Archived posting to the Leica Users Group, 2006/02/25

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Subject: [Leica] Re:JPEG compression
From: lrzeitlin at optonline.net (lrzeitlin@optonline.net)
Date: Sat Feb 25 17:47:33 2006
References: <200602251842.k1PIfL4F006362@server1.waverley.reid.org>

<<Since jpeg? 
compression is not lossless and relies on masking to make a not too? 
hideous job of throwing data away each time it is re-stored as a? 
jpeg, after any changes have been made a new different set of data is? 
discarded by the algorithm such that each re-compression results in? 
further degradation.>>

Question:

If I open a JPEG file in Graphic Converter (for the Mac), make a minor 
alteration, and save in Best quality, the file size more than doubles. As a 
test I down loaded a JPEG file from my wife's P&S camera (a Leica Digilux 
Zoom). The file was 197.3 KB. I then saved the file without alteration at 
the programs's Best quality. The file size was now 412.8 KB. 

What's going on? What was added to increase the file size?

I've noticed the same thing with Photoshop.

Larry Z


Replies: Reply from ericm at pobox.com (Eric) ([Leica] Re:JPEG compression)
Reply from Frank.Dernie at btinternet.com (Frank Dernie) ([Leica] Re:JPEG compression)