Archived posting to the Leica Users Group, 2006/02/25
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]I usually shoot RAW/NEF these days, but if I shoot JPEG, when I do editting on the "good ones" I save them as TIFFS in a separate sub-folder (I call it "processed"). AFAIK, when you load the image from disk, the JPEG software in your editor "reconstructs" the image from the lossily (is that a word?) compressed JPEG. So now you have an image (bitmap) in your computer's memory. Then each time you save it as a JPEG, the JPEG software in your editor again applies the lossy compression scheme to the in memory image on its way to disk. So I just save as TIFFs. Only exception is when I save to the special set of on disk folders that my Web gallery software uses. Then I save the TIFFs as JPEGs - whereupon the gallery software chews up the JPEG images anyway :-) Scott Frank Dernie wrote: > If I have understood things correctly if you make a modification to > an expanded jpeg then re-store it at as a new jpeg it is re- > compressed into a completely new lossily compressed file. 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. If you make no changes the algorithm may still > not follow exactly the same compression on the expanded file than was > done on the original unadulterated data, since some of it has been > discarded and reconstructed to some extent inaccurately. > Best not to do it, > Frank > > On 25 Feb, 2006, at 15:35, Raimo K wrote: > >> So why it is not compressed - smaller, that is - the new file can >> even be larger than the original. I know that no new information >> cannot be created but does not compressing make files smaller - that >> is the very idea. >> All the best! >> Raimo K >> Personal photography homepage at: >> http://www.uusikaupunki.fi/~raikorho >> >> >> ----- Original Message ----- From: "Eric" <ericm@pobox.com> >> To: "Leica Users Group" <lug@leica-users.org> >> Sent: Saturday, February 25, 2006 2:25 PM >> Subject: Re: [Leica] Daily Dose of Spring XI >> >> >>> Raimo: >>> >>>> If you select to save JPGs using original quality it will not be >>>> compressed again - at least the programs I use do it this way. >>> >>> >>> I would be careful. All JPG compression is lossy. That is, when >>> you save >>> the jpeg file, it throws away some information. So the next time >>> when you >>> open the file, it doesn't have 100%. Which is fine for saving once >>> and >>> viewing. But if you save again, then you're tossing out more >>> information. >>> Viewing jpegs is fine. And there are some programs that can rotate >>> jpegs >>> without losing information. But if you save again, you will lose >>> information. If you save using the original quality, I'm guessing >>> that >>> means use the same level of compression that was first used. If >>> you change >>> an image and then save the jpeg again, it *will* be compressed again. >>> That's the way jpeg works. >>> >>> >>> >>> -- >>> Eric >>> http://canid.com/ >>> >>> _______________________________________________ >>> Leica Users Group. >>> See http://leica-users.org/mailman/listinfo/lug for more information >> >> >> >> _______________________________________________ >> Leica Users Group. >> See http://leica-users.org/mailman/listinfo/lug for more information > > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information -- Pics @ http://www.adrenaline.com/snaps Leica M6TTL, Bessa R, Nikon FM3a, Nikon D70, Rollei AFM35 (Jihad Sigint NSA FBI Patriot Act)