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Re: [PanoToolsNG] Re: White (Neutral) Balance in Panoramas

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  • Snowy Aldon
    Hi All, any colour balance work requires a spectrally neutral target to balance from. One which has little or no florescent materials. The targets that William
    Message 1 of 23 , Mar 1, 2008
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      Hi All,

      any colour balance work requires a spectrally neutral target to
      balance from. One which has little or no florescent materials.

      The targets that William has suggested would work well for tonal
      adjustments but will almost certainly give colour casts under most
      conditions.

      >>
      >> I prepared a hardback 8x11 notebook (with 100 pages of lined note
      >> paper) for colour
      >> balance & correction:
      >>
      >> I went to a charity shop, and bought an old black velvet dress to
      >> cut up for patches.
      >>
      >> I glued several pieces of the black velvet (with the "grain" in
      >> various directions) into the
      >> front cover. Now, when the camera sees it, some of the patches
      >> look dark black, and
      >> some look gray. The lined note paper looks white



      It is best to use a calibrated target like a macbeth chart or a QP card.

      The placement of the target in the scene is very critical. In the
      example being used of the room lit with tungsten balanced lighting
      and also getting light from a window. the closer the neutral target
      is placed to the lamp the more tungsten light and the bluer the
      daylight and vice versa.

      The same effect will be present in a landscape. If the target is
      fully illuminated by the sun it will give a different result than in
      the shade.

      If you are on a lawn and the target is backlit so no sunlight is
      falling on the target and it is shaded from the blue sky, a major
      source of illumination will be bright green light from the lawn. If
      this is then used to "neutralise" the images a magenta cast will
      almost certainly be introduced.

      In the case of VR Panoramas one must "correct" the image so that it
      appears a faithful representation of the scene captured ( on a
      profiled monitor). This of course forms an integral part of the
      creative process. Relying on a mechanical approach to white balance
      of digital will not give the best results. these targets and useful
      guides when not used in the studio.

      Hope this helps


      best

      Snowy





      On 1 Mar 2008, at 13:33, William Donelson wrote:

      > .
      >
      > You can also arranged for the front cover to be "in the shade" (of
      > itself or of some other
      > shadow) to get an even darker set of blacks.
      >
      > This gives us a very good range of blacks, grays and whites to use
      > in Photoshop
      > correction.
      >
      > And, the notepaper can be used to mark down info about the shot.
      >
      > Cheers
      > William
      >



      [Non-text portions of this message have been removed]
    • William Donelson
      ... Yes, you do have to be careful, and aware of reflections and other light sources, as you mention. But the technique I outlined has given us the best
      Message 2 of 23 , Mar 4, 2008
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        --- In PanoToolsNG@yahoogroups.com, Snowy Aldon <lists@...> wrote:
        > The targets that William has suggested would work well for tonal
        > adjustments but will almost certainly give colour casts under most
        > conditions.
        Yes, you do have to be careful, and aware of reflections and other light sources, as you
        mention.

        But the technique I outlined has given us the best results we've had in 15 years of doing
        panoramas.

        Properly used, it never gives colour casts, or false colours, except in extreme circumstances.

        We tried using colour charts and grayscale charts, but these were essentially useless, as they
        are far too dependent on the lighting conditions.

        The "best black" can be achieved by building a box, lined with black velvet, and open on
        one side, so that the interior is completely unlit. But, we have found this to be unnecessary,
        except in unusual circumstances.
      • Snowy Aldon
        Hi, I m really interested in this technique. The comments we re made as an extrapolation of colour management in the studio and on location. I have been using
        Message 3 of 23 , Mar 4, 2008
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          Hi,

          I'm really interested in this technique.

          The comments we're made as an extrapolation of colour management in
          the studio and on location. I have been using various method and
          targets with some success.

          It seems strange that the velvet gives a neutral value when
          illuminated to be in the mid-tone. I would have have supposed that
          the colour bias of the dyes would become apparent and introduce a cast.

          Do you colour balance/correct/neutralise to the velvet and adjust the
          images to give an equal RGB value grey? And how does achieving a
          truly "black" black give any information regarding the colour balance
          of the image?

