Some Questions About These Results

[pmeenan]

gzip is just a generic compression utility and doesn't care what bytes it is operating on. Usually we don't gzip encode image streams because there aren't additional savings - most of the image formats already squeeze out as much as possible but in some cases you can actually get a little more savings.

gzip should be used for favicons that are using the actual ico format because that is an uncompressed bitmap format and for some font formats which are also binary so it applies to more than just text. It just happens that your jpeg fell into the small set of images that get some additional savings by gzipping but I really don't recommend doing it (browsers will handle it fine, there's just no good reason to do it).