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Re: Some more tests on Optimal Cubefaces.

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  • Erik Krause
    ... This may be due to the fact that Pano2VR uses a non-sharpening anti- aliasing interpolator. On http://wiki.panotools.org/Anti-aliasing_interpolators the
    Message 1 of 24 , Nov 1, 2008
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      Am Friday, October 31, 2008 um 23:36 schrieb Hans Nyberg:

      > I have discovered that Pano2VR seems to have problems with downsizing.
      > The 1904 is softer than the CubicConverter version.

      This may be due to the fact that Pano2VR uses a non-sharpening anti-
      aliasing interpolator. On
      http://wiki.panotools.org/Anti-aliasing_interpolators the Filters
      with ID 18 and higher are sharpening ones (the deeper the
      "depression" on both sides of the peak the more).

      I don't know what kind of interpolator CubicConverter uses, but the
      result of a not anti-aliased downsize always gives a sharper
      impression because pixel "jaggies" subjectively look sharper (but
      increase shimmering in the resulting pano - if the viewer doesn't
      anti-alias itself).

      More info on http://wiki.panotools.org/Aliasing

      best regards
      --
      Erik Krause
      Offenburger Str. 33
      79108 Freiburg
    • Hans Nyberg
      ... Yes and No. You may also do that But If you read my page again you will see that I use the full resolution equirectangular as the source image to convert
      Message 2 of 24 , Nov 1, 2008
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        --- In PanoToolsNG@yahoogroups.com, "philipp_koch_als_name_gibts_oft" <pk@...>
        wrote:
        >
        > Hans,
        >
        > thanks for your efforts to share your findings with us! Hhm, but I
        > must admit I'm not sure if I do understand this correctly. Do you mean
        > it's possible to shrink the equirectangular image to 70% of its
        > original size and divide the corresponding image width by pi without
        > visible image detail loss? Sorry, maybe this is a dumb question, but I
        > simply could not get the same values when looking at the example on
        > your website.
        >
        > To make it simple: Say, there is an equirectangular image with 1000 x
        > 500 px.
        >
        > 1000 x 0.7 = 700
        > 700 / pi = 222.8169203
        >
        > So, one could shrink the equirectangular image to 700 x 350 px in
        > Photoshop and convert this image to six 222 x 222 px cube faces?
        >
        > Or am I getting something totally wrong here?

        Yes and No. You may also do that
        But If you read my page again you will see that I use the full resolution equirectangular as
        the source image to convert directly to the cubefaces. Just ignore any default cubefaces by
        the converter.
        In that way you are using all your information for the conversion so that you get full
        quality in all areas of the cubeface.

        Of course the 70% rule is only applicable if you are using the max resolution from your
        camera as it is the interpolation in the camera which gives you a false resolution.

        In reality you could probably also already in the Raw converter downsize the original
        images without loosing any details.

        For example all these Gigapixel images which are so popular are in most cases using
        panoramas with a resolution which they could easy schrink to 70%

        Just zoom in on them to the so called full resolution and you see that the quality is often
        really bad. But of course 10 gigapixels sounds more impressive than 7.

        Hans
      • Philipp B. Koch
        ... Ah, ok. So in the example given above one would take the 1000 x 500 equirectangular and convert it directly to cube faces with 222 x 222... ... I m always
        Message 3 of 24 , Nov 1, 2008
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          Hans Nyberg schrieb:
          > --- In PanoToolsNG@yahoogroups.com, "philipp_koch_als_name_gibts_oft" <pk@...>
          > wrote:
          >
          >> (...)
          >>
          >> To make it simple: Say, there is an equirectangular image with 1000 x
          >> 500 px.
          >>
          >> 1000 x 0.7 = 700
          >> 700 / pi = 222.8169203
          >>
          >> So, one could shrink the equirectangular image to 700 x 350 px in
          >> Photoshop and convert this image to six 222 x 222 px cube faces?
          >>
          >> (...)
          >>

          >> Yes and No. You may also do that
          >> But If you read my page again you will see that I use the full resolution equirectangular as
          >> the source image to convert directly to the cubefaces. Just ignore any default cubefaces by
          >> the converter.
          >> In that way you are using all your information for the conversion so that you get full
          >> quality in all areas of the cubeface.
          >>
          Ah, ok. So in the example given above one would take the 1000 x 500
          equirectangular and convert it directly to cube faces with 222 x 222...

