Am 27.01.2011 21:20, schrieb stbenge:
> On 1/27/2011 11:47 AM, Alain wrote:
>> A factor of only 255 seems like very small, given that you can easily
>> find HDR images with a range of 50 000:1 and more.
>> If the Sun does show in the image and you have dark details in deep
>> shadows, the range can easily shoot past 1 million to 1.
>
> So, what would be a safe value to use? I heard that HDR images support
> 32 bits for each color channel.

Err, OpenEXR and Radiance do use a 16bit *floating point* 
representation. There is also TIFF that would support up to 32bit float 
HDR images (and more!) but this is currently not supported by POV-Ray.

The problem is: to say what maximum is possible is not so simple. E.g. 
you can represent light intensity of 50000:1 but cannot represent at the 
same time details within dark regions with enough precision.


So a value of 4,294,967,295 would work,
> right?

No!!!

My suggestion of using 10000 is a kind of educated guess (to find the 
exact value one had to look up how many bits are used for mantissa and 
exponent within the 16 bit (half) floating point format as used by 
OpenEXR in compare to the 32bit float format to find out what maximum 
value can be used without starting to loose precision.
But this would still not mean that you can cover high dynamic ranges 
like 50000:1 AND preserve precision! Thats the kind of nature of 
floating points ;)
So sorry, there is no value that will work in all cases until you 
examine the image itself and use the maximum that is used there.

-Ive

Post a reply to this message