Re: [Gimp-developer] Cubic Interpolation vs No Halo

[Øyvind Kolås <pippin gimp org>]

On Wed, Apr 27, 2016 at 10:03 AM, C R <cajhne gmail com> wrote:
> I assume the reasoning behind using cubic as the default for all the scale
> and transform tools is to cut back on the complaints of how slow GIMP is at
> the moment, but the quality loss in the current cubic interpolation
> algorithm is quite bad.
>
> Can we shift the default to No Halo or Lo Halo?
> Also, it's probably safe to assume that if the user chooses an
> interpolation type in the tool, they are saying something about the quality
> of the results they are after vs speed. I think setting the value in one
> tool should set the value automatically in other tools, and treat it as a
> "global" value of sorts.

I've pushed code to GEGL master that makes the resamplers called
"linear" and "cubic" do a tiny bit more than just interpolation. These
operations now do a (possibly sparse) box-filtering when scaling down
instead of scaling up. Doing point sampling with interpolated values
is probably not what a user expect "cubic" or "linear" scaling down to
be anyways,. even if this is what it currently is. GEGL now does a 2x2
averaging of values for bilinear and a 4x4 sparse box filter averaging
for cubic. Due to how this code uses whole pixels for averaging it
might yield slightly sharper result than nohalo in many cases.