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0.2847, 0.3004 higher than ALPR and the specificity values of HelpMe with k
equals 2,3,4 are respectively 0.1875, 0.2352, 0.2813 higher than ALPR). Thus our
method HelpMe can provide much higher hit rate than ALPR (0.2598 higher in
sensitivity and 0.2347 higher in specificity averagely). And the larger k value
is, more accurate the method is. But the growth of sensitivity and specificity
becomes less obvious with the k value increases.
Fig. 6. Comparison of Sensitivity and
Specificity of ALPR with HelpMe ( k =2,
Fig. 7. Comparison of Precision and Ac-
curacy of ALPR with HelpMe ( k =2, 3,
Fig. 7 shows the precision and accuracy values of ALPR comparing with
HelpMe with k value equals 2, 3, 4. Obviously, the precision and accuracy of
HelpMe are much higher than the traditional method ALPR. The precision
of HelpMe with k value equals 2, 3, 4 are 0.2132, 0.2899, 0.3007 higher than
ALPR respectively. To accuracy, HelpMe is 0.2571 higher than ALPR averagely.
Besides, the change law of precision and accuracy of HelpMe is just like the sen-
sitivity and specificity of HelpMe. With k increases, the precision and accuracy
become higher but do not increase apparently like before.
Comparison of HelpMe and ALPR in ROC curve. ROC curve is an integrated
indicator which reflects continuous variables of sensitivity and specificity. ROC
curve reveals the relationship between sensitivity and specificity using the method
of composition. The more area under the curve, the higher the prediction accu-
racy is. On the ROC curve, the coordinates of the point closest to the upper left
of figure have both higher threshold of sensitivity and specificity.
The ROC curves of ALPR and HelpMe with k valueequals2,3,4arepre-
sented in Fig. 8. Considering the area under the curve, HelpMe with k value
equals 3 and 4 almost have the equivalent scale of area and the area of HelpMe
with k value equals 4 is just a little larger than that with k value equals 3.
Moreover, ALPR gets the smallest area.Thatistosay,ALPRhasthelowest
prediction accuracy. And considering the shape of all four ROC curves, the coor-
dinates of points on HelpMe ROC curves are much closer to the upper left of the
figure than ALPR. Consequently, HelpMe has higher sensitivity and specificity