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Merge before or after panorama?

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  • Peter Gawthrop
    I use exposure bracketing to get three sets of 8 images for my panoramas: normal exposure, under exposure and over exposure. Up to now, I have stiched three
    Message 1 of 9 , Aug 2, 2006
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      I use exposure bracketing to get three sets of 8 images for my
      panoramas: normal exposure, under exposure and over exposure. Up to
      now, I have stiched three versions and merged in gimp (as described at
      http://www.lightspacewater.net/Tutorials/PhotoPano2/paper/index.html).

      However, I now think it is more efficient to merge beforhand (using
      ImageMagick) and stich the 8 merged images. In particular, this saves
      the slow enblend step being run three times.

      Any comments, or links to previous discussions, on the relative merits
      of before and after merging?

      FWIW here is a fragment of the Image Magick commands that I use -
      replace $under by the under exposed image etc.; merged.tif is the
      result.

      normal=$1
      under=$2
      over=$3

      ### Merge under exposure
      ## Mask for under exposed
      convert -type Grayscale $under _mask.tif
      ## Masked version
      composite -compose CopyOpacity _mask.tif $under _under_masked.tif
      ## Merge with background
      composite -compose Darken _under_masked.tif $normal _composite.tif

      ### Merge over exposure
      ## Mask for over exposed
      convert -negate -type Grayscale $over _mask.tif
      ## Masked version
      composite -compose CopyOpacity _mask.tif $over _over_masked.tif
      ## Merge with background
      composite -compose Lighten _over_masked.tif _composite.tif merged.tif


      Peter.
    • Luca Vascon
      I use Juffre s photomatix... I run it on images before stitching, usually, and I ve to say I take 5 shots in difficult situations. It is a FANTASTIC HDR
      Message 2 of 9 , Aug 2, 2006
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        I use Juffre's photomatix...
        I run it on images before stitching, usually, and I've to say I take 5 shots in difficult situations.
        It is a FANTASTIC HDR software.
        In most common cases I simply tahe one picture more to that "single window driving you crazy" and merge it manually with photoshop.
        (actually it is one picture more in the ptgui project, that I output alone...)
        ----- Original Message -----
        From: Peter Gawthrop
        To: PanoToolsNG@yahoogroups.com
        Sent: Wednesday, August 02, 2006 10:35 AM
        Subject: [PanoToolsNG] Merge before or after panorama?


        I use exposure bracketing to get three sets of 8 images for my
        panoramas: normal exposure, under exposure and over exposure. Up to
        now, I have stiched three versions and merged in gimp (as described at
        http://www.lightspacewater.net/Tutorials/PhotoPano2/paper/index.html).

        However, I now think it is more efficient to merge beforhand (using
        ImageMagick) and stich the 8 merged images. In particular, this saves
        the slow enblend step being run three times.

        Any comments, or links to previous discussions, on the relative merits
        of before and after merging?

        FWIW here is a fragment of the Image Magick commands that I use -
        replace $under by the under exposed image etc.; merged.tif is the
        result.

        normal=$1
        under=$2
        over=$3

        ### Merge under exposure
        ## Mask for under exposed
        convert -type Grayscale $under _mask.tif
        ## Masked version
        composite -compose CopyOpacity _mask.tif $under _under_masked.tif
        ## Merge with background
        composite -compose Darken _under_masked.tif $normal _composite.tif

        ### Merge over exposure
        ## Mask for over exposed
        convert -negate -type Grayscale $over _mask.tif
        ## Masked version
        composite -compose CopyOpacity _mask.tif $over _over_masked.tif
        ## Merge with background
        composite -compose Lighten _over_masked.tif _composite.tif merged.tif

        Peter.





