[HDRI] Scaling artifacts in Photoshop CS2 w/ Radiance files?

[Mark Banas (lists)]

On Jun 15, 2006, at 2:39 PM, Gregory J. Ward wrote:

> Hi Mark,
>
> The Radiance RGBE format is not able to record negative pixel  
> values, so such primary values should be clamped to zero.   
> Apparently, Photoshop is not doing this.  Photosphere (and the  
> Radiance tools) check for and truncate negative primaries, writing  
> them out as 0's.  OpenEXR doesn't have this issue, as it can read  
> and write negative primary values -- in fact, you are better off  
> using OpenEXR for your intermediates also as it is a higher- 
> precision format.  It doesn't really make sense to use a lower- 
> precision format like RGBE for intermediate results then write out  
> your final as OpenEXR, as you've lost information along the way.   
> It would make more sense the other way around

Hi Greg,

Aarrgh... right you are. A very long time ago I set up a workflow  
that was all Radiance file based because: 1) my 3D software only  
understood that file type, and 2) I read "somewhere" that Radiance  
format could store a much greater range than OpenEXR. Despite reading  
many other details about both formats, I stuck with my initial,  
oversimplified understanding which was "Radiance holds more  
brightness than EXR."

Basically, I should've read your HDR Image Encodings page even more  
carefully - not only is the precision in OpenEXR much higher, but  
most of the extra brightness latitude in RGBE is essentially unused,  
even for my very-wide-range "light probe" panoramas. EXR is very  
widely accepted now, and I think 10.7 orders of magnitude is enough  
for my purposes... ;-)

Good thing I posted what I did... I doubt I'll forget it now.

-Mark