Color Image Processing

Image Processing

CSE 166

Lecture 9

Announcements

• Assignment 3 is due today, 11:59 PM

• Midterm exam is on May 4

• Reading

– Sections 7.1-7.6: Color Image Processing

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Electromagnetic spectrum

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Separating visible light

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Human eye cones

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Mixing light

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Light

Pigment

Primary and secondary colors are swapped

Note that green, cyan, and blue are not accurate colors in the book. More

accurate colors below.

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BLUE

GREEN

RED

CYAN

MAGENTA

YELLOW

RGB color model

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RGB coordinates

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RGB color cube

XYZ color model andchromaticity coordinates

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Not actual colors

locations; just gives an idea

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Color gamuts

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Averageperson

Computermonitor

Printer

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HSI color model:Relationship to RGB color model

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All colors with cyan

hue

RGB color cube rotated such that line joining black and white

(intensity axis) is vertical

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HSI color model

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RGB color cube rotated such that

observer is on intensity axis, beyond white looking towards

black

Shape does not matter, only angle from red14

RGB color cube

HSI intensity axis

HSI color model

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HS-plane is orthogonal to intensity axis

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HSI

RGB

CMYK

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Color models

CMY

Pseudocolor image processing

• Intensity slicing

• Intensity to color transformations

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Intensity slicing

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Grayscale to 2 colors

Intensity slicing

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Grayscale to 2 colors

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Intensity slicing

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Grayscale to 8 colors

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Intensity slicing

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Grayscale to 256 colors

Colorbar

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Intensity to color transformations

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Grayscale input image

RGBoutput image

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Intensity to color transformations

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X-ray grayscale input image

Misses explosive

RGB output images

Without explosive

With explosive

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Intensity to color transformations

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Multiple grayscale

input images

SingleRGB

output image

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Intensity to color transformations

Near infrared (NIR)

Red (R)

NIR,G,B as RGB R,NIR,B as RGB25

Green (G) Blue (B)

Multiple satellite

grayscale input

images

Output RGB images

Intensity to color transformations

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SingleRGB

output image

Multiple grayscale input images,

some outside of visible spectrum

Close up

Physical and chemical

processes likely to affect sensor

response

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Full-color image processing

• Two approaches

– Process each channel independently

– Process color vector space

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Full-color image processing

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Spatial filtering: process each channel independently

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Full-color image processing

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All RGB channels

HSI intensity channel only

Spatial filtering: image smoothing

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Difference

Full-color image processing

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All RGB channels

HSI intensity channel only

Spatial filtering: image sharpening

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Difference

Full-color image processing

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Histogram equalization: do not process each channel independently

1. RGB to HSI2. Histogram

equalize HSI intensity channel

3. HSI to RGB31

4. HSI saturation adjustment

Next Lecture

• Midterm exam review

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