GNR607 Principles of Satellite Image Processing Instructor: Prof. - - PowerPoint PPT Presentation

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GNR607 Principles of Satellite Image Processing Instructor: Prof. - - PowerPoint PPT Presentation

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GNR607 Principles of Satellite Image Processing Instructor: Prof. B. Krishna Mohan CSRE, IIT Bombay bkmohan@csre.iitb.ac.in Slot 2 Lecture 2 Introduction to Digital Image Processing July 22, 2014 10.35 AM 11.30 AM IIT Bombay

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GNR607 Principles of Satellite Image Processing

Instructor: Prof. B. Krishna Mohan CSRE, IIT Bombay bkmohan@csre.iitb.ac.in

Slot 2 Lecture 2 Introduction to Digital Image Processing July 22, 2014 10.35 AM – 11.30 AM

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Contents of the Lecture

  • Concept of a digital image
  • Digitization
  • Components of a digital image

processing system

  • Steps in digital image processing

IIT Bombay Slide 1 GNR607 Lecture 2 B. Krishna Mohan July 22, 2014 Lecture 2 Intro. Image Processing

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What is a Digital Image?

A digital image is a representation of the real world, discretized in space with energy reflected / emitted / transmitted by the objects in the image quantized to a finite number of levels

IIT Bombay Slide 2 GNR607 Lecture 2 B. Krishna Mohan

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Camera

Real World Scene Digital Image

Pixel

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 3

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Digitization

  • Digitization involves three steps:

–Sampling –Quantization –Coding

IIT Bombay Slide 4 GNR607 Lecture 2 B. Krishna Mohan

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Sampling

  • View area divided into cells
  • Each cell is a picture element pixel
  • The image now is a matrix of M rows, and

N columns

  • M = Length of View area / Length of Cell
  • N = Width of View area / Width of Cell
  • Smaller cell size better ability to

distinguish between closely spaced

  • bjects

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 5

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Sampling

  • In remotely sensed images the sampling is

essentially ground sampling – i.e., on the ground a virtual grid is placed and the energy reflected / transmitted / emitted from each grid cell is collected by the sensors and stored as a pixel value

  • The grid cell corresponds to a pre-defined area
  • n the ground; e.g., 5.8m x 5.8m as in case of

ISRO’s Resourcesat Satellite

IIT Bombay Slide 6 GNR607 Lecture 2 B. Krishna Mohan

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Sampling

  • Smaller the grid cell area better the details

visible in the image

  • The grid cell corresponding to a pre-

defined area on the ground; e.g., 5.8m x 5.8m

  • This is similar to dpi settings in desktop

image scanners. Higher dpi, smaller size

  • f dot, more pixels or cells in the image

IIT Bombay Slide 7 GNR607 Lecture 2 B. Krishna Mohan

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Spatial Resolution

IIT Bombay Slide 7a GNR607 Lecture 2 B. Krishna Mohan

Source not known, to be located!

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Impact of Pixel Size

  • Pixel size corresponds to the

Instantaneous Field of View (IFOV) of the sensing system

  • Smaller the IFOV, better is the ability to

resolve closely spaced objects (RESOLUTION)

  • Price to pay – larger size of data
  • Noise sensitivity of the sensor determines

the maximum possible resolution

IIT Bombay Slide 8 GNR607 Lecture 2 B. Krishna Mohan

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Point to Note

  • IFOV is 10 metres x 10 metres square does

not mean that objects smaller than this size will not be visible

  • If a smaller object has very high or very

low reflectance relative to its background, such object will be visible despite its size being smaller than the pixel’s IFOV

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 9

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Quantization

  • Reflected / transmitted / emitted energy from

the object is converted into an electrical signal

  • The electrical signal converted to a digital

signal by an analog-to-digital converter (ADC).

  • Digital signal takes a range of values

according to the specification of the ADC

IIT Bombay Slide 10 GNR607 Lecture 2 B. Krishna Mohan

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Shades in Image and Digital Values

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 11 0 255

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ADC

  • 8-bit ADC  28 distinct values, represented in

binary as 00000000 – 11111111, or 0 to 255 in decimal form or 00 to FF in hex

  • 11-bit ADC  211 values, 0 to 2047
  • The number of levels indicate the number of

distinct individually differentiable levels of received energy

IIT Bombay Slide 12 GNR607 Lecture 2 B. Krishna Mohan

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64 levels (6 bit) – more shades visible 4 levels (2 bit) – severe contouring effect IIT Bombay Slide 13

Impact of quantization levels

GNR607 Lecture 2 B. Krishna Mohan

Source unknown, to be found!

