David E. Pitts

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Overview of Image Processing

by David E. Pitts

Aug 22, 2010copyright 2005, 2006, 2007, 2008, 2009, 2010

David E. Pitts

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A Digital Image is an Array of Numbers Spatially Arranged in a Predetermined FashionEach number in the Array represents one Picture Element

One Pixel

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Digital Image

-Light intensity across the image is a function of x and

-grey level range in each pixel is often 8 bits (256 grey levels)(the human eye resolves about 32)

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Sources of Images

- Film Cameras (film is sensitive from 0.3 to 0.9 µm)-transparencies-prints

-Video Cameras (silicon is sensitive into near infrared 1.1 µm)-X-rays (e.g. Computerized Tomography)-MRI (Magnetic Resonance Imaging)-Ultrasound (medical images)-Infrasound-Seismic-Aircraft and Spacecraft scanners-Telescopes

-Radio, Optical, Gamma Ray, X-ray-Positron Emission Tomography

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Image Artifacts

-Random noise (e.g. blank TV screen)

-Periodic Noise (e.g. herringbone patterns)

-Poor gain (image is too bright or too dark)

-Poor contrast (image is too uniform in brightness)

-Nonuniform response across image (e.g. corners darker than center)

-Smear (e.g. subject moving during image acquisition)

-Curvature of field (e.g. fish eye lens)

- Poor Color

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Approach for Removing Artifacts

- Use off the shelf applicaitons- Photoshop http://www.adobe.com/

- NIH Image http://rsbweb.nih.gov/nih-image/

- Multispec http://dynamo.ecn.purdue.edu/~biehl/MultiSpec/

- Dimple http://www.process.com.au/AboutDIMPLE.shtml

- Develop your own algorithms based on fundamental principles

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Mathematical Operators Used in Imaging

AdditionSubtractionMultiplicationDivision

Linear TransformsNon-Linear Transforms

DifferentiationIntegration

Fourier Transforms

Morphological Operators

Boolean Operators

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Because of the Nature of Digital ImagesOperators are Discrete (e.g. Integration is replaced by Summation)

Operations can be:Between Two or More ImagesOver an Entire ImageWithin a Window ≥ 2 x 2 pixels

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Operations Can Involve Any One of Many Characteristics of an Image

Grey Scale Content (Brightness and Contrast)Color Content (Hue and Saturation)Geometry of Image (2 D, 3 D)Frequency Content of Image (e.g. Noise, Edges, Texture)Shapes of FeaturesAssociation of Patterns (e.g. Shadows)

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Purpose of Imaging Processing

Correct Image DefectsBlurringDistortionsImprove Brightness or ContrastImprove ColorMinimize NoiseRemove Non-Uniform Lumination

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Purpose of Imaging Processing (cont.)

Segmentation of Image (Isolate Desired Features in order to determine characteristics)

SizeLocationShapeOrientationPerimeterMajor and Minor Dimensions

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Single Pixel Operations Within One Digital Image

Operation

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Single Pixel Operations Within One Digital Color Image

Operation

RG

B

RG

B

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Linear Algebraic Operations Between Digital Images

Operation

X Y Z

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Operations Within Windows in One Digital Image

Operation

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Operations Within Windows in One Digital Image

Example: Edge Enhancement of the function g(x,y)

Laplacian =

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Operations Within Windows in One Digital Image

Median Filter = Sort Values from Pixels in Window

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Operations Within Windows in One Digital Image

Average Value Filter

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TEXTURE INFORMATION TECHNIQUES

GRAY LEVEL STATISTICS

FOURIER POWER SPECTRUM

GRAY LEVEL DIFFERENCE STATISTICS

DECORRELATION METHODS

MARKOV RANDOM FILED

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3 X 3 WINDOW WITH GRAY LEVEL 0 TO 3

1 2 3

1 1 2

0 1 2

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A GREY LEVEL CO-OCCURRENCE MATRIX (P )IS DEVELOPED FOR THE DESIRED ORIENTATIONHORIZONTAL, VERTICAL, OR DIAGONAL.

i j

REPRESENTS THE NUMBER OF TIMES i and jARE NEIGHBORS

0 1 2 3 i

0

1

2

3

j

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MANY MEASURES OF TEXTURE CAN BE USED

ANGULAR SECOND MOMENT

∑ { P /R }

ENTROPY

∑ { P /R } LOG { P /R }

2

i j

i j

i j

i j

i j

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INVERSE DIFFERENCE MOMENT

∑ { P /R }/{1/(1+(I-J) )}

AD HOC CHOICES OF # OF GREY LEVELS,ANGULAR ORIENTATION AND SIZE OF WINDOWMUST BE MADE ACCORDING THE TEXTURE TOBE DETECTED

i ji j

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Multiple viewing angle videography

Developed by Carnegie Mellon School of Computer Science

Technique was first used at 2001 Superbowl

Technique uses many synchronized video cameras arrangedin a circle around the scene. At any given time morphing techniques can be utilized to “fly around the scene”.

http://www.cs.cmu.edu/virtualized-reality/main.html

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Image Processing Software

Photoshop by Adobe is the most widely used software. Cost $599Photoshop Elements by Adobe contains most commonly used features of

Photoshop. Mac & Windows, Cost $89

Other Image Processing Software was reviewed in the March/April 2003 issue of Photoelectronic Imaging, pg 14-15.

Asiva Photo by Shapiro Consulting - Windows $378LuminaXYs by Tetrix Technologies - Mac & Windows $99Dfine Photoshop plug-in for noise reduction www.nikmultimedia.comiCorrect Professional 4.0 by Pictographics Mac & Windows $79PhotoKit by Pixel Genius is a Photoshop plug-in, Mac & Windows $49