Archived posting to the Leica Users Group, 2006/02/26
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Hi Larry, nothing was added but on re-compression less was thrown away. When you expand the jpeg a picture is created which has spurious data in it computed from the compressed file and approximating the "believeable" to replace the data thrown away as partially masked when originally compressed. When re-compressed using a less lossy setting of the jpeg algorithm less of the file is discarded in the compression but you have gained nothing as part of the data retained was reconstituted rather than real anyway. On 26 Feb, 2006, at 01:47, lrzeitlin@optonline.net wrote: > > <<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 > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information