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Re: Some more tests on Optimal Cubefaces.

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  • Hans Nyberg
    ... 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
    Message 1 of 24 , Oct 31, 2008
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      --- In PanoToolsNG@yahoogroups.com, "erik leeman" <erik.leeman@...> wrote:
      >
      > --- In PanoToolsNG@yahoogroups.com, "erik leeman" <erik.leeman@> wrote:
      >
      > > Other than that I noticed the loading indicators of both windows going
      > > to the same 4MB+ amount, which would seem to suggest both panos were
      > > the same size. Is everything working as intended?
      > >
      > > Erik Leeman
      > >
      >
      > Reloaded the page once more (third time). Sure enough, something like
      > 4325kB both left and right. Loading times were about equal too.
      >
      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
    • 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 2 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 3 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 4 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 5 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 6 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 7 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 8 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 9 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 10 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 11 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 12 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 13 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 14 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 15 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 16 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 17 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 18 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 19 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 20 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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