        [Non-text portions of this message have been removed]
      • Erik Krause
        ... This works if (and only if) the process of merging does anything the very same way without regard to the actual brightness of the images. Any automatic
        Message 3 of 9 , Aug 2, 2006
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          Peter Gawthrop <peter@...> writes:

          > I use exposure bracketing to get three sets of 8 images for my
          > panoramas: normal exposure, under exposure and over exposure. Up to
          > now, I have stiched three versions and merged in gimp (as described at
          > http://www.lightspacewater.net/Tutorials/PhotoPano2/paper/index.html).
          >
          > However, I now think it is more efficient to merge beforhand (using
          > ImageMagick) and stich the 8 merged images. In particular, this saves
          > the slow enblend step being run three times.

          This works if (and only if) the process of merging does anything the very same
          way without regard to the actual brightness of the images. Any automatic
          adjustment of brightness or colors for the single image will cause a brightness
          difference that probably can't be eliminated by enblend or smartblend (no, both
          programs don't change the brightness of a whole image - they work in the overlap
          only).

          best regards
          Erik
        • JD Smith
          ... Since you ve done all the work to create 3 stitched exposures, you might have more luck merging the exposures interactively in the Gimp, which allows you
          Message 4 of 9 , Aug 2, 2006
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            On Wed, 02 Aug 2006 08:35:21 +0000, Peter Gawthrop wrote:

            > I use exposure bracketing to get three sets of 8 images for my panoramas:
            > normal exposure, under exposure and over exposure. Up to now, I have
            > stiched three versions and merged in gimp (as described at
            > http://www.lightspacewater.net/Tutorials/PhotoPano2/paper/index.html).
            >
            > However, I now think it is more efficient to merge beforhand (using
            > ImageMagick) and stich the 8 merged images. In particular, this saves the
            > slow enblend step being run three times.
            >
            > Any comments, or links to previous discussions, on the relative merits of
            > before and after merging?
            >
            > FWIW here is a fragment of the Image Magick commands that I use - replace
            > $under by the under exposed image etc.; merged.tif is the result.
            >
            > normal=$1
            > under=$2
            > over=$3
            >
            > ### Merge under exposure
            > ## Mask for under exposed
            > convert -type Grayscale $under _mask.tif ## Masked version
            > composite -compose CopyOpacity _mask.tif $under _under_masked.tif ##
            > Merge with background
            > composite -compose Darken _under_masked.tif $normal _composite.tif
            >
            > ### Merge over exposure
            > ## Mask for over exposed
            > convert -negate -type Grayscale $over _mask.tif ## Masked version
            > composite -compose CopyOpacity _mask.tif $over _over_masked.tif ## Merge
            > with background
            > composite -compose Lighten _over_masked.tif _composite.tif merged.tif

            Since you've done all the work to create 3 stitched exposures, you
            might have more luck merging the exposures interactively in the Gimp,
            which allows you to fine tune the blended appearance (make it look
            more natural, and emphasize certain regions, either by spatial
            segregation, or by adjusting the masks' curves). See:

            http://turtle.as.arizona.edu/jdsmith/exposure_blend.php

            JD
          • Peter Gawthrop
            ... I do, indeed now use your excellent tool for post merging (I mention that in the tutorial). Unfortunately, it can t be used for pre merging as the same
            Message 5 of 9 , Aug 4, 2006
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              JD Smith <jdsmith@...> writes:

              > Since you've done all the work to create 3 stitched exposures, you
              > might have more luck merging the exposures interactively in the Gimp,
              > which allows you to fine tune the blended appearance (make it look
              > more natural, and emphasize certain regions, either by spatial
              > segregation, or by adjusting the masks' curves). See:
              >
              > http://turtle.as.arizona.edu/jdsmith/exposure_blend.php
              >
              > JD
              >

              I do, indeed now use your excellent tool for post merging (I mention that in
              the tutorial). Unfortunately, it can't be used for pre merging as the same
              operation must be applied to each of the 8 triples. So I guess that counts
              as an advantage for merging after stiching.

