Re: Resizing changes sharpness

[Stephane Delcroix <stephane delcroix org>]

Hi Jurian and all the interested people,

As I said yesterday, I spend some time doing resizing tests.

- Current F-Spot resizing code is as good a _scaling_ code could be
(tested against the different scaling algorithm of The GIMP)
- There's no visible difference between a Bilinear or Hyperbolic
downsizing
- ImageMagick always use a filter (check -filter option) with -resize,
which, by default
- some sharpening of the output image does indeed some good job:
http://picasaweb.google.com/sdelcroix/FSpot/photo#5092958866136503826
(without sharpening on the left half of the circle, with sharpening on
the right half)
- the sharpening code is already in f-spot (the above screenshot is the
sharpen tool of f-spot)

It's really easy to hook the sharpening filter on the exporters, bu twe
need to agree on the various sharpening factors...

regards

s

On Sun, 2007-07-29 at 16:11 +0200, Jurian Sluiman wrote:
> Op zondag 29-07-2007 om 15:10 uur [tijdzone +0200], schreef Stephane
> Delcroix: 
> > Hi,
> > 
> > Currently f-spot uses a bilinear algorithm to resize images. It's not
> > the best in class, but it's quite good. But f-spot doesn't use any
> > resharpening after resizing. And evaluating resizing capabilities of a
> > photo software with a non-photo image is not really fair ;)
> Funny, the pictures I uploaded were photos of a harbour in Dusseldorf
> (Germany), so it were no renders or something :p 
> > 
> > I can do some tests with an hyperbolic algorithm, and with some extra
> > sharpening, but I'll need some eyes (and maybe some test pictures) to
> > evaluate the results. In the meantime, can you send me your original
> > test image ?
> > 
> > regards
> > 
> > s
> > 
> > 
> I have uploaded three new photos, with quite more details than earlier. It's the trevi fountain in Rome:
> http://download.juriansluiman.nl/fspot/trevi-fspot.jpg
> http://download.juriansluiman.nl/fspot/trevi-flickr.jpg
> http://download.juriansluiman.nl/fspot/trevi-original.jpg
> 
> These photos are full of small details, so you can see the differences
> easy. Thanks for your help.
> 
> Regards,
> Jurian 
> > 
> > On Sun, 2007-07-29 at 12:42 +0200, Jurian Sluiman wrote:
> > > Hi all,
> > > I'm using f-spot for quite a time now, but every time I want to resize
> > > a picture, the sharpness changes significantly. I compared the resizes
> > > from f-spot, eog, gThumb and flickr, and it seems f-spot has the worst
> > > resizing algorithm. To see the differences, compare these two
> > > pictures:
> > > http://download.juriansluiman.nl/fspot/fspot.jpg
> > > http://download.juriansluiman.nl/fspot/flickr.jpg
> > > 
> > > It's clear the flickr resized picture is more sharpened than the fspot
> > > one. I couldn't find anything about it on the wiki or the archives, so
> > > I'm asking it here. I really like the program, all the features and
> > > the usability. But the resizing problem struggles me. Is it possible
> > > to fix it?
> > > 
> > > Thanks a lot, you're doing a great job ;)
> > > 
> > > Jurian Sluiman 
> > > _______________________________________________
> > > F-spot-list mailing list
> > > F-spot-list gnome org
> > > http://mail.gnome.org/mailman/listinfo/f-spot-list
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