Stereo Help

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

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 master widget). 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.