[Radiance-general] remove light probe image from background

[Roland William Fleming]

Well, for most purposes setting the clipping volume is a fine  
alternative, so it probably isn't worth worrying about this too much  
more.  But I still don't understand how it could be happening.  Do you  
manually specify the rays yourself and render the image with rtrace?

weird ...

-- Roland


On Apr 20, 2007, at 2:39 PM, Katja Doerschner wrote:

> 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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>>         Radiance-general at radiance-online.org
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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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