          TIA

          Snowy

          On 4 Mar 2008, at 14:53, William Donelson wrote:



          >> --- In PanoToolsNG@yahoogroups.com, Snowy Aldon <lists@...> wrote:
          >> > The targets that William has suggested would work well for tonal
          >> > adjustments but will almost certainly give colour casts under most
          >> > conditions.
          >> Yes, you do have to be careful, and aware of reflections and other
          >> light sources, as you
          >> mention.
          >>
          >> But the technique I outlined has given us the best results we've
          >> had in 15 years of doing
          >> panoramas.
          >>
          >> Properly used, it never gives colour casts, or false colours,
          >> except in extreme circumstances.
          >>
          >> We tried using colour charts and grayscale charts, but these were
          >> essentially useless, as they
          >> are far too dependent on the lighting conditions.
          >>
          >> The "best black" can be achieved by building a box, lined with
          >> black velvet, and open on
          >> one side, so that the interior is completely unlit. But, we have
          >> found this to be unnecessary,
          >> except in unusual circumstances.
          >


          [Non-text portions of this message have been removed]
        • William Donelson
          ... You have to be careful which patch of velvet you use. Some are not black. ... We do not use the box-of-velvet anymore, as our 4 patches of velvet at
          Message 4 of 23 , Mar 4, 2008
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            --- In PanoToolsNG@yahoogroups.com, Snowy Aldon <lists@...> wrote:
            > It seems strange that the velvet gives a neutral value when
            > illuminated to be in the mid-tone. I would have have supposed that
            > the colour bias of the dyes would become apparent and introduce a cast.

            You have to be careful which patch of velvet you use. Some are not black.

            > Do you colour balance/correct/neutralise to the velvet and adjust the
            > images to give an equal RGB value grey? And how does achieving a
            > truly "black" black give any information regarding the colour balance
            > of the image?

            We do not use the box-of-velvet anymore, as our "4 patches of velvet" at different
            orientations works very well. Some of the patches look blacker than others, and some can
            be used as gray-level samples.

            Having an in-scene black is useful if you are shooting on film (as we usually do - Seitz
            Super Roundshot 220).

            Having specular (over-exposed) white patches are not useful, so we use a variety of
            techniques in Photoshop to set the top white level.

            In the end, the velvet-patches are a short-cut to getting NEAR to correct colour, and we
            use Photoshop to adjust the colour to "Correct" levels by eye and memory.

            Hope this helps.
          • Rik Littlefield
            ... Using black velvet this way is a very clever trick. What happens, I believe, is that the gray appearance is caused by a myriad of specular reflections
            Message 5 of 23 , Mar 4, 2008
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              --- In PanoToolsNG@yahoogroups.com, "William Donelson" <wd@...> wrote:
              >
              > --- In PanoToolsNG@yahoogroups.com, Snowy Aldon <lists@> wrote:
              > > It seems strange that the velvet gives a neutral value when
              > > illuminated to be in the mid-tone. I would have have supposed
              > > that the colour bias of the dyes would become apparent
              > > and introduce a cast.
              >
              > You have to be careful which patch of velvet you use.
              > Some are not black.
              >
              > > Do you colour balance/correct/neutralise to the velvet
              > > and adjust the images to give an equal RGB value grey?
              > > And how does achieving a truly "black" black give any
              > > information regarding the colour balance
              > > of the image?
              >
              > We do not use the box-of-velvet anymore, as our
              > "4 patches of velvet" at different orientations
              > works very well. Some of the patches look blacker
              > than others, and some can be used as gray-level samples.

              Using black velvet this way is a very clever trick. What happens, I
              believe, is that the "gray" appearance is caused by a myriad of
              specular reflections from the surfaces of the fibers. Specular
              reflections are always non-colored, so indeed this method should
              produce a very neutral gray as long as the body of the fibers is very
              dark in comparison.

