[Digikam-users] jpeg compression

[Bjørn Kvisli]

Torsdag 28 juni 2007 23:09, skrev Jakob Østergaard:
> On Thursday 28 June 2007 18:20:43 Daniel Bauer wrote:
> > On Donnerstag, 28. Juni 2007, Bjørn Kvisli wrote:
> > > If I understand this right, assuming that the Kodac C340 uses jpeg
> > > quality of 70 internally, it makes no sense to set a higher value in
> > > Digikam?
> >
> > it still makes sense, because every new save looses some more
> > information. Although its not that dramatic in reality, you could think
> > of percents just to better understand: then if you save the 70% with 100%
> > you get 70% again, if you save it with 70% you get only 49% (70% of 70%)
> > and so on.
> >
> > I found that a jpg value of 88 in digiKam gives approx. same results as
> > 80 in photoshop (in quality and size). That's the value I use for my web
> > pics.
> >
> > However, as long as you work with the pictures better use a lossless file
> > format and only save the final pictures to .jpg (if at all). And leave
> > the originals untouched.
>
> A tip;
>
> When order paper photos from my digital images at the local shop (which
> uses a Fujicolor service which means the actual paper photos get developed
> somewhere in germany then shipped back to .dk so I can pick them up at the
> local shop), I found that JPEG images are a lot better than uncompressed
> TIFF.
>
> It turns out, that if I deliver TIFFs, the "clever" kiosk system will
> convert them (most likely to JPEG) with a pretty heavy compression. If I
> deliver JPEGs (at 95% quality) the images are not further compressed, and
> they look crisp and sharp on paper.
>
> I tried a test run with several different pictures, two copies of each
> picture (one JPEG one TIFF), and the TIFFs were very noticeably "smudged"
> or "blurred", suffering the artifacts of a heavy JPEG compression (or other
> compression that cuts out high frequencies).
>
> That's one case where I've found JPEGs to be superior to TIFFs, although
> not for the reasons one would usually expect  ;)


Interesting! I'll probably do as you in the futures. keep my images in a 
lossless format and convert to jpg before sending them off to the print shop.

Now, I've heard about two lossless formats here on the mailing list: tiff and 
png. Which one is bes to use with Digikam? It seems like you keep all the 
exif data with png, but lose them with tiff.
-Bjørn