[Radiance-general] Luminance contrast calculation

[Marija Velickovic]

Hi Greg and Jan,

Thanks for input. Although contrast requirements, like 3:1, are often
mentioned, I haven't found some nice discussion on practical issues and
calculation, so it is very useful to hear and learn something useful on
this topic.

###
Related to Gregs' answer, I agree with you that calculation of surfaces
contrast is rather not well defined. I have a request for a project to
calculate contrast values, while definition of contrast itself is not very
precise.

As you said we can calculate either average or maximum - but values can
vary extremely. This is especially visible in daylight offices, with clear
skiy and sun light coming directly into the space. As Jan said, if sun
reflection is visible, it will give extremely high light peak - and extreme
contrast.
(Generally I don't think these contrast related things are defined well
enough)

Related to Jans' answer about surfaces luminance, I haven't tried the
method you suggest (I'll read your presentation), with evalglare and masked
images.

Instead, I use method like this:

   - I use rtrace with -ovs or -ovm option turned on (so I detect materials
   or surface for each pixel).
   - Calculate image with rtrace and same parameters and ambient file -to
   have it faster,
   - From image extract with pcomb/pvalue solid angles for each pixel.
   - After these steps I have for each pixel info about its solid angle,
   radiance and material.
   - I analyse these data with Python numpy library to extract average
   values for all surfaces/materials in the scene.

Maybe there is some more automatic way to do this with Radiance commands
only (without numpy), but I couldn't find it, and since I'm writing program
in Python it was not a problem to use numpy library.

Thanks again,
Marija
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