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 16:50:09 +0000
Hello again: from a practical point of view, when I'm unable to shot a
spectrally neutral card I shot and read the nearest to neutral reference in
the scene in the camera LCD display with histogram in RGB mode to check
that channels are aligned. It isn't easy in nature scenes because the
absence of references except the one that you include.
2013/8/18 José Ángel Bueno García <email@hidden>
> 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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