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 Processing 1.1 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 Computer Output Image Storage Console Image Recorder Program Library

1.2.1 The Terminology of DIP  Physical images –Distributions of matter or energy (may be visible or nonvisible) –Multi-spectral images----those having more than one local properties at each location. Color image  Abstract images –Continuous or discrete functions

Types of images Objects 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 content 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

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

Examples of Fields that use DIP (supplement)  Images categorized by electromagnetic (EM) energy spectrum Energy of one photon Gamma rays X-rays Ultra- violet Visible InfraredMicrowavesRadio 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 radiography) –Computerized axial tomography –Astronomy –Applications (e.g. X-ray inspection)

X-ray imaging An angiogram imageHead 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 TaxolCholesterolSurface 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 Output image attributes Output images Knowledge base

Components of an image processing system Image displays Computer Mass storage Hardcopy Specialized 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