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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,

3, 4)

Fig. 7.
Comparison of Precision and Ac-

curacy of ALPR with HelpMe (
k
=2, 3,

4)

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