Image Processing

1
Image Processing

• MR1510
• Lecture 5

2
Image Processing

• Definition
• Image Processing is defined as the "examination,
  processing and analysis of (remotely sensed)
  images for the purpose of identifying objects and
  extracting information"
• Image analysts study remotely sensed data and use
  visual and computer-based processing techniques,
  tools and equipment to detect, identify,
  classify, measure and evaluate physical and
  cultural objects (the environment), their spatial
  patterns and relationships

Data Information Pathway
3
Image Processing

• Images are available in two forms - photographic
  film form and digital form.
• Aerial Photographs (oblique and vertical) taken
  with a camera/film/filter combination are
  considered to be traditional forms of remotely
  sensed imagery known as ANALOG format
• Analysed and Interpreted using Photo-interpretatio
  n (mirror and pocket stereoscopes)
• Variations in the scene characteristics are
  represented as variations in brightness on
  photographic films. A particular part of scene
  reflecting more energy will appear bright while a
  different part of the same scene that reflecting
  less energy will appear black.
• Today, most remotely sensed imagery (as opposed
  to photography) is recorded in a DIGITAL format
  for processing by desktop computers (PCs) to
  produce computer-based images for (online)
  interpretation purposes.

4
Image Processing
128
128
255

• Digital images consist of discrete picture
  elements called PIXELS. Associated with each
  pixel is a number represented as DN (Digital
  Number), that depicts the average radiance of
  relatively small area within a scene. The size of
  this area affects the reproduction of details
  within the scene. As the pixel size is reduced
  more scene detail is preserved in digital
  representation (spatial resolution).

DN
255
128
PIXEL
PIXEL
255
Matrix of Numbers
5
Image Processing

• Analysis of remotely sensed data is undertaken
  using various image processing techniques and
  tools including
• Analog image processing. (traditional)
• Digital image processing. (computer)
• Visual or Analog processing techniques are
  applied to hard copy data/and softcopy or
  on-screen such as photographs or printouts,
  computer displays. Image analysis in visual
  techniques adopts certain elements of
  interpretation, which are as follows
• Tone, Texture, Colour, Shape, Size, Association.
• The use of these fundamental elements depends not
  only on the area being studied, but the knowledge
  the analyst has of the study area. For example
  the texture of an object is also very useful in
  distinguishing objects that may appear the same
  if the judging solely on tone (i.e., water and a
  tree canopy, may have the same mean brightness
  values, but their texture is much different).

6
Aerial Photography
Characteristics
Film Type and Focal length of lens
Bubble Level
Clock
Mask
Altimeter (height)
9 (23cm)
Principal Point (PP)
Fiducial Marks
9 (23cm)
Documentation
7
Aerial Photography
Stereoscopy
Aircraft
Flightline
Photo 1
Photo 2
2D plane
40 gain
60 overlap

• Stereocover (Geonex software Photogrammetric
  Flight Planner)
• Stereoscopic viewing
• Pocket stereoscope
• Mirror stereoscope
• Stereoscopic pair
• Baselining
• Eyebase (distance between photo frames)
• Viewing
• 3D model
• Magnification Exaggeration
• Aid to mapping
• Photogrammetry (quantitative measurements from
  photographs including heighting/contouring)

Height (topography)
3D world
Ground
Sea level
8
Image Processing

• Association, for example, is a very powerful
  image analysis tool when combined with general
  knowledge (apriori) of the site.
• Collateral, Contextual or Ancillary data and
  personal knowledge of the task assist in image
  processing.
• The combination of examining remotely sensed data
  in the form of multispectral, multitemporal,
  multiscale imagery, in conjunction with
  multidisciplinary approaches provide us with a
  clue to identity of a feature
• Analog image processing techniques also include
  optical photogrammetric techniques
  (photgrammetry) allowing for precise measurement
  of the height, width, location, etc. of an
  object.

9
Digital Image Processing

• Digital Image Processing is a collection of
  techniques for the manipulation of digital images
  by computers. Raw data received from sensors on
  the satellite platforms contains flaws and
  deficiencies.
• To overcome these flaws and deficiencies in order
  to get the original data several steps of
  processing are required.
• This varies from image to image depending on the
  type of image format, initial condition of the
  image and the information of interest and the
  composition of the image scene.
• Pre-processing
• Feature Extraction
• Display and enhancement
• Information extraction

1
2
3
1
4
2
3
4
10
Digital Image Processing

• Pre-processing prepares image data for subsequent
  analysis and attempts to correct or compensate
  for systematic errors present in all images.
• The digital images are corrected for geometry and
  atmospheric noise (amongst other things),
• These errors are systematic and can be removed
  before they reach the user.

