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Re: Some more tests on Optimal Cubefaces.

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  • 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 1 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 2 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 3 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 4 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 5 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 6 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 7 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 8 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 9 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 10 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 11 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 12 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 13 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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