[英]How to find the location of a point in an image in millimeters using camera matrix?
我使用的是標准的 640x480 網絡攝像頭。 我已經在 Python 3 的 OpenCV 中完成了相機校准。這是我正在使用的代碼。 該代碼正在運行,並成功地為我提供了相機矩陣和失真系數。 現在,如何在我的場景圖像中找到640 像素中有多少毫米。 我將網絡攝像頭水平連接在桌子上方,並在桌子上放置了一個機械臂。 使用相機我找到了一個物體的質心。 使用相機矩陣,我的目標是將該對象的位置(例如 300x200 像素)轉換為毫米單位,以便我可以將毫米給機械臂以拾取該對象。 我已經搜索過但沒有找到任何相關信息。 請告訴我有什么方程式或方法可以解決這個問題。 非常感謝!
import numpy as np
import cv2
import yaml
import os
# Parameters
#TODO : Read from file
n_row=4 #Checkerboard Rows
n_col=6 #Checkerboard Columns
n_min_img = 10 # number of images needed for calibration
square_size = 40 # size of each individual box on Checkerboard in mm
criteria = (cv2.TERM_CRITERIA_EPS + cv2.TERM_CRITERIA_MAX_ITER, 30, 0.001) # termination criteria
corner_accuracy = (11,11)
result_file = "./calibration.yaml" # Output file having camera matrix
# prepare object points, like (0,0,0), (1,0,0), (2,0,0) ....,(n_row-1,n_col-1,0)
objp = np.zeros((n_row*n_col,3), np.float32)
objp[:,:2] = np.mgrid[0:n_row,0:n_col].T.reshape(-1,2) * square_size
# Intialize camera and window
camera = cv2.VideoCapture(0) #Supposed to be the only camera
if not camera.isOpened():
print("Camera not found!")
quit()
width = int(camera.get(cv2.CAP_PROP_FRAME_WIDTH))
height = int(camera.get(cv2.CAP_PROP_FRAME_HEIGHT))
cv2.namedWindow("Calibration")
# Usage
def usage():
print("Press on displayed window : \n")
print("[space] : take picture")
print("[c] : compute calibration")
print("[r] : reset program")
print("[ESC] : quit")
usage()
Initialization = True
while True:
if Initialization:
print("Initialize data structures ..")
objpoints = [] # 3d point in real world space
imgpoints = [] # 2d points in image plane.
n_img = 0
Initialization = False
tot_error=0
# Read from camera and display on windows
ret, img = camera.read()
cv2.imshow("Calibration", img)
if not ret:
print("Cannot read camera frame, exit from program!")
camera.release()
cv2.destroyAllWindows()
break
# Wait for instruction
k = cv2.waitKey(50)
# SPACE pressed to take picture
if k%256 == 32:
print("Adding image for calibration...")
imgGray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
# Find the chess board corners
ret, corners = cv2.findChessboardCorners(imgGray, (n_row,n_col),None)
# If found, add object points, image points (after refining them)
if not ret:
print("Cannot found Chessboard corners!")
else:
print("Chessboard corners successfully found.")
objpoints.append(objp)
n_img +=1
corners2 = cv2.cornerSubPix(imgGray,corners,corner_accuracy,(-1,-1),criteria)
imgpoints.append(corners2)
# Draw and display the corners
imgAugmnt = cv2.drawChessboardCorners(img, (n_row,n_col), corners2,ret)
cv2.imshow('Calibration',imgAugmnt)
cv2.waitKey(500)
# "c" pressed to compute calibration
elif k%256 == 99:
if n_img <= n_min_img:
print("Only ", n_img , " captured, ", " at least ", n_min_img , " images are needed")
else:
print("Computing calibration ...")
ret, mtx, dist, rvecs, tvecs = cv2.calibrateCamera(objpoints, imgpoints, (width,height),None,None)
if not ret:
print("Cannot compute calibration!")
else:
print("Camera calibration successfully computed")
# Compute reprojection errors
for i in range(len(objpoints)):
imgpoints2, _ = cv2.projectPoints(objpoints[i], rvecs[i], tvecs[i], mtx, dist)
error = cv2.norm(imgpoints[i],imgpoints2, cv2.NORM_L2)/len(imgpoints2)
tot_error += error
print("Camera matrix: ", mtx)
print("Distortion coeffs: ", dist)
print("Total error: ", tot_error)
print("Mean error: ", np.mean(error))
# Saving calibration matrix
try:
os.remove(result_file) #Delete old file first
except Exception as e:
#print(e)
pass
print("Saving camera matrix .. in ",result_file)
data={"camera_matrix": mtx.tolist(), "dist_coeff": dist.tolist()}
with open(result_file, "w") as f:
yaml.dump(data, f, default_flow_style=False)
# ESC pressed to quit
elif k%256 == 27:
print("Escape hit, closing...")
camera.release()
cv2.destroyAllWindows()
break
# "r" pressed to reset
elif k%256 ==114:
print("Reset program...")
Initialization = True
這是相機矩陣:
818.6 0 324.4
0 819.1 237.9
0 0 1
失真系數:
0.34 -5.7 0 0 33.45
再見,
我實際上認為您應該能夠以簡單的方式解決您的問題:
mm_per_pixel = real_mm_width : 640px
假設相機最初與要拾取的對象平行於計划移動 [即固定距離], real_mm_width
可以找到real_mm_width
測量與圖片的640
像素對應的物理距離。 舉個例子,假設你發現real_mm_width = 32cm = 320mm
,所以你得到mm_per_pixel = 0.5mm/px
。 在固定距離下,這個比率不會改變
官方文檔中似乎也有建議:
這種考慮有助於我們僅找到 X、Y 值。 現在對於 X,Y 值,我們可以簡單地將點傳遞為 (0,0)、(1,0)、(2,0)、...表示點的位置。 在這種情況下,我們得到的結果將是國際象棋棋盤格大小的比例。 但是如果我們知道正方形的大小(比如 30 毫米),我們可以將值傳遞為 (0,0), (30,0), (60,0), ... 。 因此,我們得到以毫米為單位的結果
然后您只需要使用以下方法將質心坐標(例如(pixel_x_centroid, pixel_y_centroid) = (300px, 200px)
] 轉換為 mm:
mm_x_centroid = pixel_x_centroid * mm_per_pixel
mm_y_centroid = pixel_y_centroid * mm_per_pixel
這會給你最終的答案:
(mm_x_centroid, mm_y_centroid) = (150mm, 100mm)
另一種看待同一事物的方式是這個比例,其中第一個成員是可測量/已知比率:
real_mm_width : 640px = mm_x_centroid : pixel_x_centroid = mm_y_centroid = pixel_y_centroid
祝你有美好的一天,
安東尼諾
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