We intend to use the system for illustrating talks to members of the the public visiting the Unit and also for student classes. We would be projecting mainly SEM images.

We would like to hear from anyone who has tried this or any other alternative method of displaying 3D images to groups of people.

Richard Easingwood
richard.easingwood@stonebow.otago.ac.nz

We have used the silver screen method of projecting 3-D slides of all varieties for over 10 years. We find it by far the best method for displaying 3-D material to a large group of people. We use separate projectors with cross polarizers (I have heard of but not seen large screen projector wich takes a single slide containing two images).The down side of the procedure is the time it takes to align the two projectors and the necessity that all slides be exactly aligned in the same way. Nothing will make an audience sea sick faster than realigning projectors between stereo-pairs to accomodate different alignments. We sometime spend an entire day making sure a group of slides is all set up similarly. For this reason, for showing one or two people our stereo work we use premounted pairs in small, hand held viewers. However, this is not nearly as dramatic as a huge image on a screen. Any one who has ever stood in front of an audience and presented a stereo presentation will also tell you that the second down side of the method is trying to keep your composure while looking out at an audience full of people wearing silly dark glasses in darkened room.

Jay Jerome
jjerome@bgsm.edu

Dear Richard

A simple way of projecting stereo images is to get a friendly photographer to double expose your stereo pair through red and green filters onto slide film. All you need then is to hand out the old red green glasses and appeal for them to be returned! Its cheaper that way!

The other main item that you need to know is that there is a convention as to which way around the exposures are made so as to register re. the red and green and whch way around the glasses are held.

Keith Ryan
KPR@wpo.nerc.ac.uk

I have projected stereo images successfully by creating red/green anaglyphs on transparency material. We took our digital images, combined them using PhotoShop or similar program, and printed them on a dye-sublimation printer. Using a standard overhead projector and the red/green glasses, the images greatly impressed my audience. The dual projector system seems a bit specialized.

Henk Colijn
colijn.1@osu.edu

We followed the same procedure as Henk (using PhotoShop to produce red/green anaglyphs from pixel shifted z-sections) but then digitized the images onto slide film (Kodak Elite) using a Polaroid Palette. A single projector then did a great job (in fact it actually worked with red/blue glasses...)

C. Michael Stanley
images1@biosci.mbp.missouri.edu

Hello Mark Gould and Richard Easingwood,

I have done just as you suggest. Using a portable silver lenticular (sp?) screen (~$200.00) which does not depolarize the images, a beautiful 3D image slide show can be projected.

In our department, we have had the capability of mixing 2D and 3D images in a single slide presentation for about 5 years now and I have even done a few 3D demonstrations at a local high school -- with great success (held their attention from start to finish)!

As you have outlined, two matched projectors are required as well as polaroid transparancy sheets and glasses. Using a single piece of Scotch Tape to attach (hang) a piece of the polaroid transparancy over the front of the objective lens of each slide projector (each piece oriented 90 degrees to the other) is sufficient to project a polarized image on the screen.

The glasses, which each person viewing the projected images must have, represents a bit of work. I made a template for the eyes (no ear supports/hangers needed - see below dowell sticks) and traced the template image for as many glasses as I needed on firm, but flexible, cardboard that could be cut with a good pair of sharp tipped sissors.

After tracing and cutting the cardboard, using carefully applied small pieces of Scotch Tape, I taped the polaroid 'lens pieces' from the same sheet of polaroid material used in front of the projector lenses [CORRECTLY ORIENTED] for left and right eye. By correctly oriented, I referring to the necessity of having all glasses with the angular orientation of the polaroid pieces identical -- all left and right eye orientation must be the same in the glasses and matched to the orientation of the pieces in front of the projector lenses. This way, all observers receive the same (correct) image in the left and right eye.

When the 'lenses' were all taped in place, I then taped these glasses by their right or left edge (makes no difference) to a 12 inch length of 1/4 inch wooden dowell stick so that viewers could hold the glasses in front of their eyes (and personal prescription glasses if that's the case) much like holding those small masks at a masquerade party. This may seem a little amusing, and sometimes gets a laugh at the beginning of a 3D presentation, but it was the method I developed to circumvent any health hazard concerns from the repeated public use these glasses -- this is why there are no ear supports as on regular glasses.

From the SEM image standpoint, I take two photos of the same subject (carefully aligned to be nearly the same field) at angles of +/- 5 degrees off verticle by stage tilts. I can then make direct positive slide transparancies with B/W 35 mm microfilm for projection. Both images are matched for size when projected on the screen and simply superimposed -- the glasses and polaroid pieces do all the separation of images to create a very clear and satisfactory 3D image for the viewers.

Hope this helps. This note has been a sort of 'stream of thought' description so please don't hesitate to ask any questions

. Good luck -- Jerry Harrison
jerry@biochem.dental.upenn.edu

The Anaglyph system is indeed simple and easy to use and requires only an ordinary projector and screen but it does have at least two snags. Apart from the opportunities that it gives to "Murphy" to attack when two exposures must be recorded on the same piece of film in register and through different colored filters, many people get very uncomfortable when the color of the image presented to one eye is very different from that presented to the other. The phenomenon is referred to as "color bombardment" and was much discussed by Vernon Barber in the late seventies/early eighties with reference to Scanning Electron Microscopy.

The second snag is that you cannot show colored images using this system. For instance you cannot use it to show stereo views of confocal data in which you have superimposed separate 3D images obtained from 2 or 3 different fluorescent dyes in the same specimen. Likewise, you cannot show stereo SEM images in which the SE signal is recorded in tones of grey while the BSE image is superimposed in shades of red.

