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Re: Some more tests on Optimal Cubefaces.

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  • erik leeman
    ... I think for a valid comparison you should do the scaling and sharpening in Photoshop, carefully optimizing each set to the highest possible quality
    Message 1 of 24 , Nov 1, 2008
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      --- In PanoToolsNG@yahoogroups.com, "Hans Nyberg" <hans@...> wrote:
      > Sorry you are right, I have exchanged them to CubicConverter movies.
      >
      > I have discovered that Pano2VR seems to have problems with downsizing.
      > The 1904 is softer than the CubicConverter version.
      >
      > Hans


      I think for a valid comparison you should do the scaling and
      sharpening in Photoshop, carefully optimizing each set to the highest
      possible quality attainable for that size. Now too much depends on the
      perhaps less fortunate settings and limitations of those VR tools.

      After finding what is technically possible with t.l.c. in Photoshop,
      some experimentation is necessary to see if those VR tools can come
      close to that, and how they need to be set up for the best possible
      results.

      Since I produce only a limited volume of panos I do all my scaling and
      sharpening in Photoshop. For me it is worth the extra time and effort.

      Erik Leeman

      http://www.erikleeman.com/
      http://flickr.com/photos/erik-nl/
    • philipp_koch_als_name_gibts_oft
      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
      Message 2 of 24 , Nov 1, 2008
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        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?

        Thanks in advance,
        Philipp

        --- In PanoToolsNG@yahoogroups.com, "Hans Nyberg" <hans@...> wrote:

        >
        > I have made some more tests on the optimal cubeface sizes.
        > http://www.panoramas.dk/cubefaces/
        >
        > Hans
        >
      • Erik Krause
        ... Nice test. However, we all know that using a large cube face size and not allowing zoom in to 1:1 pixel display is a waste of bandwidth. It is no surprise
        Message 3 of 24 , Nov 1, 2008
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          Am Friday, October 31, 2008 um 21:26 schrieb Hans Nyberg:

          > I have made some more tests on the optimal cubeface sizes.
          > http://www.panoramas.dk/cubefaces/

          Nice test. However, we all know that using a large cube face size and
          not allowing zoom in to 1:1 pixel display is a waste of bandwidth. It
          is no surprise that viewing a panorama at a given zoom setting yields
          the same quality as long as the cubefaces are larger than necessary.

          Hence this test only shows the interpolator and anti-aliasing quality
          of the viewer...

          As for Ken's 70% rule: Your images show impressively that he is
          absolutely right. However, the reason he gives (bayer interpolation)
          needs a closer look: While it is true that color information is
          upsampled this is not necessarily the case for brightness
          information.

          It depends on the used interpolation algorithm whether this affects
          the output resolution or not. This is the reason why you sometimes
          get a colored moiree if you shoot regular structures that are in the
          range of sensor pixel density. And it is the reason (among others)
          why different raw converters give different results.

          Hence the quality loss if downsampling to 70% might depend on the
          image content. Evenly bright images with a lot of color contrast
          might not suffer at all, while almost black and white images might
          suffer more.

          All this gets more and more meaningless with digital cameras having a
          pixel density (in some cases far) above the resolution of the used
          lenses...

          best regards

          --
          Erik Krause
          Offenburger Str. 33
          79108 Freiburg
        • 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 4 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 5 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 6 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 7 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 8 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 9 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 10 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 11 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 12 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 13 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 14 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 15 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 16 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 17 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 18 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 19 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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