[Radiance-general] Brightness to cd/m2?

[Greg Ward]

Hello Iris,

If the picture has been re-exposed by some other program (such as pfilt), then there will be an EXPOSURE= line in the header, which you can see with the getinfo command.  In any case, you can use the "pvalue -o -b" option to undo this exposure and convert to brightness, then multiply the output by 179 to get luminance in cd/m^2.

This is of course assuming your picture was generated by Radiance in the first place using a properly calibrated scene.  If it is just an HDR image you got from somewhere, it is unlikely that the pixels have an absolute basis.

Best,
-Greg

> From: Iris Moonen <moonen.iris at gmail.com>
> Subject: [Radiance-general] Brightness to cd/m2?
> Date: October 23, 2015 9:19:32 AM PDT
> 
> Hello,
> 
> I have a question. I want to get cd/m2 values by using the pvalue. Now
> I'm not sure how to get those cd/m2 values - I read somewhere that you
> should multiply the values you get from pvalue with 179, but if I do
> that I get crazy high values (about 15941203). Do I do something
> wrong? I have been trying to search for what pvalue exactly gives you
> (I know it's the brightness value but I can't find what unit it is
> in), but had no luck on that so far. I also wanted to know if this
> value is dependent on the area of your luminance picture or not.
> 
> Thank you so much in advance!
> Iris