Le 19/05/2018 à 10:48, Lorenzo Bolzani a écrit : > Just work on the jpeg. As you say, this file is never modified so there > is no quality loss depending on how many times you "edit" it, in the > same session or multiple sessions. > > Converting a jpeg to a lossless format before editing will give you zero > advantages. > > When you export the file to a lossy format, like jpeg, there is a very > small loss of quality. If you use a high quality setting during the > export this loss will be so small to be practically none (especially if > your original file was already compressed). If you really do not want > this minimal loss export to png. > > The only case where you may want a lossless format is this: you open the > file in DT, do some edits, export. Then open this exported file with > gimp (or something else) and do some more edits. Now save with gimp and > open the result with DT and do some more edits with DT. In this case > there will be a very small difference if you use a lossless (png) format > to "share" the edited file. In this scenario, in theory, using a huge 16 > bit tiff file is even better but if your workflow starts with an 8-bit > jpeg there is a minimal advantage in "adding bits" later (more or less > depending on the specific image).
Thank you for this clear answer. Another question: is there a way to include the xmp data in a file while exporting, for gimp seems to be unable to read a separate .xmp file associated to an image file? Thank you. > Bonjour, > > If you open a jpeg photo in darktable, you can modify it (exposition, > contrast, etc.). As far as I understand the way dt works, the jpeg file > is not modified but all changes are recorded in the xmp file and a new > jpeg file is created when you export your photo at the end of the > treatment (am I right?). > > So my question is: is there some loss when I export the photo to a jpeg > file after treatment with dt and is there a cumulative loss of quality > if I reopen the original jpeg with dt (not the exported one) in order to > add or modify some module actions? > > What is the best strategy to work with dt on jpeg photos? Work directly > with the jpeg format or convert this one to another lossless format > (using imagemagick for instance) and work with this format before > exporting to the jpeg format? > > I expect that what I say is enough understandable.... > > Thank you. > > -- > François Patte > UFR de mathématiques et informatique > Laboratoire CNRS MAP5, UMR 8145 > Université Paris Descartes > 45, rue des Saints Pères > F-75270 Paris Cedex 06 > Tél. +33 (0)6 7892 5822 > http://www.math-info.univ-paris5.fr/~patte > <http://www.math-info.univ-paris5.fr/~patte> > > > > ____________________________________________________________________________ > darktable user mailing list to unsubscribe send a mail to > [email protected] -- François Patte UFR de mathématiques et informatique Laboratoire CNRS MAP5, UMR 8145 Université Paris Descartes 45, rue des Saints Pères F-75270 Paris Cedex 06 Tél. +33 (0)6 7892 5822 http://www.math-info.univ-paris5.fr/~patte
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