0
$\begingroup$

Question:

Is it possible to measure the albedo of a surface using a standard camera (DSLR or from a mobile device)?

It is highly probable that 'albedo' is not the correct term because, to me (feel free to correct me if I am wrong) it is a unit-less measure on how much energy is reflected back by a surface in relation to the incoming energy onto this surface. That is why, to me, it is dependent not only on the surface properties but also on the incoming light properties and incident angle. And it's more a word coming from climate sciences/astronomy.

So, it is not exactly what I want; I would like to be able to, let say "estimate" (instead of "measure"), "the ability of a surface to reflect light" (i.e. its "whiteness"), more specifically sunlight with a simple consumer grade camera. Is the correct word for this "reflectance", "luminance" or other?
There is a large vocabulary and different definition when dealing with light fluxes: https://en.wikipedia.org/wiki/Radiant_flux
I first want to be sure on which equation(s) to use, especially regarding the camera settings (for example focal length, aperture or f-number, iso sensitivity, shutter speed, sensor size)

I was not sure where to ask this question, so let me know if I'm on the wrong place.
Hint, I'm not a physicist, feel also free to make a comprehensive answer.

$\endgroup$

2 Answers 2

1
$\begingroup$

with a set of reflectance standards, this should be feasible. In the old days of photographic film, precisely-printed greyscale test cards were used to calibrate light meters and obtain proper performance out of the wet-chemistry systems used to develop film. these cards were rated in terms of reflectance- for example, a 70% reflectance card absorbed 30% of all incident light and reflected 70%. You aimed the camera or meter at the card, took a picture or a reading, and went to work.

I do not know if reflectance standard cards are still available, but a search would reveal the answer.

$\endgroup$
1
$\begingroup$

Yes, of course albedo can be determined from a photo; it is common practice to put a reference surface (roughly 18% reflectance, neutral gray) card into a test picture, to guide the photographer later in his darkroom or color-tinkering software. As long as the illumination and angles are similar, the photo objects can have their albedo measured thus.

This 'albedo', however, can only be camera-determined for a simple light model which (like human color vision) has three-color character. A complete spectrum requires some more imagination. Astronomers use gratings to make a small spectral smear off each point of light, and analyze their photos for the range of light frequencies to which the film is sensitive, after determining the source (zero order diffraction) for a smear (first order diffraction). That could determine albedo, too, if your camera setup included some properly dark backgrounds that such smears could be viewed against.

$\endgroup$
1
  • $\begingroup$ For the greatest accuracy, you don't want to use JPEG images as a nonlinear transfer curve has been applied to the raw data. You want to access the raw image data. Maybe someone can suggest how to do that. Or the above suggestion of using reference cards should work. $\endgroup$ Apr 3, 2020 at 18:07

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.