Re: Neutral grey under different lighting
Re: Neutral grey under different lighting
- Subject: Re: Neutral grey under different lighting
- From: Roger Breton <email@hidden>
- Date: Sun, 02 Sep 2007 18:56:20 -0400
Dear Markus/Nov06,
You should definitely consider "calibrating" your eyes as a first step
towards ruling your color vision out of the equation.
Although, I don't think your vision has anything wrong with it since many
people on this list have frequently reported observing the optical effects
you describe.
But submitting your eyes to a 100-hue Farnsworth-Munsell test would not hurt
(figuratively and litterally).
> in evaluating photographic labs I had them printing graduated gray
> gradients to see how neutral their process is (and check for
> potential black and white cut-offs).
When you write "how neutral" there is some implicit reference to some kind
of "absolute" or "abract" notion of what a gray is. True, a Kodak 18%
neutral gray card can be construed as such a suitable physical reference.
But if left to your eyes alone, we have to be aware of the tricks our vision
can play on our perception of gray.
This being said, I commend you for pursuing a true, time-tested ideal.
BTW, you don't say anything at how your labs arrives at the graduated gray
gradients you describe: do you supply then some kind of RGB scales?
> What I have noticed is that the
> prints looks more or less neutral at daylight (between 5000 and 7000
> K according to my Eye-One)
That's good news. And what kind of "daylight" do you refer to? Color
temperature does not convey much about the nature of the light sources you
use to observe the prints.
For example, have you observed the prints under direct sunlight? (my
favorite "daylight") Have you managed to measure its spectrum using your
EyeOnePro? I have never succeeded here. Always get some overflow. I think
the EyeOnePro is limited to 30k or 40 lux -- direct sunlight can be as high
as 100k lux, if I'm not mistaking.
> but have a pinkish/magenta-ish cast when
> viewed under normal fluorescent office light (about 4000 K).
I wonder if this has anything to do with some kind of "metamerism"? Or what
could be describes as some "instability" in the appearance of the prints,
due to the interaction of various light sources spectral characteristics and
the spectral characteristics of the colorants in the print that make up
those grays?
I'll let others comment.
> Interestingly, my standard grey reference card shows none (or much
> less) of these differences.
Easy. The gray card's appearance remains constant across various types of
illumination. Maybe because its spectrum is rather flat whereas the prints
must not be -- my two cents.
Maybe you could post the spectra of your print's gray and the spectra of
your neutral card? A direct comparison should yield interesting stories of
the stability of your labs prints across various light sources.
Some advanced software packages can help evaluate (and predict) the shift in
appearance as you go from "daylight" to "incandescent/fluorescent".
> I know color photographic paper will never produce a perfectly
> neutral grey
Perfect in the sense that its neutral apperance would remain constant
irregardless of the observing conditions?
> but is this effect common with photographic paper or
> should calibrate my eyes?
It's possible prints made on Kodak digital paper using their dyes don't
suffer as much from this phenomenon than, say, prints by Fuji? I never made
this direct comparison.
> Markus
Roger Breton
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