Key Features:
- No of Pages: 55
- No of Chapters: 07
- Diagram
- Images
Introduction:
Abstract
Abstract
The current methods for measuring the quality of computer stored digital images are
subjective. There are a multitude of different file formats available for the storage of such
images, each with its own unique features which may work for or against it. For an average
user or system developer, to decide on the most suitable format for their purpose requires a
knowledge of the available file formats, their features and how they affect the quality of
images, as well as the kind of image data they will be storing.
This places undue pressures on the user which my lead to a format unsuitable for them and the
application. Therefore it is important to make the right choice first time, while the opportunity
is still open.
In this project I have set out to identify any methods currently used in related industries to
measure the quality of an image stored in a wide variety of these file formats and how they can
be implemented successfully. From this information, and details on the specifics of popular file
formats and their compression methods, I have carried through the ideas, incorporating my
own opinions, to formulate suggestions on how this could be done on a wider general level.
To fortify my understanding of the problems associated with file formats and how their
compression and storage methods affect image quality, a software component to this project
has involved writing a graphics library to allow the conversion between a number of the most
popular graphics formats.
Table of Content
TABLE OF CONTENTS
CONTENTSPAGE
1 INTRODUCTION..............................................................................................................4
1.1 Project Motivation..................................................................................................4
1.2 Aims And Objectives ..............................................................................................4
1.3 Report Structure.....................................................................................................6
2 DESCRIPTION OF CURRENT IMAGE QUALITY MEASURES.................................................7
2.1 Background ............................................................................................................7
2.2 Information Sources ...............................................................................................8
2.3 Feedback ................................................................................................................9
3 PERSONAL OPINION ON IMAGE QUALITY...................................................................... 11
3.1 ASAP Inc. ............................................................................................................ 11
3.2 National Remote Sensing Centre (NRSC) ............................................................. 11
3.3 Centre Of Medical Imaging Research (CoMIR)..................................................... 12
4 FILE FORMATS AND COMPRESSION METHODS.............................................................. 13
4.1 Format Types ....................................................................................................... 13
4.1.1 Vector ........................................................................................................... 13
4.1.2 Bitmap........................................................................................................... 14
4.1.3 Metafile ......................................................................................................... 15
4.1.4 Scene Description .......................................................................................... 16
4.1.5 Animation ...................................................................................................... 16
4.2 Bitmap Compression Algorithms........................................................................... 16
4.2.1 Symmetric And Asymmetric........................................................................... 16
4.2.2 Non-Adaptive, Semi-Adaptive, And Adaptive Encoding................................. 17
4.2.3 Lossless V. Lossy .......................................................................................... 18
4.2.4 Pixel Packing ................................................................................................. 18
4.2.5 Run-Length Encoding (RLE) ......................................................................... 19
4.2.6 Lempel-Ziv Welch (LZW).............................................................................. 20
4.2.7 Huffmann Coding........................................................................................... 22
4.2.8 Arithmetic Coding.......................................................................................... 24
4.3 Colour Spaces And Other Considerations............................................................. 25
4.3.1 Colour Space ................................................................................................. 25
4.3.2 Other Considerations ..................................................................................... 27
4.4 Advanced Image Formats ..................................................................................... 27
4.4.1 JPEG ............................................................................................................. 27
4.4.2 MPEG ........................................................................................................... 30
4.4.3 Fractal ........................................................................................................... 31
2
5. MEASURING IMAGE QUALITY...................................................................................... 34
5.1 Factors Affecting Image Quality............................................................................ 34
5.1.1 Image Format Factors .................................................................................... 34
5.1.2 Higher Level Factors...................................................................................... 35
5.2 Suggestions On Measuring Image Quality............................................................. 36
5.2.1 Exhaustive Testing......................................................................................... 36
5.2.2 Quality Rating................................................................................................ 38
6. IMAGICA TECHNICAL DOCUMENTATION...................................................................... 42
6.1 Design Principles .................................................................................................. 42
6.2 Problems Encountered And How They Were Overcome ....................................... 43
7. CONCLUSION AND EVALUATION................................................................................. 46
7.1 Evaluation Of Objectives And Aims ...................................................................... 46
7.2 Evaluation Of Project Management....................................................................... 48
7.3 Further Work........................................................................................................ 49
8. BIBLIOGRAPHY........................................................................................................... 51
8.1 General References ............................................................................................... 51
8.2 Specific References............................................................................................... 51
8.3 Internet References ............................................................................................... 52
Appendices
Appendix 1: Project Plan Gantt Chart
Appendix 2: Imagica Source Code
Introduction
Introduction
1.1 Project Motivation
As a user of graphics file formats and conversion applications I have been interested in this
field since my interest in computing began. My own experiences of using graphic images for
course-work has led me to ponder many questions as to why there are so many formats and
methods for storing these images. This project has given me the opportunity to explore the
world of graphics files to find out the answers to my questions.
