cv2边缘检测 填充_JetBot AI计算机视觉自动驾驶机器人 -- 车道检测

通常,汽车道路上都会有白色的分道线,汽车在路上行驶时,必须在车道内行驶,这样才能保持道路秩序;想要自动驾驶,也就需要车道识别,才能让汽车沿着车道行驶。传统的车道识别通过摄像头实时采集道路信息,通过计算机视觉处理,来识别出车道。
具体的做法是,摄像头读入一帧图像,对图像进行畸变校正,变成黑白图片,高斯降噪,然后用二值化边缘检测(canny)或 sobel,分析边缘信息,得到车道信息(角度、是否偏离车道等)。
下面描述 jetbot 下,使用Python 和 OpenCV 做车道检测的具体过程:
- 相机校准
- 图像采集
- 边缘检测
- 矩形二维映射
- 车道识别与拟合
相机校准
我们知道,摄像头特别是广角摄像头,拍摄的照片通常都会有畸变(桶形畸变、枕形畸变),这样在通过摄像头采集的图片就需要校正,以修正失真。通常的校准方法是通过采集摄像头的棋盘格拍摄图像,然后通过OpenCV进行计算校准。具体算法和原理,大家可以网上搜。
准备图片

如上图所示的棋盘格图片,下载后打印到A4纸上,固定贴到墙上或者贴到硬板上,然后按下图的位置,拍摄20张图片,(不同角度、不同位置)
这里代码中提供了独立的摄像头采集图片代码:
python tegra_cam.py --width 320 --height 240 --path cap_imgs
每按一次's'键就会保存一张图片。

准备好图片后,就可以运行代码,进行校准了;
python calibrate_camera.py --imgpath cal_imgs --imgfile calibration.jpg
这里假设图片保存在运行代码的cal_imgs目录,图片以calibration1-20.jpg命名。运行后会保存校准参数文件到camera_cal320-240.p中,这里的320 240是之前采集的图片文件的分辨率。
车道检测
图像采集:

校正图片:
image=cv2.imread(image_file)
height = image.shape[0]
width = image.shape[1]
#读入校准参数
cal_file = 'ncamera_cal' + str(width) + '-' + str(height) + '.p'
with open(cal_file, 'rb') as f:
# with open('camera_cal640-480.p', 'rb') as f:
save_dict = pickle.load(f)
mtx = save_dict['mtx']
dist = save_dict['dist']
#校准图片
undis_image = cv2.undistort(image, mtx, dist, None, mtx)

二值化边缘检测:
canny_image = canny( undis_image )
def canny( image ):
gray = cv2.cvtColor(image, cv2.COLOR_RGB2GRAY)
#双边滤波,平滑去噪的同时很好得保存边沿
# blur = cv2.bilateralFilter(gray, 11, 17,17)
blur = cv2.GaussianBlur(gray, (5,5), 0)
canny = cv2.Canny(blur, 25, 150)
return canny

二维映射:
我们知道,车道是一个长条的矩形,在图片中,按照成像原理,会有会聚效应,看着是个梯型,这样想要准确还原车道的角度,就需要做二维映射,还原,opencv提供了很好的映射算法。
m, m_inv, src = transform_matrix_640()
if width == 320:
m, m_inv, src = transform_matrix_320()
wraped_image = cv2.warpPerspective(canny_image, m, (width, height), flags=cv2.INTER_LINEAR)
def transform_matrix_320():
src = np.float32(
[[0, 239],
[82,120], #196,160
[237,120], #443, 160 223
[319, 239]])
dst = np.float32(
[[50, 239],
[50, 0],
[269, 0],
[269, 239]])
# dst = np.float32(
# [[0, 239],
# [0, 0],
# [319, 0],
# [319, 239]])
m = cv2.getPerspectiveTransform(src, dst)
m_inv = cv2.getPerspectiveTransform(dst, src)
return m, m_inv, src
这里的转换矩阵是如何确定的呢,首先我们可以使用二值化边缘检测后的图片(确保采集时摄像头是正的,且居中)。象图中红线那样,确定四个角点即可。


映射后得到的车道图片
车道检测:
上图中的二值图片,我们有几个方式得到车道的几何信息,比如:可以通过 cv2.HoughLinesP 来得到车道的几何信息。
这里我们通过点的二阶拟合的方式得到车道信息,首先需要知道车道点在哪里,采用直方图的方式沿x轴统计点数,在左右车道处会有峰值,得到起始点,在此起始点上,通过滑动窗口的方式,得到两个车道的所有点,然后通过二阶拟合,得到车道信息。

