Chapter VII

Backward and forward

On the anaglyph, two pixels that reconstruct one stereo 3D point have an horizontal offset (Parallax).
The position of a stereo-reconstructed point depends on the distance between its left and right pixels.
Stereo points lying on the physical screen surface have no offset.

Moving the stereo image relatively to the screen will simply result in changing the distances between the left and right pixels.
If you do so on an anaglyph you will notice some rather blurry stripes when looking at the sides with the red-cyan glasses.
This is because the stereoscopic window is not set.
With stereo paper prints, the window is set by cutting those stripes.

If a stripe is cut from the left of the left image and another stripe is cut from the right of the right image, the entire stereo image moves backward.

Animated stereoscopic window

Click to open the animation

If a stripe is cut from the right of the left image and another stripe is cut from the left of the right image, the entire stereo image moves forward.
A version of that operation is for a computer anaglyph to roll the red band then cut the ghosting stripes appearing on the sides.
Notice that, as a consequence, the moved stereo image will be represented by an anaglyph which will be more narrow than the original images of the stereo pair.