              Peter.
            • JD Smith
              ... Very nice tutorial. I forget if Hugin easily allows you to change the file name without affecting the control points. Do you first rename all of your
              Message 6 of 9 , Aug 7, 2006
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                On Sat, 05 Aug 2006 06:23:54 +0000, Peter Gawthrop wrote:

                > JD Smith <jdsmith@...> writes:
                >
                >> Since you've done all the work to create 3 stitched exposures, you
                >> might have more luck merging the exposures interactively in the Gimp,
                >> which allows you to fine tune the blended appearance (make it look
                >> more natural, and emphasize certain regions, either by spatial
                >> segregation, or by adjusting the masks' curves). See:
                >>
                >> http://turtle.as.arizona.edu/jdsmith/exposure_blend.php
                >>
                >> JD
                >>
                >
                > I do, indeed now use your excellent tool for post merging (I mention that in
                > the tutorial). Unfortunately, it can't be used for pre merging as the same
                > operation must be applied to each of the 8 triples. So I guess that counts
                > as an advantage for merging after stiching.

                Very nice tutorial. I forget if Hugin easily allows you to change the
                file name without affecting the control points. Do you first rename
                all of your inputs the same in each of your normal/ bright/ dark/
                subdirs?

                Certainly you could have the Gimp do all the "pre-merging" for you,
                but the real disadvantage is, you must use the same merge method for
                all input images to ensure the final results looks good, which will be
                limiting. The real advantage of having the full scene assembled in
                one place is you can have great flexibility in assigning the weights
                to the 3 bracketed panos, either by stretching and manipulating the
                mask levels, or directly editing them.

                JD
              • Bruno Postle
                ... So there are various ways of dealing with a bracketed panorama: * Use contrast blending to merge each bracketed view, then stitch these 8bit images into
                Message 7 of 9 , Aug 16, 2006
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                  On Wed 02-Aug-2006 at 08:35 +0000, Peter Gawthrop wrote:

                  > I use exposure bracketing to get three sets of 8 images for my
                  > panoramas: normal exposure, under exposure and over exposure. Up to
                  > now, I have stiched three versions and merged in gimp (as described at
                  > http://www.lightspacewater.net/Tutorials/PhotoPano2/paper/index.html).
                  >
                  > However, I now think it is more efficient to merge beforhand (using
                  > ImageMagick) and stich the 8 merged images. In particular, this saves
                  > the slow enblend step being run three times.

                  > Any comments, or links to previous discussions, on the relative merits
                  > of before and after merging?

                  So there are various ways of dealing with a bracketed panorama:

                  * Use 'contrast blending' to merge each bracketed view, then stitch
                  these 8bit images into an 8bit panorama.

                  Disadvantage: you have to use the same 'exposure' when merging each
                  shot, but you don't know what that needs to be until you have
                  finished and can see the result (not a problem if you use a 16bit
                  workflow).

                  * Stitch each exposure step into a complete 8bit panorama, then merge
                  these with 'contrast blending' into an 8bit panorama.

                  Disadvantages: running enblend multiple times is slow. Ghosting
                  unless your panoramas are aligned perfectly.

                  * Merge each bracketed view into an HDR image, stitch these into an
                  HDR panorama and then reduce to 8bit with tone mapping.

                  Disadvantages: local tone mapping operators produce ugly artefacts
                  in equirectangular panoramas. Currently this workflow is only
                  possible with hugin.

                  * Stitch each exposure step into a complete 8bit panorama, then
                  merge these into an HDR panorama and reduce to 8bit with tone
                  mapping.

                  Disadvantages: running enblend multiple times is slow. local tone
                  mapping operators produce ugly artefacts in equirectangular
                  panoramas. Ghosting unless all your panoramas are aligned
                  perfectly.

                  > FWIW here is a fragment of the Image Magick commands that I use -
                  > replace $under by the under exposed image etc.; merged.tif is the
                  > result.

                  This looks useful, can it go into the wiki?