          >> Of course the 70% rule is only applicable if you are using the max resolution from your
          >> camera as it is the interpolation in the camera which gives you a false resolution.
          >>
          >> In reality you could probably also already in the Raw converter downsize the original
          >> images without loosing any details.
          >>
          >> (...)
          I'm always shooting at best resolution (7.4 MP in my case, with Olympus
          E-330 and Olympus fisheye). I'll have to investigate this with my
          personal setup.

          So, again, thanks for letting me know :-)
        • 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
          Message 4 of 24 , Nov 1, 2008
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            --- In PanoToolsNG@yahoogroups.com, "Erik Krause" <erik.krause@...> wrote:
            >
            > Am Friday, October 31, 2008 um 23:36 schrieb Hans Nyberg:
            >
            > > I have discovered that Pano2VR seems to have problems with downsizing.
            > > The 1904 is softer than the CubicConverter version.
            >
            > This may be due to the fact that Pano2VR uses a non-sharpening anti-
            > aliasing interpolator. On
            > http://wiki.panotools.org/Anti-aliasing_interpolators the Filters
            > with ID 18 and higher are sharpening ones (the deeper the
            > "depression" on both sides of the peak the more).
            >
            > I don't know what kind of interpolator CubicConverter uses, but the
            > result of a not anti-aliased downsize always gives a sharper
            > impression because pixel "jaggies" subjectively look sharper (but
            > increase shimmering in the resulting pano - if the viewer doesn't
            > anti-alias itself).

            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.

            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.

            Hans
          • Erik Krause
            Am Saturday, November 01, 2008 um 11:33 schrieb ... No. To simplify the calculation you can simply divide by 4.5 (app. pi/0.7) In any case: It might be best to
            Message 5 of 24 , Nov 1, 2008
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              Am Saturday, November 01, 2008 um 11:33 schrieb
              philipp_koch_als_name_gibts_oft:

              > Sorry, maybe this is a dumb question, but I
              > simply could not get the same values when looking at the example on
              > your website.
              >
              > To make it simple: Say, there is an equirectangular image with 1000 x
              > 500 px.
              >
              > 1000 x 0.7 = 700
              > 700 / pi = 222.8169203
              >
              > So, one could shrink the equirectangular image to 700 x 350 px in
              > Photoshop and convert this image to six 222 x 222 px cube faces?
              >
              > Or am I getting something totally wrong here?

              No. To simplify the calculation you can simply divide by 4.5 (app.
              pi/0.7)

              In any case: It might be best to not first reduce the equirect and
              then create cubefaces but use a good anti-aliasing interpolator and
              create the smaller cubefaces directly from the larger equirect. This
              saves one interpolation step.

              BTW.: While photoshop creats nice small JPEGs at good quality it
              might be no good idea to use it for cubefaces stripes. In any stripe
              there are at least two joints where the single cubefaces don't fit.
              At these joints the jpeg compression creates artifacts that are later
              visible in the resulting panorama. See
              http://www.photopla.net/wwp0703/stripes.php for details.

              If I remember correctly Pano2VR and Pano2QTVR create stripes using a
              different compression scheme near the edges, which avoids these
              artifacts.

              best regards
              --
              Erik Krause
              Offenburger Str. 33
              79108 Freiburg
            • Hans Nyberg
              ... An image says more than..... Here is a screenshot with movies made from the 8600x4300 test image. Resized to 1904 cubefaces directly. From left Pano2VR
              Message 6 of 24 , Nov 1, 2008
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                --- In PanoToolsNG@yahoogroups.com, "Hans Nyberg" <hans@...> wrote:
                >
                > --- In PanoToolsNG@yahoogroups.com, "Erik Krause" <erik.krause@> wrote:
                > >
                > > Am Friday, October 31, 2008 um 23:36 schrieb Hans Nyberg:
                > >
                > > > I have discovered that Pano2VR seems to have problems with downsizing.
                > > > The 1904 is softer than the CubicConverter version.
                > >
                > > This may be due to the fact that Pano2VR uses a non-sharpening anti-
                > > aliasing interpolator. On
                > > http://wiki.panotools.org/Anti-aliasing_interpolators the Filters
                > > with ID 18 and higher are sharpening ones (the deeper the
                > > "depression" on both sides of the peak the more).
                > >
                > > I don't know what kind of interpolator CubicConverter uses, but the
                > > result of a not anti-aliased downsize always gives a sharper
                > > impression because pixel "jaggies" subjectively look sharper (but
                > > increase shimmering in the resulting pano - if the viewer doesn't
                > > anti-alias itself).
                >
                > CubicConverter uses Bicubic which seems to be called Cubic in wiki.

