The Project

Having returned from the ISU conference with memories of the Ekeren3D Cobox in my head, I decided that it would not be a difficult thing to make for myself Figure 1.  Perhaps I should first explain the basic principle involved when viewing stereo images with two LCD monitors.

TARDIS consists of two LCD monitors oriented perpendicular to each other with a semi-reflective mirror bisecting the angle formed between the two displays

Figure 2.

The three items are mounted in an enclosure to protect them from disturbance and extraneous ambient light.  For the purposes of this description, I shall refer to the vertical monitor as 'Rear' and the horizontal monitor as 'Top'.  This reference is supported by my acronym for TARDIS which is 'Top And Rear Displays In Stereo'.

The objective of a stereoscopic display is to efficiently present a left eye image to the left eye that is isolated from a right eye image presented to the right eye. This allows us to merge the two images resulting in the perception of depth, or stereopsis.  With TARDIS this stereo perception is achieved using the inherent polarisation of the LCD monitors which coincides with that of the 45º/135º polarised glasses used for stereoscopic slide projection and IMAX film presentations. The plane of polarisation for the image displayed by the Rear monitor (left eye image) is unchanged in passing through the mirror. However, the polarisation plane in the Top monitor display (Right eye image) is effectively vertically flipped as reflected.

When stereo pair images from the two monitors are viewed through crossed-polarizing glasses, the user only sees the Rear monitor display with the eyepiece having the 45º oriented polariser and the Top monitor display with the eyepiece having the 135° polariser. The result is a single, merged stereoscopic image.

A further requirement is a computer with an appropriate graphic card and software to enable slideshows to be displayed.  I chose to build a dedicated PC but some laptops and most desktops are suitably equipped for the job - more on this as we go on.

Since the top display is seen in reflection, there is a need to perform vertical flip operation on the right hand image of a stereo pair.  This is accomplished by image manipulation software on the PC. The PC is fitted with dual-head graphics card to drive the two monitors.  The drivers for the graphic card enables double width images (stereo pairs) to be spread across two monitors.  It should be said that a dual-head graphic card is not essential if your PC has both DVI and VGA connectivity included.

There is a choice of software available for preparing slides and building slideshows, some costing little or nothing.

Before looking at the project in more detail, you may wish to know the cost involved.  I purchased two LG 17" monitors from PC World for £154 each.  The mirror cost £63 and the cabinet with covering and fittings a further £25 or so.  I added a sound system using redundant computer speakers, dismantled from their original housings and fitted into the cabinet.  You could say that TARDIS cost £400, without the PC of course.  My dedicated PC cost around £300, including the graphic card.

Let us now examine the key components in more detail.

LCD  Monitors

I selected LG 1717s 17" monitors  Figure 3. on the basis of cost and physical dimensions; the 17" is a diagonal measurement by the way.   Having checked several monitors, I think it is safe to say that the 45º polarisation is the same for all brands.  You can check this for yourself by observing no image through the right eyepiece.

It is essential that both monitors are of the same manufacturer and model for consistent performance.  The base mounting is a point to consider, they are obtrusive for this application and it is helpful to remove them.  The full resolution of the LCD monitors is displayed.  For for the 17" LG monitors and most others, the native resolution is SXGA (1280 x 1024 pixels) this means that our stereo pairs can, or should be exactly 2560 x 1024 pixels, not all monitors boast this resolution though.  This is a high resolution when compared to low cost DLP digital projectors (less than £1000 each lets say) which operate at XGA (1024 x 768 pixels).

Unlike current 'autostereo' monitors, there is no restrictive “sweet spot” requiring precise body positioning.  This adds to viewing comfort, as does the flicker free display synonymous with LCD monitors.

If you purchase monitors with a silver finish, then apply some black sticky-back plastic to the bezel for appearances sake.

Semi-Reflective Mirror

The mirror purchased for TARDIS is 15" square with a 3mm thickness. This dimension of 15" is the same as the monitor  width and makes for a simpler cabinet design. The mirror surface is coated by an electro-vacuum process using Titanium as the reflective medium. This makes the surface very durable and allows it to be treated as ordinary glass when cleaned.

Some light shift is caused by the spectral behaviour of the mirror. This is not critical as LCD monitors have display adjustments like Gamma, Brightness/Contrast and RGB levels which become the default settings once set. To avoid confusion, I chose to make all the adjustments on the top monitor only.

The mirror was specified to have a 30/70 split on reflection/transmission characteristics - a standard option of the manufacturers. I suspect that this ratio allows for the inherent reflectivity of the glass itself. With my example, I suspect that the coating is a little 'thin', this could be due to the manufacturing tolerance rather than incorrect specification.  Again, the top monitors can be adjusted to compensate.