              --Rik
            • johncharlesriley
              ... Sorry, I have to jump in here. I am not sure what you might be thinking of, but specular reflections have the same color as the incident light. When you
              Message 6 of 23 , Mar 7, 2008
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                >
                > Using black velvet this way is a very clever trick. What happens, I
                > believe, is that the "gray" appearance is caused by a myriad of
                > specular reflections from the surfaces of the fibers. Specular
                > reflections are always non-colored, so indeed this method should
                > produce a very neutral gray as long as the body of the fibers is very
                > dark in comparison.
                >
                > --Rik
                >

                Sorry, I have to jump in here. I am not sure what you might be thinking of, but specular
                reflections have the same color as the incident light. When you see yourself in a mirror,
                that is a specular reflection. A specular reflection is simply when light is reflected in a
                mirror-like fashion from a smooth surface. Examples are the glare off of a car (or water
                or snow) from the sun. They are problematic because you are seeing a reflection of the
                sun and not the object itself. Since specular reflections are partially polarized (or
                completely if at Brewster's angle), polarized sunglasses can drastically reduce their
                intensity. Then you can see the object itself by the diffusely reflected light, which is
                scattered in all directions.

                Sorry for being pedantic, but I am a physics professor and just can't help it 8-) Now, what
                else might be going on with the fibers of black velvet, I don't know, but it could be
                interesting to hear.

                John
              • Georgia Real Tours
                ... Exactly. The grain of the fabric acts as a rudimentary polarization filter. Further, since it is diffuse, the light reflected is a culmination of the
                Message 7 of 23 , Mar 8, 2008
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                  On 3/7/08, johncharlesriley <johnriley@...> wrote:
                  > >
                  > > Using black velvet this way is a very clever trick. What happens, I
                  > > believe, is that the "gray" appearance is caused by a myriad of
                  > > specular reflections from the surfaces of the fibers. Specular
                  > > reflections are always non-colored, so indeed this method should
                  > > produce a very neutral gray as long as the body of the fibers is very
                  > > dark in comparison.
                  > >
                  > > --Rik
                  > >
                  >
                  > Sorry, I have to jump in here. I am not sure what you might be thinking of, but specular
                  > reflections have the same color as the incident light. When you see yourself in a mirror,
                  > that is a specular reflection. A specular reflection is simply when light is reflected in a
                  > mirror-like fashion from a smooth surface. Examples are the glare off of a car (or water
                  > or snow) from the sun. They are problematic because you are seeing a reflection of the
                  > sun and not the object itself. Since specular reflections are partially polarized (or
                  > completely if at Brewster's angle), polarized sunglasses can drastically reduce their
                  > intensity. Then you can see the object itself by the diffusely reflected light, which is
                  > scattered in all directions.
                  >
                  > Sorry for being pedantic, but I am a physics professor and just can't help it 8-) Now, what
                  > else might be going on with the fibers of black velvet, I don't know, but it could be
                  > interesting to hear.

                  Exactly. The grain of the fabric acts as a rudimentary polarization
                  filter. Further, since it is diffuse, the light reflected is a
                  culmination of the ambient light in the room. The average of all
                  those random specular reflections is what is sought.

                  But you knew that and were just testing us! Very tricky, Mr. Riley,
                  but it's turtles all the way down!

                  ;c)

                  R~


                  --
                  Mid GA: 478-599-1300
                  ATL: 678-438-6955
                  garealtours.com
                • Ken Warner
                  I get that :-) Georgia Real Tours wrote: [stuff deleted] Very tricky, Mr. Riley, but it s turtles all the way down!
                  Message 8 of 23 , Mar 8, 2008
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                    I get that :-)

                    Georgia Real Tours wrote:
                    [stuff deleted]

                    Very tricky, Mr. Riley, but it's turtles all the way down!
                  • Rik Littlefield
                    ... Yes, exactly. Previous writers were concerned about the color of the fibers producing something other than a non-neutral gray. When I wrote that the
                    Message 9 of 23 , Mar 8, 2008
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                      --- In PanoToolsNG@yahoogroups.com, "johncharlesriley"
                      <johnriley@...> wrote:
                      >
                      > >
                      > > Using black velvet this way is a very clever trick.
                      > > What happens, I believe, is that the "gray" appearance
                      > > is caused by a myriad of specular reflections
                      > > from the surfaces of the fibers. Specular
                      > > reflections are always non-colored, so indeed
                      > > this method should produce a very neutral gray
                      > > as long as the body of the fibers is very
                      > > dark in comparison.
                      > >
                      > > --Rik
                      > >
                      >
                      > Sorry, I have to jump in here. I am not sure what
                      > you might be thinking of, but specular reflections
                      > have the same color as the incident light.

