Re: Media Testing for maclife.de
Re: Media Testing for maclife.de
- Subject: Re: Media Testing for maclife.de
- From: "edmund ronald" <email@hidden>
- Date: Wed, 10 Sep 2008 19:00:12 +0200
Ken,
The Colorchecker SG has white squares in the center and along the
edges, which one can use to verify the correctness of the exposure. I
find that about 1 or 2 points point in 250 luminosity difference
across the target are attainable in practice. Of course, as you
indicate, no real-world lens and lighting system will allow a target
to be *perfectly* uniformly exposed. This is one reason why
target-based camera profiling will only get one so far. But then who
ever said it should work ?
Edmund
On Wed, Sep 10, 2008 at 6:49 PM, Fleisher, Ken <email@hidden> wrote:
> Yes, I'm referring to something that should be done when shooting a target
> to build a profile. The biggest problem you could have is incorrect
> measurement data. For example, if there is more light in the center of the
> target than on the edges (a hot spot--even if subtle), then the
> measurements, or your camera responses, are not sampling the test chart
> uniformly. This could throw off the software's ability to properly build a
> good profile because it has unevenly skewed camera responses.
>
> Another approach, if you don't have software to handle it, is to be
> tediously careful to ensure that the lighting is even by taking measurements
> in the center and on all corners (such as promoted by ColorEyes). This still
> won't account for lens falloff though. You might combat lens falloff by
> keeping the target fairly small and centered in the frame, but it's better
> if you can make the adjustment with something like Equalight.
>
>
> On 9/10/08 12:38 PM, "Uli Zappe" <email@hidden> wrote:
>
>>> This is the process of correcting for spatial non-uniformities in
>>> the lighting, lens falloff, etc. This is a critical step
>>> for camera calibration and can become very problematic if not done
>>
>> What kind of (profiling related) problems could arise?
>>
>> Are you referring to something that should be done when shooting a
>> target to build a profile?
>
>
> --
> Ken Fleisher
>
> Photographer
> Imaging & Visual Services
> National Gallery of Art
> Washington, D.C.
>
> Phone: (202) 712-7471
> email@hidden
>
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