Re: WB, Gray Cards and Cloudy Days
Re: WB, Gray Cards and Cloudy Days
- Subject: Re: WB, Gray Cards and Cloudy Days
- From: José Ángel Bueno García <email@hidden>
- Date: Mon, 19 Aug 2013 16:43:15 +0000
Hello Ben: do you own any of the materials you mention?.
On the other hand, as have been said back in time, I prefer a non white
spectrally neutral reference because reflects only part of the light, but
this can be part of the problem and the exposition of Mr Dina, but allow me
the doubt. Said that, I would like to have all the neutral references in
the market, including the expensive ones but...
Salud
Jose Bueno
2013/8/19 Ben Goren <email@hidden>
> On Aug 18, 2013, at 5:11 PM, Louis Dina <email@hidden> wrote:
>
> > spectrally neutral gray card
>
> Incidentally, you have to spend obscene amounts of money to get something
> with a flatter spectral reflectivity than a styrofoam coffee cup. Put it in
> the scene and you can sample the light from a 180° radius, for scenes with
> mixed lighting. Or put the cup over your lens and the result is a perfectly
> equal integration of all the light in the scene, which is also often a good
> starting point for manual white balance. And cups are generally of such a
> transmission amount that whatever your meter thinks is the proper exposure
> with the cup probably actually is the right exposure.
>
> The not-currently-in-production target from BabelColor is the cheapest of
> the better-than-a-coffee-cup targets:
>
> http://www.babelcolor.com/main_level/White_Target.htm
>
> The next cheapest step up the ladder is a full-sized Spectralon target:
>
> http://www.labspherestore.com/category-s/5.htm
>
> Other cheap options are Teflon thread seal tape (which is, within
> photographic margins of error, as spectrally flat as Spectralon but nowhere
> near as durable nor as large) and Tyvek.
>
> Tyvek you can get practically for free in the form of tear-proof
> envelopes. You can also get large format banner media with a standard
> coating on one side and bare Tyvek on the other, if you need anything
> inordinately large. It's about 98.5% reflective compared to the 99%+
> reflectivity of the Teflon stuff, but it's damned near indestructible. The
> surface texture is a bit funky, but any situation in which it would cause
> problems in photography is one in which anything else except for Spectralon
> is also going to have problems.
>
> So, if all you're after is something spectrally flat, you can't beat that
> coffee cup -- not for spectral quality, not for price, not for ubiquity.
>
> But my <i>real</i> recommendation remains to use an actual color chart
> (such as the ColorChecker Passport) and use the profiling mechanism to
> determine the white point....
>
> Cheers,
>
> b&
>
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