Chapter 8 Computer Vision

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# Chapter 8 Computer Vision - PowerPoint PPT Presentation

Chapter 8 Computer Vision. Contents. What is Image Processing? Digital Image Processing Electromagnetic Spectrum Steps in Digital Image Processing. What is Image Processing?. Application Area. Image Processing Fields. Image Processing Fields. Digital Image Processing.

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## Chapter 8 Computer Vision

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### Chapter 8 Computer Vision

Contents
• What is Image Processing?
• Digital Image Processing
• Electromagnetic Spectrum
• Steps in Digital Image Processing

Chapter 9

Digital Image Processing
• “Digital Image”?
• Digital
• Image
• “Image Processing”?

Chapter 9

Digital Image Processing

What is a signal?

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

Chapter 9

Digital Image Processing

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

Chapter 9

Digital Image Processing
• Image
• An image is a two-dimensional signal

A signal is called two-dimensional

if the domain is two-dimensional

Chapter 9

Digital Image Processing
• Image
• An image is a two-dimensional signal

Chapter 9

Digital Image Processing
• Digital Image
• Vs Analog image?
• Digital vs analog signal

Chapter 9

Signal Types
• Domain
• Range
• Countable
• Quantized Signal

Chapter 9

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

Chapter 9

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

Chapter 9

Digital Image Processing
• Digital Image

Chapter 9

Digital Signal
• 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

Chapter 9

Domain and Range
• 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

Chapter 9

Digital Images: 80 years ago

1921

Range has 5 values!

1922

1929

Chapter 9

3. UV Imaging

Chapter 9

4. Visible Range

1964

Chapter 9

Ultrasound Image

Chapter 9

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5

6

7

8

3

11

2

9

1

10

Steps in Digital Image Processing

Chapter 9

1

Chapter 9

2

Chapter 9

Distorted image

Restore image

3

Chapter 9

4

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Chapter 9

Knowledge Base

11

Chapter 9

Image Enhancement

in the Spatial Domain

Contents
• Spatial Domain
• Point Process
• Transformation functions
• Histogram
• Spatial Filtering
• Image Enhancement
• Smoothing Filter

Chapter 9

Image Processing
• An image processing system maps an input image to an output image

Output images

Input images

Chapter 9

Image Processing
• Output pixel depends on the input image pixels
• Usually:

Chapter 9

Transformation functions

1. contrast stretching

2. point processing : Thresholding Function

Transformation function

s= T [r]

Chapter 9

Transformation functions

light

dark

s

s= T [r]

r

Chapter 9

dark light

Transformation functions

original image

negative transformation

s= L-1 -r

Chapter 9

Power-Law Transformations

 = 3

 = 4

 = 5

s= cr

มืดลง

Chapter 9

Histogram
• Count the number of pixels with each gray level

Chapter 9

Histogram

Chapter 9

Histogram

Chapter 9

Spatial Filtering

ค่าน้ำหนัก

ค่าPixels

Chapter 9

Line Detection
• 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.

Chapter 9

Example

Chapter 9

Example

Chapter 9