11
Digital Image Processing

• Geometric Corrections
• Raw digital images often contain serious
  geometrical distortions that arise from Earth
  curvature, platform motion, relief displacement
  of the ground, scanning device. The distortions
  involved are of two types
• Non-systematic Distortion
• Systematic Distortions
• Rectification is the process of projecting image
  data onto a plane or surface and making it
  conform to a map projection system.
• Registration is the process of making image data
  conform to another image. A map coordinate system
  is not necessarily involved.
• Rectification involves rearrangement of the input
  pixels onto a new grid which conforms to the
  desired map projection and coordinate system.
• Rectification and Registration therefore involve
  similar sets of procedures for both the
  distortions.

12
Digital Image Processing

• Atmospheric Corrections
• The output from the instrument on satellite (the
  image) depends on the intensity and spectral
  distribution of energy that is received at the
  satellite.
• The intensity and spectral distribution of
  energy/radiation travels through the atmosphere
  and accordingly suffers both attenuation
  (reduction) and augmentation (addition) in the
  course of journey.
• A problem for interpretation concerns not being
  able to regenerate the correct radiation
  properties of the target body (at the ground) on
  the Earths surface with the data generated by
  the remote sensing
• Restore image

13
Digital Image Processing

• Feature Extraction
• Statistical" characteristics of image data such
  as individual bands or a combination of band
  values that carry information concerning
  systematic variation within the scene.
• In a multi-spectral dataset it helps to portray
  the necessary elements of the image.
• It reduces the number of spectral bands that have
  to be analyzed.
• Finally it leads to increases in the speed of
  analysis and reduces the cost of analysis.

14
Digital Image Processing

• Image Enhancement Techniques Image Enhancement
  techniques are used to make satellite (as opposed
  to aerial photography) imagery more informative
  and to help achieve the goal of image
  interpretation.
• Enhancement means alteration of the appearance of
  an image in such a way that the information
  contained in that image is more readily
  interpreted visually in terms of a particular
  need.
• The image enhancement techniques are applied
  either to single-band images or separately to the
  individual bands of a multi-band image set. These
  techniques can be categorized into two
• Spectral Enhancement Techniques
• Multi-Spectral Enhancement Techniques

15
Digital Image Processing

• Image Enhancement serves to improve the
  interpretability of the image by increasing
  apparent contrast among various features in the
  scene.
• The enhancement techniques depends upon two
  factors
• The digital data (i.e. with spectral bands and
  resolution)
• The objectives of the interpretation
• As an image enhancement technique often
  drastically alters the original numeric data, it
  is normally used only for visual (manual)
  interpretation and not for further numeric
  analysis.

16
Image Enhancement
MAT (i,j) - n x n
e.g. FILTERING
FILTMAT (i,j) - 3 x 3
Column (j)
Column (j)
?
Row (i)
?
Row (i)
17
Digital Image Processing

• Information Extraction is the final step in image
  analysis.
• After pre-processing, feature extraction, and
  image enhancement the remotely sensed data is
  subjected to quantitative analysis to assign
  individual pixels to specific classes.
• Classification of the image is based on the known
  and unknown identity to classify the remainder of
  the image consisting of those pixels of unknown
  identity.
• After classification is complete, it is necessary
  to evaluate its accuracy by comparing the
  categories on the classified images with the
  areas of known identity on the ground
  (ground-truthing)
• The final result of the analysis consists of a
  map (or image)

18
Digital Image Processing

• Typical Examples of Digital Image Processing
  software
• Erdas Imagine (UoA) Geography folder
• Idrisi Kilimanjaro (UoA) Geography folder
• Multispec (free download)
• PCI Geomatics
• ERMapper
• ENVI
• Pixoneer PGSteamer
• Also training package from UNESCO .. BILKO

19
Digital Image Processing
http//www.ncl.ac.uk/tcmweb/bilko/
20
Digital Image Processing

• BILKO EXERCISES (DULY COMPLETED)
• Introduction to Digital Image Processing
• Applications x 2
• Read instructions. Introduction familiarises you
  with the software (BILKO) and the two
  applications allow you to carry out a couple of
  simple exercises using the software
• Available on the website
• http//www.abdn.ac.uk/geo223/index.htm
• Further details about BILKO at
• http//www.ncl.ac.uk/tcmweb/bilko/index.htm