Amateur Digital Stereoscopic Photography
(for Rebels)

Seeing stereoscopically

Two flat images show the third dimension. Two flat pictures of exactly the same scene are taken from two sites, separated horizontally, just as our eyes are separated horizontally. The pictures are presented separately to each eye, simultaneously, by one of many methods we will explore. The brain interprets the scene as three dimensional. Two flat pictures end up in 3D - amazing!

Stereoscopic photography presents a very convincing illusion of three dimensions on a flat surface. Our native 3D vision only works really well for objects within arm's reach and drops off rapidly with distance, by an inverse square law. Stereo-photography can vastly increase the range of three dimensional perception, into the far distance and down into the microscopic realm.

Near objects show stereoscopic depth well, but binocular vision fails to provide 3D in the distance. All is not lost. The same depth tricks painters use in 2D take over. Stereoscopic photography uses both stereoscopic (two eyes) and monoscopic (one eye) depth clues, which smoothly merge into each other, to give a satisfying and entertaining illusion.

Unfortunately static stereoscopic images, unlike well made 3D movies, do not provide motion clues to depth. It is amusing but sad to see people who are viewing stereoscopically move their heads, in an effort to "see around an obstruction." Movement parallax works so well in real life, but is not available with stereoscopic pictures. (Holography allows movement 3D but is beyond this web site.)

Stereoscopic depth at great distances can be produced from cameras separated by more than the distance between our eyes. (Hyperstereoscopy). Stereo at very close distances (stereo macro photography) uses cameras closely spaced (Hypostereoscopy). Both methods produce an "unnatural" depth experience, because it is not available in real life. It is these un-expected depth experiences which I especially enjoy.

Stereo-photographer's problem with their audience

Everybody has trouble with 3D if the photographer has made a mess of his job and presents the two images badly. This web site should hopefully teach you how to avoid that disaster, usually caused by poorly aligned image pairs.

Stereo photography is normally done by people with excellent stereoscopic vision, which turns out to be a problem. Stereo experts can easily fuse pictures with wide stereo disparity and it is difficult for them to realise that many people cannot do that. So we end up making deep 3D images for the pleasure of other experts; but have to make a second, gentle set, for the general population.

Distortions of reality occur once we go beyond simple 3D photography and use wider or narrower camera separations than the distance between human eyes. Telephoto lenses cause an upset if objects look like card-board cut-outs, rather than having full, rounded depth. There are ways to avoid "card-boarding" but they always cause other problems, as we will review. Why people who accept "cubism" and worse extremes of modern art should get upset by "card-boarding" is interesting.

A perfect 3D experience is possible, but rarely on a computer.

Breaking the rules versus "Presence"

Amateur photographers like to "break the rules," but you can't break rules which you do not know. So I will give you some rules, which are probably the most controversial part of this web site, but then encourage you to go out and break them for "3d Art." Just do not show your awful double eye creations to innocent people, who will soon reject all 3D, even the good stuff, because of headaches and nausea.

In 3DTV, it is possible to enhance the experience if viewers feel the TV screen is a window to a three-dimensional world. That virtual world becomes an extension of their living room. If this is your aim, called "presence," then rules apply to how the scenes are photographed and rule breaking becomes a problem. Perceived depth must be realistic, although many observers in psychological experiments find a slight exaggeration of stereo depth can enhance reality and give a more acceptable "presence" than reduced depth. Others prefer flat "stereo," because it does not give them eye pain, but usually they suffer a disorder of stereoscopic vision.

There is one rule you had better not break. Stereoscopic pictures which give normal people headaches are not acceptable. The more extreme versions of 3D should only be shown to experts who can handle eye gymnastics and enjoy getting in deep.

Anaglyphs: an undesired necessity

You will need red/cyan anaglyph goggles to see stereoscopic pictures on the early pages of this web site.

Click the glasses to find out where to get them.

Oh yes, I don't like anaglyphs either, what with their partial colour blindness and ghosts, but anaglyphs are the easiest way for most people to see 3 dimensions on a computer screen.

