Re: Metamerism
Re: Metamerism
- Subject: Re: Metamerism
- From: Igor Asselbergs <email@hidden>
- Date: Wed, 31 Oct 2001 08:48:20 +0100
Grant Symon wrote:
>
As a photographer I've always lived with metamerism....as has everyone else
>
in the world. In everyday life nobody pays the least bit of attention to the
>
phenomenon. No one, when looking at a movie, notices that the relationship
>
between two colours changes when the source light changes temperature
In this case either the bulb in the projector or the light used when
shooting the movie might be regarded as source light. Either way, or both
ways, it's not metamerism we're dealing with but colour constancy.
A definition of colour constancy by J. Troost, 1992:
"Under normal circumstances color is often regarded as an invariant property
of objects, irrespective of changes in illumination. If one is asked to
describe an object, one will almost certainly mention its color, along with
its properties as size and shape. Even at low luminance levels, under wich
color perception is poor, colors are assigned to objects. This understanding
of color is reflected spontaneously in the communication about the objects
that surround us."
To wich he adds:
"However, in color science, color is considered as a perceptual rather than
a physical property of objects."
>
and
>
yet....their relationship does change.
Normally, the relationship between the colours hardly changes. It's the
colours as a whole that change. For instance, all colours become more
blueish or more reddish under different lighting. And this change as a whole
is not perceived, being a result of colour constancy.
If the relationship between the colours DOES change, you will surely notice
it.
Once we were testing software when some some parts of a picture, displayed
by the software, had a strong reddish hue about them. For days we searched
in vain for the bug causing this trouble. In the end it appeared we had
searched in the wrong direction: It was the picture as a whole that had gone
greenish, with the exclusion of some parts that didn't 'really' change but
now appeared reddish as a result of colour constancy.
Igor Asselbergs