PanoTools NG:
Re: Re: Some more tests on Optimal Cubefaces.
Thomas Rauscher 2008-Nov-01 18:35:31
Erik Krause wrote, On 01.11.2008 15:20:
> Am Saturday, November 01, 2008 um 13:17 schrieb Hans Nyberg:
>
>> CubicConverter uses Bicubic which seems to be called Cubic in wiki.
>> Why not use the Bicubic definition if it is the same. I never heard
>> anyone call it just cubic. Photoshop today has 3 Bicubic versions.
>
> I don't know whether it is really the same. However, apparently the
> algorithm was called cubic in the originating paper:
> http://ieeexplore.ieee.org/search/wrapper.jsp?arnumber=1163711
The "bi" in bicubic comes from the fact that the filter is used 2 times,
one time in X and one time in Y direction. If you use such a filter on a
CT scan they are often called "Tricubic". As Panotools and Pano2VR
provide more then one filter the "bi" is kind of redundant as it should
be clear that they are used in both directions. Otherwise the filters
should have been called "Bigaussian", "Bilanczos", "Bimitchell"...
>> From what I understand Pano2VR uses Mitchell as default but Mitchell softens the
>> cubefaces slightly compared to CubiConverter. They need 0,4 100% unsharp mask to get
>> back to the same quality if you do an conversion with editing cubefaces and convert back
>> to equirectangular. This does not make sense after reading your comment as Mitchell
>> should have the same effect as Cubic.
>>
>> Lazcos 3 gives normally same quality as CubicConverter but I found that I had to get up
>> to Blackman/sinc Filter to get the same when doing downsizing.
>
> Interesting. I think Thomas should clarify...
I also use a kernel size of width/4 for the conversion. This is between
the two extremes of width/Pi and width/(Pi*sqtr(2)) (see my previous
post about the cube face sizes) and is a compromise between "too soft"
and aliasing. If you don't mind aliasing you can turn of the "dynamic
kernel" in the preferences and you should get a sharper image.
--
MfG,
Thomas
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