                An image says more than.....

                Here is a screenshot with movies made from the 8600x4300 test image.
                Resized to 1904 cubefaces directly.
                From left Pano2VR with different interpolators. Then CubicConverter 1904 and also 1
                default 2736. Plus the original image in Photoshop at 100%.
                http://www.panoramas.dk/cubefaces/cubefaces-interpolation.jpg

                Hans
              • Philipp B. Koch
                ... Thanks a lot, that really simple :-) ... I m using Eric Gerds DOSUP (Pano2Faces.bat) for conversion. As far as I know it s using spline64 as interpolator.
                Message 7 of 24 , Nov 1, 2008
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                  Erik Krause schrieb:
                  > To simplify the calculation you can simply divide by 4.5 (app.
                  > pi/0.7)
                  >
                  > In any case: It might be best to not first reduce the equirect and
                  > then create cubefaces but use a good anti-aliasing interpolator and
                  > create the smaller cubefaces directly from the larger equirect. This
                  > saves one interpolation step.
                  >
                  Thanks a lot, that really simple :-)

                  > BTW.: While photoshop creats nice small JPEGs at good quality it
                  > might be no good idea to use it for cubefaces stripes. In any stripe
                  > there are at least two joints where the single cubefaces don't fit.
                  > At these joints the jpeg compression creates artifacts that are later
                  > visible in the resulting panorama. See
                  > http://www.photopla.net/wwp0703/stripes.php for details.
                  >
                  > If I remember correctly Pano2VR and Pano2QTVR create stripes using a
                  > different compression scheme near the edges, which avoids these
                  > artifacts.
                  >
                  I'm using Eric Gerds' DOSUP (Pano2Faces.bat) for conversion. As far as I
                  know it's using spline64 as interpolator. So do you think I could expect
                  good results when applying the "simplified rule of 70" (e.g. divide
                  equirectangular image width by 4.5) here? (Good enough to use it as
                  standard workflow)?

                  Best regards,
                  Philipp Koch
                • Erik Krause
                  ... I don t know whether it is really the same. However, apparently the algorithm was called cubic in the originating paper:
                  Message 8 of 24 , Nov 1, 2008
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                    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

                    > 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...

                    best regards
                    --
                    Erik Krause
                    Offenburger Str. 33
                    79108 Freiburg
                  • Sacha Griffin
                    I think this proves an important point. You can t simply throw away pixels hoping they are bayer artifacts. The top left is so terrible compared to the others.
                    Message 9 of 24 , Nov 1, 2008
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                      I think this proves an important point. You can't simply throw away pixels
                      hoping they are bayer artifacts.

                      The top left is so terrible compared to the others. So using a high quality
                      interpolator is clear. As well as deciding on the final resolution

                      At least to my eyes there clearly a loss of resolution/clarity at 1904 from
                      2736.

                      I think also a contributing factor here, is jpeg compression. At 1904
                      compression artifacts are obscuring destroying details, and at full
                      resolution they are less noticeable.





                      Sacha Griffin

                      Southern Digital Solutions LLC

                      http://www.southern-digital.com

                      http://www.seeit360.net

                      404-551-4275






                      An image says more than.....

                      Here is a screenshot with movies made from the 8600x4300 test image.
                      Resized to 1904 cubefaces directly.
                      From left Pano2VR with different interpolators. Then CubicConverter 1904 and
                      also 1
                      default 2736. Plus the original image in Photoshop at 100%.
                      http://www.panoramas.dk/cubefaces/cubefaces-interpolation.jpg

                      Hans

                      .


                      <http://geo.yahoo.com/serv?s=97359714/grpId=18227848/grpspId=1705006496/msgI
                      d=24218/stime=1225548125/nc1=3848642/nc2=4763759/nc3=5349282>




                      [Non-text portions of this message have been removed]
                    • Keith Martin
                      ... Exactly, and well pointed out! This is an interesting trade-off that s worth remembering. With very high resolution images, JPEG damage isn t as noticable
                      Message 10 of 24 , Nov 1, 2008
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                        Sometime around 1/11/08 (at 10:59 -0400) Sacha Griffin said:

                        >I think also a contributing factor here, is jpeg compression. At 1904
                        >compression artifacts are obscuring destroying details, and at full
                        >resolution they are less noticeable.

                        Exactly, and well pointed out!