                      Yes, exactly. Previous writers were concerned about the color of the
                      fibers producing something other than a non-neutral gray. When I
                      wrote that the reflection was "non-colored", what I meant was that
                      the color of the reflected light would not be altered by the color of
                      the underlying fiber, so the myriad of specular reflections taken
                      together would act like a neutral gray diffuse reflector. Sorry I
                      did not use enough words to make that completely clear.

                      --Rik
                    • Georgia Real Tours
                      ... Oops, my bad. You used enough words; I just failed to use all of them. Kinda makes a difference when you get em all rounded up. :c R~ -- Mid GA:
                      Message 10 of 23 , Mar 10, 2008
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                        On 3/9/08, Rik Littlefield <rj.littlefield@...> wrote:
                        >
                        > --- In PanoToolsNG@yahoogroups.com, "johncharlesriley"
                        > <johnriley@...> wrote:
                        > >
                        > > >
                        > > > Using black velvet this way is a very clever trick.
                        > > > What happens, I believe, is that the "gray" appearance
                        > > > is caused by a myriad of specular reflections
                        > > > from the surfaces of the fibers. Specular
                        > > > reflections are always non-colored, so indeed
                        > > > this method should produce a very neutral gray
                        > > > as long as the body of the fibers is very
                        > > > dark in comparison.
                        > > >
                        > > > --Rik
                        > > >
                        > >
                        > > Sorry, I have to jump in here. I am not sure what
                        > > you might be thinking of, but specular reflections
                        > > have the same color as the incident light.
                        >

                        > together would act like a neutral gray diffuse reflector. Sorry I
                        > did not use enough words to make that completely clear.


                        Oops, my bad. You used enough words; I just failed to use all of
                        them. Kinda makes a difference when you get 'em all rounded up. :c\

                        R~


                        --
                        Mid GA: 478-599-1300
                        ATL: 678-438-6955
                        garealtours.com
                      • Luca Vascon
                        I simply use a white plastic drinking cup. One of those very cheap ones you buy at supermarket. I put it in front of the lens with transparent tape. I shoot
                        Message 11 of 23 , Mar 10, 2008
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                          I simply use a white plastic drinking cup.
                          One of those very cheap ones you buy at supermarket.
                          I put it in front of the lens with transparent tape.
                          I shoot one picture against main lightsource, completely out of focus.
                          Like it was taking incident light.
                          I make white on that.
                          Those things are made of a plastic whose physical propreiety is also to
                          be... perfectly white.
                          If you fisheye-shoot one from inside you have a kind of light dome of
                          all light sources and principal chrominance of light reflection.
                          You don't need anything else.

                          Georgia Real Tours ha scritto:
                          >
                          > On 3/9/08, Rik Littlefield <rj.littlefield@...
                          > <mailto:rj.littlefield%40computer.org>> wrote:
                          > >
                          > > --- In PanoToolsNG@yahoogroups.com
                          > <mailto:PanoToolsNG%40yahoogroups.com>, "johncharlesriley"
                          > > <johnriley@...> wrote:
                          > > >
                          > > > >
                          > > > > Using black velvet this way is a very clever trick.
                          > > > > What happens, I believe, is that the "gray" appearance
                          > > > > is caused by a myriad of specular reflections
                          > > > > from the surfaces of the fibers. Specular
                          > > > > reflections are always non-colored, so indeed
                          > > > > this method should produce a very neutral gray
                          > > > > as long as the body of the fibers is very
                          > > > > dark in comparison.
                          > > > >
                          > > > > --Rik
                          > > > >
                          > > >
                          > > > Sorry, I have to jump in here. I am not sure what
                          > > > you might be thinking of, but specular reflections
                          > > > have the same color as the incident light.
                          > >
                          >
                          > > together would act like a neutral gray diffuse reflector. Sorry I
                          > > did not use enough words to make that completely clear.
                          >
                          > Oops, my bad. You used enough words; I just failed to use all of
                          > them. Kinda makes a difference when you get 'em all rounded up. :c\
                          >
                          > R~
                          >
                          > --
                          > Mid GA: 478-599-1300
                          > ATL: 678-438-6955
                          > garealtours.com
                          >
                          >
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