Re: Neutral grey under different lighting
Re: Neutral grey under different lighting
- Subject: Re: Neutral grey under different lighting
- From: Marco Ugolini <email@hidden>
- Date: Sat, 08 Sep 2007 22:58:37 -0700
- Thread-topic: Neutral grey under different lighting
In a message dated 9/6/07 2:30 PM, Roger Breton wrote:
> In a message dated 9/6/07 12:49 AM, Peter Morovic wrote:
>
>> If there is no illuminant or observer for which the two spectrally
>> different surfaces mismatch, there is no metamerism and the two surfaces
>> can be considered identical in terms of their color rendering properties
>> as they induce identical color stimuli regardless of viewing conditions.
>> [*not an exhaustive list of "viewing conditions"]
>
> What are the conditions, in your opinion, that would make such a match
> exist? Maybe you give an answer below, I'll read on...
Hi, Peter and Roger.
It would seem to me that if two colored objects match under all illuminants,
they are very likely to match spectrally too, which also makes it highly
likely that they are made from the same, or very similar, materials and
pigments.
>> This is not surprising if you look at the vastly different spectra of
>> common illumination, e.g. a tungsten filament based light source SPD
>> and a fluorescent SPD. So, if some surfaces (a single surface) look
>> neutral under one light source but exhibit a hue shift under another,
>> this is color inconstancy, not metamerism.
>
> OK. That much is clear to me. But in the same way we have "metameric
> failure", would it be a terminological or conceptual abuse to coin the
> expression "color inconstancy failure" to describe the apparent hue shift?
I think that "color inconstancy" already properly conveys its full meaning
(i.e., a failure in maintaining the color perceptually constant among
different illuminants, once the human observer's eyes have undergone
chromatic adaptation and discounted the illuminant).
"Color inconstancy failure" would probably be redundant, in that light.
>> As to the usefulness or otherwise of
>> metamerism: input devices (cameras, scanners) struggle with device
>> metamerism, output devices (printers, monitors, projectors) cannot live
>> without observer metamerism - color reproduction is intrinsically
>> metameric (for now).
>
> "Device" metamerism, Peter? Do you mean different spectras inducing the same
> device RGB code values or response? Why, because of the choice of color
> filters used with the CCD or CMOS?
I think that Peter intends "device metamerism" to mean that two different
cameras (or scanners, or what have you) will record and produce the same
tristimulus values from two colored objects for which (under a given
illuminant) a human observer will instead observe a metameric failure. Is
that correct, Peter?
Best.
Marco Ugolini
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