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The problem of determining an objective means for assessing local characteristics of television subpictures in a Hadamard transform multicoder scheme is stated and discussed. Detailed investigations of transform domain coefficient statistical characteristics for different test images have been conducted. Both monochrome and colour signals were used, as well as different transform sizes and shapes. " Directing Indexes " are proposed which, depending on the inter-relationships among transform coefficients and groups of coefficients, direct each subpicture to the appropriate coder. Three indexes in the case of monochrome signals are proposed, each with its own computational procedures and application requirements. Necessary modifications and changes for application of some indexes on colour signals are also discussed. The proposed technique of indexing eliminates the necessity of equal distribution of subpictures among 'activity classes', a major disadvantage encountered in present activity index. Coders to be used with each directing index are devised and tested, subject to an arbitrary bit rate of 2 bits per pixel, with satisfactory performance compared with some published results for other techniques.

No description available.

The problem of determining an objective means for assessing local characteristics of television subpictures in a Hadamard transform multicoder scheme is stated and discussed. Detailed investigations of transform domain coefficient statistical characteristics for different test images have been conducted. Both monochrome and colour signals were used, as well as different transform sizes and shapes. " Directing Indexes " are proposed which, depending on the inter-relationships among transform coefficients and groups of coefficients, direct each subpicture to the appropriate coder. Three indexes in the case of monochrome signals are proposed, each with its own computational procedures and application requirements. Necessary modifications and changes for application of some indexes on colour signals are also discussed. The proposed technique of indexing eliminates the necessity of equal distribution of subpictures among 'activity classes', a major disadvantage encountered in present activity index. Coders to be used with each directing index are devised and tested, subject to an arbitrary bit rate of 2 bits per pixel, with satisfactory performance compared with some published results for other techniques.

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No description available.

No description available.

[pt] Esta Dissertação destina-se ao desenvolvimento de novas técnicas de realce aplicadas no domínio da transformada. O estudo das transformadas bidimensionais motivaram o desenvolvimento de técnicas baseadas nestas ferramentas matemáticas. Análises comparativas entre os métodos de realce no domínio espacial e no domínio da transformada logo revelaram as vantagens do uso das transformadas. É proposta e analisada uma nova técnica de realce no domínio da Transformada Cosseno Discreta (DCT). Os resultados mostraram que esta nova proposta é menos afetada por ruído e realça mais a imagem que as técnicas apresentadas na literatura. Adicionalmente, considera-se uma estratégia com o objetivo de eliminar o efeito de escurecimento da imagem processada pelo Alpha-rooting. É também apresentada uma nova proposta de realce no domínio da Transformada Wavelet Discreta (DWT). As simulações mostraram que a imagem resultante possui melhor qualidade visual que a de técnicas relatadas na literatura, além de ser pouco afetada pelo ruído. Além disso, a escolha do parâmetro de realce é simplificada. / [en] This Dissertation is aimed at the development of new enhancement techniques applied in the transform domain. The study of the bidimensional transforms motivated the development of techniques based on these mathematical tools. The comparative analysis between the enhancement methods in the spatial domain and in the transform domain revealed the advantages of the use of transforms. A new proposal of enhancement in the Discrete Cosine Transform (DCT) domain is analysed. The results showed that this new proposal is less affected by noise and enhances more the image than other techniques reported in the literature. In addition, a strategy to eliminate the darkening effect of enhancement by Alpha-rooting is considered. A new proposal of enhancement in the Discrete Wavelet Transform (DWT) domain is also presented. Simulation results showed that the enhanced images have better visual quality than other ones presented in the literature and is less affected by noise. Moreover, the choice of the enhancement parameter is simplified.

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