Topic 5 Concept of Computer Graphics

• Introduction

• Output Primitives and Attributes

• Two dimensional Viewing

• Graphical User Interfaces

• Three Dimensional Concepts

• Three Dimensional Display in Nuclear Medicine

Computer Graphics

• Everything on computers that is not text or sound.

• Computer graphics as drawing pictures on computers.

• Nuclear Medicine uses computer graphics to display images

Graphic Software

• General Programming Package (Graphic Library in C etc)

• Application Package (For None-programmer)

• Modelling Transformation=>World Coordinates=>Normalised Coordinates

User Graphic Interface

• Consist of windows, pull-down and pop-up menus, icons, pointing device.

• Popular graphic user interface: X windows, MS windows, Macintosh, OpenLook and Motif

• Graphic package: Specialised interactive dialogue• General Graphic Package: interface to standard

window system: PHIGS for X windows.

User Graphic Interface

Output Attributes

Transformation Pipeline

Display Processor in Graphic System

From Object Model to Display Device

Object Rendering

Basic Building Blocks For Pictures

• Output Primitives– Characters, – Geometric Entities.– Lines, – Filled Areas, – Colours– Polygons

Output Primitives -Lines and Points

Output Primitives - Circles

Output Primitives - Polygon

Properties of the Output Primitives

• How it is displayed:– Intensity– Colour– Style– Pattern

Geometric Transformation

• Change size, position or orientation:– translation– rotation– scaling

• Altering or Manipulating Display

Transformations

Transformations

Two Dimensional Viewing

• Specify which part of the picture– which part of the picture– where to put the picture

• Algorithms– Point Clipping– Line Clipping– Polygon Clipping– Text Clipping

Two Dimensional Viewing

3D Object Representation

• Object Boundaries: – Plane, – Curved Surfaces

• Object Interiors:

• Solid Objects:– Boundary Representation– Space-partition Representation

3D Object Representation

3D Transformation

• Transformation– translation, rotation, scaling

• Rotation in 3D– a composite of 3 rotations

• X-axis rotation

3D Transformation

3D Display

• View an object from any spatial position: front, top etc.

• Projection onto a flat viewing surface.

3D Display

Projection

• Specify a view plane

• Projections– Parallel– Perspective

• Projection transformation

• Clipping

Parallel Projection

Perspective Projection

Different Viewing Directions

Changing of Reference Point

3D Surface

• 3D Surface Detection:– Identify the visible surface– example: ray-casting method

• Depth Cueing– the intensity of lines decreases from the front to

the back of the object.

3D Surface Detection

Depth Cueing

Types of Depth Cues

• Stereoscopic display (different image for different eye)

• Hidden lines/surface removal

• Depth weighting (less intensity for distant object)

• Illumination (surface lighting)

• Rotation (cine loops)

Surface Illumination

• Surface illumination: – the intensity of light that we should see.

• Surface rendering algorithm– calculation of the light based on physical laws.– Radiosity algorithm: based on the propagation

of radiant energy between the surface and the source.

Surface Illumination

Shading Techniques

Reflection and Transparency

Radiosity

Lighting Conditions

Colours in Computer Graphics

Colour Models

• Colour Model:– The method for explaining the properties or

behaviour of colour within some particular context.

• RGB Model: – based on tristimulus theory

Colour Models

Grey Scale

Logarithmic & Exponential

Colour Translation

Pseudo Colour Display

True Colour Display

3D Display in Nuclear Medicine

• Slice-and-Dice Display– orthogonal slices, oblique slices

• Ray Tracing – Volume Rendering- summed projection, maximum activity projection,

volumeric compositing.

• Surface Rendering– polygon tiling, binary voxel rendering.

• Mapping– Bull’s eye, cylindrical display

Slice-and-Dice

Ray Tracing

Surface Rendering

Volume Rendering

Bull’s Eye Mapping

Clinical Applications in Nuclear Medicine

• Hot Spot Imaging– Volume rendering with maximum activity projection

• Cardiac Imaging– Perfusion imaging(Bull’s eye), surface rendering with colour.

– Functional imaging (oxygen consumption), colouring blood-pool surface.

– Gated Blood Pool Studies: cine display, surface rendering, maximum activity projection.

• Brains.