在特定颜色上查找并绘制 opencv 中的最大轮廓 (Python)

Question

我正在尝试获取红皮书的最大轮廓。我的代码有点问题，因为它得到的是最小对象（blob）的轮廓而不是最大的对象，我似乎无法弄清楚为什么会这样

我使用的代码：

camera = cv2.VideoCapture(0)
kernel = np.ones((2,2),np.uint8)

while True:
    #Loading Camera
    ret, frame = camera.read()

    blurred = cv2.pyrMeanShiftFiltering(frame, 3, 3)
    hsv = cv2.cvtColor(blurred, cv2.COLOR_BGR2HSV)

    lower_range = np.array([150, 10, 10])
    upper_range = np.array([180, 255, 255])
    mask = cv2.inRange(hsv, lower_range, upper_range)

    dilation = cv2.dilate(mask,kernel,iterations = 1)

    closing = cv2.morphologyEx(dilation, cv2.MORPH_GRADIENT, kernel)
    closing = cv2.morphologyEx(dilation, cv2.MORPH_CLOSE, kernel)

    #Getting the edge of morphology
    edge = cv2.Canny(closing, 175, 175)
    _, contours,hierarchy = cv2.findContours(edge, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

    # Find the index of the largest contour
    areas = [cv2.contourArea(c) for c in contours]
    max_index = np.argmax(areas)
    cnt=contours[max_index]

    x,y,w,h = cv2.boundingRect(cnt)
    cv2.rectangle(frame,(x,y),(x+w,y+h),(0,255,0),2)


    cv2.imshow('threshold', frame)
    cv2.imshow('edge', edge)

    if cv2.waitKey(1) == 27:
        break


camera.release()
cv2.destroyAllWindows()

As you can see on this picture

希望有人能提供帮助

Answer 1

您可以先定义一个掩码，在您要找的书的红色色调范围内。

那你就可以找到面积最大的等高线，画出书本的长方形

import numpy as np
import cv2

# load the image
image = cv2.imread("path_to_your_image.png", 1)

# red color boundaries [B, G, R]
lower = [1, 0, 20]
upper = [60, 40, 220]

# create NumPy arrays from the boundaries
lower = np.array(lower, dtype="uint8")
upper = np.array(upper, dtype="uint8")

# find the colors within the specified boundaries and apply
# the mask
mask = cv2.inRange(image, lower, upper)
output = cv2.bitwise_and(image, image, mask=mask)

ret,thresh = cv2.threshold(mask, 40, 255, 0)
if (cv2.__version__[0] > 3):
    contours, hierarchy = cv2.findContours(thresh, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)
else:
    im2, contours, hierarchy = cv2.findContours(thresh, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)

if len(contours) != 0:
    # draw in blue the contours that were founded
    cv2.drawContours(output, contours, -1, 255, 3)

    # find the biggest countour (c) by the area
    c = max(contours, key = cv2.contourArea)
    x,y,w,h = cv2.boundingRect(c)

    # draw the biggest contour (c) in green
    cv2.rectangle(output,(x,y),(x+w,y+h),(0,255,0),2)

# show the images
cv2.imshow("Result", np.hstack([image, output]))

cv2.waitKey(0)

使用您的图片：

如果你想要这本书旋转你可以使用 rect = cv2.minAreaRect(cnt) 因为你可以找到它 here.

编辑:

您还应该考虑除 RGB 之外的其他颜色空间，例如 HSV 或 HLS。通常，人们使用 HSV，因为 H 通道在阴影或过度亮度方面保持相当一致。换句话说，如果你使用 HSV 颜色空间，你应该会得到更好的结果。

具体来说，在OpenCV中Hue的范围是[0,179]。在下图中（由 @Knight 制作），您可以在 V = 255 中找到该圆柱体的二维切片，其中水平轴为 H，垂直轴为 [=15] =].从该图中可以看出，要捕获红色，您需要同时包含色调值的较低区域（例如，H=0 到 H=10）和较高区域（例如，H=170 到 H=179）。

Answer 2

使用此工具将灰度蒙版转换为矩形

def mask_to_rect(image):
    '''
    
        Give rectangle cordinates according to the mask image
        
        
        Params: image : (numpy.array) Gray Scale Image
        
        Returns: Cordinates : (list) List of cordinates [x, y, w h]
    
    '''
    
    # Getting the Thresholds and ret
    ret,thresh = cv2.threshold(image, 0, 1, 0)
    
    # Checking the version of open cv I tried for (version 4)
    #    Getting contours on the bases of thresh
    if (int(cv2.__version__[0]) > 3):
        contours, hierarchy = cv2.findContours(thresh.astype(np.uint8), cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)
    else:
        im2, contours, hierarchy = cv2.findContours(thresh.astype(np.uint8), cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)
    
    # Getting the biggest contour
    if len(contours) != 0:
        # draw in blue the contours that were founded
        cv2.drawContours(output, contours, -1, 255, 3)

        # find the biggest countour (c) by the area
        c = max(contours, key = cv2.contourArea)
        x,y,w,h = cv2.boundingRect(c)
        
    return [x, y, w, h]

结果

在特定颜色上查找并绘制 opencv 中的最大轮廓 (Python)

Find and draw the largest contour in opencv on a specific color (Python)

python

draw

contour