大尺度遥感线性地物（道路）提取后细化（骨架提取）

2023年5月30日 265点热度 3人点赞 0条评论

提出问题

遥感影像研究中，经常出现线性地物需要对其连通性进行分析，重要的一步是对其骨架进行提取，或者叫做细化操作。该步骤如果直接对整个地物进行细化，往往出现如下问题，如图1，边缘毛刺很多。

解决方法

为了解决上述问题，我们首先对大尺度影像进行裁剪，裁剪成512*512像素，裁剪拼接代码这里不给出，其他博客可搜索。然后，对小块影像进行细化操作。最后拼接成大块。细化操作代码如下：

import cv2
import numpy as np
import matplotlib.pyplot as plt
import glob
import os

# hilditch thining
def hilditch(img):
    # get shape
    H, W, C = img.shape

    # prepare out image
    out = np.zeros((H, W))
    out[img[..., 0] > 0] = 1

    # inverse pixel value
    tmp = out.copy()
    _tmp = 1 - tmp

    count = 1
    while count > 0:
        count = 0
        tmp = out.copy()
        _tmp = 1 - tmp

        tmp2 = out.copy()
        _tmp2 = 1 - tmp2

        # each pixel
        for y in range(H):
            for x in range(W):
                # skip black pixel
                if out[y, x] < 1:
                    continue

                judge = 0

                ## condition 1
                if (tmp[y, min(x+1, W-1)] * tmp[max(y-1,0 ), x] * tmp[y, max(x-1, 0)] * tmp[min(y+1, H-1), x]) == 0:
                    judge += 1

                ## condition 2
                c = 0
                c += (_tmp[y, min(x+1, W-1)] - _tmp[y, min(x+1, W-1)] * _tmp[max(y-1, 0), min(x+1, W-1)] * _tmp[max(y-1, 0), x])
                c += (_tmp[max(y-1, 0), x] - _tmp[max(y-1, 0), x] * _tmp[max(y-1, 0), max(x-1, 0)] * _tmp[y, max(x-1, 0)])
                c += (_tmp[y, max(x-1, 0)] - _tmp[y, max(x-1, 0)] * _tmp[min(y+1, H-1), max(x-1, 0)] * _tmp[min(y+1, H-1), x])
                c += (_tmp[min(y+1, H-1), x] - _tmp[min(y+1, H-1), x] * _tmp[min(y+1, H-1), min(x+1, W-1)] * _tmp[y, min(x+1, W-1)])
                if c == 1:
                    judge += 1

                ## condition 3
                if np.sum(tmp[max(y-1, 0) : min(y+2, H), max(x-1, 0) : min(x+2, W)]) >= 3:
                    judge += 1

                ## condition 4
                if np.sum(out[max(y-1, 0) : min(y+2, H), max(x-1, 0) : min(x+2, W)]) >= 2:
                    judge += 1

                ## condition 5
                _tmp2 = 1 - out

                c = 0
                c += (_tmp2[y, min(x+1, W-1)] - _tmp2[y, min(x+1, W-1)] * _tmp2[max(y-1, 0), min(x+1, W-1)] * _tmp2[max(y-1, 0), x])
                c += (_tmp2[max(y-1, 0), x] - _tmp2[max(y-1, 0), x] * (1 - tmp[max(y-1, 0), max(x-1, 0)]) * _tmp2[y, max(x-1, 0)])
                c += (_tmp2[y, max(x-1, 0)] - _tmp2[y, max(x-1, 0)] * _tmp2[min(y+1, H-1), max(x-1, 0)] * _tmp2[min(y+1, H-1), x])
                c += (_tmp2[min(y+1, H-1), x] - _tmp2[min(y+1, H-1), x] * _tmp2[min(y+1, H-1), min(x+1, W-1)] * _tmp2[y, min(x+1, W-1)])
                if c == 1 or (out[max(y-1, 0), max(x-1,0 )] != tmp[max(y-1, 0), max(x-1, 0)]):
                    judge += 1

