Core_Computer Studies: Lossy Compression

This term describes a process that compresses the image file such as a JPEG which destroys a portion of data and produces an unreconstructable loss of data. In other words, to compact the image it throws away parts of an image.

Obviously you can't just discard any old piece of information. So in the case of JPEG file how does it work?

JPEG, is a lossy compression method. What the JPEG algorithm does is to divide the image into blocks which you can see on badly-compressed JPEGs. The algorithm called Discrete Cosine Transformation turns each block of data into curves, of different sizes. The algorithm then throws away the less significant part of the data (the smaller curves). This means that, unlike GIF, you can compress your image at various levels. This compression method can produce unwanted artifacts such as blockiness if not used carefully.

These notes are written for students who undertake the Core Computer course at School of Art, Australian National University. Students of the course should feel free to contact any member of staff with comments questions and general suggestions..

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