[Digikam-users] jpeg compression
joe at evalesco.com
Thu Jun 28 22:09:41 BST 2007
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.
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 ;)
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