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Re: Some more tests on Optimal Cubefaces.

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  • Erik Krause
    ... I don t know whether it is really the same. However, apparently the algorithm was called cubic in the originating paper:
    Message 1 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 2 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 3 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 4 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 5 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 6 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 7 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 8 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 9 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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