Stereo provides an image which truly appears 3D. The relative depth of
structures is often times perceived much better in stereo than in mono.
The stereo widget is gotten from the Goodies menu on the DAVE Master widget.
Stereo is much easier on the Dells with their dual screens.
Before you get into stereo mode on a system with just one screen (i.e., anything
except the Dells):
It is recommended that you move all of your DAVE widgets to the upper half
of the screen (and along an edge which has no other windows along it). It is
ok if they must overlap to do this.
If you really want to know why: Stereo on Graphics is produced by creating
two images (one for the left eye and one for the right eye). One image is put
in the top half of the monitor and the other in the bottom half. The monitor
is then put in a funny display mode that stretches the screen vertically by a
factor of two. Thus, an image in the top half fills the whole screen. But,
what to do with the image in the bottom half? No problem, just redraw the
image on the monitor really quickly, this time drawing the bottom half (which
is also stretched by a factor of two so it too fills up the screen). Thus the
two images appear sort of ghostlike on top of each other. When you are wearing
the stereo glasses they shutter on and off the image to one eye or the other
so you see stereo. Now, back to the widgets. If you have nonstereo images
(e.g., images of widgets, other windows, etc) being displayed on the monitor,
they too undergo this funny transformation. So, stuff that is on the top of
the monitor will appear as a ghostly image on top of stuff in the bottom half
of the monitor. Thus, it is simplest to make sure there is nothing in the
bottom half of the monitor to confuse us.
You may also want to resize your main viewing window prior to entering
stereo, since it is not allowed to change a window's size after entering stereo.
So, if you are planning on viewing raytraced images (which are too slow to
draw unless the window is tiny - see the rendering widget's help) you should
resize the window prior to entering stereo mode.
The cursor can also be in the top half or the bottom half of the screen, and
you will have a hard time telling. It will also move vertically twice as
fast as you are used to (since half the monitor fills the whole screen).
When in doubt, just keep moving it up until it will no longer go any further
(if it was in the bottom, it will appear to wrap around and reappear at the
bottom, keep going). This is assuming all your widgets are in the top half
so that is where you want to move your cursor to.
Getting into and out of Stereo Mode
By clicking on the MONO toggle, you will toggle the system into stereo
mode. You can then click on STEREO to return to mono mode. Pressing an S when
the cursor is in the viewing window will also toggle between mono and stereo
modes. It is recommended you leave
your image in low resolution until the picture pops up correctly (as this will
speed up generation of any incorrect images along the way).
On the Linux systems, you need to flip up the switch on the back of the
Stereographics sync doubler (on top of the 2nd monitor) and flip the range switch,
so a red transmission light appears on the sync doubler. The Dell dual-display
systems will automatically put the stereo image on the CRT display,
you should leave all your DAVE widgets on the flat screen display. You may need
to power on the CRT. If the monitor goes blank after you switch on
the sync doubler you need to change its display
frequency by typing Ctrl-Alt-+ (the Control, Alt, and far right Plus key all
at once). If you see streaky lines across your image once in sync doubled mode,
it is probably due to a non-black screen background. Right click on the background,
pick Configure Desktop, then Background, then make sure your background and wallpaper
are flat and black. Once the stereo glasses are on your head, tip your head about
45 degrees when looking at the (mono) flat screen monitor to get the best view.
Adjust the stereo angle slider until the separation between the two images
is large enough to produce stereo, but not so large that the two images are
very different (and hence hard to fuse into one stereo image). Usually the
more magnified the image and the more the image points into/out of the screen,
the smaller the angle should be.
The stereo glasses do not have to be plugged in, they use batteries.
Once in stereo mode, press the button on the right side of
the glasses to activate them. Pressing the button again will turn them off.
You have to be within about 3 feet of the monitor and looking at it for the
glasses to be active, otherwise they automatically just go clear. There are
3 pairs of glasses if several people need to view stereo simultaneously.
On the dual-screen Dells, once the stereo glasses are on your head, tip your head
about 45 degrees when looking at the (mono) flat screen monitor to get the best view.
Please turn the glasses off before leaving stereo mode.
Stereo pictures can be created for viewing on slides or in print. The
best way to do this is to first pick the static stereo view you want. Then go
back into mono mode. Stretch the viewing window to be as large as possible.
Then use Write Image... (in the File menu), or "snapshot", to save the image
you see on the screen. Next, rotate the
image about the y-axis by twice the number of degrees you specified for your
stereo separation (e.g., 3 degrees). This can be done by setting the Rotation
Angle on the DAVE Master Widget to 3 degrees and then clicking once on the
arrow to the right of the slider. You should see a new rendering of the scene
from a slightly different view. Save this image. You now have a stereo pair
(I always forget which is the left eye and which is the right). If you take
slides of this stereo pair we can view them using our stereo slide viewer.
You can also make prints, and then resize the prints using the color copier in
the library. Slides have better color range and fidelity, higher spatial
resolution, and (using our viewer) produce images which appear much larger.
They are recommended unless you need hardcopy.
For best pictures with volume data you may want to turn dithering off
(toggle on Goodies menu) and go into Single Buffer mode
(which is the default if you're not in it already, the toggle is in the
Goodies menu). The status of these modes is shown in the Viewing Window
title bar. You may also want to be in the highest resolution possible.
Also don't forget you can zoom in on the image.
Hints for better stereo viewing
1). The "angle" slider bar specifies the angular difference between the two
images of the stereo pair. The larger the number, the deeper the image will
seem. Too large a number may make the two images of the stereo pair so
different that it becomes difficult for your brain to fuse the two images.
When this happens the perception of stereo is lost.
2). The perception of stereo is also sometimes diminished if the object
you are viewing goes right to the border of the window. The window
clipping the object conflicts with the 3D stereo cues.
3). Z-clipping (see Help for the DAVE master widget) does not tend to work
well with stereo (since 2 slightly inconsistent images are produced).
4). The more distinct the objects the better the stereo tends to be. So if you
are looking at volume data, if you can set the opacity and thresholds to get
fairly opaque sparse data it will tend to look better.
5). Keep your head level and straight in front of the monitor. You cannot
see a different view by moving your head. However, if you move your head
further from the monitor the image should appear to gain depth.
6). Sometimes objects of constant width appear to widen off in the distance
when in stereo mode. This can be fixed by putting the rendering into
perspective mode (by clicking on the O.View/P.View toggle in the DAVE
7). Changing the contrast and brightness of the monitor a little bit helps
sometimes. Please try to remember to change this back when you are done.
Copyright 1995 by Lawrence M. Lifshitz and the University of
Massachusetts Medical School. All rights reserved.