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Figure 13.12 Ocular comfort in stereoscopic vision with relation to disparity given in minute of arc,
Wöpking, 1995
taking local spatial frequencies into account. Reduced visual strain is based on spatial
frequencies and disparities, using a visual comfort function in the image. This function
makes it possible to determine whether a point of the image tires the observer and
whether the image point should be processed. The comfort function was determined
through experiments by several researchers. We use the stereoscopic comfort function
obtained from data by Wöpking (1995). Wöpking carried out comfort tests (related to
visual strain) depending on the disparity and on the frequential content in each image
point: when the spatial frequencies are high, the fusion of stereoscopic images is more
difficult and more tiring (for example, for objects represented only by their contours
and that are therefore at high frequency). When the disparity is 1 . 5(90 ), visual strain
is uncomfortable for a high spatial frequency of 23 cpd, slightly uncomfortable at
5.6 cpd and unnoticeable at 1 cpd (Figure 13.12). Frequency f iltering method
One of the solutions, when large disparities are present, is to truncate the spatial
frequency content for facilitating fusion of images (to find oneself in a comfort zone
on the Wöpking curve) This solution is called the adaptive blurring.
Jérôme Perrin worked on this technique applied to fixed stereoscopic images. The
pair of unprocessed images is visible in Figure 13.13.
This adaptive blurring (Figure 13.14) is implemented by Wavelet processing. At
every point of the image, the frequential content is adapted to the local disparity: high
frequencies that are “difficult to merge'' are suppressed. The image is broken down
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