Proofing Stereo Panoramas

[Thomas Sharpless]

My recent tutorial covers only shooting and stitching stereoscopic panoramas. This post is about the equally important topic of how you and your audience can view them.

To stitch successfully you must have a good stereo display on which to proof your panoramas. The better that is, the better your work will be. On a low quality 3D display it is easy to miss stereo registration errors that would be seen as glaring defects on a high-end system.

The most accessible method is anaglyph. All you need is a color monitor, a pair of red/cyan glasses, and a way to convert stereo pairs to single anaglyph images. I recommend the excellent free all-purpose stereo pano/video player sView (http://www.sview.ru/en/). sView can display equirectangular stereo pairs as grayscale or color anaglyph, lets you adjust horizontal and vertical convergnce, and much more. Grayscale is preferable because color makes it harder to see stereo details.

A real stereoscopic display will show a great deal more depth detail, along with natural colors. A few years ago it was possible to buy a variety of 3D monitors, 3D TV sets, and even laptop computers with 3D screens. Today the 3D market is limited to home theater-quality TVs, and hardcore gaming computers. The computers sides is dominated by nVidia, which has tried pretty successfully to tie 3D display to its own hardware and services. But in fact you can make a nice 3D display facility for your stitching computer that does not owe nVidia anything.

There are two basic 3D screen systems, switched and passive. Switched systems display left-eye and right-eye images alternately in time, and rely on synchronized LCD shutter glasses to block the current image from the eye that should not see it. This requires a very low persistence monitor that can switch images perhaps 120 times a second. It is the method favored by gamers and pushed by nVidia. Switched 3D has been popular since the CRT era, so there is plenty of old gear around and it is not hard to put together such a system at low cost. However to get switching speed, this system sacrifices a great deal of the color and tone quality that we photographers value.

The passive 3D system displays left and right images continuously, interleaved on alternate rows of the screen. Each row has a circular polarizing strip in front of it, and the viewer wears glasses with left and right circular polarizing lenses. This system can deliver high image quality and is the one commonly used in movie theaters and home theater TVs. Its main drawbacks are some aliasing due to the halved vertical resolution, and a restricted viewing angle range. On a 4K screen the aliasing is hardly noticeable.

My main proofing display is a 3 year old ASUS VG23A passive 3D monitor connected to the gaming laptop I use for stitching. It has much better color quality than the laptop’s screen, so also serves well for color and tone adjustment. The stereo display software is sView, which can generate interleaved stereo, and switched stereo, too, in several formats. If you can find a used passive 3D monitor, I strongly suggest you snap it up.

My “other screen” is an LG 4K OLED TV with passive 3D. 55 inches of pure image quality, with good 3D apart from a tendency for highly saturated reds to appear double. LG is the only company now selling passive 3D TVs, but Sony and Samsung sold them not so long ago, so if you are interested you could comb the used TV market — or scrape up $1700 for a new LG. Using a 4K TV with a PC is a bit challenging technically, because TVs normally have only HDMI ports, while high performance PC displays tend to use DVI or DisplayPort connections. To drive a 4K TV at native UHD (3480 x 2160, 60Hz) requires an HDMI signal that conforms to the BluRay standard, HDCP 2.2. HDMI ports on PCs tend to be HDCP 2.0, which supports UHD at 30 Hz, or even 1.4, which won’t drive a UHD TV at all. Several current PCI video cards have 2.2 ports. Most current laptops have hdcp 2.0 ports, but so far as I know there is no laptop with HDMI 2.2. This limitation has nothing to do with the power of the GPU. Current gaming gpus could easily drive an 8K screen at 120 Hz, if the screen had a DisplayPort. The problem is in the chipset that drives the HDMI port. On laptops that is universally an Intel Integrated Graphics chipset. Desktop video card makers have more choice, and some of them (notably ASUS) offer hdcp 2.2 HDMI ports. I get by with 30Hz UHD from a recent gaming laptop, but am seriously thinking of building a small “desktop” unit just to drive the TV.

VR displays offer the most convincing stereoscopic experience, and the most critical stereo proofing, despite their very limited resolution. I use a Samsung Gear VR with a Galaxy S6 phone. The GearVR is less convenient for proofing than the 3D monitor because you must prepare an over/under equi file and copy it onto the phone over USB or WiFi, then put the phone in the headset and fire up Oculus 360Photos. But I almost always do a final check in VR before publishing a stereo pano — and often find something that needs fixing. A Rift or Vive setup would be quicker for proofing and better for in-house demos, but with the GearVR you can carry a 3D portfolio around with you.

More when I get back….

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