[Radiance-general] HDR

[Gregory J. Ward]

Hi Kirk,

Peter is quick.  He has just set up a new mailing list, hdri at radiance- 
online.org, which I suggest you subscribe to and we will move the  
discussion there.

HDRI generation is a separate issue from tone-mapping, and although  
Photosphere attempts to do both, it only makes a weak effort in the  
tone-mapping department.  Hdrgen makes no effort to tone-map images,  
and it should not.  In fact, I don't recommend tone-mapping HDR  
images into HDR, but directly into the destination display's color  
space, as an HDR image should maintain it's scene-referred color  
space.  Some of these issues are discussed and spelled out on  
hdrsoft's excellent FAQ page:

	http://www.hdrsoft.com/resources/dri.html

Since you bring up RAW (also discussed by hdrsoft), I should mention  
that although it is tempting to shoot RAW in preparation for creating  
HDR images, I have found it not to be helpful in most cases.  The  
additional range/resolution obtained is modest, and the confusion  
resulting from the many "development" options you mention means that  
reproducibility is an issue.  Unless you have a method to go straight  
from RAW into HDRI, you are better off shooting high-quality JPEGs on  
most cameras.

I'll make an announcement under a new topic about the HDRI mailing  
list, and let's continue the discussion there.

-Greg

> From: Kirk Thibault <kthibault at biomechanicsinc.com>
> Date: January 16, 2006 8:49:46 AM PST
>
> IMHO, HDRI may or may not require the color reproduction and  
> saturation to be as accurate or appealing.  IIt seems to me that,  
> in general, saturation and color issues are less important when  
> using a HDRI for image-based lighting than when using the technique  
> of converting a sequence of LDRI to a single HDRI for increased  
> dynamic range in a tone-mapped photograph, where the final output  
> will be an image of the scene as opposed to a light probe image for  
> IBL.
>
> Could hdrgen/Photosphere possibly benefit from more control over  
> tone-mapping in a way similar to the CameraRaw presents options for  
> exposing a RAW image?  If the use of HDRI for general photography  
> (which I am really getting interested in, BTW) would other users  
> find it useful to expand the ability of hdrgen/Photosphere to  
> present the user more control over the tone mapping process?  This  
> kind of discussion could probably fill a whole new forum, and I  
> would be all for it, if it is not too much of a hassle.
>
> Interesting as always!
>
> kirk