2 BACKGROUND SEPARATION
BASED ON FRAME
DIFFERENCE METHOD
Background separation is the key process to realize the
system function, which it is used for the display in a
page, thereby it is necessary and irreplaceable. There
are two methods to obtain the background separation
of video. The first one is based on the Mixture Gauss
Principle. Especially, the background segmentation
can be realized by using three background dividers
including KNN, MOG2, GMG, which are provided by
the Background Subtractor class in OpenCV. This
method can obtain a high detection rate by using a
concise process. However, it also has some
shortcomings. For example, it would consume too
much system resources due to its inherent principle of
the implementation. When a static object moves
suddenly, some redundant objects can be partitioned
out. Therefore, this method makes the actual system
perform poorly in some real-time application scenarios.
The second one is based on the frame difference
method. In this approach, the frame difference method
can effectively solve the problem of low real-time
performance. However, due to the fact that the
boundary of smoke surface is usually not clear, the
separated image may encounter the dilemma of
burning into ghosting. In order to address the above
problem, we use three frame difference method for
background segmentation in this paper.
Assume that the current frame is S(t), the previous
frame is S (t-1), and the next frame is S(t+1) Then, the
image I
1
is obtained by S(t) and S(t-1) after using this
algorithm, and the image I
2
is obtained by S(t+1) and
S(t). We can obtain that I = I
1
I
2
is the final image.
After that, the picture is processed by the morphology,
which can eliminate ghosting. In order to reduce the
image noise and to highlight the edge features, we refer
to the idea of multi-objective optimization and global
optimization. The purpose of these methods is to find
an appropriate way to obtain a satisfactory detection
accuracy.
3 CALCULATION OF SMOKE
AREA BASED ON
BINARIZATION METHOD
The existing methods usually use the image contour to
calculate the area of smoke, which needs
morphological processing. These methods detect the
image contour by using the edge detection function,
and calculate the area of each contour by using self-
defined area function, and then accumulate it.
Because the camera captures only one angle of smoke,
the smoke area refers to the cross-sectional area seen
from the camera angle. The camera is installed above
the position of smoke. In this paper, the area is
calculated by a binarization method, and the final
image is obtained by morphological processing. The
morphological processing is orient to a binary image
and it uses median filter to clear the noises. Then, the
picture is traversed and the number of white pixels is
recorded. Note that, the length h and width w of the
picture are calculated by the called shape method. The
total number of white pixels is recorded as whitenum .
The proportion of white pixels in whole image can also
be called the proportion of smoke, represented as
Eq.(1). Because the camera is fixed, the area of smoke
can regard as whitenum, multiplying area
photographed.
𝑎𝑟𝑒𝑎 = 𝑤ℎ𝑖𝑡𝑒𝑛𝑢𝑚/(ℎ ∗ 𝑤) (1)
Compared with other algorithms, this method has
less codes and a more simple logic. This means the
code complexity is simplified by this method in
background separation.
4 SMOKE VOLUME ESTIMATION
MODEL
The smoke is discharged from a small outlet and it
gradually spreads outward and upward. In order to
estimate the volume of smoke, the shape of smoke can
be roughly regarded as a cylinder. The camera is
installed on the top position of the smoke, so the
bottom area height varies with time. When installing
monocular camera condition, the height of smoke
can’t be measured by image recognition, which
requires a mathematical model to estimate the
relationship between smoke emission and bottom area.
The height of smoke increases gradually at the
beginning of process, then stabilizes, and finally
gradually decreases. The changing process is shown in
Figure 1. Because of the Fourier's Law, the gas
emission can be estimated through the rule of the
concentration change. The concentration C x y z t( , , , )
can be expressed as Eq.(2). The trend of gas emission
with time is shown in Eq.(3) . Among them, Q is the