Information Technology Reference
In-Depth Information
where,
p
(
i, j
)=
0:if 1
254
1:if
Y
(
i, j
) = 0 or 255
.
≤
Y
(
i, j
)
≤
(6)
I
p
is set to minimal value of 0.1 to allow a limited amount of burned pixels that
may occur in any image without resulting in disturbing effects. We compute our
definition of the brightness
I
as:
I
=(
I
l
+
I
c
)
/I
p
. Fig. 3 shows the luminance,
contrast, and amount of burned pixels in three example frames.
(a)
I
= 2.89,
I
l
= 0.16,
I
c
=0.55,
I
p
= 0.24.
(b)
I
= 1406,
I
l
= 84.17,
I
c
= 56.48,
I
p
= 0.10.
(c)
I
= 2627,
I
l
= 235.8,
I
c
= 26.89,
I
p
= 0.10.
Fig. 3.
Example test frames with (a) low, (b) medium and (c) high brightness. The
measured values are: brightness (
I
), luminance (
I
l
), contrast (
I
c
) and amount of burned
pixels (
I
p
).
2.4 Shakiness
Shakiness in a video is caused by the instability of a camera, such as when a
camera man walks or applies fast zooming or panning operations. Such actions
induce motion in unwanted directions, which adversely affects the video quality.
In order to measure shakiness in a video, we used the method described in [9].
The camera speed in the horizontal, i.e.
pan
, and vertical direction, i.e.
tilt
,is
measured using a luminance projection method [10]. In this method, the lumi-
nance values of every row are summed up in a vertical projection and of every
column in a horizontal projection. If the camera is moved vertically or hori-
zontally, the corresponding projections will also shift in the same direction. For
example, if there is a panning in the right direction, the values of the horizontal
projection will shift towards right. The camera motion, pan and tilt, is calcu-
lated by correlating the projections along the frames. The speed of the camera
is measured in screens per minute, where one screen is equivalent to the hori-
zontal dimension of the frame in case of pan and to the vertical dimension of
the frame in case of tilt. The high-frequency components of the camera speed
are the result of shakiness, while the low-frequency components are the results
of intended camera motion. The amount of shakiness is given by the difference
in the pan and tilt speeds before and after applying a low-pass FIR filter (25
tabs). If pan, tilt values before and after filtering is represented by
p
,
t
and
p
f
,
t
f
, respectively, then for each frame the shakiness measure
J
is given by:
J
=
(
p
−
p
f
)
2
+(
t
−
t
f
)
2
.
(7)
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