1 Digital Image Processing Jen-Hui Chuang Department of Computer Science National Chiao Tung University 2 6 Color Image Processing 6.1 Color Fundamentals 6.2 Color Models 6.3 Pseudocolor Image Processing 6.4 Basics of Full-Color Image Processing 6.5 Color Transformations 6.6 Smoothing and Sharpening 6.7 Image Segmentation Based on Color 6.8 Noise in Color Images 6.9 Color Image Compression 3 Color Spectrum 6.1 Color Fundamentals 4 6.1 Color Fundamentals Spectrum of Electromagnetic Waves 5 6.1 Color Fundamentals Three basic quantities to describe the quality of a chromatic light source: Radiance — … energy … light source Luminance — … energy … observer Brightness —… a subjective descriptor … 6 Absorption of light by cones in human eye Primary colors (CIE): R: 700 nm G: 546.1 nm B: 435.8 nm 2% 32% 65%
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Digital Image Processing
Jen-Hui Chuang
Department of Computer ScienceNational Chiao Tung University
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6 Color Image Processing6.1 Color Fundamentals 6.2 Color Models 6.3 Pseudocolor Image Processing 6.4 Basics of Full-Color Image Processing 6.5 Color Transformations 6.6 Smoothing and Sharpening 6.7 Image Segmentation Based on Color 6.8 Noise in Color Images 6.9 Color Image Compression
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Color Spectrum
6.1 Color Fundamentals
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6.1 Color Fundamentals
Spectrum of Electromagnetic Waves
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6.1 Color Fundamentals
Three basic quantities to describe the quality of a chromatic light source:
Radiance — … energy … light source
Luminance — … energy … observer
Brightness —… a subjective descriptor …
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Absorption of light by cones in human eye
Primary colors (CIE):
R: 700 nmG: 546.1 nmB: 435.8 nm
2% 32% 65%
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Primary and secondary colors
Trisitimulus values: X, Y, and Z
Trichromatic coefficients:
x = X / (X + Y + Z)y = Y / (X + Y + Z)z = Z / (X + Y + Z)
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Chromaticity Diagram
88888
z = 1 – x – y
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Typical color gamut of color monitors andcolor printing devices
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6.2 Color Models6.2.1 The RGB Color Model
Ex. 6.1 The RGB color cube
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Ex. 6.1 The RGB color cube (cont.)
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Ex. 6.1 The RGB color cube (cont.)
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The RGB safe-color cube
11111111111111133 14
6.2.2 The CMY and CMYK Color Models
6.2.3 The HSI Color ModelConceptual relationship between RGB and HSI models
C = 1 – RM = 1 – G subtractive Y = 1 – B
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Hue, Saturation and Intensity
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Hue, Saturation and Intensity
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GBif-360GBif
H
})])(()[(
)]()[(21
{cos 2/121
BGBRGR
BRGR
)],,[min(31 BGRBGR
S
)(31 BGRI
= 1 – min(R,G,B)/I
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Ex. 6.2 HSI values and the RGB color cube
H S I
)(31 BGRIS = 1 – min(R,G,B)/IH
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Manipulating HSI component images
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?
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H
S I
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Manipulating HSI component images (cont.)
H S
I20
6.3 Pseudocolor Image Processing
6.3.1 Intensity Slicing
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6.3.1 Intensity Slicing
Ex. 6.3
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Ex. X-ray image of a weld
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Ex. 6.4 Use of color to highlight rainfall levels
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Ex. 6.4 Use of color to highlight …
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Ex. 6.4 Use of color to highlight …
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6.3.2 Gray Level to Color Transformations
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Ex. 6.5 Use of pseudocolor to highlight explosives