The mirror was obtained from Vacuum Coatings Ltd. of Walthamstow at a total cost of £63 inclusive of VAT and delivery.

The Cabinet

I constructed the cabinet entirely from 6mm MDF which is available from B&Q in smallish sheets that will fit in the car Figure 4.  Some strengthening was added with 15mm x 20mm section timber.

The side members of the cabinet were made by laminating MDF profiled panels onto a full side panel such that the effect of rebates or slots was achieved.  These are dimensioned to receive the monitors and mirror which can all be slid into position when the cabinet is complete Figure 5 / 6 / 7.

The top of the cabinet uses a single panel of MDF and had cut-outs Figure 8.to take ventilators.  The ventilators are also from B&Q.

The base of the cabinet was constructed as a separate enclosure with a removable front panel to accommodate a sound system  Figure 10 / 11.  This smaller enclosure, along with the top panel and a pelmet, are the main stays between the two side panels.

The back panel is also removable to allow access to the monitors and mirror.  These can quite readily be removed at any time.

The cabinet was covered in a grey cloth material from Maplin (part KS45Y) which is stretched over the cabinet and glued at critical points with contact adhesive.  Spring loaded carrying handles are fixed to the side panels, also from Maplin (part L20AA).

Figure 9. shows details of the support strip for the mirror which has cellular rubber strip attached.  The black felt used to line the cabinet can also be seen.  This material is a stiff card like material used by milliners to make hats and can be obtained from craft shops.

In addition to the portable cabinet that is TARDIS, I have utilised a redundant TV cabinet to store the unit, along with the PC Figure 12 / 13.

The Sound System

I am not going to dwell on this. Suffice it to say that you can pick up computer speaker systems, amplified or otherwise, quite cheaply and hack them up to fit into the cabinet.  Alternatively, you could leave them as free standing, external speakers, especially if you don't intend TARDIS to be portable.

The PC

Some explanation is required as to why I built a dedicated desktop PC.  My first thought was to use a Laptop such as an Acer Travelmate 4651LMi which is one of the few that has both DVI and VGA connectivity for external monitors.  After some deliberation, I decided that a better option was to build a small form factor PC with the basic requirements for presentation and the potential for upgrading if required.  The system that I have built is small, light and looks OK too.  I shall not bore you with all the detail, but I did decide to install a dual head graphic card and settled for one with two VGA outputs.  It is a PNY Quadro 4 280 NVS Low Profile PCI Express and cost £130.  

An alternative to using a dual head graphic card is to upgrade your current one with an adapter such as the Matrox DUALHEAD2GO Figure 14 / 15. for Notebook and Desktop PC's.  This takes the existing single monitor display output (i.e. external VGA output) from your system and expands it into dual display outputs, allowing you to run your Windows desktop at up to 2560 x 1024 resolution stretched across two displays, ideal for stereo our purpose.  Using DualHead2Go in conjunction with the built-in display of your computer, you actually benefit from 3 displays at a time.  The included Matrox PowerDesk software seamlessly manages window positioning and message pop-up. The more powerful your existing graphics, the more powerful the DualHead2Go multi-display environment. The Matrox DualHead2Go costs around £100 and is compatible with a wide range of laptop and desktop computer systems.  Check first at http://www.matrox.com/mga/offhome/dh2go/compatibility.cfm

The PC has a wireless mouse and keyboard and will be used to drive two projectors in addition to TARDIS.

Software

With both TARDIS and digital projectors, it is possible to produce elaborate slideshows with titles, transitions, FX, narration and music and even animation, all  synchronised and providing consistent repeatable performances.  Much of the software used to create such presentations is low cost or free. 

I first opted to use 'Picture To Exe', which cost around £15 and is constantly being improved.   It's attraction is that a completed slideshow can be saved as an executable file that will work on any PC and stored on any plug-in memory device of the type used in digital cameras.  A 256MB memory card will hold a 10 minute show of say 50 slides with music and narration.  I now  use  'ProShow Gold' by Photodex which much more flexible, especially in the area of sound synchronisation.  I shall discuss software elsewhere on the website sometime in the future.  In the meantime, I welcome any questions on this subject. 

Downloads

For those who already have a suitable display system, please feel free to download my demonstration slideshows.  Clicking on the title will present you with the choice to 'Run' or 'Download' the The slideshows.  The slideshows are EXE files that have an integral player and will take only a few minutes to download with a broadband connections.

Barry Aldous, Updated August 2006.

Any questions? Please contact barry@aldous.net

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