Re: kosher jpgs

Kenneth P. Turvey wrote:
On Fri, 31 Oct 2008 12:33:22 -0700, Roedy Green wrote:

I noticed that winzip sometimes issues a warning message that it can't
compress a jpg with its proprietary jpg compression method. This
suggests that some of my jpgs are not completely kosher.

This lead be to wonder if there is some java code to detect if jpgs are
completely kosher, ditto pngs, and possibly correct them if not.

Alternatively, perhaps some utility will do this.

I also wondered what it might be about the images that Winzip does not
like.

This made me wonder.. how much more can you really expect to compress a .jpg file? It is already compressed using a lossy compression algorithm. Would taking on another lossless compression algorithm on top really buy you much if anything?

All compression ratios are inversely proportionate to entropy. Lossy compression allows you to throw out entropy, while lossless only minimizes non-entropy data. Lossy compression may result in in some data that still has some non-entropy in it.

--
Daniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/>
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