> 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...)

Personally I think the test is being run under flawed conditions
(using nonlinear sRGB rather than linear RGB, which produces errors of
up to 50% because interpolation is done linearly despite the
colorspace being nonlinear.). However, those are the conditions the
user is predominantly working under.
I'm considering doing a separate test run where I first convert to
linear RGB and finally convert back to sRGB.

> 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.

All these seem good, so I've included them. I'm currently searching
for Geert's images.
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