qtvr the paintbrush way

QuickTime Virtual Reality (QTVR) is the oldest and most mature of a group of competing technologies known collectively as interactive imaging. As is true for most of the competition QTVR operates on a cylindrical model. The author captures a series of still pictures by rotating his or her camera through 360 degrees, then stitches them seamlessly into a panorama The user is then able play the panorama as a movie, while controlling their point of view. This user control is the hallmark and great power of interactive imaging. Paintbrush was founded in 1996 specifically to exploit this rapidly emerging technology. While it is possible to create both panoramas and objects in rendering programs our focus has been on photographic panoramas.

selecting equipment
The first rule in equipment selection is that most things will work. We have successfully shot panoramas every way from hand held to using our top end professional equipment. The guidelines given here are what we have found to be optimal. (For a chewing gum and bailing wire approach visit the folks at Outside the Lines (www.outsidethelines.com/).

Your tripod should be heavy and stable with easily adjustable and positive locking legs (we use a Bogen 3221 unless we are hiking a long ways). We roughly level the tripod using the legs. The tripod needs a head which is easy to level in two directions and which stays in position after it is set. We use a knob adjustable gear head (Bogen 3275), which allows for rapid accurate leveling. On top of the tripod head you need a QTVR pan head. We are currently using several products from Kaidan (www.kaidan.com/) -- the Kiwi is shown. The pan head allows your camera to rotate in a plane around the focal point of your lens (more on that under parallax further down). It also provides an indexing system so that your pictures can be taken at regular intervals.

All of our work has been done on film. For us digital photography is still in it's infancy while film is a mature science. By sticking with film we gain two things, a great deal of control in the image capture (lacking in modestly priced digital cameras), and archival quality images (which are not dependent on current technology). As playback speed increases, we are able to increase the resolution of our digital images by rescanning our negatives. Any 35 mm SLR which allows manual exposure control will work fine for QTVR. We have used a variety of bodies from Pentax and Cannon. In choosing a lens there are a two primary criteria. First for the QTVR stitcher to work you must use a rectilinear lens. Second, your vertical field of view is limited to what you can see in one shot. For the most part this means working with focal lengths of 28 mm and down. As a photographer you have to find a balance between maximizing the interest of the photo (close ups) and allowing maximum field of view. We have used a Sigma 18-35 zoom for most of our work.

adjusting equipment
Once you have collected the equipment there is still some set up to do. Most QTVR photography is done with the camera in portrait orientation to allow maximum vertical field of view. After the camera has been mounted it needs to be leveled both from front to back and from side to side. (It is possible to shoot with the camera in a different orientation, but the QTVR playback engine assumes that the panorama was collected in this way and pans showing sky/ground/sky/ground going by horizontally can be very disorienting.) The most valuable tool for leveling the camera is a double bubble hot shoe level, available at any camera store. It is necessary to rotate the camera through the entire 360 degrees checking for level in both directions. The camera must be rotating in a plane--which is one of the main roles of the pan head.

With the camera set up and level you are ready to adjust your pan head for parallax. For most people this is the most confusing part of the entire set up process. Fortunately it only needs to be done once for each lens/camera combination. When a ray of light enters your camera lens is moving approximately parallel to the sides of the lens barrel. As it passes through the lens(1) itself each ray is bent towards a single point -- the focal point(3). After passing through the focal point it the rays move apart and come in contact with the film(2). When you rotate the camera for your pan, you must be rotating around the focal point of the lens, or you will create a parallax error. Essentially the camera starts "seeing around corners," which is confusing to the stitcher. In the pictures shown you can see that in one pair there is no shift in perspective, in the other pair the point of view appears to move with the camera. The second role of the pan head is to position the focal point of the lens over the center of rotation. This is accomplished by moving the camera forward and back and in and out on the head until there is no apparent motion between near and far objects when the camera is rotated. We have our pan heads marked for each of our common lens/body combinations. Parallax becomes an increasing problem as the length of the lens becomes shorter; it is typically a problem in situations where you have both foreground and distant objects.

image collection
Finally you are ready to take pictures. It seems basic, but careful location selection can avoid many problems. Frequently moving just a few feet can get you away from erratically moving things (people for example), or keep you from having to shoot straight into the sun (always an interesting experience with an SLR). Both of these situations can be dealt with, and add interest to the final movie, but they will definitely add difficulty. We use color print film (usually Kodak Gold 100 or 200 ASA) because of its greater exposure latitude, and lower cost (start thinking in terms of one or two pictures per roll). We like to shoot panos with about 55% overlap between successive images. This gives us good blending in high contrast situations and allows us to salvage a pano with a bad image. It does mean capturing from 12 (14 mm lens) to 18 (28 mm lens) pictures per panorama. We also reshoot any questionable shots and like to save one shot for record keeping.

