Tiled Displays

The following discusses the relative merits of tiling conventional displays in order to achieve a high resolution display. The main use of such displays in visualisation is to be able to see detail as well as the big picture. On a lower resolution display one is required to zoom in to see the detail at which point the context is lost. Similarly, when the whole image is visible the detail is smaller than a single pixel and thus lost.

An intentional design criteria in the installation discussed here was the use of a single computer in order to maximise the support across commercially available software, at the cost of performance compared to using a cluster. This can be partly justified by the expectation of increased graphics performance in time.

The design is based upon the Apple or DELL 30 inch displays, each one 2560x1600 pixel resolution, the highest on the market at the time. The displays are from the same factory, unfortunately the frame is about the same thickness for both and cannot readily be removed. The DELL displays were chosen simply because of the dark frame vs the lighter frame for the Apple version. The maximum number of dual pipe dual link DVI graphics cards that could be installed in the machine of choice (Apple Mac Pro) was 4, in other words 8 displays. The 2x4 arrangement with the panels on their sides gives the most convenient aspect ratio of 5:4 (6400 x 5120).

While the gaps between each frame is an obvious disadvantage, in order to achieve the raw pixel resolution it is more cost effective than using tiled data projectors. Not only is there the cost benefit but also the software complexity dealing with edgeblending between tiled projector displays (assuming a seamless display is the target). It should be noted that these 30 inch monitors at 2560x1600 pixels have almost twice the pixels of a HD projector (2560x1600 compared to 1920x1080).

The colour depth of these displays would seem to be better than what one can achieve with data projectors, this includes the black levels. The first two images are fresh from the repaired Hubble Space Telescope, these first offerings at the time of writing were in the range of 3K and 4K square. The total resolution of the display is 4*1600 pixels horizontally by 2*2560 pixels vertically, a total of 6400 by 5120 (32MPixels).

The following image is a high definition photograph of the Boolardy station in West Australia and the site of the ASKAP (Australia Square Kilometer Array Pathfinder), the site of the proposed SKA. The image is 32,000 by 32,000 pixels.

An example of a tiling of high resolution images, courtesy of Florian Fusseis. Notice the second display from the top left is a different colour, this is due to it being a replacement screen where the displays were originally a running sequence of serial numbers. Colour space adjustments on the panels have subsequently been made to create consistent colours across all panels.

A further example from the recent high resolution images from the Hubble Space Telescope.

The above were all using standard Mac applications (eg: PhotoShop and Preview), the main issue with this is the inability to take account of the gaps between the displays giving quite an unnatural sensation as one tracks content between displays. A particularly elegant way to deal with this is the Quartz Visualiser. The following example uses a Quartz Composer composition to display the image, allow the user to scale, pan, and rotate. Quartz Visualiser then takes that are handles the image across the tiled display and automatically adjusts for a user specified interdisplay gap. While perhaps not evident here, the way the image disappears behind the frames between the display area results in a much more believable result, not surprising perhaps since we are accustomed to viewing scenary through frames windows. The only slight complication is that Quartz Visualiser ignoresmouse and keyboard IO, this simply means a separate QC composition is created that runs on a separate computer and controls the translation, zooming, and rotation through a network patch. The two QC compositions are provided to give an idea of how this is achieved.

At the time of writing (Snow Leopard 10.6.1) seems to have a number of bugs when it comes to supporting this number of displays. Serious bugs such as the display preferences for arranging the displays runs very slowly and often fails to display the panels at all.