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Volumerenderer and raw data
#1
Quite a regular
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Hello,

I have changed the RawImageLoader to load from an unsigned char array. I use this loader in an Image3DTexture object which in turn I want to render. My initial char arrays are RGB volumes. Hence they are of dimension 256 x 256 x 256 x 3. Loading all works fine. Now I want to display this volume. I have tried the VolumeRenderer but my volume gets displayed tiled 3 times in all 3 directions, hence I get it displayed 27 times, whereby the RGB channels appear to be split over those instances. The reference manual for VolumeRenderer states 3 transfer functions from "the scalar value" which makes me believe that VolumeRenderer can only be used with scalar volumes (greyscale). Is this true?
If I am wrong and VolumeRenderer is supposed to work with RGB volumes, than the reason for the tiling could also be a wrong 1D mapping in my 1D unsigned char array containing my initial data.
Could someone clarify if class VolumeRender can be used with RGB volumes?
Thanks
Johann

Posted on: 2006/12/13 10:18
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Re: Volumerenderer and raw data
#2
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The volume renderer in the current version of VHTK can not be used with raw RGB(a) volumes. The trunk version can, though. If you like, I can send you a patch or maybe release a new version of VHTK.

Posted on: 2006/12/18 5:51
KJ Lundin Palmerius
C Research
Linköping University, Sweden
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Re: Volumerenderer and raw data
#3
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We'd prefer a new release of VHTK depending on how soon this could happen. Obviously we'd like to be able to do RGB as soon as possible.
Thanks and a merry christmas to the entire h3d team.
Johann

Posted on: 2006/12/19 7:00
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Re: Volumerenderer and raw data
#4
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I'm confident that we are able to produce a release 1.4 before Christmas.

Posted on: 2006/12/19 9:38
KJ Lundin Palmerius
C Research
Linköping University, Sweden
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Re: Volumerenderer and raw data
#5
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Release 1.4 of VHTK for H3DAPI 1.5 now in the download section.

Posted on: 2006/12/21 11:50
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Re: Volumerenderer and raw data
#6
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Many thanks. Just restarted after the christmas holidays and will try it ASAP.
Johann

Posted on: 2007/1/6 12:22
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Re: Volumerenderer and raw data
#7
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I have tried the new version of VolumRenderer now. As I want to see the raw RGB values I have not defined a colour function. Now I only see the red channel rendered in greyscale, when I define an alpha function. Omitting the alpha function as well I only get a black cube, which makes sense to me since the blending is not handled appropriately. Looking into the black cube though I can see my colourd texture.
How can I define a blending without having it all turn greyscale and only display my first channel? I have played with the blendMode property and found that I can vaguely see the red, the green and the blue channel if I set the background of the scene to 0.5/0.5/0.5 and the blendMode to ATTENUATE.
Any help appriciated.
Johann

Posted on: 2007/1/8 13:30
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Re: Volumerenderer and raw data
#8
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If you have no colour or alpha function defined, the volume renderer should just apply the specified texture to the proxy geometry. If you specify an alpha function, then the renderer activates a shader that maps the value of the texture to an opacity value. That mapping is not really defined for an RGB texture, so you shouldn't do that.

My suggestion is that you pre-process your RGB texture and make it RGBA, with alpha included in the data you read. Otherwise I don't really know how you want to define the opacity as a function of the texture. The alpha function in a function in R -> R, so it does not make sense using it as R^3 -> R.

Posted on: 2007/1/8 14:49
KJ Lundin Palmerius
C Research
Linköping University, Sweden
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Re: Volumerenderer and raw data
#9
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Thanks for the response. Making an RGBA volume is what I have done in the meantime.
Johann

Posted on: 2007/1/9 4:56
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Re: Volumerenderer and raw data
#10
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Just out of curiosity, what is your volume? Is it the colour volume from Visible Human? Or is it maybe a secret?

Posted on: 2007/1/9 11:31
KJ Lundin Palmerius
C Research
Linköping University, Sweden
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