3. Image separation of the strip raster image with lenticular film
To create a virtual spatial image, the image pairs merged in the strip raster image must be optically separated again.
To do this, the image strip pairs of the strip raster image are arranged under a lenticular sheet to match the individual lenses in order to take advantage of the optical refraction of the lenticular sheet: The left image strips are presented to the right eye and the right image strips are presented to the left eye.
The test cards are thus based on the same principle as commercially available lenticular postcards with wiggle images or 3D depth effects. In both cases, the lenticular screen serves to separate the image (haploscope).
➤ Floating figures when viewed with both eyes
The optical refraction of the lenticular sheet creates a different visual stimulus in each eye of the binocular viewer, causing the test figures to appear as floating surfaces at different levels above the background. At higher cross-disparity, the figures appear more prominent, while at very low cross-disparity they appear to hover just above the background. The Lang-Stereopad® with 6 test figures and cross-disparities from 50" to 1,000" is suitable for measuring individual stereo vision thresholds.
➤ When the test figures remain invisible
However, if the test card is viewed with only one eye, the figures remain completely camouflaged by the random dot pattern and are not recognisable.
The test figures remain equally invisible if the visual cortex of the brain is missing half of the image information or if the visual cortex of the brain is not processing the information correctly. Further medical examinations for diagnosis are necessary.
Even if the test card is turned 90 degrees so that the lenticular grid is horizontal, the figures will disappear.