Portable Network Graphics files (.PNG)

PNG files are a recent newcomer to the web page scene. They have been produced in response to the litigious nature of the owners of the GIF patent. Software developers had been forced to license what was essentially an open standard that was snatched by a big corporation for its own gain. The PNG file format is public domain, lossless and supports a range of colour mappings from palette based to true colour, however, the most common format uses 24bit colour. It is still not widely used, but it is gaining momentum.

It suffers from the same problem as GIF files in that it does not handle photographic images very well, but a further downside is that using 24bit colour the files are potentially 3 times bigger. However, on the plus side the algorithm is much more efficient for drawn images. The examples below demonstrate this.

Original Windows Bitmap - 176KB PNG formatted photograph - 126KB
PNG formatted detailed picture - 10KB PNG formatted simple block picture - 1KB

Golden Rule 2 - don't use GIF or PNG format for photographs

By their very nature, photographs do not compress as well with the GIF and PNG formats. JPEG is designed specfically to handle compression of photographs and optimum choice of compression quality will give and appropriate balance between amount of detail and final file size.

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