[Radiance-general] remove light probe image from background

[Katja Doerschner]

Hi Roland,
Thanks for your response!
The error is about 2-3 pixels (maybe less) all around the object. I do 
oversample, but I first combine the oversampled images (since I assumed 
the shapes would be more or less identical) and then downsample the 
result - this is the opposite order of  your approach. Just to check, I  
shall  try it  your way + crossfading.

I am quite sure I didn't  make a mistake somewhere along the image+masks 
generation & combination pipeline, but given that you never encountered 
this  artifact before makes me doubt that now ...

Viele Gruesse,
katja

Roland William Fleming wrote:
>
>
> Hi Katja ---
>
> This is very strange. I have done exactly what you describe countless 
> times and never seen artifacts. How many pixels error do you see? Do 
> you oversample the alpha mask to get anti-aliased edges? I use the 
> small rim of fractional values in the downsampled alpha matte to 
> crossfade between the rendering image and the mask, which always gives 
> pixel-perfect cropping....
>
> -- Roland
>
>
>
>
> On Apr 19, 2007, at 10:14 PM, Katja Doerschner wrote:
>
>     Hi Rob,
>     Thank you for your suggestion.
>     I tried something like that before, and encountered an interesting
>     artifact (well maybe not so interesting).
>     I have a perfectly specular object illuminated by a light probe.
>     In a second image I used the same shape but made the object glow
>     (material) and the environment black - This created something like
>     a mask. Then I wrote a small program which picks all the non-black
>     pixels in the mask and replaces them with the content from the
>     first (specular) image.
>     To my surprise these shapes never matched up perfectly, the mask
>     created with the non-specular material was always a few pixels
>     bigger than the specular shape, as a result there were always a
>     few background pixels selected. I tried other materials in
>     combination with different lights(ambient etc) - always
>     encountering the same problem. 
>
>     katja
>
>     On Apr 19, 2007, at 2:58 PM, Fitzsimmons, Rob wrote:
>
>         I've done it by creating a duplicate scene (your rif file) and
>         subsititute a overcast gensky (just something that will make
>         the sky white, change all your materials to black with no
>         specular. Then render with -ab 0 - to get a black and white
>         "mask" Render will not take long with no bounces.
>         I've then converted the mask pic to a standard ldr tiff - use
>         it in photoshop as a masking layer.
>         You could also do it with the original hdrs through pcomb -
>         you'd have to check the manual on that.
>          
>         Rob F
>
>         *From:* Katja Doerschner [mailto:doers003 at umn.edu]
>         *Sent:* Thursday, April 19, 2007 12:43 PM
>         *To:* radiance-general at radiance-online.org
>         *Subject:* [Radiance-general] remove light probe image from
>         background
>
>         Hello,
>
>         (I apologize if this email went out twice ... I forgot to
>         update my subscription to my current email...)
>
>
>         I am illuminating a scene with a light probe.
>         In the resulting rendered image I do not want to have the
>         probe image in the background.
>
>         Does anyone know if there is a setting in Radiance that would
>         make this possible?
>
>         Thanks for your help!
>
>         Kind Regards,
>          
>         katja
>
>
>         Katja Doerschner
>         University of Minnesota
>         Psychology Department
>         218 Elliott Hall
>         75 East River Road
>         Minneapolis, MN 55455-0344
>         Phone:+1 612 626-8551
>
>
>
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>
>     Katja Doerschner
>     University of Minnesota
>     Psychology Department
>     218 Elliott Hall
>     75 East River Road
>     Minneapolis, MN 55455-0344
>     Phone:+1 612 626-8551
>     http://vision.psych.umn.edu/~doerschner
>
>
>
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