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Re: [PanoToolsNG] Re: Chromatic Aberration on fisheye lenses images (comparative test)

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  • michel thoby
    http://tinyurl.com/2zzjsl Based on other experiment that you may replicate, I have proposed some additional conjectures on the same subject. Regards, Michel
    Message 1 of 6 , Jul 2, 2007
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      http://tinyurl.com/2zzjsl

      Based on other experiment that you may replicate, I have proposed
      some additional conjectures on the same subject.

      Regards,

      Michel


      Le 1 juil. 07 à 20:03, Rik Littlefield a écrit :

      > --- In PanoToolsNG@yahoogroups.com, "Serge Maandag (yahoo)"
      > <yahoo@...> wrote:
      > >
      > > > Six different fisheye lenses have been subjected
      > > > to a comparative test in order to assess
      > > > their respective propensity to TCA.
      > > > The influence of light illumination spectrum
      > > > on TCA has also been studied.
      > > >
      > > > You may read the report here:
      > > > http://tinyurl.com/32jjdz
      > >
      > > That's a weird result...
      > >
      > > You would expect the blue abberation to be more pronounced
      > > under light that simply contains a bigger part of the
      > > blue spectrum. But not that the light source would
      > > change the scaling of the abberation.
      >
      > Serge,
      >
      > The thing to remember is that the aberration depends on wavelength,
      > not just on "red" versus "green" versus "blue".
      >
      > Two different wavelengths may both record only in the "blue" channel,
      > but nonetheless be shifted by different amounts.
      >
      > What gets recorded in the "blue" channel is a kind of weighted
      > average of the shifts over all of the different "blue" wavelengths
      > that were present in the illumination.
      >
      > If the different light sources have different proportions of various
      > wavelengths in the "blue" band, then those sources will show
      > different TCA.
      >
      > In summary, it is the detailed shape of the spectrum -- where are the
      > peaks and valleys? -- that cause TCA to be different for different
      > light sources.
      >
      > The phenomenon called "metamerism" is due to a similar cause. Much
      > info about that can be found by googling. A good place to start is
      > to Google "define: metamerism" and to read
      > http://en.wikipedia.org/wiki/Metamerism_(color) .
      >
      > --Rik

      >
      >



      [Non-text portions of this message have been removed]
    • Serge Maandag (yahoo)
      ... Ah, it is sort of like a quantification error. Then I just got Michel wrong. This does sound logical to me. I can imagine colours leaning towards infrared
      Message 2 of 6 , Jul 2, 2007
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        > What gets recorded in the "blue" channel is a kind of weighted
        > average of the shifts over all of the different "blue" wavelengths
        > that were present in the illumination.

        Ah, it is sort of like a quantification error. Then I just got Michel wrong.
        This does sound logical to me. I can imagine colours leaning towards infrared or
        ultraviolet could have a substantial influence.

        > In summary, it is the detailed shape of the spectrum -- where are the
        > peaks and valleys? -- that cause TCA to be different for different
        > light sources.

        I believe ignited-gas lamps usually have weird peaked spectrums, so I can imagine
        them causing these weird aliasing type of effects.

        > The phenomenon called "metamerism" is due to a similar cause. Much
        > info about that can be found by googling.

        Ah, I knew the effect, but not the name.

        Thanks for the great explanation (as usual)!
        Serge.
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