                  --
                  Bruno
                • Roger D. Williams
                  Well, as a complete newbie to DSLRs and the need for HDR, etc., I am probably behind the field here. And everything I say may be common knowledge/practice, but
                  Message 8 of 9 , Aug 17, 2006
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                    Well, as a complete newbie to DSLRs and the need for HDR, etc., I am
                    probably behind the field here. And everything I say may be common
                    knowledge/practice, but it's all pristine to me. <grin>

                    On Thu, 17 Aug 2006 07:05:28 +0900, Bruno Postle
                    <bruno@...> wrote:

                    > On Wed 02-Aug-2006 at 08:35 +0000, Peter Gawthrop wrote:
                    >
                    >> I use exposure bracketing to get three sets of 8 images for my
                    >> panoramas: normal exposure, under exposure and over exposure. Up to
                    >> now, I have stiched three versions and merged in gimp (as described at
                    >> http://www.lightspacewater.net/Tutorials/PhotoPano2/paper/index.html).
                    >>
                    >> However, I now think it is more efficient to merge beforhand (using
                    >> ImageMagick) and stich the 8 merged images. In particular, this saves
                    >> the slow enblend step being run three times.
                    >
                    >> Any comments, or links to previous discussions, on the relative merits
                    >> of before and after merging?
                    >
                    > So there are various ways of dealing with a bracketed panorama:

                    ------excellent summary by Bruno deleted------

                    I shoot a five-bracket shot for each of six + 1 (zenith) using a D200
                    and the lovely Nikkor 10.5mm fisheye (RAW). Why 5? the D200 only allows
                    1EV steps, so even so I only go two stops above and below standard.

                    I develop one of the standard images of the five using Sylkipix to create
                    a 16-bit TIFF, then batch convert all the other images in the same way.
                    This is fairly slow but not as slow as creating a panorama in PTgui.
                    And it has to be done anyway, so there is no penalty in doing it at this
                    stage.

                    Then I take one set of five TIFF images and create an HDR image using
                    Photomatix. I use the tone-mapping sliders to create an attractive
                    version (if there are significant differences in the dynamic range from
                    shot to shot, I choose one with the greatest dynamic range) as a TIFF,
                    save the tone-mapping settings to a suitable filename, then I use the
                    auto/batch mode to create similar HDRs for the complete sets of images.

                    Then I batch convert each of the other sets of five images, now HDRs,
                    into similary TIFFs, using the tone-mapping file I've just created.

                    Both auto/batch processes are much faster and easier on system resources
                    than doing them individually. I was surprised to find how well the TM
                    settings in the file apply to other sets in the same series.

                    Finally, I stitch the 6 + 1 tone-mapped images in PTgui, which nicely
                    takes care of any slight differences between the different tone-mapped
                    HDR images. Then I think what to do about the hole in the floor. <g>

                    Having worked only with film before last month, I was a bit distressed
                    to find out how much work it is to create an image with good rendering
                    of a scene with large dynamic range using a DSLR, but the workflow is
                    not too bad when you get used to it. Of course all of this is greatly
                    complicated if you have moving subjects in the fied of view. <pained
                    grin> Not much good for panoramas of the Tokyo Marathon taken from
                    inside a darkened room.

                    Roger W.

                    --
                    Work: www.adex-japan.com, Play: www.usefilm.com/member/roger
                  • Bruno Postle
                    ... That s one workflow I didn t think of. I ve pasted all this into a wiki page: http://wiki.panotools.org/Bracketing ...though it could do with somebody
                    Message 9 of 9 , Aug 18, 2006
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                      On Fri 18-Aug-2006 at 10:22 +0900, Roger D. Williams wrote:
                      >
                      > Finally, I stitch the 6 + 1 tone-mapped images in PTgui, which nicely
                      > takes care of any slight differences between the different tone-mapped
                      > HDR images.

                      That's one workflow I didn't think of.

                      I've pasted all this into a wiki page:

                      http://wiki.panotools.org/Bracketing

                      ...though it could do with somebody adding a better discussion of
                      bracketing at the top.

                      --
                      Bruno
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