Viewing Stereoscopic Images

We view the world stereoscopically

With two eyes, each with a slightly different view of the same scene which the brain fuses together to obtain information about the relative distance between objects and the viewer. Stereoscopic images ( 3D pictures ) are made as a pair, one as seen by the right eye and one as by the left eye and then to view them in such a way that the brain can fuse them together and increase the perception of depth compared to a normal 2D photo Since the the original Wheatstone Stereoscope built in 1832 many ways have been developed to view stereo pairs. but they generally fall into one of three categories, side by side, anaglyphs or interleaved.

Side by Side Images

Holmesviewer2

Images displayed with a 66mm separation( the average distance between an adult’s pupils) can be free viewed without any viewer in both parallel and cross eyed modes. The “ Holmes viewers” which have magnifying prism lens can be used to view slightly larger images mounted on card with an approximately 77mm separation. These are the viewers frequently seen in antique shops.

Larger parallel images can be viewed with a suitable viewing aid such as the Mirrorscope or prismatic spectacles. For more details on free viewing and viewing other side by side stereo pairs see the notes at the end of this page.

A modern twist to side by side viewing is “SBS 50”, a side by side digital format with the horizontal axis anamorphically squeezed that is recognised and decompressed by many 3d televisions.

Anaglyphs

AnaglyphglassesThis is the system often used in magazines where they give you a pair of spectacles with red and cyan filters There are alternatives using other complementary colours . The left eye image is printed in cyan and viewed through the red filter while the right eye image is printed in red and viewed through the cyan filter. The parallax difference between the two eyes makes it look as if the images are not printed in register.

Colour Anaglyphs are made with the cyan and red filters over the camera lens when taking the original pair of photographs. The colour values are distorted but mostly the 3D perception is there. Subjects with a lot of red in them can look very confusing sometimes

A better solution is to use the Dubois computer algorithm to modify the colours, the colour values are still distorted but the 3D prospective is far better

Interleaved Images

rNCBlW1dLSL500AA3003d Televisions, computer screens and projection systems are viewed with special glasses. The two images are superimposed ( interleaved ) and the glasses (Passive or Active) sort out the appropriate image to the correct eye. Passive systems use polarised glasses to separate the two images while the active system transmits alternatively the left and right eye images at high frequency and the spectacles open and shut each lens so the correct image is seen by each eye. The Society’s projection systems use the passive polarising spectacles which are available for loan at each meeting.

The HTML5 Stereo Viewer

To display the Stereoscopic society members work on the web site we use the HTML5 Stereo Viewer to display the work of Folio groups K and VM and expect more groups to follow. This system allows the viewer to choose between Side by side, Anaglyph and Interlaced viewing modes with the facility to zoom to a suitable size for the screen

Notes on the practicalities of viewing side by side images

It takes a little practice to view images in 3D, but it’s well worth the effort. In order to see side-by-side images in 3D it is necessary to ensure that your left eye only sees the left image and the right eye only sees the right image. Your brain then should put the two images together as a single 3D image. At first you may see 3 images; if so concentrate on the central image, which should jump out 3D. It will appear exactly as if you were there. For Methods 1, 2 and 3, below, the images should be up to about 175mm width, either on a computer screen, or as prints. Here are some suggestions for viewing in 3D:

1. Free-viewing. Try to defocus your eyes so that they look straight ahead, with lines of sight parallel, as if viewing MagicEye photos. You may see 3 images; if so concentrate on the central image, which should appear in 3D. This method is easiest for smaller images, say less than 120mm width..

2. Cross eyed viewing is a variation on free-viewing where the images are deliberately transposed right to left and left to right. Raising a finger halfway between the image and your eyes then focusing on the tip of your finger will cross your eyes. The images will be out of focus so if you then move your finger towards the images concentrating on the finger tip the images can be brought into focus and merge.

3. Using a card as a barrier. Cut out a piece of cardboard about 300mm long and place it vertically, edge on, so that one edge is close to the nose and the other is close to the dividing line between the two images on the computer screen or print. The card will prevent your left eye seeing the right image etc. Now try to set your eyes to view parallel to see in 3D.

4. Viewing through holes in a card. Take a piece of cardboard and cut two holes of about 20mm diameter, with centres about 65mm apart. Place this card in front of your face so that the left eye sees through the left hole to the left image and the right eye sees through the right hole to the right image.

5. Using a Loreo viewer. This is a simple folded card viewer with good quality lenses for viewing prints. Stereoscopic Society members can obtain them from the Supplies Secretary, see the Supplies Page. Non-members can obtain them from the internet.

6. Using a pair of prismatic spectacles. Adjustable prismatic spectacles can be worn so that the left eye only sees the left image and the right eye only sees the right image, and is probably the best method. Stereoscopic Society members may obtain NVP Prismatic spectacles from the Supplies Secretary. These can be used to view 3D images from 170mm to 1.5m wide. The prismatic specs can be worn over prescription specs.

7. Using a Mirror Stereoscope. A Mirrorscope is a simple viewer with adjustable mirrors that can be rotated to ensure that the left eye only sees the left image and the right eye only sees the right image. They can be used over a wide range of image sizes and subject to viewer distances. These are also obtainable from the Supplies Secretary, for Society members.