Image Modeling &

SegmentationAly Farag and Asem Ali

Image Modeling &

Segmentation Introduction

Intensity Model. Spatial Interaction Model.

Segmentation Framework.

Introduction

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Is a graphic representation of a scene in 2D/3D discrete spaces.

Is stored as a raster data set of integer values These values represent the intensity of reflected light,

heat, or other range of values on the electromagnetic spectrum.

Location of each measurement is a “image element” called a pixel/voxel. Object or class in an image is represented by a group of pixels.

Image

Pixel

Object / Class

Image

Light

Camera

Scene

Image

Introduction

RGB

IntroductionExamples

DepthIntroductionExamples

Thermal

IntroductionExamples

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2D video frame of a real 3D scene Remotely sensed image

Examples

CT slice Ultrasound image

X-ray image

Introduction

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Image Modeling: is to quantitatively specify visual characteristics of the image in few parameters so as to understand natural constraints and general assumptions about the imaging process

What is the information in the image? And how can it be mathematically modeled?

The following information that could capture the visual characteristics

The distribution of the intensity in each object.

The interaction between the pixels in each object.

The shape of the objects.

Introduction

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Intensity ModelImage Modeling

gray level histogram Binary Image

gray level histogramBinary Image

Introduction

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Spatial InteractionImage Modeling

gray levels histogram Binary imageHuman brain uses “contextual information” by assuming that the true color of a pixel depends on the colors at spatially neighboring

Contextual information: eliminate ambiguities, correct errors, recover messing information

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Introduction

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ShapeImage Modeling

In some cases, image non-homogeneities are outside the domain of uniform spatial interaction

Adopted Cremers’02

Introduction

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ImageShape

Spatial

Interaction

Intensity

Image Segmentation

Image ModelingIntroduction

Others

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Partitioning of an image into non–overlapping, connected regions which are homogeneous with respect to some characteristic such as intensity or texture.

Extract the major components of scene while ignoring small intracomponent variations.

When the constraint that regions be connected is removed, the proposed approach is called pixel classification

Image Segmentation

Segmentationpixel classification

Introduction

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Edge-based methods: detect contours around objects, then connect together broken contour lines. These method are too prone to failure in the presence of blurring.

Segmentation Methods

Threshold techniques: make decisions based on local pixel information, are effective when the intensity levels of the objects fall outside the range of levels in the background.

Region-based methods: the image is partitioned into connected regions by grouping neighboring pixels of similar intensity levels / texture. Adjacent regions are then merged under some criterion (homogeneity or sharpness of region boundaries).

Introduction

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Segmentation Methods

Markov random field models: allow for taking account of spatial interaction between adjacent or nearby pixel signals for image segmentation. are typically used to take into account the fact that, most pixels belong to the same class as their neighboring pixels.

o If the strength of spatial interaction is too high, it may result in an excessively smooth. If it is too low, it may result in some holes in the segmented object

Deformable models: delineate region boundaries using closed parametric curves that deform under the influence of internal and external forces.

o The main advantages are robustness to noise and spurious edges. disadvantage is that they require manual interaction to place an initial model

Introduction

Read the following image segmentation introduction

http://lmb.informatik.uni-freiburg.de/lectures/segmentierung/Intro.pdf

and answer these questions:

1. Define the image?

2. Pixel values can represent different measurements such as brightness, and

what?

3. What is the difference between image classification and image segmentation?

4. What are the basic techniques for image segmentation?

5. What are the different types of model-based image segmentation approaches?

6. Mention the disadvantages of threshold-based image segmentation approach?

7. Explain the main idea of the region growing-based image segmentation

approach?

8. What are the major classes of the deformable models and their formulations?

9. Define the image modeling?

10. What are the different information that we can model in images?

Image segmentation Homework #1