                        This is an interesting trade-off that's worth remembering. With very
                        high resolution images, JPEG damage isn't as noticable simply because
                        the pixel-level alterations are relatively smaller than with
                        lower-res images. This is definitely the case in print work, where
                        high-res can mean *very* high. But it has some bearing on what we do
                        for panoramas too; in my experience you can frequently use a somewhat
                        higher compression setting for a higher-res cubeface than for a
                        lower-res cubeface without ending up with obvious compression damage.

                        (I don't mean you can make a higher-res cubeface *smaller*, but you
                        can often get noticably better quality output without dramatically
                        larger file sizes.)

                        I think the key phrase here is "your mileage may vary", but I am
                        reading all posts with great interest in the hope of gleaning further
                        understanding in this area.

                        I've also set Pano2VR's default interpolation filder from my previous
                        choice of Lanczos3 to Blackman/sinc and will run some tests when I
                        have time.

                        k
                      • Erik Krause
                        ... spline64 isn t an anti-aliasing interpolator hence it s not optimal for downsizing. You can specify different interpolators on the DOSUP command line, but
                        Message 11 of 24 , Nov 1, 2008
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                          Am Saturday, November 01, 2008 um 15:03 schrieb Philipp B. Koch:

                          > I'm using Eric Gerds' DOSUP (Pano2Faces.bat) for conversion. As far as I
                          > know it's using spline64 as interpolator. So do you think I could expect
                          > good results when applying the "simplified rule of 70" (e.g. divide
                          > equirectangular image width by 4.5) here? (Good enough to use it as
                          > standard workflow)?

                          spline64 isn't an anti-aliasing interpolator hence it's not optimal
                          for downsizing. You can specify different interpolators on the DOSUP
                          command line, but it seems to be limited to the "old" panotools
                          interpolators.

                          If you have a more recent panotools version (pano12 version 2.7.10 or
                          newer) you can use the anti-alaising interpolators: open
                          pano2faces.bat in notepad (or similar text editor) and locate the
                          lines (numbers 369 and 370 in the current version)

                          SET interpolate=i4
                          SET interp=spline64

                          Change them to

                          SET interpolate=i19
                          SET interp=Mitchell

                          for a neutral or

                          SET interpolate=i21
                          SET interp=Lanczos3

                          for a sharpening anti-aliasing interpolator. The i-numbers correspond
                          to the ID in http://wiki.panotools.org/Anti-aliasing_interpolators

                          best regards

                          --
                          Erik Krause
                          Offenburger Str. 33
                          79108 Freiburg
                        • Philipp B. Koch
                          Thanks a lot, Erik! I ve tried both Lanczos3 and Mitchell with DOSUP like you proposed. The visual difference is surely worth the (much) longer processing time
                          Message 12 of 24 , Nov 1, 2008
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                            Thanks a lot, Erik! I've tried both Lanczos3 and Mitchell with DOSUP
                            like you proposed. The visual difference is surely worth the (much)
                            longer processing time it takes compared to spline64...

                            Best regards,
                            Philipp Koch


                            Erik Krause schrieb:
                            > Am Saturday, November 01, 2008 um 15:03 schrieb Philipp B. Koch:
                            >
                            >
                            >> I'm using Eric Gerds' DOSUP (Pano2Faces.bat) for conversion. As far as I
                            >> know it's using spline64 as interpolator. So do you think I could expect
                            >> good results when applying the "simplified rule of 70" (e.g. divide
                            >> equirectangular image width by 4.5) here? (Good enough to use it as
                            >> standard workflow)?
                            >>
                            >
                            > spline64 isn't an anti-aliasing interpolator hence it's not optimal
                            > for downsizing. You can specify different interpolators on the DOSUP
                            > command line, but it seems to be limited to the "old" panotools
                            > interpolators.
                            >
                            > If you have a more recent panotools version (pano12 version 2.7.10 or
                            > newer) you can use the anti-alaising interpolators: open
                            > pano2faces.bat in notepad (or similar text editor) and locate the
                            > lines (numbers 369 and 370 in the current version)
                            >
                            > SET interpolate=i4
                            > SET interp=spline64
                            >
                            > Change them to
                            >
                            > SET interpolate=i19
                            > SET interp=Mitchell
                            >
                            > for a neutral or
                            >
                            > SET interpolate=i21
                            > SET interp=Lanczos3
                            >
                            > for a sharpening anti-aliasing interpolator. The i-numbers correspond
                            > to the ID in http://wiki.panotools.org/Anti-aliasing_interpolators
                            >
                            > best regards
                            >
                            > --
                            > Erik Krause
                            > Offenburger Str. 33
                            > 79108 Freiburg
                            >
                            >
                            > ------------------------------------
                            >
                            >
                          • Thomas Rauscher
                            ... 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
                            Message 13 of 24 , Nov 1, 2008
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                              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
                            • Thomas Rauscher
                              ... The reason for these artifacts is chroma subsampling http://en.wikipedia.org/wiki/Chroma_subsampling . In Pano2VR and Pano2QTVR the subsampling is turned
                              Message 14 of 24 , Nov 1, 2008
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                                Erik Krause wrote, On 01.11.2008 14:52 Uhr:

