On Sun, 10 Jun 2007 05:53:57 +0200, <[EMAIL PROTECTED]> wrote:

> I think cubic (catmull-rom as per scale up) should give better results.  
> It
> may be necessary to decide a policy for reductions greater than 4:1 to
> avoid ignoring some data points.

As I suspected the catmull-rom spline works better than the existing code  
on small reductions (tested at 65%). At larger reductions it introduced  
some intrusive colour distortions so the existing pixel averaging code  
produced better results in this case.

I think "cubic" interpolation probably should be changed to actually do  
cubic and let the user find out where it is better or worse.

There is also a slight lack of clarity in calling what the code does now  
"linear". Averaging colours over 4.35 pixels , for example, cannot be  
described as linear interpolation!

Maybe the name "linear" should be changed to better reflect what the code  
does. Perhaps "pixel mean" or "average".

This would accurately reflect what the code does in both directions since  
linear scale up does not actually do a linear interpolation anyway (ie fit  
a first order polynomial), it does a mean which gives the same result.

It does not sound a good since we're all so used to linear but it is  
understandable to just about anyone and does accurately describe what the  
code does in both cases.

Any other suggestions?

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