In addition, although there is usually less overlap between the red and blue filters than between the red and the green, the light output in the blue from most projectors is insufficient to convey many grey levels to the screen and back.

Once you accept the difficulty of finding an "aluminized" screen, the Pol system has much to recommend it.

Jim Pawley
JBPAWLEY@FACSTAFF.WISC.EDU

With regard to using 3D aluminised screens for projecting polarised images , I can only add in support of Jim Pawley's comments on the advantages for imaging colour - in my case cell reconstructions with colour coded organelles - which come out only with the polarised system.

As regards sourcing a screen try your Chemistry colleagues who probably have one lurking somewhere as they may project molecular graphics in this way for teaching. This is where I borrow my portable screen from here in Glasgow !

Laurence Tetley
email gbza40@udcf.gla.ac.uk

Dear Mark,
We have two large screens--they are aluminum, but look silvery; I assume these are what you want--for 3D display with polarized light & dual projectors. The images are quite spectacular and always make a big impres- sion. If you have many 3D images to display, this kind of system may be well worth the initial investment. The screens last for a very long time; ours are >~25 years old and are as good as ever. I have no idea of the current price for these screens.

Yours, Bill Tivol
tivol@wadsworth.org

A few comments on this thread from our experience:

We have mounted on polarizers on the ends of cardboard tubes. The tubes are approximately the diameter of the Kodak projector lens barrel. We put a lenght of the thin packing sponge material that our hazzardous chemicals come wrapped in around the inside of the tube to provide friction and hold the tube in place. This allows the polarizers to be rotated to get maximum extinction with the glasses. We order bulk glasses for a nominal cost. Most come with the polarizers set at 45 degrees to the horizon. However, some glasses come with the polarizers horizontal and vertical. The tube system allows us to adjust or projector polarizers to match either set of glasses.

Jay Jerome
jjerome@bgsm.edu

I have had over a dozen requests for this information so I am posting it directly to the list:

We have always purchased our stereo glasses from Ted Pella 1-800-237-3526 outside of California They are in cardboard mounts and relatively inexpensive. However, I did not see them listed in the current catalog. I hope they still carry them. Any one know of an alternate supplier?

Jay Jerome
jjerome@bgsm.edu

Folks;
I am looking for software to display stereo pairs on a computer. The input images would be two digitized EM images with appropriate parallax differences. The result would be a single digitized image file in which one image would be displayed using only in red, and the other with green. The viewer would wear standard red-green glasses for stereo pairs. The trick here, it seems, is going to be aligning the two digitized images before aligningthem into one 16 bit image file. Does anyone out there know of any software that can carry out this task? Thanks.

John Mardinly
Jmardinly@imo.intel.com

If you are using a Mac, there are several different resources as part of NIH's Image freeware. I believe the best access is at http://rsb.info.nih.gov/nih-image/ This is a very good program for image manipulation for Macsters (that's why I'm posting to the list). A PC version is in the works too.

I know that I've seen stereo pairs, of the red/green variety, discused in the recent past. If there is nothing directly listed at NIH's web page there is an Image list that should have archives. The listproc address is LISTPROC@SOILS.UMN.EDU, and the list is NIH-IMAGE. (Cap.s not necessary.)

Erik Pauls
erik@uclink.berkeley.edu

I have successfully done this on a PC and Mac using Adobe Photoshop and 2 appropriately parallaxed images. Both must be changed to RGB color, the left (or zero degree) image saturated to red, and the other image saturated to either green or blue. Copy one image to the clipboard and then paste it to the other. Set the composite controls to 50% opacity with preview on. Viewing the image through red/green glasses, you can then properly register the pair.

It's a fairly crude technique, but it does work.

-=W.L. Steffens=-
STEFFENS.B@calc.vet.uga.edu

we use adobe photoshop on the mac for viewing anaglyphs (R/G pairs), and it works great. but of course macs don't have Intel Inside, so they may be difficult to get inside Intel. 8-)

Gary Fan
gary@alex.ucsd.edu

Hi John,

I don't know of any sofware specifically designed to do this but I've done it many times on different platforms using different programs in different ways.

* Using NIH Image on a Mac; Call up the left image, then the right image TWICE and finally click on 'Windows to Stack'. This instruction creates a stack whereby the 3 active windows are tied to each other, emulating (becoming) a typical RGB image (as you might get out of a colour CCD camera) where the left view becomes the red component and the 2 right views the green and blue components (which add to cyan). You might also want to use another instruction 'RGB to 8-bit' to turn the 24-bit RGB stack into an 8-bit (256) colour file. This is only necessary if you want to transport the image to systems which don't handle 24/32-bits.

* Using PhotoStyler on a PC is just as easy; under 'Image' click on 'Combine' then 'by RGB' and a dialog box then asks you to select the files you want in which of the three separate channels.

As for aligning images, PhotoStyler allows you to repostion an image within it's 'frame' via a pixel offset of nominated size (under 'Image' then 'Shift'). Another way to do this (I think, I haven't tried it yet) is to create a custom filter for pixel displacement. Imagine (drawing it would be so much simpler) a 3x3 kernel or tic-tac-toe grid full of zeros except for say the top left square which has a 1 in it. By applying this filter to the image it should shift the image one pixel to the right and one line down. By extension, using a 9x9 kernel can move your image 5 pixels up/down &/or left/right.

BTW, the above methods give you red/cyan anaglyphs (rather than red/green) which is a better combination for the perennial problem of crosstalk, and which obviously require red/CYAN glasses.

And, for viewing on a computer screen (or more appropriately, at a distance of approx. 0.5m) you'll want an angle of around 7 degrees between views.

Hope this helps,
Geoff Avern
geoffa@amsg.austmus.oz.au

For references on where to purchase red/green glasses click on here