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

[Chris Cox]

This is because of the sharpening aspect of bicubic kernels (they really
don't work for HDR images), and can be made worse in the Radiance file
format because we weren't clamping negative values correctly.

Chris



On 6/15/06 6:10 AM, "Mark Banas (lists)" <listmail at mab3d.com> wrote:

> I've seen this a lot before: resizing a 32-bit file in Photoshop CS2
> with their bicubic interpolator produces artifacts that look like
> "excessive sharpening halos" around high contrast details. Because of
> this, I simply stopped scaling images in Photoshop and instead use
> Photosphere (no problems).
> 
> However, I was recently perusing the Adobe user-to-user forums, and
> it was determined that the "sharpening artifacts" are only present if
> you subsequently save the file in Radiance format. It was then
> proposed by an Adobe employee that "the radiance file format code may
> have some problems dealing with extreme values." (keep in mind these
> are user-to-user forums, not developer comments).
> 
> Here is the thread in question:
> http://www.adobeforums.com/cgi-bin/webx/.3bbe9c64
> 
> Now I know that Photoshop's Bicubic does some sharpening (even
> without using "Bicubic Sharper"), and that sharpening of any kind on
> an HDR file results in extreme values, but does the Radiance file
> format itself have a problem with extreme values? Or is this a combo
> of PS Bicubic and their Radiance I/O? I pretty much store all of my
> "in progress" files in Radiance format and then create "final HDR
> files" from them in EXR, so this has effected me and my workflow.
> 
> -Mark
> 
> BTW, I've also found a huge flaw in Photoshop CS2's "Merge to HDR"
> when small, bright details are moving between shots (think ghosted
> leaves in a mild breeze) - so I don't even use PS CS2 for *creating*
> HDRs anymore, but the PS CS2 "clone tool" and the plugin Flexify 2
> are pretty much indispensable for retouching HDRs, so I'm using
> Photoshop in any case.
> 
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