使用opencv2 python在图像中区分矩形和正方形

Question

我正在学习如何识别所提供图像中的形状。我能够通过几何体上存在的边数来识别形状。但是现在我想知道有没有办法区分图像中的正方形和矩形？ 这是我的代码。目前，我只是在绘制几何图形的轮廓。

import cv2

raw_image = cv2.imread('test1.png')
cv2.imshow('Original Image', raw_image)
cv2.waitKey(0)

bilateral_filtered_image = cv2.bilateralFilter(raw_image, 5, 175, 175)
cv2.imshow('Bilateral', bilateral_filtered_image)
cv2.waitKey(0)

edge_detected_image = cv2.Canny(bilateral_filtered_image, 75, 200)
cv2.imshow('Edge', edge_detected_image)
cv2.waitKey(0)

_, contours, hierarchy = cv2.findContours(edge_detected_image, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

contour_list = []
for contour in contours:
    approx = cv2.approxPolyDP(contour,0.01*cv2.arcLength(contour,True),True)
    area = cv2.contourArea(contour)
    if ((len(approx) >= 3)):
        contour_list.append(contour)

cv2.drawContours(raw_image, contour_list,  -1, (0,0,0), 2)
cv2.imshow('Objects Detected',raw_image)
cv2.waitKey(0)

Answer 1

It is a square if its width and height are same. Otherwise its a rectangle.

for contour in contours:
    approx = cv2.approxPolyDP(contour,0.01*cv2.arcLength(contour,True),True)
    area = cv2.contourArea(contour)
    if ((len(approx) == 4)):
        (x, y, w, h) = cv2.boundingRect(approx)
        if  ((float(w)/h)==1):
            cv2.putText(raw_image, "square", (x, y), cv2.FONT_HERSHEY_SIMPLEX, 0.7, 0, 2)
        else:
            cv2.putText(raw_image, "rectangle", (x, y), cv2.FONT_HERSHEY_SIMPLEX, 0.7, 0, 2)

        contour_list.append(contour)

This change only detects squares and rectangles. Make necessary changes in the for loop to detect circles. You can work with len(approx) to make that distinction.

Answer 2

我有另一种方式：

1. 查找所有已连接的组件。

2. 在原始图像中找到要素点，因为在这种情况下我们有简单的几何体而不是复杂的对象，您可以使用角点作为特征点，使用Harris角算法。

3. 将这些要素点分组在相同的连接组件上。

4. 使用所有连接组件上这些要素点之间的关系（距离/角度），因此您可以对这些几何形状进行分类。

Answer 3

The difference between a rectangle and a square is that a square has 4 equal sides making it a special rectangle. I learned this in kindergarden.

There are countless ways of identifying a square.

Its circumference always equals sqrt(area) hence its circularity is always 0.0625

The distance between all corners is either a or a * sqrt(2)

The centroid has the same distance a / 2 to all 4 sides

...

You name it.

Answer 4

我在评论中读到形状可能会旋转。在那种情况下，cv2.boundingRect（）不会给出正确的结果，因为此函数始终会给出一个直立的矩形。一般而言，要检测矩形（是否旋转），应尝试cv2.minAreaRect（），该函数将返回一个矩形，该矩形将根据轮廓旋转，并具有覆盖轮廓的最小面积。然后，您可以检查其长宽比，以查看它是正方形还是矩形。