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

Started 3 months ago | Questions thread
alanr0 Senior Member • Posts: 2,484
100% of what?

Mandem wrote:

spider-mario wrote:

J A C S wrote:

It might have something to do with diffuse vs. directed (specular) reflections.

Indeed. Those reference levels are for 18% and 100% diffuse reflections (from Lambertian surfaces). With such surfaces, as the name “diffuse” suggests, not all the light that lands on a given point from a given source is reflected in the direction of the camera. With specular reflections, it can be. See section 1.3 of BT.2390-9 for some discussion on this. This image from the first link is also a great illustration.

So when we look at the graph where we start dealing with above 100% reflectance, is that just specular reflectance getting translated into it's equivalent in terms of diffuse reflectance. Which, in other words, means that 100% spectral reflectance is the true 100% reflectance of all the light, X, that was incident on the object whereas 100% diffuse reflectance is not?

It does not need to be specular reflectance. It could just be to handle parts of the scene which are more strongly illuminated than others.

A more extreme subject might be stained glass windows in a church interior.

I am not a video photographer, but surely the whole point of log gamma encoding to allow one to capture scenes which are not uniformly illuminated.

There may be a standard, but I suspect the reference point corresponding to 100% scene luminance is somewhat arbitrary, and chosen by the camera manufacturer or the photographer to accommodate scenes which include parts which are much brighter than the intended average.

Perhaps the "reflectance" tag in your screen shot is simply sloppy terminology - but for all I know, it could be accepted usage in the video community.

-- hide signature --

Alan Robinson

Post (hide subjects) Posted by
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow