MicroMV 人脸识别

• 基本原理

MicroMV捕捉人脸获取人脸坐标 通过pid.py算法计算出舵机将要转动的角度，并通过串口发送给microduino microduino接收数据后控制舵机

1、快速上手

把pid.py复制到MicroMV生成的U盘空间中
pid.py:

from pyb import millis
from math import pi, isnan
class PID:
    _kp = _ki = _kd = _integrator = _imax = 0
    _last_error = _last_derivative = _last_t = 0
    _RC = 1/(2 * pi * 20)
    def __init__(self, p=0, i=0, d=0, imax=0):
        self._kp = float(p)
        self._ki = float(i)
        self._kd = float(d)
        self._imax = abs(imax)
        self._last_derivative = float('nan')

    def get_pid(self, error, scaler):
        tnow = millis()
        dt = tnow - self._last_t
        output = 0
        if self._last_t == 0 or dt > 1000:
            dt = 0
            self.reset_I()
        self._last_t = tnow
        delta_time = float(dt) / float(1000)
        output += error * self._kp
        if abs(self._kd) > 0 and dt > 0:
            if isnan(self._last_derivative):
                derivative = 0
                self._last_derivative = 0
            else:
                derivative = (error - self._last_error) / delta_time
            derivative = self._last_derivative + \
                                     ((delta_time / (self._RC + delta_time)) * \
                                        (derivative - self._last_derivative))
            self._last_error = error
            self._last_derivative = derivative
            output += self._kd * derivative
        output *= scaler
        if abs(self._ki) > 0 and dt > 0:
            self._integrator += (error * self._ki) * scaler * delta_time
            if self._integrator < -self._imax: self._integrator = -self._imax
            elif self._integrator > self._imax: self._integrator = self._imax
            output += self._integrator
        return output
    def reset_I(self):
        self._integrator = 0
        self._last_derivative = float('nan')

把face_detection1024.py替换到MicroMV生成的U盘空间中的main.py做为主程序
face_detection1024.py:

import sensor, time, image
from pyb import UART
from pid import PID
from pyb import LED
import json
red_led   = LED(1)
green_led = LED(2)
blue_led  = LED(3)
ir_led    = LED(4)
pan_pid = PID(p=0.42, i=0.01, imax=90)
tilt_pid = PID(p=0.22, i=0.005, imax=90)
pan_servo_pos=90
tilt_servo_pos=90
pan_center = 60
tilt_center = 40
# Reset sensor
sensor.reset()
# Sensor settings
sensor.set_contrast(1)
sensor.set_gainceiling(16)
# HQVGA and GRAYSCALE are the best for face tracking.
sensor.set_framesize(sensor.HQQVGA)
sensor.set_pixformat(sensor.GRAYSCALE)
sensor.set_brightness(-3)
# Load Haar Cascade
# By default this will use all stages, lower satges is faster but less accurate.
face_cascade = image.HaarCascade("frontalface", stages=25)
print(face_cascade)
# FPS clock
clock = time.clock()
uart = UART(4, 115200)
while (True):
    clock.tick()
    # Capture snapshot
    img = sensor.snapshot()
    # Find objects.
    # Note: Lower scale factor scales-down the image more and detects smaller objects.
    # Higher threshold results in a higher detection rate, with more false positives.
    objects = img.find_features(face_cascade, threshold=0.75, scale_factor=1.25)
    # Draw objects
    for r in objects:
        red_led.on()
        img.draw_rectangle(r)
        pan_center = int(r[0]+r[2]/2)
        tilt_center = int(r[1]+r[3]/2)
        img.draw_cross(pan_center, tilt_center)
        pan_error = pan_center-img.width()/2
        tilt_error = tilt_center-img.height()/2
        pan_output=pan_pid.get_pid(pan_error,1)/3
        tilt_output=tilt_pid.get_pid(tilt_error,1)
        pan_servo_pos=int(pan_servo_pos-pan_output)
        tilt_servo_pos=int(tilt_servo_pos+tilt_output)
        if pan_servo_pos>=170:
           pan_servo_pos=170
        if pan_servo_pos<=10:
           pan_servo_pos=10
        if tilt_servo_pos>=160:
           tilt_servo_pos=160
        if tilt_servo_pos<=30:
           tilt_servo_pos=30
        output_str="[%d,%d,%d]" % (pan_servo_pos,tilt_servo_pos,r[2])
        print('you send:',output_str)
        uart.write(output_str+'\n')
        red_led.off()

IDE运行效果为

屏幕中有人脸就会用方框注明

2、知识延伸

函数：

• 函数说明