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

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  • 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 1 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 2 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 3 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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