python - 如何使用 OpenCV 根据特定标准裁剪图像？

Question

我想使用 python 的 OpenCV 库裁剪如下图所示的图像。感兴趣的区域位于顶部和底部的波浪线以及侧面的线内。问题是每个图像都略有不同。这意味着我需要一些自动裁剪感兴趣区域的方法。我猜顶部和侧面会很容易，因为您可以将其裁剪 10 像素左右。但是我怎样才能裁剪出线条不直的图像的下半部分呢？我已包含此示例图像。接下来的图像以粉红色突出显示我有兴趣保留的图像区域。

Answer 1

这是使用 Python/OpenCV 的一种方法。

读取输入

获取中心点(假设它在所需区域内)

图像转灰度

填充灰色图像并将背景设置为黑色

获取最大轮廓及其边界框

绘制黑色背景上填充的最大轮廓作为蒙版

将蒙版应用于输入图像

裁剪蒙版的输入图像

输入:

import cv2
import numpy as np

# load image and get dimensions
img = cv2.imread("odd_region.png")
hh, ww, cc = img.shape

# compute center of image (as integer)
wc = ww//2
hc = hh//2

# create grayscale copy of input as basis of mask
gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)

# create zeros mask 2 pixels larger in each dimension
zeros = np.zeros([hh + 2, ww + 2], np.uint8)

# do floodfill at center of image as seed point
ffimg = cv2.floodFill(gray, zeros, (wc,hc), (255), (0), (0), flags=8)[1]

# set rest of ffimg to black
ffimg[ffimg!=255] = 0

# get contours, find largest and its bounding box 
contours = cv2.findContours(ffimg, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
contours = contours[0] if len(contours) == 2 else contours[1]
area_thresh = 0
for cntr in contours:
    area = cv2.contourArea(cntr)
    if area > area_thresh:
        area = area_thresh
        outer_contour = cntr
        x,y,w,h = cv2.boundingRect(outer_contour)

# draw the filled contour on a black image
mask = np.full([hh,ww,cc], (0,0,0), np.uint8)
cv2.drawContours(mask,[outer_contour],0,(255,255,255),thickness=cv2.FILLED)

# mask the input
masked_img = img.copy()
masked_img[mask == 0] = 0
#masked_img[mask != 0] = img[mask != 0]

# crop the bounding box region of the masked img
result = masked_img[y:y+h, x:x+w]

# draw the contour outline on a copy of result
result_outline = result.copy()
cv2.drawContours(result_outline,[outer_contour],0,(0,0,255),thickness=1,offset=(-x,-y))


# display it
cv2.imshow("img", img)
cv2.imshow("ffimg", ffimg)
cv2.imshow("mask", mask)
cv2.imshow("masked_img", masked_img)
cv2.imshow("result", result)
cv2.imshow("result_outline", result_outline)
cv2.waitKey(0)
cv2.destroyAllWindows()

# write result to disk
cv2.imwrite("odd_region_cropped.png", result)
cv2.imwrite("odd_region_cropped_outline.png", result_outline)

结果:


绘制轮廓的结果: