5th intensive course on soil micromorphology naples 2001 12th - 14th september image analysis...

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


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


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


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.


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:


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


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:


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


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


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


Simple MeasurementManual Method directly on photograph

Overlaying a scale.

Is case, a special scale was constructed consistent with magnification.

Units are in microns


Simple MeasurementManual Methods

Interactive using a cursor.

Click on one point

Move cursor

Click on second point

Distance is automatically recorded


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


Use “handles” to adjust width of selected intensity values


Many of the settings for SigmaScan must be first set using this menu

The next two slides show sub-options of these settings


Selecting which parameters to measure


Selecting which overlay to use for annotation


Using MEASURE OBJECTS labels each object with an unique identifier


Each Feature is measured according to parameters selected and displayed in an EXCEL Worksheet

5th intensive course on soil micromorphology naples 2001 12th - 14th september image analysis...

Documents

image analysis lecture

image analysis lecture

image overlays

separation of image

th intensive course

original image

course slide

soil micromorphology