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Point to Note

  • When an image contains regions of fine

detail, high spatial resolution (e.g. a stadium with large crowd) is important

  • When the image contains large regions of

very little change such as a close-up of a person, high number of quantization levels is important

IIT Bombay Slide 14 GNR607 Lecture 2 B. Krishna Mohan

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Pixel Size Less Important

Original (After dpi reduced by 50%) IIT Bombay Slide 15 GNR607 Lecture 2 B. Krishna Mohan

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Quantization Levels More Important

256 levels 8 levels IIT Bombay Slide 16 GNR607 Lecture 2 B. Krishna Mohan

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Pixel Size Important

160 x150 80 x 75 IIT Bombay Slide 17 GNR607 Lecture 2 B. Krishna Mohan

24-bit 24-bit

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Number of Levels less Important

160 x150 160 x 150 IIT Bombay Slide 18 GNR607 Lecture 2 B. Krishna Mohan

24-bit 8-bit

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Encoding

  • Normally the quantized image is binary

encoded.

  • If the number of quantization levels is

between 0 and 255, each pixel is represented by 1-byte

  • If the number of levels exceeds 255, each

pixel is assigned two-bytes.

  • At present, American satellites Quickbird,

Ikonos, Indian satellites Cartosat and a few others have 11 bit and 10 bit ADCs and store data in 2 bytes per pixel on disk.

IIT Bombay Slide 19 GNR607 Lecture 2 B. Krishna Mohan

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Motivation for Digital Image Processing

  • Why Digital Image Processing for Remote

Sensing? – Nature of data (inherently digital) – Flexibility offered by computers – Reducing the bias of human analysts – Standardizing routine operations – Rapid handling of large volumes of data

IIT Bombay Slide 20 GNR607 Lecture 2 B. Krishna Mohan

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Motivation for Digital Image Processing

  • Why Digital Image Processing for Remote

Sensing? – Certain operations cannot be done manually (removal of distortions) – Generation of different views – Archival in compact/compressed mode – Easy to share and disseminate

IIT Bombay Slide 21 GNR607 Lecture 2 B. Krishna Mohan

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The Origins of Digital Image Processing

Early 1920s: One of the first applications in the news- paper industry, cable transmission between NY and London ––Source: http://www. imageprocessingplace.com

IIT Bombay Slide 22 GNR607 Lecture 2 B. Krishna Mohan

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Historical Developments

  • Mid to late 1920s: Improvements to the

Bartlane system resulted in higher quality images–New reproduction processes based on photographic techniques–Increased number of tones in reproduced imagesImproved digital image.

IIT Bombay Slide 23 GNR607 Lecture 2 B. Krishna Mohan

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Space Race for Moon

  • Improvements in computing technology and

the onset of the space race for moon led to a surge of work in digital image processing

  • Computers used to improve the quality of

images of the moon taken by the Ranger 7 probe–Such techniques were used in other space missions including the Apollo landings

IIT Bombay Slide 24 GNR607 Lecture 2 B. Krishna Mohan

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Medicine

  • Digital image processing begins to be used

in medical applications–1979:Sir Godfrey N. Hounsfield& Prof. Allan M. Cormack share the Nobel Prize in medicine for the invention

  • f tomography, the technology behind

Computerised Axial Tomography (CAT) scans

IIT Bombay Slide 25 GNR607 Lecture 2 B. Krishna Mohan

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1980’s and later

  • 1980s -Today: The use of digital image

processing techniques has exploded and they are now used for all kinds of tasks in all kinds of areas

  • –Image enhancement/restoration
  • –Artistic effects
  • –Medical visualization
  • –Industrial inspection
  • –Law enforcement
  • –Human computer interfaces

IIT Bombay Slide 26 GNR607 Lecture 2 B. Krishna Mohan

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Wavelengths used for Imaging

  • Gamma Rays Wavelength
  • X-Rays
  • Visible/Infrared Rays
  • Microwaves
  • Radio waves
  • Ultrasound waves
  • Seismic waves Frequency

IIT Bombay Slide 27 GNR607 Lecture 2 B. Krishna Mohan

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Components of an Image Processing System

