Re: scaling images with Script-Fu

["lasm.rm" <lasm@xxxxxxxxxxxxxx>]

--- In script-fu@xxxxxxxxxxxxxxx, "David Kotchen" <dtkotchen@xxxx> 
wrote:
>
> --- In script-fu@xxxxxxxxxxxxxxx, "David Kotchen" <dtkotchen@xxxx> 
wrote:
> >
> > --- In script-fu@xxxxxxxxxxxxxxx, "lasm.rm" <lasm@xxxx> wrote:
> > >
> > > --- In script-fu@xxxxxxxxxxxxxxx, "David Kotchen" 
<dtkotchen@xxxx> 
> > > wrote:
> > > >
> > > > I have been playing around with the "gimp-drawable-transform-
scale"
> > > > procedure and have written some simple scripts. However, I 
cannot 
> > > seem
> > > > to match the defaults given by "gimp-image-scale". I thought 
that
> > > > these two commands would produce the same result:
> > > > 
> > > > (gimp-drawable-transform-scale (car (gimp-image-get-active-
drawable
> > > > theImage)) 0 0 568 426 0 1 0 3 0)
> > > > 
> > > > (gimp-image-scale theImage 568 426)
> > > > 
> > > > I believe that I have the correct "default" values plugged 
into the
> > > > first procedure above.
> > > > 
> > > > I have posted the same image produced by each of these 
procedures 
> > > here:
> > > > http://www.stop-the-
madness.net/GimpScale/ScaledImageTest.html
> > > > 
> > > > The full scripts for each are also posted on the web page.
> > > > 
> > > > There are significant differences between the two images. In
> > > > particular, the image produced by "gimp-image-scale" is 
smoother 
> > > and
> > > > has a smaller file size.
> > > > 
> > > > What accounts for the difference between the two? Are 
the "default"
> > > > values that I have plugged into "gimp-drawable-transform-
scale" not
> > > > the default values used in "gimp-image-scale"? Or is there 
> > > something
> > > > included in "gimp-image-scale" that is not reflected in
> > > > "gimp-drawable-transform-scale"?
> > > > 
> > > > (By the way, if it is at all helpful, the original image is 
posted 
> > > here:
> > > > http://www.stop-the-madness.net/GimpScale/IMG_1322.jpg
> > > > It's large: 2.1 MB)
> > > > 
> > > > I'd be grateful for any thoughts on this. Many thanks!
> > > >
> > > 
> > > Hi David,
> > > 
> > >    I am not sure if this helps, but browsing throught the PDB 
> > > Browser, i saw a series of default provided by the same author,
> > > so you can use gimp-drawable-transform-scale-default,
> > > instead of gimp-drawable-transform-scale. The default
> > > seems to use no interpolation according to documentation.
> > > 
> > > lasm
> > >
> > 
> > lasm,
> > 
> > Thanks for your reply. Do you know how "supersampling" and
> > "recursion_level" work and what they do? (These are among the
> > parameters required for gimp-drawable-transform-scale.)
> >
> 
> For that matter, is there anybody out there who can describe in 
plain
> English how interpolation, supersampling, and recursion level work
> when scaling an image? I have searched high and low and cannot 
find a
> description of this.
>

Not exactly layman's terms, but take a look at these slides
http://www.siggraph.org/education/materials/HyperGraph/aliasing/alias
2b.htm

http://www.cs.virginia.edu/~cs551dl/lecture8/sld016.htm

lasm









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