17-04-2012, 12:09 PM
MEASURING IMAGE QUALITY
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Introduction
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.
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.
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.
Centre Of Medical Imaging Research (CoMIR)
This case highlights differing viewpoints. On the one hand, Mr. Efford is involved in the
Computer Science aspect, as a member of the academic staff at the University of Leeds.
Generally, the technical aspects of the technology used is of more importance, and how it can
best be improved and utilised to the full. On the other hand, his links to medical imaging
provide a perspective from the medical point of view which are more concerned with the
contents of the image, rather than how it was captured.
Conclusion And Evaluation
Evaluation Of Objectives And Aims
This project has turned out to be challenging in many ways. Each stage has presented its own
problems to be overcome.
When collecting information from industrial sources, as covered by the first objective, I
expected a lack of response. Previous experience had taught me that only a small percentage
of sources are likely to respond at all. I tried to compensate this by applying to many varied
sources, to improve the chance of receiving varied answers which could typify a cross-section
of the graphics community. What I was not prepared for, however, was the lack of ideas for
measuring quality used in industry. The general consensus of opinion of those who replied
seems to be that a measurement system is not required for the most part, as the people working
in this field already have experience with graphics file formats. In hindsight, it may have been
better to also apply to some personnel not directly involved with the file formats, who would
have less knowledge of the technicalities whilst still having an interest in their use. This could
have highlighted more of a need for a quality measurement system such as discussed in this
report. The responses I have received, however, have introduced some other problems I had
not envisaged, such as proprietary formats supplied with each new application. When running
more than a few of these simultaneously, difficulties can arise when there is a need to move
data between different software systems. Although OLE (object linking and embedding) has
been designed with this in mind, it is not always possible to transfer data if the structure is
foreign to that recognised by other systems.