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Re: [PanoToolsNG] Re: Pano2VR makes different default cubefaces

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  • Thomas Rauscher
    ... Yes. correct. Because the cube faces *could* contain more information in the corners. If the source was a equirectangular with 1/Pi as factor for the cube
    Message 1 of 11 , Nov 1, 2008
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      fierodeval wrote, On 01.11.2008 21:59 Uhr:
      > Yes, I understand. But when you speak about the "sqrt(2)", you are
      > speaking about the figure in the right of this image
      > http://www.devalvr.com/fiero/equicube.jpg . Te correct figure is in
      > the left and this figure is valid in the two directions.
      >
      > Then, if I understand correctly, you say that the figure for
      > equirect->cube conversion is the left image and for cube->equirect is
      > the right image?

      Yes. correct. Because the cube faces *could* contain more information in
      the corners.

      If the source was a equirectangular with 1/Pi as factor for the cube
      faces size then it is safe to just use the left type of conversion again
      because the pixels in corners are stretched by a factor of sqrt(2).

      If the source images are cube faces, for example of a rendering from a
      3D software, then you need to use the conversion on the right side to
      avoid losing resolution/information.

      The factor Pi*sqrt(2) would also be true if the equi->cube was executed
      with a factor smaller then 1/Pi*sqrt(2) to get the maximum out of the
      cube faces. Another case would be if you recover a equirectangular from
      a QTVR where you don't know the original resolution.

      --
      MfG,
      Thomas
    • fierodeval
      Hi Thomas, But, if the default value is width/4 you are using this figure: http://www.devalvr.com/fiero/equicube2.jpg , loosing a lot of information in the
      Message 2 of 11 , Nov 2, 2008
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        Hi Thomas,

        But, if the default value is width/4 you are using this figure:
        http://www.devalvr.com/fiero/equicube2.jpg , loosing a lot of
        information in the conversion.

        If you take the output equirect from PTGui, all values superior to
        3.14 in the divisor are loosing information in the conversion.

        regards!
        fiero



        --- In PanoToolsNG@yahoogroups.com, Thomas Rauscher <yahoo@...> wrote:
        >
        > fierodeval wrote, On 01.11.2008 21:59 Uhr:
        > > Yes, I understand. But when you speak about the "sqrt(2)", you are
        > > speaking about the figure in the right of this image
        > > http://www.devalvr.com/fiero/equicube.jpg . Te correct figure is in
        > > the left and this figure is valid in the two directions.
        > >
        > > Then, if I understand correctly, you say that the figure for
        > > equirect->cube conversion is the left image and for cube->equirect is
        > > the right image?
        >
        > Yes. correct. Because the cube faces *could* contain more
        information in
        > the corners.
        >
        > If the source was a equirectangular with 1/Pi as factor for the cube
        > faces size then it is safe to just use the left type of conversion
        again
        > because the pixels in corners are stretched by a factor of sqrt(2).
        >
        > If the source images are cube faces, for example of a rendering from a
        > 3D software, then you need to use the conversion on the right side to
        > avoid losing resolution/information.
        >
        > The factor Pi*sqrt(2) would also be true if the equi->cube was executed
        > with a factor smaller then 1/Pi*sqrt(2) to get the maximum out of the
        > cube faces. Another case would be if you recover a equirectangular
        from
        > a QTVR where you don't know the original resolution.
        >
        > --
        > MfG,
        > Thomas
        >
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