My knowledge of this field at the start of the project was casual. I knew generally about
bitmaps without knowing anything specific about the formats, compression techniques and
overall structure of the graphic images I was using. As this is a subject I am interested in
making my career in, measuring the ‘quality’ of images and how this can be affected by the
right or wrong choice of a file format seemed a natural choice of study which I knew would be
both challenging and interesting.
The learning curve embarked on has been considerably steeper than previous work I have
undertaken. The software component constitutes my first true software development
culminating in a final product. My previous knowledge of the C language did not cater for the
scale of this work, and my skills in Pascal, as used in Borland Delphi, were only of a basic
level. Through the development I have learnt everything necessary about these languages and
how they can be applied to creating file conversion software.
From the theory aspect, I have done much research into the principles of image storage and its
related areas including compression and decompression, colour spaces and conversion between
colour systems, image displaying, conversion between file formats and some advanced
techniques used to enhance compression ratios and allow such features as real-time full-motion
video.
1.2 Aims And Objectives
The core objectives which have been designated as fundamental to the project are:
• Identify, understand and describe a range of industry-based methods for quantitatively
measuring the quality of an image represented in various graphic file formats.
Information gathered from related industries as well as from other image processing
sources will be described with its relevance to this study.
• Suggest methods for measuring an image’s quality in varying graphic file formats.
Using the information gathered as a base, I will build up my own ideas on ways ‘quality’
can be identified and measured fairly between different formats and techniques.
• Research, understand and describe current popular static graphic file formats, the
compression methods utilised as well as colour spaces etc.
Emphasis will be on the common compression and decompression techniques used
widely, and how their use impacts the quality of the image representation, not just in
visual terms, but overall efficiency and suitability.
Introduction
5
• Gain an understanding of relevant advanced algorithm concepts, such as JPEG,
MPEG, and Fractal compression.
Although not covered in great detail, an understanding of these advanced representation
methods is useful in the context of the project.
• Research Windows API programming.
Although the software will involve little direct API programming, it is useful to know
about the facilities and restrictions I will be working with.
• Learn Borland Delphi and ObjectPascal.
To be learnt specifically for the project.
• Use shareware JPEG and GIF encoding/decoding routines to create routines which
allow transfer to and from the Microsoft Windows BMP format.
The BMP format will be used as the central format by which the other supported formats
will be converted to and manipulated.
• Write ZSoft PCX encoding/decoding routines to and from Microsoft Windows BMP
format.
Along with the JPEG, GIF and BMP routines, a 16-bit Dynamic Link Library compatible
with Microsoft Windows 3.1 or greater will be constructed with high-level format
conversion routines accessible to external software.
• Design and implement a user-interface with Borland Delphi which makes use of the
routines.
This will provide a front-end to the graphics library created in the objectives above. This
application will allow the conversion between JPEG, GIF, PCX and BMP formats.
In addition, the advanced aims which are desirable if time is permitting are:
• Implement tools for clipboard transfer of image selections, as well as simple
manipulation tools covering fixed rotation (i.e. 90, 180 or 270 degrees), scaling,
horizontal and vertical axis flipping.
Of these extra utilities the ability to use the clipboard will increase the compatibility of
the application. Therefore, it is more important than magnification, rotation and axisflipping, which are not essential, but enhance the functionality of the software.
• Construct an online help system within the software package.
Although this will mainly contain procedural information on how to use the application,
it would provide software testers with an instant information source if problems are
encountered using the system.
Introduction
6
1.3 Report Structure
Chapter 2 introduces the major factors which bias the measuring of image quality, as well as
listing the industry sources used to collect information. My opinions on the information
described is contained in Chapter 3. File formats are discussed in Chapter 4, in general terms
with examples from file formats. In Chapter 5 I follow-up the work from the previous chapters
by suggesting methods in which image quality could be measured whilst avoiding the bias
factors mentioned in Chapter 2. Chapter 6 is described below. Finally, in Chapter 7, I
conclude by evaluating the work I have done, the problems I have encountered, the areas of
future work which could be done, and a self-appraisal of my success in attaining the objectives
and aims and overall management of the project.
The technical documentation for the software component of this project is contained in
Chapter 6. This includes the design principles, structure of the application, problems
encountered and details of how they were overcome. Specific details on how to use the
application can be found in the on-line help system available through the software. An
evaluation of my success in writing this software is contained in Chapter 7, as are future
improvements which could be made. Appendix 2 contains the source code of the application
written by myself. The entire source code is not included, as a majority of the library low-level
functions were taken from the previously mentioned shareware packages.
A project plan, in the form of a Gantt Chart can be found in Appendix 1. This plan outlines the
initial plan at the offset of the project. The evaluation in Chapter 7 discusses how reality has matched up to the plan.
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