[Radiance-general] Brightness to cd/m2?

[Greg Ward]

Hi Iris,

You really need to share your entire command chain with us.  The total program will compute averages, but only with the "-m" option.

Cheers,
-Greg

> From: Iris Moonen <moonen.iris at gmail.com>
> Subject: Re: [Radiance-general] Brightness to cd/m2?
> Date: October 26, 2015 10:08:32 AM PDT
> 
> Hello,
> 
> I've tried that but it doesn't say exposure in the header, and while
> using this the values still stay this high. I did notice that when I
> change the image size, the values differ. I use "| total" because I
> need the average cd/m2 value. Is it possible that I need to divide
> this number that I get by pvalue | total before multiplying it with
> 179?
> 
> With kind regards,
> Iris
> 
> 2015-10-23 18:31 GMT+02:00 Greg Ward <gregoryjward at gmail.com>:
>> 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