                c = 0
                c += (_tmp2[y, min(x+1, W-1)] - _tmp2[y, min(x+1, W-1)] * _tmp2[max(y-1, 0), min(x+1, W-1)] * (1 - tmp[max(y-1, 0), x]))
                c += ((1-tmp[max(y-1, 0), x]) - (1 - tmp[max(y-1, 0), x]) * _tmp2[max(y-1, 0), max(x-1, 0)] * _tmp2[y, max(x-1, 0)])
                c += (_tmp2[y, max(x-1,0 )] - _tmp2[y, max(x-1,0 )] * _tmp2[min(y+1, H-1), max(x-1, 0)] * _tmp2[min(y+1, H-1), x])
                c += (_tmp2[min(y+1, H-1), x] - _tmp2[min(y+1, H-1), x] * _tmp2[min(y+1, H-1), min(x+1, W-1)] * _tmp2[y, min(x+1, W-1)])
                if c == 1 or (out[max(y-1, 0), x] != tmp[max(y-1, 0), x]):
                    judge += 1

                c = 0
                c += (_tmp2[y, min(x+1, W-1)] - _tmp2[y, min(x+1, W-1)] * (1 - tmp[max(y-1, 0), min(x+1, W-1)]) * _tmp2[max(y-1, 0), x])
                c += (_tmp2[max(y-1, 0), x] - _tmp2[max(y-1, 0), x] * _tmp2[max(y-1, 0), max(x-1, 0)] * _tmp2[y, max(x-1, 0)])
                c += (_tmp2[y, max(x-1, 0)] - _tmp2[y, max(x-1, 0)] * _tmp2[min(y+1, H-1), max(x-1, 0)] * _tmp2[min(y+1, H-1), x])
                c += (_tmp2[min(y+1, H-1), x] - _tmp2[min(y+1, H-1), x] * _tmp2[min(y+1, H-1), min(x+1, W-1)] * _tmp2[y, min(x+1, W-1)])
                if c == 1 or (out[max(y-1, 0), min(x+1, W-1)] != tmp[max(y-1, 0), min(x+1, W-1)]):
                    judge += 1

                c = 0
                c += (_tmp2[y, min(x+1, W-1)] - _tmp2[y, min(x+1, W-1)] * _tmp2[max(y-1, 0), min(x+1, W-1)] * _tmp2[max(y-1, 0), x])
                c += (_tmp2[max(y-1, 0), x] - _tmp2[max(y-1, 0), x] * _tmp2[max(y-1, 0), max(x-1, 0)] * (1 - tmp[y, max(x-1, 0)]))
                c += ((1 - tmp[y, max(x-1, 0)]) - (1 - tmp[y, max(x-1, 0)]) * _tmp2[min(y+1, H-1), max(x-1, 0)] * _tmp2[min(y+1, H-1), x])
                c += (_tmp2[min(y+1, H-1), x] - _tmp2[min(y+1, H-1), x] * _tmp2[min(y+1, H-1), min(x+1, W-1)] * _tmp2[y, min(x+1, W-1)])
                if c == 1 or (out[y, max(x-1, 0)] != tmp[y, max(x-1, 0)]):
                    judge += 1

                if judge >= 8:
                    out[y, x] = 0
                    count += 1

    out = out.astype(np.uint8) * 255

    return out

# Read image
image_path = './xihua/input/*.jpg'
for img_path in glob.glob(image_path):
    name_out = os.path.split(img_path)[1]
    print ('正在处理{}'.format(name_out))
    img = cv2.imread(img_path).astype(np.float32)
    _,RedThresh = cv2.threshold(img,127,255,cv2.THRESH_BINARY)
    RedThresh = cv2.medianBlur(RedThresh, ksize=3)
    #OpenCV定义的结构矩形元素
    kernel = cv2.getStructuringElement(cv2.MORPH_RECT,(3, 3))
    eroded = cv2.erode(RedThresh,kernel,iterations = 1)        #腐蚀图像
    dilated = cv2.dilate(eroded,kernel,iterations = 1)      #膨胀图像
    # hilditch thining
    out = hilditch(dilated)

    # Save result
    cv2.imwrite('./xihua/output/{}'.format(name_out), out)