Anaglyphs clarify the concepts of stereo photography, because the right and left eye views are colour coded, allowing alignments and measurements between the two superimposed pictures to be judged, even without wearing the "3D gogs." Anaglyphs demonstrate, much better than stereo pairs, the concepts needed for showing stereo to the general public on screens (projection or TV) Screens, rather than stereoscopes, are where 3D presentation is required these days.

Anaglyphs cannot be digitally colour compressed without causing bad ghosts. Ghosts occur when parts of the picture intended for one eye are faintly seen by the other eye. After badly aligned pairs, ghosts are a big cause of headaches. Broad band internet is better than dial-up for these minimally compressed, bigger than average picture files.

Edition 1 of this presentation used the even cheaper, free-view stereo, especially cross-eye (X stereo) and free-view has no ghosts. But only a few experts are skilled at optical gymnastics. Two side-by-side pictures are needed on screen, reducing the size of the 3D image by half when compared with a full screen anaglyph. Because eyes in X stereo are over-converged, everything looks stereoscopic, but too small. Anaglyphs actually give better spatial resolution than stereo pairs, for a smaller file size, but worse colour. Later pages will use true colour stereo pairs, once improved methods to view them are presented.

Feel free to comment

If you wish to comment on the stereoscopic pictures, many can be accessed on Flickr just by clicking the image.

Constance Westmacott

Constance was the daughter of the sculptor, James Sherwood Westmacott, 1823-1900.
This marble plaque is in the Victoria and Albert Museum, London: Number A.12-1968

Photographs of sculptures are much better presented in 3D than as flat, 2D images.

Stereoscopic red/cyan anaglyph by John Wattie.
Click on the image to add your comment
or to see bigger versions .

500 pixel vertical size, DI = 1

Most people cannot diverge their eyes.

Stereoscopic pictures should not make you do this.

Marty Feldman stock photo from internet

The distance between adult's eyes (interocular distance) averages about:
63mm (females) or 65mm (males) and ranges from 55mm to 75mm.

Stereoscopic viewing difficulty index (DI)

These web site pictures are supposed to be viewed on a computer monitor (but can be projected with a 1024x768 pixel digital projector).

Maximum uncrossed disparity on a 22 inch monitor (470mm width) running at 1680x1050 pixels defines the viewing difficulty.

10mm maximum disparity: DI = 1

60mm maximum disparity: DI = 6

100mm disparity (experts): DI = 10

Sky television 3D standards, when measured this way, only allow a DI of 0.9

Pictures too big for your monitor?

The size of an image is measured by its vertical height in pixels. Measuring the width is less useful, since pictures can be narrow portrait format or wide panoramas, but usually the height on this web site is limited to 768 pixels for the simpler images. (The pages seem to fit on an iPad, fortuitously as it happens).

Internet Explorer 9 and Safari allow resizing of web pages (including images) to suit the monitor you are using:
ctrl+   and ctrl-    Explorer 8 and Firefox.
cmd+ and cmd-   Safari.

F11 on Explorer and Firefox will remove the menu bars (but not the scroll bars).
(Safari doesn't do that, worse luck).

iPad and Acer portable 3D computer running Windows 7 allow resizing by pinching or opening your fingers on the screen or touch-pad.

Mouth parts of a Humble Bee (Bumble bee)

(b, upper lip; d, mandible; e, maxilla; f, maxillary palpus; g, tongue; ih, labium and tabial palpi; k, eye.)

Source: Our Common Insects
A Popular Account of the Insects of Our Fields, Forests, Gardens and Houses
By Alpheus Spring Packard
Available from www.gutenberg.org Published: 1873

Stereo macro photography in wide screen format rivals a low power stereo microscope.

Use anaglyph glasses to see in 3D.

The "sponge" for extracting nectar, at the tip of a bumble bee's tongue, is shown at original camera magnification in an inset.

Macrophotography in 3D