def line_fit_with_image( image ):
width = image.shape[1]
height = image.shape[0]
# Take a histogram of the bottom half of the image
histogram = np.sum(image[200:,:], axis=0) #height//2
midpoint = np.int(histogram.shape[0]/2)
leftx_base = np.argmax(histogram[0:midpoint])
rightx_base = np.argmax(histogram[midpoint:]) + midpoint
# Choose the number of sliding windows
nwindows = 8
# Set height of windows
window_height = np.int(height/nwindows)
# Identify the x and y positions of all nonzero pixels in the image
nonzero = image.nonzero()
nonzeroy = np.array(nonzero[0])
nonzerox = np.array(nonzero[1])
# Current positions to be updated for each window
leftx_current = leftx_base
rightx_current = rightx_base
# Set the width of the windows +/- margin
margin = int(width/16)
# Set minimum number of pixels found to recenter window
minpix = 15
# Create empty lists to receive left and right lane pixel indices
left_lane_inds = []
right_lane_inds = []
# Step through the windows one by one
for window in range(nwindows):
# Identify window boundaries in x and y (and right and left)
win_y_low =height - (window+1)*window_height
win_y_high =height - window*window_height
win_xleft_low = leftx_current - margin
win_xleft_high = leftx_current + margin
win_xright_low = rightx_current - margin
win_xright_high = rightx_current + margin
# Identify the nonzero pixels in x and y within the window
good_left_inds = ((nonzeroy >= win_y_low) & (nonzeroy < win_y_high) & (nonzerox >= win_xleft_low) & (nonzerox < win_xleft_high)).nonzero()[0]
good_right_inds = ((nonzeroy >= win_y_low) & (nonzeroy < win_y_high) & (nonzerox >= win_xright_low) & (nonzerox < win_xright_high)).nonzero()[0]
# Append these indices to the lists
left_lane_inds.append(good_left_inds)
right_lane_inds.append(good_right_inds)
# If you found > minpix pixels, recenter next window on their mean position
if len(good_left_inds) > minpix:
leftx_current = np.int(np.mean(nonzerox[good_left_inds]))
if len(good_right_inds) > minpix:
rightx_current = np.int(np.mean(nonzerox[good_right_inds]))
# Concatenate the arrays of indices
left_lane_inds = np.concatenate(left_lane_inds)
right_lane_inds = np.concatenate(right_lane_inds)
# Extract left and right line pixel positions
leftx = nonzerox[left_lane_inds]
lefty = nonzeroy[left_lane_inds]
rightx = nonzerox[right_lane_inds]
righty = nonzeroy[right_lane_inds]
if lefty is None or righty is None:
return None, 0
if len(lefty ) == 0 or len(righty ) == 0 :
return None, 0
line_image = np.zeros((height, width, 3), dtype=np.uint8)
# line_image = (np.dstack((image, image, image))*255).astype('uint8')
window_img = np.zeros_like(line_image)
#二阶拟合,求切线
left_line, left_fit, left_x0, kl = line_of_poly( leftx, lefty, int(height-height/4-1), height -1, int( height / 6) ) # x = ay^2 + by + c
right_line, right_fit, right_x0, kr = line_of_poly( rightx, righty, int(height-height/4-1), height-1, int(height/6) )
#中间目标线
k0 = (kl + kr)/2
x0 = (left_x0 + right_x0)/2
y0 = height - 1
y1 = int(height/6)
x1 = k0 * (y1 - y0) + x0
avg_theta = math.atan2( y1 - y0, x1-x0 )
x0 = int(x0)
x1 = int( x1 )
goal_line = np.array([x0, y0, x1, y1 ])
# Color in left and right line pixels
line_image[nonzeroy[left_lane_inds], nonzerox[left_lane_inds]] = [234, 217, 53]
line_image[nonzeroy[right_lane_inds], nonzerox[right_lane_inds]] = [234, 217, 53]
cnt = int(height / 10)
ploty = np.linspace(0, height -1, cnt )
left_fitx = left_fit[0]*ploty**2 + left_fit[1]*ploty + left_fit[2]
right_fitx = right_fit[0]*ploty**2 + right_fit[1]*ploty + right_fit[2]
for i in range(cnt - 1) :
xl0 = int( left_fitx[i])
xr0 = int(right_fitx[i])
y0 = int(ploty[i])
xl1 = int(left_fitx[i + 1])
xr1 = int(right_fitx[i+1])
y1 = int(ploty[i+1])
cv2.line( line_image, (xl0,y0), (xl1, y1), (76, 177, 34), 1 )
cv2.line( line_image, (xr0,y0), (xr1, y1), (76, 177, 34), 1 )
# x1,y1,x2,y2 = lines[0].reshape(4)
# cv2.line( line_image, (x1,y1), (x2, y2), (0, 0, 255), 2 )
# x1,y1,x2,y2 = lines[1].reshape(4)
# cv2.line( line_image, (x1,y1), (x2, y2), (0, 0, 255), 2 )
x1,y1,x2,y2 = goal_line.reshape(4)
cv2.line( line_image, (x1,y1), (x2, y2), (36, 28, 237), 3 )
left_line_window1 = np.array([np.transpose(np.vstack([left_fitx-margin, ploty]))])
left_line_window2 = np.array([np.flipud(np.transpose(np.vstack([left_fitx+margin, ploty])))])
left_line_pts = np.hstack((left_line_window1, left_line_window2))
right_line_window1 = np.array([np.transpose(np.vstack([right_fitx-margin, ploty]))])
right_line_window2 = np.array([np.flipud(np.transpose(np.vstack([right_fitx+margin, ploty])))])
right_line_pts = np.hstack((right_line_window1, right_line_window2))
# Draw the lane onto the warped blank image
cv2.fillPoly(window_img, np.int_([left_line_pts]), (29,230, 181))
cv2.fillPoly(window_img, np.int_([right_line_pts]), (29,230, 181))
line_image = cv2.addWeighted(line_image, 1, window_img, 0.3, 0)
d_center =int( width/2 - (left_x0 + right_x0)/2)
return line_image, avg_theta, d_center

控制计算,还原:

代码:
