Adobe Fireworks uses the PNG file format as its native format, storing metadata in “private chunks” of the file that aren’t used to render it. Unfortunately, if you publish your unoptimized images, the browser still has to download all of that metadata. In the above case, the server sent down a 10×30 pixel asset with just 164 bytes of image data (the IDAT chunk) and over 46kb of Adobe Fireworks private data. Fiddler’s ImageView Inspector will show you when your PNG file contains unneeded data, and if you’d like to explore further, check out this great free PNG chunk decoder: http://entropymine.com/jason/tweakpng/ Lesson learned? If you don’t need it, optimize your images and strip unnecessary meta-data from your image …

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Strip unnecessary meta-data from your images!