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: Sun, 18 Aug 2013 16:42:20 +0000
Hello Louis:
You can find information of your interest here
http://www.rmimaging.com/information/neutral_references.html
and can select more from here
http://www.rmimaging.com/information/information_index.html
Thanks to Mr. Robin Myers
Jose Bueno
2013/8/18 Spinnaker Photo Imaging Center <
email@hidden>
> Hello Lous.
>
> I am interested in what you use and consider as a 'gray' card. Not
> meaning to be critical of what you do, I have at least three (3) so called
> gray cards
> that give me different results in the same operating conditions.
>
> Kodak gray card for portraiture, it has three different grays. Passport
> ColorChecker. A large pop open device that has white on one side, white,
> black and gray on the other side.
>
> For me, not for anyone else, I need some standard. I chose the "gray"
> part of the ColorChecker Passport.
>
> Here is an essay "
> My very un-scientific white balance card comparison - ImageMaven" where
> the writer uses more than one gray card. I just came across this essay
> while looking up
> the large snap open device I use.
>
> Cheers
>
> David
>
>
> David B Miller, Pharm. D.
> member
> Millers' Photography L.L.C.
> dba Spinnaker Photo Imaging Center
> Bellingham, WA
> www.spinnakerphotoimagingcenter.com
> 360 739 2826
>
> On Aug 18, 2013, at 5:32 AM, Louis Dina <email@hidden> wrote:
>
> > I'd like feedback on this topic, especially if there are any hard color
> > science and studies to back it up. I'm also interested in general
> opinions
> > and observations, even if not backed up by science.
> >
> > If I use a spectrally neutral gray card on a heavily overcast day, and
> use
> > it to set WB in my Raw Converter, I usually find that my images end up
> > being much warmer than the scene I perceived. This phenomenon is
> > independent of the camera profile, raw converter, monitor calibration and
> > other links in the color chain, and while they all affect the result,
> > sometimes significantly, my interest is primarily in how best to use a
> gray
> > card to approach reality as we perceive it. What I do with the color
> > afterward for artistic purposes is a separate matter.
> >
> > I know our visual systems do an internal Auto WB to correct for the color
> > temperature of the prevailing light. However, if I drive around on a very
> > heavily overcast, rainy day, the scene before my eyes still remains
> > decidedly cool and deficient in the longer, warmer wavelengths. By
> > contrast, a sunny day adds life a warmth to the same foliage. And at
> > sunset, there is a distinct warmth and glow. It is my belief that our
> > visual systems move the internal WB in the direction of neutralizing the
> > light, but don't take it all the way to perfectly neutral. So, a gray
> card
> > shot in "normal" daylight, heavy overcast and at sunset, will be
> perceived
> > differently. At noon under 'white light' it will appear neutral, on a
> rainy
> > day it will appear slightly bluish, and at sunset it will appear more
> > yellow-orange.
> >
> > Back to my example. If I shoot a gray card under gloomy skies, and accept
> > that as the correct color temp for this image in my raw converter, I am
> > forcing the card to be perfectly neutral, when I believe our brains see
> it
> > as cool-gray, no longer spectrally neutral. This makes sense to me
> because
> > the trees look cool and less warm just driving around on a gloomy day. If
> > this is correct, and I think it is, accepting the gray card WB forces the
> > scene to be artificially warm and overly yellow. Same thing happens under
> > incandescent light, around a campfire, at sunset, but this time the scene
> > is forced to be artificially cool compared to what our brains really see.
> >
> > I still like using the gray card, because it provides a stable,
> measurable,
> > neutral point of departure, a baseline, if you will. But, if ACR/LR gives
> > me an overcast reading of 6500K/+5 Tint with the gray card, I find the
> > resulting image to be overly warm. Lowering the temp by approximately
> 500K
> > seems to always give me a more realistic image, more in line with my
> > remembered perception of the scene. I know, this is perception, not
> > science, and I also understand choice of camera profile, converter,
> monitor
> > calibration, etc, all play a role in the final color, but the same
> > phenomenon is at play.
> >
> > I'd be interested in hearing others' thoughts on this subject. I am
> > particularly interested in any in-depth studies on the subject that
> relate
> > to how the human visual system does its WB, and if it forces gray to be
> > totally neutral as the light source diverges farther and farther from
> > "normal" daylight.
> >
> > Thanks,
> >
> > Lou
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