On Wed, 16 Jul 2008 17:15:38 +0200, Liam R E Quin <[EMAIL PROTECTED]> wrote:

> On Wed, 2008-07-16 at 22:14 +0930, David Gowers wrote:
>> > The one thing I definitely can't do is
>> > * Host webpage.
> I can do that if you want, although gimp.org would be better.
> As long as it's under a gigabyte or so.
> Here are some images that may help show some problems -- colour photos
> tend to hide problems, partly because the eye sees the subject more
> easily and auto-corrects flaws, and partly because the hardest thing
> for rescaling is often preserving both texture and sharpness.  Of
> course, most people are working with colour photos these days...)

I posted some good test images when I was working on the lanczos part of  
this code and the rotation distortions. Concentric circles and the like.  
These geometric patterns make any defect instantly visible whereas it may  
not be obvious in one operation on a photo-like image.

care should be taken not to assume the criteria is one or two simple ops  
on photos. Gimp vision specifies graphics as well as photos so defects in  
geometric shapes are highly relevant.

I also posted a woodpecker photo that had a near horizontal beak section.  
I found this was a very sensitive test for staircasing defects that may be  
relevant here.

Search bugs for lanczos or rotation to find these bug reports containing  


> For potential problems with vertical artifacts, see the
> 1600x1200 image at
> http://www.fromoldbooks.org/Green-ShortHistory/pages/0187-Remains-of-Cloisters/
> (I had to resize it to 1024x768 using cubic and then sharpen)
> The 1518x916 one at
> http://www.fromoldbooks.org/YouthsInstructer/pages/072-New-Post-Office-London/
> has near-horizontal lines which are difficult.
> http://www.fromoldbooks.org/YouthsInstructer/pages/181-Dunluce-Castle/181-Dunluce-Castle-q59-1447x923.jpg
> has diagonals and is an RGB image instead of grayscale.
> http://www.fromoldbooks.org/ThomasBewick-WoodEngravings/pages/30-the-horse/1790x1307-q75.html
> is a fairly clean woodcut.
> I have some much larger images too if you want them.
> Liam


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