5th Intensive Course on Soil Micromorphology Naples 2001 12th - 14th September Image Analysis Lecture 3 Image Processing/Analysis Basic Requirements
Mar 28, 2015
5th Intensive Course on Soil Micromorphology
Naples 2001
12th - 14th September
Image Analysis
Lecture 3Image Processing/Analysis
Basic Requirements
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 3: Basic Requirements
Basic requirements of image processing/analysis
e.g. need to threshold or not,
problems of subjectivity,
hydrid approaches (user/computer methods).
manual methods of measurement
Introduction to Sigma Scan Software
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 3: Basic Requirements
Most Analysis requires some preliminary processing
Segmentation
•involves separation of image into regions of similar features•simple form - 2 phases - solids and particles >> binary image•multi-phase form - may be several different discrete grey levels in an image.•More complex segementation methods may involved segmentation based on texture/morphology/orientation.
Thesholding•selection of a grey-level intensity which separates two phases.•For binary images ---------------one threshold•For multiphase images -----------several thresholds
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 3 Basic Requirements
Segmenting a Binary Image using Thresholding
e.g. Change Grey-Level Image into 2 phases - solids and voids
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 3 Basic Requirements
Segmenting a Binary Image using Thresholding
First Example is ideal - selection of threshold value to separate black from white
Second Example: also ideal - clear definition of where threshold should be.
However: Non uniform illumination may present problems.
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 2 Image acquisition
Illumination issues
Non-uniform illumination will create problems in later thresholding and analysis
Normal Image
Centralised Illumination
Gradation from top left
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 3 Basic Requirements
Thesholding:
If intensity distribution is of simple form, and automatic threshold may be set (provided illumintaion is uniform)
With grey-level images - intensity distribution often does not show a discrete minimum - making automatic thresholding difficult.
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 3 Basic Requirements
Thesholding:
Interactive selection of threshold will be unreliable and may well differ significantly from one person to another.
Data from 2nd and 3rd Intensive Courses:
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 3 Basic Requirements
Thesholding: Multi-phase situations
A new objective method will be discussed in Lecture 10
Intensity distribution of multi-phase image. The optimum points for separation between phases are the minima
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 3: Basic Requirements
Human eye is poor at intensity discrimination
computer is good at intensity discrimination
Human eye is good at texture recognition
difficult to derive suitable computer algorithms to discriminate textures.
Morphological effects - e.g. surface roughness can mask intensity effects -
e.g. quartz and felspar have similar intensities in back-scattered SEM, but the morpholoigcal appearance (texture changes in grey levels) are usually easily discriminated by human eye.
Segmentation based on other methods:
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 3: Basic Requirements
Segmentation based on other methods:
Manual delineation methods can be useful. These aim to take the advantages of the human eye in pattern recognition and define areas of equal grey-level which are the ideal for feature size analysis
In this example, regions which are near vertical are coded red.
There will be an exercise on this later in course
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 3: Basic Requirements
Region within red area has similar grey-level, but has difference in calcium concentration. Segmentation by thresholding is not possible.
BSE image of volcanic deposition:
Sample from Monserrat
calcium map of area
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 3: Basic Requirements
Traditionally - features would be measured by laying a rule against the feature of interest.
This facility can be achieve more readily with digital images by using an overlay cursor.
Measurement requires the use of overlays these are binary images which can be overlain directly over the image without affecting the original image.
Often several different overlays are available. Sigmascan has 5 image overlays and one for annotation.
Simple Measurement
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 3: Basic Requirements
Simple MeasurementManual Method directly on photograph
Overlaying a scale.
Is case, a special scale was constructed consistent with magnification.
Units are in microns
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 3: Basic Requirements
Simple MeasurementManual Methods
Interactive using a cursor.
Click on one point
Move cursor
Click on second point
Distance is automatically recorded
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 3: Basic Requirements
SIGMA SCAN is a package directly available over the Internet which has a 30 day demonstration license.
Thus ideal for use in this teaching course
What does SIGMA SCAN do
allows several basic image processing procedures
limited capabilities for more advanced operation.
All quantitative work is done via the overlay planes
Introduction to Sigma Scan Introduction to Sigma Scan
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 3: SIGMASCAN
Using SigmaScan to Threshold
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 3: SIGMASCAN
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 3: SIGMASCAN
Use “handles” to adjust width of selected intensity values
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 3: SIGMASCAN
Many of the settings for SigmaScan must be first set using this menu
The next two slides show sub-options of these settings
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 3: SIGMASCAN
Selecting which parameters to measure
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 3: SIGMASCAN
Selecting which overlay to use for annotation
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 3: SIGMASCAN
Using MEASURE OBJECTS labels each object with an unique identifier
5th Intensive Course on Soil Micromorphology - Naples 2001Image Analysis - Lecture 3: SIGMASCAN
Each Feature is measured according to parameters selected and displayed in an EXCEL Worksheet