Digital Image Processing

Hongtao Lu

Dept. of Computer Science

Sept. 2006

Text Book

DIGITAL IMAGE PROCESSING

Kenneth R. Castleman

清华大学出版社 / Prentice Hall

1997

Reference Books

Digital Image Processing (Second Edition)

Rafael C. Gonzalez and Richard E. Woods

电子工业出版社 原版影印 2002 年 数字图像处理学，阮秋琦 编著，电子工

业出版社， 2001 年

Chapter 1 Images and Digital Processing1.1 Introduction

What is an image?

An image may be defined as a two-dimensional function, f(x,y), where x and y are spatial (plane) coordinates, and the amplitude of f at any pair of Coordinate (x,y) is called the intensity or gray level of the image at that point.

What is a digital image?– When x, y and the amplitude f(x,y) of an image

are all finite, discrete quantities, an image is called a digital image.

– A digital image is composed of a finite number of elements, each such element is called a picture element or a pixel.

– A digital image is a numerical representation of an object

What is Digital Image Processing?– Processing image by means of a digital

computer– Digital image processing is a process that

subjecting a numerical representation of an object to a series of operations in order to obtain a desired result.

1.2 The elements of digital image processing Digitization

– Process of converting a physical image to a digital image

– Spatial sampling (Rectangular sampling)

Physical

Image

– Quantization: representing the continuous intensity value with finite number of integers.

A typical image-processing system

Image Digitizer

Input Image Storage

ComputerOutput Image Storage

Console

Image Recorder

Program Library

1.2.1 The Terminology of DIP

Physical images– Distributions of matter or energy (may be visibl

e or nonvisible)– Multi-spectral images----those having more tha

n one local properties at each location. Color image

Abstract images– Continuous or discrete functions

Types of imagesObjects

Images

Visible images

Pictures

Photographs

Drawings

Paintings

Optical images

Mathematical functions

Continuous

Discrete

Non-visible physical images

Computer Graphics– Processing and display of images of things that

exist conceptually or as mathematical descriptions.

– Generation of a image, given a model that describes the object, its illumination, and the geometry of an imaginary camera.

Computer vision– Developing systems that can interpret the conte

nt of natural scenes.

Chapter 2 Digitizing Images

2.1 Introduction– The Elements of a digitizer

• Sampling aperture

• Mechanism for scanning the image

• Light sensor

• Quantizer

• Output storage medium

2.2 Characteristics of an image digitizer– Pixel size– Image size– Local property measured– Linearity– Noise

2.3 Types of image digitizer– Scan-in and Scan-out Digitizing

2.4 Image-Digitizing Components– 2.4.1 Light Sources

• Incandescent Bulbs

• Lasers

• Phosphors

• LEDs

2.4.2 Light Sensors– Photoemissive Devices ( 光电发射器件 )– Silicon Sensors– Photodiodes( 光敏二极管 )– Phototransistor( 光敏三极管 )

2.4.3 Scanning Mechanisms– Mechanical scanning devices– Electron beam scanning

– Electrostatic deflection ( 静电偏转 )– Magnetic Deflection ( 磁偏转 )– Beam focus ( 电子束聚焦 )

Chapter 3 Digital Image Display

3.1 Introduction– 3.1.1 Image quality

3.2 Display Characteristics– Displayed image size– Photometric resolution ( 光度分辨率）– Gray-scale linearity– Display calibration– Low frequency response

• Pixel polarity

• Pixel interaction

• The Gaussian display spot

• Display spot interaction

)( 22

),( yxeyxp

Examples of Fields that use DIP (supplement) Images categorized by electromagnetic (E

M) energy spectrum

510 410 310 210 110 010 110 210 310 410 510 610 710

Energy of one photon

Gamma rays

X-rays Ultra-violet

Visible Infrared Microwaves Radio waves

Gamma-Ray Imaging– Nuclear medicine– Astronomical observations

Positron emission tomography PET A PET image

X-ray Imaging

– X-ray medical diagnostics– Angiography (contrast-enhancement radiograp

hy)– Computerized axial tomography– Astronomy– Applications (e.g. X-ray inspection)

X-ray imaging

An angiogram image Head CT

X-ray imaging

An X-ray image of circuit board

Imaging in the Ultraviolet band

– Fluorescence microscopy– Lithography– Industrial inspection– Astronomical observations

A Fluorescence microscope

Imaging in the visible and infrared bands

– Light microscope

Taxol Cholesterol Surface of audio CD

Remote sensing (multispectral imaging)

Weather observation and prediction

– Automated visual inspection in manufacture industrial

– Pattern recognition

Imaging in the microwave band

Radar

Radar image of Southeast Tibet

Imaging in the Radio band– Medicine (MRI: Magnetic resonance imaging)– Astronomy

MRI Knee

Examples of other imaging modalities Imaging using “Sound”

– Geological exploration (Using sound in the low end of the sound spectrum (hundreds of Hertz)

– Medicine (ultrasound imaging, 1-5 MHz)

Electron microscope

Synthetic image (generated by computer)

– Fractal– 3-D modeling

Fundamental steps in DIP

Color image processing

Wavelets and multiresolution

Compression Morphological processing

Image restoration

Image enhancement

Image acquisition

Segmentation

Representation & description

Object recognition

Problem domain

Ou

tpu

t image attrib

utes

Output images

Knowledge base

Components of an image processing system

Image displays

Computer Mass storage

HardcopySpecialized image processing hardware

Image processing software

Image sensors

Problem domain

Network

Elements of visual perception

Perceived brightness is not a simple function of intensity

An example of simultaneous contrast

Some well-known optical illusion