[英]How should I crop out a non-rectangular, non-polygon ROI in opencv?
[英]What's the most efficient way to select a non-rectangular ROI of an Image in OpenCV?
我想創建一個二進制圖像蒙版,在python中僅包含一和零。 感興趣的區域(白色)是非矩形的,由4個角點定義,例如:
在我的方法中,我首先計算ROI上下邊界的線方程,然后檢查每個遮罩元素是否小於邊界元素。 該代碼可以正常工作,但是速度很慢。 2000x1000遮罩最多需要4秒鍾來處理我的機器。
from matplotlib import pyplot as plt
import cv2
import numpy as np
import time
def line_eq(line):
"""input:
2 points of a line
returns:
slope and intersection of the line
"""
(x1, y1), (x2, y2) = line
slope = (y2 - y1) / float((x2 - x1))
intersect = int(slope * (-x1) + y1)
return slope,intersect
def maskByROI(mask,ROI):
"""
input:
ROI: with 4 corner points e.g. ((x0,y0),(x1,y1),(x2,y2),(x3,y3))
mask:
output:
mask with roi set to 1, rest to 0
"""
line1 = line_eq((ROI[0],ROI[1]))
line2 = line_eq((ROI[2],ROI[3]))
slope1 = line1[0]
intersect1 = line1[1]
#upper line
if slope1>0:
for (x,y), value in np.ndenumerate(mask):
if y > slope1*x +intersect1:
mask[x,y] = 0
else:
for (x,y), value in np.ndenumerate(mask):
if y < slope1*x +intersect1:
mask[x,y] = 0
#lower line
slope2 = line2[0]
intersect2 = line2[1]
if slope2<0:
for (x,y), value in np.ndenumerate(mask):
if y > slope2*x +intersect2:
mask[x,y] = 0
else:
for (x,y), value in np.ndenumerate(mask):
if y < slope2*x +intersect2:
mask[x,y] = 0
return mask
mask = np.ones((2000,1000))
myROI = ((750,0),(900,1000),(1000,1000),(1500,0))
t1 = time.time()
mask = maskByROI(mask,myROI)
t2 = time.time()
print "execution time: ", t2-t1
plt.imshow(mask,cmap='Greys_r')
plt.show()
創建這樣的蒙版的更有效方法是什么?
對於numpy,OpenCV或類似的庫提供的非矩形形狀是否有任何類似的解決方案?
用fillPoly
繪制遮罩:
mask = np.ones((1000, 2000)) # (height, width)
myROI = [(750, 0), (900, 1000), (1000, 1000), (1500, 0)] # (x, y)
cv2.fillPoly(mask, [np.array(myROI)], 0)
這大約需要1ms。
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