Multiple description coding for robust transmission and redundant storage of images
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One of the most common forms of errors related to transmission of image/video over error prone channels is due to transient channel shutdowns. The first part of this thesis addresses issues related to transmission of image/video over erasure channels. In this work we use Multiple Description Coding (MDC) using a Multiple Description Scalar Quantizer (MDSQ) to generate two descriptions of an image which are transmitted over two channels. If only one channel works the information received over it is sufficient to achieve a minimum fidelity. On the other hand if both channels work, combining information from both channels achieves higher fidelity. The second part of this thesis addresses the issues related to downloading images stored on a single site. If any part of the network route leading to a site is congested, viewers wishing to view an image on that site will be faced with debilitating delays. A solution to this problem is to place low resolution versions of the image at multiple sites. In this thesis a new image encoding scheme is implemented for generating multiple descriptions of the image for storage across multiple servers based on the Over complete Discrete Wavelet Transform. Even if some of the sites are congested, viewers can satisfy themselves with a lower resolution version of the image reconstructed using the sites that become available within a reasonable delay. If all the sites can be accessed, then the viewer would get a high resolution version of the image.