Signal Processing for Stereoscopic and Multi-View 3D Displays - Signal Processing Systems - page 38

a b c

Fig. 27 2D non-separable filter: ( a ) ideal, ( b ) impulse response and ( c ) magnitude response:
contour plot for − 3dB( inner curve ), − 6dB( middle )and − 30 dB ( outer curve )

4.2.2 Passband Approximation with a Separable Filter

The computational complexity of a 2D filter is rather high and considerable
computational savings can be achieved when it is possible to separate the 2D filter
into two 1D filters, one filtering in the horizontal direction and one in the vertical
direction. One approach to the design of separable passband-optimizing filter is
discussedbyBoevetal.[ 69 , 70 ] .
Based on the known interdigitation pattern and angular visibility of each element,
one can derive the pattern of visible pixels as seen from the sweet spot of one view.
As discussed in Sect. 3.1.2 , this pattern behaves as a sub-sampling mask. As an
example, the mask of a 24-view 3D display is shown in Fig. 18 . The spectrum of
this mask is shown in Fig. 28 a . Each of the peaks in this spectrum corresponds to
a source of aliasing. In order to avoid aliasing (Moire artifacts), a filter has to be
designed in such a way that its passband does not overlap with any of its copies
generated by moving its center to any of those aliasing sources. It is possible that
there are several different separable filters that can be used as antialiasing filters
for this display, as shown in Fig. 28 b . Each of those filters will perform proper
antialiasing, but due to different shapes the visual quality of displayed images will
be different. Which separable filter would yield best visual results depends on the
content. The experiments presented in [ 70 ] suggest that for textual information such
as subtitles, filters with a passband close to square perform better than filters with
elongated passbands. For designing 1D filters with the desired cut-off frequencies,
the windowing technique with the Kaiser window of length 24 can be used (see also
Sect. 4.2.1 ) . As an example, the magnitude responses ( 6 dB contour) of several

separable 2D filters suitable for the said 24-view display are shown in Fig. 28 c .

−

4.2.3 Passband Approximation with a Tunable Filter

The results in [ 70 ] suggest that the filter that fully suppresses aliasing does not
always give the best perceptual quality. Some people prefer sharper-looking images
at the expense of some Moire artifacts. In order to allow the user to control the