# A Novel Approach to Wearable Image Recognition Systems to Aid Visually Impaired People
## 3 Model and Algorithm
### Point of Interest Capture Algorithm Based on Multi-Sensor  
The smart devices proposed in [19] and [23] obtain results by continuously scanning spatial information, which can bring more complete scene information and experience to users, but it will also bring a series of negative effects. First, continuous scanning requires hardware devices with extremely high processing power to ensure real-time performance.  
Secondly, when there are many objects and people in the scene, even if the recognition speed is fast, the speed of the speech feedback to the user cannot keep up, because the pace of speech usually needs to be uniform to make people understand. Finally, continuous scanning can also lead to increased power consumption and impact on usage time.  
Therefore, in this paper, an algorithm is designed to obtain the \"point of interest\" for recognition. Ultrasonic sensors and IR sensors are used to identify \"points of interest\" (usually people, larger objects, etc.) and then let the user select whether to identify through a touch button.  
The calculation formula of ultrasonic ranging is shown in Equation (1):  
\[S=\frac{1}{2}c\times t \tag{1}\]  
where \(S\) is the measured distance, \(c\) is the ultrasonic propagation speed, and \(t\) is the transit time.  
The speed of sound in an ideal gas is shown in Equation (2).  
\[c=\sqrt{\frac{vRT}{\mu}},v=1.40,R=8.314\ \mathrm{kg}/(\mathrm{mol}\cdot K),T,\mu=2. 8\times 10^{-3}\ \mathrm{kg}/\mathrm{mol} \tag{2}\]  
After substituting the parameters, the approximate formula for the speed of sound is shown in Equation (3).  
\[c=331.5+0.6t \tag{3}\]  
where \(t\) is centigrade, \(t=T-273.5\).  
If the ultrasonic sensor detects an obstacle within the detection range, the infrared sensing sensor detects whether the target contains the human body. This situation can be denoted by \(X\). If the human body is detected, a prompt tone is immediately sent back to the user. The user can choose whether to start the identification by himself or not, and the status is denoted by \(P\). It is mainly for the visually impaired to quickly understand the situation of the surrounding people, such as finding friends at the party and looking for family members indoors. \(X\) and \(P\) as two state functions can be expressed as Equations (4) and (5).  
\[X=\left\{\begin{array}{l}1,if\big{|}d\big{|}\big{|}\big{|}\big{|}d_{0}\big{|} \big{|}\big{|}\big{|}\big{|}\big{|}\big{|}\big{|}\big{|}\big{|}\big{|}\big{|} \\ 0,if\ \mathrm{others}\end{array}\right. \tag{4}\]  
where \(d\) represents the distance measured by the ultrasonic sensor, \(d_{0}(=\)100 cm) represents the set maximum distance of detection, \(r\) represents the distance detected by the infrared sensor, and \(r_{0}(=100\ \mathrm{cm})\) represents the maximum detection range.  
\[P=\left\{\begin{array}{l}1,if\ \mathrm{user\ \mathit{press}\ \mathit{the}\ \mathit{button}\\ 0,if\ \mathrm{others}\end{array}\right. \tag{5}\]  
Detailed execution steps are shown in Figure 6. The recognition result will include the number of people in the scene, personnel information (name, expression), the name of the object contained in the scene and the text information. The feedback mechanism will be introduced in the next section. Figure 6 shows the detailed algorithm flow chart of the scheme.