermography
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IE PŁ P. Strumiłło, M. Strzelecki
Psudo-colours represent blood flow velocity
Images recorded in the Moscow Institute of Electronic Technologies
Indexed images in medicine
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IE PŁ P. Strumiłło, M. Strzelecki
Multimodal images come from different imaging techniques of
the same objects, these images are called modalities
PhotoThermogram
~2µm 380-700 nm
Different modalities of an integrated circuit
Multimodal images
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IE PŁ P. Strumiłło, M. Strzelecki
RGB image Thermographic image Stereovision image(depth map)
Multimodal images
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IE PŁ P. Strumiłło, M. Strzelecki
Matching (Registration) – geometric transformation of different
modalities into one coordinate system
Reference points method
1.Detection of the same characteristic points
2.Matching
Multimodal images
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IE PŁ P. Strumiłło, M. Strzelecki
Image fusion is combining of modalities for display into
a single image.
Next slades show PET and CT modalities and their
fusion techniques.
[The images are dowloaded from public domain
repository:
http://en.wikipedia.org/wiki/Positron_emission_tomography]
Multimodal images
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IE PŁ P. Strumiłło, M. Strzelecki
Obrazy multimodalneObrazy multimodalneŁączenie (fuzja) obrazów polega na jednoczesnej wizualizacji różnych modalności w jednym obrazie wynikowym.
http://en.wikipedia.org/wiki/Positron_emission_tomography
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IE PŁ P. Strumiłło, M. Strzelecki
PET
+
CT
http://en.wikipedia.org/wiki/Positron_emission_tomography
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IE PŁ P. Strumiłło, M. Strzelecki
© Philips
3D image fusion