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TOPIC 9 LIGHT AND COLOUR
RAY TRACING
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Spectral colours
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Colour saturation
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With real colours an additive system is
impossible
Red Green unknown blue
unknown Red Green - blue
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The human eye
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Colour sensitivity
Luminous efficiency
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The theoretical CIE colours
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A colour combination
Normalised components
Now x y z 1 hence z 1 - x - y and
!
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Colour Gamuts
Short Persistence phosphor
Long Persistence phosphor
Red Green Blue
Red Green Blue
x 0.61 0.29 0.15 y
0.35 0.59 0.063
x 0.62 0.21 0.15 y
0.33 0.685 0.063
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The RGB cube
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The HSV model
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RGB to HSV conversion
procedure RGB_to_HSV (r,g,b real h,s,v real)
max lt-- max(r,g,b) min lt-- min(r,g,b) v lt--
max if max ltgt 0 then s lt-- (max -
min)/max else s 0 end if s 0 then
h is undefined else delta lt-- (max -
min) if r max then h lt-- (g - b)/delta
if g max then h lt-- 2 (b-r)/delta
if b max then h lt-- 4 (r - g)/delta h
lt-- h 60 convert to degrees if h lt 0
then h lt-- h 360 end
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Using colour in MATLAB
Finding the colour depth in your system
get(0,'screendepth')
For an m x n image MATLAB creates
For an RGB image an array of double m x n x 3
For a uint8 image an array of byte m x n x 3
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Displaying individual colour images
function colourdisplay To demonstrate the
splitting of an image into its primary colours A
imread('monar.jpg') subplot(2,2,1)
imshow(A) title('RGB image') Redimage
A(,,1) subplot(2,2,2) imshow(Redimage) title(
'Red image') Greenimage A(,,2) subplot(2,2,3
) imshow(Greenimage) title('Green
image') Blueimage A(,,3) subplot(2,2,4)
imshow(Blueimage) title('Blue image')
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A1 rgb2hsv(A)
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Using colour maps
colormap(hsv(16))
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Inspecting colours in an image
improfile which will reveal the colour
intensity profile along a line defined on the
image.   pixval which will interactively record
the location and colour components of each pixel
as you move a cursor across the image.   impixel
returns the RGB values for a specified pixel.
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Ray Tracing
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Ray intersection with a bounding sphere
?i (c - s) ?d
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