[Radiance-general] Brightness to cd/m2?

[Iris Moonen]

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
>
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