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Chapter 8 Computer Vision

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Chapter 8 Computer Vision

- What is Image Processing?
- Digital Image Processing
- Electromagnetic Spectrum
- Steps in Digital Image Processing

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Image Processing Fields

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- “Digital Image”?
- Digital
- Image

- “Image Processing”?

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What is a signal?

A signal is a function that maps a set (domain) to another set (range)

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A signal is a function that maps a set (domain) to another set (range)

For each point in time (t), assign a voltage value (y(t)).

Domain = time interval

Range = voltage interval

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- Image
- An image is a two-dimensional signal

A signal is called two-dimensional

if the domain is two-dimensional

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- Image
- An image is a two-dimensional signal

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- Digital Image
- Vs Analog image?

- Digital vs analog signal

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- Domain
- Range
- Countable
- Quantized Signal

- Countable

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- A signal is “digital”
- if both the domain andthe rangeare countable
- I.e., if it is a quantized discrete-time (or -space) signal

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- Digital Image
- A digital image is a two-dimensional signal with a countable domain and a countable range

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- Digital Image

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- How is a digital signal formed?
- Discrete domain
- Domain is inherently discrete, or
- Sample a continuous interval

- Discrete range
- Range is inherently discrete, or
- Sample a continuous interval

- Discrete domain

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- Continuous-time signals
- t and y (t) have physical meanings

- Digital signals
- n and y (n) do not have physical meanings and can be arbitrary

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1921

Range has 5 values!

1922

1929

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1964

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4. Multispectral: Visible+Infrared Bands

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4. Multispectral: Visible+Infrared Bands

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5. Infrared Range

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Steps in Digital Image Processing

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Distorted image

Restore image

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Image Enhancement

in the Spatial Domain

- Spatial Domain
- Point Process
- Transformation functions
- Histogram
- Spatial Filtering
- Mask Operation
- Image Enhancement
- Smoothing Filter

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- An image processing system maps an input image to an output image

Output images

Input images

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- Output pixel depends on the input image pixels
- Usually:

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Transformation functions

1. contrast stretching

2. point processing : Thresholding Function

Transformation function

s= T [r]

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Transformation functions

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Transformation functions

light

dark

s

s= T [r]

r

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dark light

Transformation functions

original image

negative transformation

s= L-1 -r

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Power-Law Transformations

= 3

= 4

= 5

s= cr

มืดลง

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- Count the number of pixels with each gray level

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Histogram

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Histogram Equalization

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Histogram Equalization

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Histogram Equalization

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Spatial Filtering

ค่าน้ำหนัก

ค่าPixels

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Image Enhancement

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Image Enhancement

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Image Segmentation

- horizontal,... +45 degree,.. vertical... and -45 degree masks
- Horizontal mask will result with max response when a line passed through the middle row of the mask with a constant background.
- the similar idea is used with other masks.
- note: the preferred direction of each mask is weighted with a larger coefficient ....(i.e.,2)than other possible directions.

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link criteria:

1). the pixels belonged to one of the set of pixels linked according to the highest count

2). no gaps were longer than 5 pixels

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The End

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