ghosting


 
Ghosting, or crosstalk, is a problem that is less evident in stereo movies and gaming due to motion of the scene and lower contrast levels as well as the presence of color in the images.  Medical images viewed in stereo are not forgiving if the viewing system has even a small level of ghosting.  This is because images are typically grayscale, static, have areas of very high contrast and also areas in which fine gradations of gray are used to differentiate structures.  The obvious and best solution for the problem is to use a optical viewing system which has no chance of ghosting.

In using any viewing system where light from the images is physically superimposed, a small percentage of the image destined for the contralateral eye does leak through the coding device, whether shutterglasses, polarized glasses, anaglyph glasses or an autostereoscopic screen.  With shutterglasses the ghosting arises from two components:  Firstly, the persistence of the image on the monitor phosphor persists for a bit longer after it has been switched off and this time lag allows some of the image to be still present at high enough levels to be perceptible when the contralateral shutter opens.  Secondly, even with the shutter closed, a small proportion of light still does leak through from the wrong image.

To eliminate perceptible ghosting, the amount of light leakage to the contralateral eye should be below 2% of what is being displayed to the that eye (the Weber fraction).

To make shutterglasses or autostereoscopic screens truly useful for radiology, the ghosting will have to be eliminated or minimized in future generations of stereoscopic equipment.
 
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