查找带有孔的多个对象的轮廓 [英] Find contour of multiple objects with their holes

问题描述

这是来自以下问题的后续问题:如何获得带孔的二元掩模的边界坐标?

This is a follow up question from: How to obtain boundary coordinates of binary mask with holes?

给出相同的图像:

我想为每个对象的外部轮廓及其内部轮廓的(x, y)坐标获取单独的列表.理想情况下，我想使用此列表在单独的空白画布上绘制对象(外部轮廓和内部轮廓).

I want to get a separate list for each object of (x, y)-coordinates of the outer contour and its inner contour. Ideally, I want to use this list to plot the object (outer and inner contour) on a separate blank canvas.

import matplotlib.pyplot as plt # For plotting
import cv2
from skimage import io         # Only needed for web grabbing images, use cv2.imread for local images


# Read image; find contours with hierarchy
blob = io.imread('https://i.stack.imgur.com/Ga5Pe.png')
contours, hier = cv2.findContours(blob, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

# Define sufficient enough colors for blobs
colors = [(255, 0, 0), (0, 255, 0), (0, 0, 255)]

# Draw all contours, and their children, with different colors
out = cv2.cvtColor(blob, cv2.COLOR_GRAY2BGR)
# Check if it's the outer contour
k = -1
# Preallocate list
obj_list = []

for i, cnt in enumerate(contours):
    if (hier[0, i, 3] == -1):
        k += 1
    # cv2.drawContours(out, [cnt], -1, colors[k], 2)
    # Add contour list to object list if it is an inner contour
    obj_list.extend([cnt])

    # Concatenate array in list    
    obj_list = np.vstack(obj_list)    
    obj_list = np.squeeze(obj_list)   
    x = obj_list[:,0].tolist()    
    y = obj_list[:,1].tolist()


cv2.imshow('out', out)
cv2.waitKey(0)
cv2.destroyAllWindows()

可接受的答案仅适用于具有内部轮廓的对象，不适用于没有轮廓的对象.我试图通过添加以下代码来修复它:

The accepted answer only works with objects with inner contours but not for objects without. I tried to fix it by adding the following code:

# Add inner contours of blob to list
cnt_idx = np.squeeze(np.where(hier[0, :, 3] == b_idx))
c_cnt_idx = np.array(cnt_idx)
if c_cnt_idx.size > 0:
    cnt_idx = b_idx

但是我收到以下错误消息:

but I received the following error message:

ValueError:大小为零的操作数的迭代未启用

ValueError: Iteration of zero-sized operands is not enabled

推荐答案

然后，我还将回答这个问题.同样，我跳过了整个绘图部分.而且，正如我先前的回答中所建议的那样，我修改了斑点的发现，以便事先使用NumPy找到正确的斑点索引"(相对于层次结构).

Then I will also answer this question. Again, I skipped the whole plotting part. And, as suggested in my earlier answer, I modified the finding of the blobs, such that the proper "blob indices" (with respect to the hierarchy) are found beforehand using NumPy.

以下是修改后的代码:

import cv2
import numpy as np
from skimage import io         # Only needed for web grabbing images, use cv2.imread for local images

# Read image; add an additional hole; find contours with hierarchy
blob = io.imread('https://i.stack.imgur.com/Ga5Pe.png')
cv2.circle(blob, (380, 120), 25, 0, cv2.FILLED)
contours, hier = cv2.findContours(blob, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

# Define sufficient enough colors for blobs
colors = [(255, 0, 0), (0, 255, 0), (0, 0, 255)]

# Get blob indices with respect to hierarchy
blob_idx = np.squeeze(np.where(hier[0, :, 3] == -1))

# Initialize blob images
blob_imgs = []

# Iterate all blobs
k = 0
for b_idx in np.nditer(blob_idx):

    # Add outer contour of blob to list
    blob_cnts = [contours[b_idx]]

    # Add inner contours of blob to list, if present
    cnt_idx = np.squeeze(np.where(hier[0, :, 3] == b_idx))
    if (cnt_idx.size > 0):
        blob_cnts.extend([contours[c_idx] for c_idx in np.nditer(cnt_idx)])

    # Generate blank BGR image with same size as input; draw contours
    img = np.zeros((blob.shape[0], blob.shape[1], 3), np.uint8)
    cv2.drawContours(img, blob_cnts, -1, colors[k], 2)
    blob_imgs.append(img)
    k += 1

# Just for visualization: Iterate all blob images
k = 0
for img in blob_imgs:
    cv2.imshow(str(k), img)
    k += 1
cv2.waitKey(0)
cv2.destroyAllWindows()

生成了两个输出(我在一个斑点中添加了另一个孔以检查多个内部轮廓):

The two outputs generated (I added another hole in one of the blobs to check for multiple inner contours):

因此，在主循环内，现在将属于一个斑点的所有轮廓存储在blob_cnts中，再次作为(x, y)坐标的列表.因此，您可以生成图或做任何您想做的事情，而不是生成此处所示的不同图像.

So, inside the main loop, you now have all contours belonging to one blob stored in blob_cnts, again as lists of (x, y)-coordinates. So, instead of generating different images as shown here, you can generate plots or do whatever you like.

希望有帮助！

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