                                > BTW.: While photoshop creats nice small JPEGs at good quality it
                                > might be no good idea to use it for cubefaces stripes. In any stripe
                                > there are at least two joints where the single cubefaces don't fit.
                                > At these joints the jpeg compression creates artifacts that are later
                                > visible in the resulting panorama. See
                                > http://www.photopla.net/wwp0703/stripes.php for details.
                                >
                                > If I remember correctly Pano2VR and Pano2QTVR create stripes using a
                                > different compression scheme near the edges, which avoids these
                                > artifacts.

                                The reason for these artifacts is chroma subsampling
                                http://en.wikipedia.org/wiki/Chroma_subsampling .
                                In Pano2VR and Pano2QTVR the subsampling is turned off for stripes.
                                Please note that the tile size must be a multiple of 16 to make this work.

                                In Photoshop different levels of subsampling are used depending of the
                                quality setting. To be on the safe side with CS2 you need to use at
                                least Quality 7 in "Save as..." and Quality 51 in "Save for Web". For
                                more information you may also have a look at:
                                http://www.impulseadventure.com/photo/chroma-subsampling.html

                                --
                                MfG,
                                Thomas
                              • Erik Krause
                                ... How much do you downsample? I did some tests some time ago and found no big difference for a 4000x2000 to cubefaces 1200 remapping tasks. -
                                Message 15 of 24 , Nov 1, 2008
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                                  Am Saturday, November 01, 2008 um 17:55 schrieb Philipp B. Koch:

                                  > Thanks a lot, Erik! I've tried both Lanczos3 and Mitchell with DOSUP
                                  > like you proposed. The visual difference is surely worth the (much)
                                  > longer processing time it takes compared to spline64...

                                  How much do you downsample? I did some tests some time ago and found
                                  no big difference for a 4000x2000 to cubefaces 1200 remapping tasks.
                                  -> http://www.panotools.org/mailarchive/msg/41713#msg41713
                                  I stopped testing, since the old fixed kernel size interpolators and
                                  the anti-alaising ones are not comparable. The kernel size (and hence
                                  the execution time) highly depends on whether downsampling or
                                  upsampling, and they increase for downsampling:
                                  http://www.panotools.org/mailarchive/msg/41703#msg41703

                                  best regards
                                  --
                                  Erik Krause
                                  Offenburger Str. 33
                                  79108 Freiburg
                                • Philipp B. Koch
                                  ... I ve made some tests with an equirectangular 4742 x 2371, downsampling it to 1052 cubes (=~ / 4.5) with spline64, Mitchell and Lanczos3. I did not count
                                  Message 16 of 24 , Nov 2, 2008
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                                    Erik Krause schrieb:
                                    > Am Saturday, November 01, 2008 um 17:55 schrieb Philipp B. Koch:
                                    >
                                    >> Thanks a lot, Erik! I've tried both Lanczos3 and Mitchell with DOSUP
                                    >> like you proposed. The visual difference is surely worth the (much)
                                    >> longer processing time it takes compared to spline64...
                                    >>
                                    > How much do you downsample? I did some tests some time ago and found
                                    > no big difference for a 4000x2000 to cubefaces 1200 remapping tasks.
                                    > -> http://www.panotools.org/mailarchive/msg/41713#msg41713
                                    > I stopped testing, since the old fixed kernel size interpolators and
                                    > the anti-alaising ones are not comparable. The kernel size (and hence
                                    > the execution time) highly depends on whether downsampling or
                                    > upsampling, and they increase for downsampling:
                                    > http://www.panotools.org/mailarchive/msg/41703#msg41703
                                    I've made some tests with an equirectangular 4742 x 2371, downsampling
                                    it to 1052 cubes (=~ / 4.5) with spline64, Mitchell and Lanczos3.
                                    I did not count the time for each task, but both Mitchell and Lanczos3
                                    took well three times as long as spline64, I'd estimate.

                                    Regards, Philipp
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