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

Started 2 months ago | Questions thread
OP Mandem Junior Member • Posts: 28
Re: How can you have a scene linear reflectance greater than 100%?

alanr0 wrote:

MrBrightSide wrote:

Those numbers from 0 to 720 look like mV values for the luminance channel. Is that what you’re asking about?

Anything is possible, but the OP is convinced they represent percentage reflectance values - possibly because that is how they are labelled on the screen shot.

The choice of 18% and 90% reflectance values seems significant. These numbers crop up in the ITU documents that spider-mario linked, including ITU report BT.2408-4, where they appear as widely used grey scale reflectance values. See for instance the figure here.

You could check out the gitbub repository for LUTCALC which I believe is the source of the graphic. My guess is careless terminology for relative exposure values, but I have not dug deeper to find out.

Quite the contrary. After our discussion, I am fully convinced the "reflectance" values on Lutcalc are indeed luminance values. The idea of an 18% or 90% is in reference to the luminance of an 18% reflectance gray card or 90% reflectance card. Like you yourself said, you can't have a reflectance greater than 100%.

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