Thesis-1992-Wang.pdf (5.22 MB)
Colour image representation by scalar variables
thesis
posted on 2012-09-27, 11:43 authored by Hua WangA number of studies have shown that it is possible to use a colour codebook, which has a limited
number of colours (typically 100-200), to replace the colour gamut and obtain a good quality reconstructed
colour image. Thus colour images can be displayed on less expensive devices retaining
high quality and can be stored in less space. However, a colour codebook is normally randomly
arranged and the coded image, which is referred to as the index image, has no structure. This prevents
the use of this kind of colour image representation in any further image processing.
The objective of the research described in this thesis is to explore the possibility of making the index
image meaningful, that is, the index image can retain the structure existing in the original full
colour image, such as correlation and edges. In this way, a three band colour image represented by
colour vectors can be transfomled into a one band index image represented by scalar variables. To achieve the scalar representation of colour images, the colour codebook must be ordered to satisfy
the following two conditions: (I) codewords representing similar colours must be close together
in the code book and (2) close code words in the codebook must represent similar colours. Some
effective methods are proposed for ordering the colour codebook. First, several grouping strategies
are suggested for grouping the code words representing similar colours together. Second, an ordering
function is designed, which gives a quantity. measurement of the satisfaction of the two conditions
of an ordered codebook. The code book ordering is then iteratively refined by the ordering
function. Finally, techniques, such as artificial codeword insertion, are developed to refine the
code book ordering further.
A number of algorithms for colour codebook ordering have been tried to retain as much structure in the index image as possible. The efficiency of the algorithms for ordering a colour codebook has
been tested by applying some image processing techniques to the index image. A VQ/DCT colour
image coding scheme has been developed to test the possibility of compressing and decompressing
the index image. Edge detection is applied to the index image to test how well the edges existing
in the original colour image can be retained in the index image.
Experiments demonstrate that the index image can retain a lot of structure existing in the original
colour image if the codebook is ordered by an appreciate ordering algorithm, such as the PNNbased/
ordering function method together with artificial codeword insertion. Then further image
processing techniques, such as image compression and edge detection, can be applied to the index
image. In this way, colour image processing can be realized by index image processing in the same
way as monochrome image processing. In this sense, a three-band colour image represented by colour
vectors is transformed into a single band index image represented by scalar variables.
History
School
- Mechanical, Electrical and Manufacturing Engineering
Publisher
© Hua WangPublication date
1992Notes
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.Language
- en