[Radiance-general] Re: Mapping from hemisphere projection to latitude-longitude format

[Greg Ward]

This discussion really belongs on the HDRI mailing list, where you  
might find some additional help.

Cheers,
-GReg

--------------
> From: Thomas Bleicher <tbleicher at googlemail.com>
> Date: December 7, 2009 6:32:25 AM PST
>
> Claus.
>
> I used ImageMagick to convert from fisheye to rectangular projections.
> I wasn't much concerned with the accuracy so I can't tell if it's
> appropriate for you. You can find more here:
>
> http://www.fmwconcepts.com/imagemagick/index.php
>
> http://www.fmwconcepts.com/imagemagick/polar/index.php
>
> I also remember that I used one of the Radiance binaries to convert
> from one projection to another. I can't remember which tool it was and
> which conversions are possible. If you use a non-Radiance source image
> you have to convert it to Radiance hdr format and add the view
> specification to allow the conversion.
>
> Regards,
> Thomas
>
> On Mon, Dec 7, 2009 at 12:41 PM, Claus B. Madsen <cbm at imi.aau.dk>  
> wrote:
>>
>>
>> Dear list members,
>>
>> I use HDRShop to convert between mappings for environment maps,  
>> e.g., from
>> mirror ball to lat-long, etc.
>>
>> I now have two other mappings that I wish to convert to lat-long  
>> (though I
>> realize that both mappings will only give me half a sphere, e.g.,  
>> top half
>> of lat-long map).
>>
>> 1) An image taken with a Sigma 8mm 180 degree field-of-view fish  
>> eye lens to
>> take a high-res image of the sky (same hemispherical mapping as  
>> RADIANCE
>> renders into when using the -vth option for rview/rpict)
>>
>> 2) An image of a diffuse hemi-sphere (diameter of 0.3 meters,  
>> turned out on
>> a lathe) spray painted with a diffuse grey
>>
>>
>> I am convinced that both mappings are identical (i.e. identical to  
>> the
>> hemi-spherical projection model in RADIANCE). So far I have used the
>> 'mirrorball closeup' format in HDRShop but found this to be the wrong
>> mapping yielding incorrect lat-long mappings. I have now understood  
>> the
>> entire geometrical issue and just need a piece of software to warp
>> hemisphere images to lat-longs ... perhaps a plugin for HDRShop?
>>
>> A couple of years ago I raised this issue with the people who wrote  
>> HDRShop
>> but they claimed the Sigma lens should be treated as mirror ball  
>> closeup
>> when re-mapping in HDRShop. I am now convinced this is not true  
>> after having
>> tested it  extensively.
>>
>> Sincerely,
>> Claus