从图像(地图)中提取多边形坐标 [英] Extract polygon coordinates from image (map)
问题描述
我有以下地图:
我想提取多边形坐标(像素),我正在使用以下代码段,但是内标的图像全为0(否):
I want to extract the polygon coordinates (pixls), I am using the following code snipt, but the inteverted labeled image is all 0's (False):
import numpy as np
from skimage import io, measure, morphology
from skimage.io import imsave, imread
img = io.imread('map.png', as_gray=True)
imsave("test.png", img)
img = morphology.binary_dilation(img, selem=np.ones((5,5)))
img_inverted = np.invert(img)
img_inverted_labeled = measure.label(img_inverted)
n_lbls = np.unique(img_inverted_labeled)[1:]
pols = []
for i in n_lbls:
img_part = (img_inverted_labeled == i)
pols.append(measure.find_contours(img_part, level=0)[0])
反转的图像如下:
我相信,该行的探针位于selem的值中:
I belive the probem is in the value of the selem in this line:
img = morphology.binary_dilation(img, selem=np.ones((5,5)))
能否请您告知此代码有什么问题.
Could you please advise what is the problem in this code..
编辑 反转图像(灰度)时的唯一值:
EDIT The unique values if the inverted image (grayscaled):
[235, 227, 219, 212, 204, 230, 215, 199, 207, 188, 184, 172, 176, 196, 192, 179, 223, 211, 203, 173, 191, 228, 216, 232, 200, 208, 171, 183, 175, 180, 195, 236, 221, 234, 233, 226, 220]
我认为我需要根据某个阈值将这些值分为两类(白色/黑色).您能否确认我的发现?如果可以,我该如何计算该值?
I think I need to classify these value into two categories (white/black) based on some threshold value. Could you please confirm my finding, and if it is so how can I calculate this value?
推荐答案
是的,这里的阈值是可行的.查看图像0.7
的最小值和最大值似乎是合理的:
Yes a threshold here would work. Having a look at the minimum and maximum values of the image 0.7
seems reasonable:
import numpy as np
from skimage import io, measure, morphology
from skimage.io import imsave, imread
from matplotlib import pyplot as plt
img = io.imread('map.png', as_gray=True)
# do thresholding
mask = img < 0.7
plt.matshow(mask, cmap='gray')
# ij coords of perimeter
coords = np.nonzero(mask)
coords
>>> (array([ 61, 61, 61, ..., 428, 428, 428]),
array([200, 201, 202, ..., 293, 294, 295]))
如果您只想要边界线而不是面积(因为它具有宽度),则可以执行以下操作:
And if you just want the perimeter line rather than area (as it has a width) then you could do:
from skimage.morphology import skeletonize
fig, ax = plt.subplots(dpi=150)
ax.matshow(skeletonize(mask), cmap='gray')
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