Open Photography Forums  

Go Back   Open Photography Forums > Digital Camera Discussion > Imaging Technology: Theory, Alternatives, Practice and Advances.

Imaging Technology: Theory, Alternatives, Practice and Advances. This is a brand independent discussion of theory, process or device. Ignore this forum unless this matters to you!

Thread Tools Display Modes
Prev Previous Post   Next Post Next
Old December 22nd, 2017, 11:29 AM
Doug Kerr Doug Kerr is offline
Senior Member
Join Date: May 2006
Location: Alamogordo, New Mexico, USA
Posts: 8,398
Default On the color of light

Part 1


It has been suggested that this article would be interesting if it had some illustrations. While I figger out what illustrations would be useful, and fetch them, I will start by merely providing a frontispiece:

Douglas A. Kerr: Carla, 2011


In the scientific sense, color is one aspect of the sensation produced in an animal's visual system in response to light striking the retina of the eye. (Here I will speak only in terms of the human animal.)

We do not know, for example, what is the actual mental impression (color-wise or otherwise) in the mind of another human viewing the same scene as we do. And we cannot directly measure the color sensation. And thus we cannot quantify (describe in numbers) the color sensation evoked by a certain kind of light. The best we can do is speak in terms of vague, qualitative properties.
"Yep, that looks like a green light to me." "Yeah, but not as deep a green as that other light over there."
Color scientists determined that the property of a certain beam of light that controls the color sensation it creates in the human visual system is its power spectral density function (PSD). We can think of that as a curve showing how the overall power in the beam is distributed over the range of visible wavelengths. (This is sometimes spoken of as the spectrum of the light beam.)

Here we see the plot of an illustrative PSD (it happens to be the one prescribed for a CIE standard illuminant, D65):

Since we cannot directly measure, and thus describe quantitatively, a certain human color sensation , we resort to describing a certain human color sensation in terms of properties of a beam of light (having a certain PSD) that will evoke that response. (I say "a" beam of light since it turns out that there are an infinity of light PSD's that will evoke the same color sensation in a human.)

As a consequence, we say that such a beam of light has a certain color, by which we of course mean that it is expected to evoke a certain color sensation in the human visual system.

Thus, "color" as a "thing" indeed refers to a sensation in a human observer, but the scientifically quantifiable property color pertains to light.

[To be continued]
Reply With Quote


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are Off
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
The Unified Color Beyond RGB (GMWAS) color space Doug Kerr CM Theory and Practice 18 July 16th, 2011 12:44 AM
The color gamut of the sRGB color space Doug Kerr Imaging Technology: Theory, Alternatives, Practice and Advances. 27 August 26th, 2010 12:00 PM
Color model vs. color space - part 1 Doug Kerr CM Theory and Practice 1 May 9th, 2008 10:18 AM
New color-filter doubles the light sensitivity in digital cameras William Velasquez Breaking News 14 June 20th, 2007 04:18 PM

All times are GMT -7. The time now is 01:52 PM.

Posting images or text grants license to OPF, yet of such remain with its creator. Still, all assembled discussion 2006-2017 Asher Kelman (all rights reserved) Posts with new theme or unusual image might be moved/copied to a new thread!