  • Image Sensors
  • Image Display
  • Image Storage
  • Computer
  • Image Processing software
  • Special Purpose graphics hardware
  • Image printers/plotters

IIT Bombay Slide 28 GNR607 Lecture 2 B. Krishna Mohan

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Image Image Image Displays Storage Hardcopy Dedicated

Digital DIP/DIA Graphic Proc. Computer Software

Image Acquisition

from real world

IIT Bombay Slide 29 GNR607 Lecture 2 B. Krishna Mohan

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PC-Based Image Processing Systems

  • Today’s personal computers with a digital

still / video camera and a printer can become full fledged image processing systems

  • Most commercial / shareware / freeware

image processing software will run on normal personal computer configurations

IIT Bombay Slide 30 GNR607 Lecture 2 B. Krishna Mohan

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Steps in Image Processing

IIT Bombay Slide 31 GNR607 Lecture 2 B. Krishna Mohan

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Steps in Digital Image Processing

Final Interpretation

IIT Bombay Slide 32 Image Acquisition Image Corrections Image Enhancement Image Transforms Feature Selection Image Classification GNR607 Lecture 2 B. Krishna Mohan

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Steps in Image Processing

  • Image Acquisition
  • Image Corrections
  • Image Enhancement
  • Image Transforms
  • Feature Selection
  • Classification and Interpretation
  • Accuracy Assessment
  • Change Detection
  • Efficient Representation and Coding
  • Applications

IIT Bombay Slide 33 GNR607 Lecture 2 B. Krishna Mohan

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Limitations of Computer Based Image Interpretation

  • Lack of access to human intuition
  • Ambiguities

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What is the background?

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http://en.wikipedia.org/wiki/Figure %E2%80%93ground_%28perception%29

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Illusions

The Bunny/Duck illusion. Mouth Mouth

IIT Bombay Slide 36 GNR607 Lecture 2 B. Krishna Mohan

http://mathworld.wolfram.com/Rabbit-DuckIllusion.html

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Illusions

IIT Bombay Slide 37 GNR607 Lecture 2 B. Krishna Mohan

Source: http://en.wikipedia.org/ wiki/Optical_illusion

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Some Applications of Image Processing and Imaging

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Quality Improvement

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 38

Source: http://www. imageprocessingplace.com

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Hubble Telescope Example

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 39

Source: http://www. imageprocessingplace.com

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S p e c i a l E f f e c t s

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 40

Source: http://www. imageprocessingplace.com

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Remote Sensing

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 41

Source: http://www. imageprocessingplace.com

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Industrial Inspection

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 42

Source: http://www. imageprocessingplace.com

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Law Enforcement

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 43

Source: http://www. imageprocessingplace.com

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Wavelengths for Image Acquisition

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EM Spectrum

To develop a basic understanding of the extent of image processing applications is to categorize images according to their source(e.g., visual, X-ray, and so on). Electromagnetic waves : propagating sinusoidal waves of varying wavelengths, massless particles, moving at the speed of light with photon (energy of bundle)

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 44

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Gamma- Ray Imaging

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 45

Source: www.imageprocessingplace. com

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X-ray Imaging

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 46

Source: www.imageprocessingplace. com

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Imaging in the Ultraviolet Band

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 47

Source: www.imageprocessingplace. com

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Imaging in the Visible and Infrared Band

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 48

Source: www.imageprocessingplace. com

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Imaging in the Visible and Infrared Band

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 49

Source: www.imageprocessingplace. com

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Imaging in the Visible and Infrared Band(con’t)

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 50

Source: www.imageprocessingplace. com

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Imaging in the Visible and Infrared Band(con’t)

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 51

Source: www.imageprocessingplace. com

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Imaging in the Visible and Infrared Band(con’t)

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 52

Source: www.imageprocessingplace. com

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Imaging in the Visible and Infrared Band (con’t)

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 53

Source: www.imageprocessingplace. com

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Imaging in the Microwave Band

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 54

Source: www.imageprocessingplace. com

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Imaging in the Radio Band

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 55

Source: www.imageprocessingplace.com

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Examples in which Other Imaging Modalities are Used

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 56

Source: www.imageprocessingplace.com

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Examples in which Other Imaging Modalities are Used(con’t)

GNR607 Lecture 2 B. Krishna Mohan IIT Bombay Slide 57

Source: www.imageprocessingplace. com

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To be continued …