[Gimp-developer] Downscaling quality.

[Liam R E Quin]

On Thu, 2007-08-09 at 19:35 +0200, Øyvind Kolås wrote:

> For downscaling (decimating) box filtering is orders of magnitude
> better than the buggy erronious use of interpolation that currently is
> used in GIMP.

For what it's worth, for www.fromoldbooks.org, I routinely scale
images down to 20% or smaller of original width; I find that
the GIMP "Lancsoz" and "Cubic" modes produce very different
results.  Sometimes one is better and sometimes the other.

It's a difficult test because the engravings often have patterns
of almost-horizontal slightly-wavy lines that are, say, between
6 and 9 pixels apart... so you get strange artifacts appearing.

Sometimes I try a gaussian blur before downsizing, too, e.g. with
a radius of 3 or 5 or so; sometimes I use "value propagate" first.

Liam

-- 
Liam Quin - XML Activity Lead, W3C, http://www.w3.org/People/Quin/
Pictures from old books: http://fromoldbooks.org/
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