We shot more than 200 panos for the Nature's Legacy: Zion National Park title we released in March of 1998. As the film started to pile up we realized that we needed a better record keeping system, both so we could improve our work, and so we could keep track of what we had done. A photograph of a data sheet showing: date, time, location, exposure, f-stop, film type, number of shots, lens length, and any problems (such as repeated shots) captured on the same roll of film as the pano provided an ideal solution. Since it captured in the field under conditions identical to the pano itself we also include a gray scale which is invaluable for color correction later on.

Your next decision in the field is exposure control. For the most part we shoot with high f-stops to maximize depth of field. One of the problems with photographing a pano is that it is very likely that you will have very bright and very dark spots within one pano -- although not necessarily within a single frame. Generally we set the shutter speed for the average and shoot the pano. For extremely bright or dark areas we reshoot at an appropriate speed and composite the images in Photoshop prior to stitching. If the sun is in a photo we block it. When there is a single shutter speed difference between successive images we generally have good success with auto exposure.

Finally you may have to deal with focus. The short lenses have phenomenal depth of field, but there are still times (standing next to a wall or tree) that you may have to adjust the focus during a single pan. The stitching software likes areas of detail. If you stitch an out of focus area to an in focus area you wind up with most of the detail from the in focus picture. Despite your best efforts you are likely to have some image flaws. We usually try to leave these alone until after the pano has been stitched, then correct them in Photoshop.

With a set of pictures on film you have several choices when it comes to digitizing them. We have had good success with both scanned negatives and Kodak PhotoCDs. What ever path you choose it is important that the scanner setting not be changed between images. It can be difficult to convince a service provider of this, but at least some have heard of QTVR and we would recommend finding one that has. We have found PhotoCD convenient but expensive ($20 and up per pano). We have had poor results working from scanned prints.

With your images digitized you are ready to stitch them. When the stitching software was released in 1995 it was expensive and ran from an arcane text driven MPW (Macintosh Programmers Workshop) base. Since that time there have been several GUI based software packages at both the consumer and professional levels released. In our opinion the best of these is the QTVR Authoring Studio from Apple (www.apple.com). Consumer level packages are available from Roundabout Logic (www.roundaboutlogic.com/home.html) and Live Picture (www.livepicture.com/)

Before starting the stitching process we like to create a folder with a meaningful name and put our source images in it. This folder becomes a mini project manager as we move it through the various stages of production.

After launching the Authoring Studio create a new stitcher and save it in your project folder. The software automatically names all the other files it creates as derivatives of the stitcher's name. Then click on the add images button (1). Your photos need to advance from left to right and be in the orientation in which you shot them. If they are not you can use the rotate and sort commands to fix this (2). Most of the default settings in the Authoring Studio are good choices, we do, however, do some customization. After you load your images and have them in the correct orientation, click on the image alignment button (3). Specifying the horizontal alignment as overlap in pixels (click the button, then press recalculate) instead of degrees between images allows you to apply a search range. It is often possible to overcome stitching problems by either tightening or relaxing the search range parameter.

The settings button (4) opens a control panel with a lot of options. The first step is to change the blending to guassian and to turn off sharpening. Gaussian blend can result in slightly softer images, but nearly always gives the cleanest stitch. We have found that while sharpening makes the intermediate panoramic photo look better, it makes the final movie look worse. Compression will already be set as shown (Cinepak 75). If you want maximum compatibility for all users we recommend this setting. For faster machines JPEG gives better results and smaller files. Finally, under the file menu it is necessary that the final movie be flattened to the data fork for it to work on non Macintosh computers.

Time to stich. Even after watching hundreds of panos assemble themselves on the screen there is still something magical about the process. With 18 images it takes about 5 minutes for this to happen on a 266 G3. And there it is your final movie-- well almost.

I have never seen a stitched panorama (saved as .pict by the authoring studio) which didn't benefit from some time in Photoshop. Issues ranging from color correction to differences in exposure and stitching flaws can be dealt with, with time and patience. See for example our before and after pictures below. One thing we have learned is that the Cinepak compressor really stomps on color, so we shoot for an oversaturated, over bright look in the stitched pict (think hexachrome). Photoshop is also valuable for resizing your pictures (and final movies). Be careful that the long dimension of the .pict file in pixels is evenly divisible by 96 and the short dimension is evenly divisible by 16 to ensure compatibility with windows based machines.

After retouching and resizing the .pict you can create a new panorama maker, import the .pict file and produce your final movie. The movie player window can be used to adjust the default zero pan angle and zoom and the final player window size.

We have been able to go from setting up the tripod to final movie in as little as 4 hours (including an hour and a half at the 1 hr photo processor); we have spent an entire day retouching a single pano in Photoshop. You can see our work on the web at www.pbproductions.com, on CD in our Nature's Legacy: Zion National Park release, and in a unique application as REALuster reflected environments for 3d rendering packages (previews of both CDs are available at our main website.

click here to download a short quicktime showing the final result of this article


Gary Mort (gm@pbproductions.com) General Manager, QTVR Photographer
Kelly Bringhurst (kelly@pbproductions.com) Interpretation, QTVR Photographer


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