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Lisa S. Avila wrote:
<BLOCKQUOTE TYPE=CITE>Hello Burkhardt,
<P>No, VTK does not directly volume render RGBA data. It is on the "to
do"
<BR>list, but will not be part of VTK 4.0.
<P>Lisa
<P>At 10:54 AM 11/21/2001, burkhardt.dorn@berlin.de wrote:
<BR>>Hi all,
<BR>>I would like to know whether VTK implements specific or
<BR>>common ray-casting algorithms also on 3-dimensional
<BR>>RGB(A)-images. The samples I inspected work all on
<BR>>pure intensity maps and the color comes from a LUT.
<BR>>Of course it is no problem, to convert RGB to Gray.
<BR>>
<BR>>But one might also try to perform a ray cast obtaining
<BR>>the intensity of a given voxel by averaging the RGB of
<BR>>its scalar and the color by taking it directly rather
<BR>>than from a fictive LUT.
<BR>>
<BR>>Is this or something similar possible with VTK? A small
<BR>>cxx or tcl sample would be useful... :-)
<BR>>
<BR>>Regards
<BR>>Burkhardt Dorn
<BR>><A HREF="mailto:burkhardt.dorn@berlin.de">mailto:burkhardt.dorn@berlin.de</A>
<BR>>
<BR>>--
<BR>>berlin.de - meine stadt im netz. Jetzt eigene eMail-adresse @berlin.de
<BR>>sichern!
<BR>><A HREF="http://www.berlin.de/home/MeineStadt/Anmeldung">http://www.berlin.de/home/MeineStadt/Anmeldung</A>
<BR>> </BLOCKQUOTE>
I've been dealing with a similar issue but I think the
solution must be domain specific so that having a RGBA capability
may not
<BR> solve your problem. Where does your data come from
?
<P>My color data comes from a Laser Scan Confocal Microscope. Different
<BR>materials are made to flouresce and the data is collected with a colored
<BR>filter on the camera. The data for different materials is put
into the
<BR>Red, Blue. or Green Channels but the color isn't real. Also there can
<BR>be more than three channels.
<P><B>I would really like to have a reference which explains image processing</B>
<BR><B>for the confocal microscope. If any VTK users have information
on this</B>
<BR><B>I'd like to find out about it. Thanks in advance.</B><B></B>
<P>If the colors represent materials there is method of putting the matterials
<BR>(i.e. colors) into a volume which is sketched out in a 1988 Siggraph
paper
<BR>by Drebin, Carpenter, and Hanrahan. Here's what I'm doing.
It's
<BR>pretty simple.
<P> Let Int(m) be the intensity for material m, m = 1,N
( Int(m) is arbitrary )
<BR> Let Opa(m) be the opacity for material m, m = 1,N
( Opa(m) is arbitrary )
<P> Let P(m)(i,j,k) be the probability that voxel(i,j,k)
contains material m. (We don't know this yet)
<P> (i) P(m)(i,j,k)
is a good approximation for the volume fraction
<BR> (ii) P(m)(i,j,k) can
calculated using a "probabilistic estimator" such as
<BR>
a "maximum likelyhood estimator". I think this isn't too hard to
write
<BR>
and there are simpler estimators.
<BR>
<BR> Therefore, Intensity(i,j,k) =
SUM (P(m)(i,j,k) * Int(m) ), m = 1,N
<BR>
Opacity(i,j,k) = SUM (P(m)(i,j,k) * Opa(m) ), m = 1,N
<P>
(Int(m) probably should be normalized by dividing by its range.)
<BR>
<BR> Maybe P(m)(i,j,k) = 1 / m would work in many cases.
I think that is equivalent to
<BR> calculating V in the HSV color system.
<P> One simple approach bases P(m)(i,j,k) on the distance
of the value of the
<BR> intensity in channel m from the mean of the
intensities in channel m.
<BR> All this stuff is explained in Image Processing
books like Gonzalez and Woods.
<P>I MAY BE GOING OFF IN A COMPLETELY WRONG DIRECTION FOR<BR>
CONFOCAL MICROSCOPES. IF ANYBODY KNOWS A MORE
<BR>CONVENTIONAL APPROACH, PLEASE LET ME KNOW.
<P>Thanks in advance,
<BR>Dave
<PRE>--
David E Jones
Du Pont Central Research
Experimental Station, Bldg 320
Wilmington, DE 19880-0320</PRE>
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