How can you have a scene linear reflectance greater than 100%?

Started 3 months ago | Questions thread
Mark Scott Abeln
Mark Scott Abeln Forum Pro • Posts: 18,137
Re: White is white except when it ain’t

Mandem wrote:

If exposure and metering theory assumes uniform light throughout the scene then the only thing I can understand causing more than a 100% reflectance is like you said previously the conversion of non-visible light into visible light through whatever subtle process. Where can I learn more specifically about this?

No, that's not what they are talking about.

As most sources online barely ever even mention scene linear reflectance when discussing about dynamic range.

A diffuse reflector that's close to 100% reflectance is practically by definition what everyone calls "white".

Now take a 100% pure specular reflector and put it in your scene:  that kind of reflector is what everyone calls a "mirror", and if you aim it just right, you'll see a very bright, perhaps blinding reflection of the light source in the mirror. That's going to be brighter than white.

That something happens to be brighter than a 100% white diffuse reflector doesn't mean that there is any fluorescence going on, it just means that there is a difference between a diffuse and a specular reflector. A diffuse 100% reflector has some good properties as a standard, not the least because everyone can immediately identify it as being white, and diffuse reflectors cover a good percentage of photographic subjects.

But you may want to reserve some of the camera's dynamic range to stuff that's brighter than such a diffuse reflector, because of specular highlights, and any light sources that happen to be within the camera frame, or lens flare, etc.

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