Colour [Compatibility Mode]
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Transcript of Colour [Compatibility Mode]
INTRODUCTION TO INTRODUCTION TO
COLOR MODELLINGCOLOR MODELLING
CONTENTS
• INTRODUCTION
• COLOR IMAGE PROCESS• COLOR IMAGE PROCESS
• COLOR MODELS
• COLOR MODELING –RGB – CMY – YIQ –
HSL – HSV
COLOR IMAGE PROCESSING
COLOR MODELS
• Color Model• A mathematical system for representing color
• The human eye combines 3 primary colors (using the 3 different types of cones) to discern all possible colors.types of cones) to discern all possible colors.
• Colors are just different light frequencies
• red – 700nm wavelength
• green – 546.1 nm wavelength
• blue – 435.8 nm wavelength
• Higher frequencies are cooler colors
4
Color Models
Primary Colors
• Primary colors of light are additive
• Primary colors are red, green, and blue
• Combining red + green + blue yields white
• Primary colors of pigment are subtractive
• Primary colors are cyan, magenta, and yellow
• Combining cyan + magenta + yellow yields
black6
CMY YIQ HSL HSV
RGB
INTRODUCTION TO COLOR MODELLINGINTRODUCTION TO COLOR MODELLING
RGB
Gamma correction
Color lookup table
values
RGB Color model
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Active displays, such as computer monitors and television sets, emit
combinations of red, green and blue light. This is an additive color model
Source: www.mitsubishi.com
CMY Color model
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Passive displays, such as color inkjet printers, absorb light instead of
emitting it. Combinations of cyan, magenta and yellow inks are used. This
is a subtractive color model.
Source: www.hp.com
RGB Vs CMY
RGB color cube
RGB 24-bit color cube
RGB Example
12
Original Green Band Blue BandRed Band
RGB and CMY Color Cubes
13
RGB AND CMY COLOR CUBES
Light Intensity
• Note that intensity is a weighted function of the r, g, b
values.
• The human eye doesn’t weight each component
identically!
• intensity = 0.299*Red + 0.587*Green +
0.144*Blue
• Assume three light sources have the same actual intensity
but are colored red, green, and blue
• The green light will appear brightest followed by red and blue
15
YIQ MODEL
YIQ is the color space used by the NTSC color TV system,
employed mainly in North and Central America, and Japan
The Y component represents the luma information, and is the
only component used by black-and-white television receivers.
YIQ(color modelling)
only component used by black-and-white television receivers.
I and Q represent the chrominance information. In YUV, the U
and V components can be thought of as X and Y coordinates
within the color space. I and Q can be thought of as a second
pair of axes on the same graph, rotated 33°; therefore IQ and
UV represent different coordinate systems on the same plane.
Color images are encoded as triplets of values.
RGB is an additive color model that is used for light-emitting devices,
e.g., CRT displays
CMY is a subtractive model that is used often for printers
Two common color models in imaging are RGB and CMY, two common
YIQ(color modelling)
Two common color models in imaging are RGB and CMY, two common
color models in video are YUV and YIQ.
YUV uses properties of the human eye to prioritize information. Y is the
black and white (luminance) image, U and V are the color difference
(chrominance) images.
YIQ uses similar idea.
Besides the hardware-oriented color models (i.e., RGB, CMY, YUV,
YIQ), HSB (Hue, Saturation, and Brightness) and HLS (Hue, Lightness,
and Saturation) are also commonly used.
Yiq colour descripton.
Example for yiq photo which is used in
televisions
HSV MODEL
HSV is another way to describe color with 3 parameters. RGB is the way
computer screens work, but not very intuitive. HSV is more intuitive, but
you need to convert it to RGB before you can draw a pixel with it. The
nicest application of this color model is that you can easily create
rainbow gradients or change the color, lightness or saturation of an
image with this color model.
HSV color obviously has the parameters H, S and V, or Hue, Saturation HSV color obviously has the parameters H, S and V, or Hue, Saturation
and Lightness Value.
Hue indicates the color sensation of the light, in other words if the color
is red, yellow, green, cyan, blue, magenta, ... This representation looks
almost the same as the visible spectrum of light, except on the right is
now the color magenta (the combination of red and blue), instead of
violet (light with a frequency higher than blue):
Hue works circular, so it can be represented on a circle instead. A hue of
360° looks the same again as a hue of 0°.
Saturation indicates the degree to which the hue differs from a neutral gray. The values run from 0%, which is no color, to 100%, which is the fullest saturation of a given hue at a given percentage of illumination. The more the spectrum of the light is concentrated around one wavelength, the more saturated the color will be.Lightness indicates the illumination of the color, at 0% the color is completely black, at 50% the color is pure, and at 100% it becomes white. In HSL color, a color with maximum lightness (L=255) is always white, no matter maximum lightness (L=255) is always white, no matter what the hue or saturation components are. Lightness is defined as (maxColor+minColor)/2 where maxColoris the R, G or B component with the maximum value, and minColor the one with the minimum value
HSL MODEL
HSL is another way to describe color with 3 parameters. RGB is the way
computer screens work, but not very intuitive. HSL is more intuitive, but
you need to convert it to RGB before you can draw a pixel with it. The
nicest application of this color model is that you can easily create rainbow
gradients or change the color, lightness or saturation of an image with this
color model.
HSL color obviously has the parameters H, S and L, or Hue, Saturation
and Lightness.
Hue indicates the color sensation of the light, in other words if the color is
red, yellow, green, cyan, blue, magenta, ... This representation looks almost
the same as the visible spectrum of light, except on the right is now the
color magenta (the combination of red and blue), instead of violet (light
with a frequency higher than blue):
Hue works circular, so it can be represented on a circle instead. A hue of
360° looks the same again as a hue of 0°.
Hue colour patterns
Graph showing relation between
(saturation,lightness,hue)
THANK YOU