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Friday, March 22, 2013


This week we looked at image file formats including GIF (Graphics Interchange Format) which uses 8 bits per pixel. It has at most 256 colors and it's compression is lossless and is ldeal for logos and graphics.

        We also looked at run length encoding which replaces multiple occurences of an item by stating the number of times that item appears. Turning an image on its side 90 degrees can either make run length encoding more or less usable therefore changing the file size of the image drastically.
        Progressive downloading was mentioned which gave the user a blurred preview image of the image they were downloading. This is not of much use anymore as everyone has high speed broadband and instantaneous downloads and could only come in handy on a mobile website.
       JPEG (Joint Photographs Experts Group) was created to make a standardised digital file format in which the degree of compression can be adjusted. It is the most common image file format on the web and is ideal for landscape images or any that don't use run length encoding.

       We also talked about luminence and chromanence, the brightness and color information in an image. Humans aren't great detecting changes in chromanence so files can be compressed by throwing away lots of the chromanence information whereas luminence information is very noticable to the human eye and can't be compressed too much without degrading the quality of the picture to anyone viewing it.

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