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RE: [PanoToolsNG] Re: Some more tests on Optimal Cubefaces.

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  • 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 1 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 2 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 3 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 4 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 5 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 6 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 7 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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