opencv - Detection of color with a trackbar and finding the contour of the desired color

Question

I want to use a trackbar to select the desired color and than get the contour with the x and y coordinates of it. When i run the code i get the next error: contours, _ = cv2.findContours(bin, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE) cv2.error: OpenCV(4.2.0) C:\projects\opencv-python\opencv\modules\imgproc\src\contours.cpp:197: error: (-210:Unsupported format or combination of formats) [Start]FindContours supports only CV_8UC1 images when mode != CV_RETR_FLOODFILL otherwise supports CV_32SC1 images only in function 'cvStartFindContours_Impl'

The input image for detecting the contour is binary so i dont know what im doing wrong here. And this is the code im using:

import cv2
import numpy as np

def nothing(x):
    pass

cv2.namedWindow("Tracking")
cv2.createTrackbar("LH", "Tracking", 0, 255, nothing)
cv2.createTrackbar("LS", "Tracking", 0, 255, nothing)
cv2.createTrackbar("LV", "Tracking", 0, 255, nothing)
cv2.createTrackbar("UH", "Tracking", 255, 255, nothing)
cv2.createTrackbar("US", "Tracking", 255, 255, nothing)
cv2.createTrackbar("UV", "Tracking", 255, 255, nothing)

while True:
    frame = cv2.imread('3blobs.jpg',1)
    font = cv2.FONT_HERSHEY_COMPLEX
    hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)

    l_h = cv2.getTrackbarPos("LH", "Tracking")
    l_s = cv2.getTrackbarPos("LS", "Tracking")
    l_v = cv2.getTrackbarPos("LV", "Tracking")

    u_h = cv2.getTrackbarPos("UH", "Tracking")
    u_s = cv2.getTrackbarPos("US", "Tracking")
    u_v = cv2.getTrackbarPos("UV", "Tracking")

    l_b = np.array([l_h, l_s, l_v])
    u_b = np.array([u_h, u_s, u_v])

    mask = cv2.inRange(hsv, l_b, u_b)

    res = cv2.bitwise_and(frame, frame, mask=mask)
    trash, bin = cv2.threshold(res, 227, 255, 1, cv2.THRESH_BINARY)

    # Detecting contours in image.
    contours, _ = cv2.findContours(bin, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

    # Going through every contours found in the image.
    for cnt in contours:

        approx = cv2.approxPolyDP(cnt, 0.009 * cv2.arcLength(cnt, True), True)

        # draws boundary of contours.
        cv2.drawContours(frame, [approx], 0, (0, 0, 255), 2)

        # Used to flatted the array containing
        # the co-ordinates of the vertices.
        n = approx.ravel()
        i = 0

        for j in n:
            if (i % 2 == 0):
                x = n[i]
                y = n[i + 1]

                # String containing the co-ordinates.
                string = str(x) + " " + str(y)

                if (i == 0):
                    # text on topmost co-ordinate.
                    cv2.putText(frame, "Arrow tip", (x, y),
                                font, 0.5, (255, 0, 0))
                else:
                    # text on remaining co-ordinates.
                    cv2.putText(frame, string, (x, y),
                                font, 0.5, (0, 255, 0))
            i += 1

    #cv2.imshow("frame", frame)
    #cv2.imshow("mask", mask)
    cv2.imshow("res", res)
    cv2.imshow("bin", bin)

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

cv2.destroyAllWindows()

Can someone help me with this issue thanks a lot!

标签： opencvopencv-contouropencv-drawcontour

Answer 1

问题是您没有将灰色图像传递给 findCountours，这是必需的。要解决它，您必须在 bitwise_and 操作后将 res 转换为灰度：

<!-- language: python -->
gray = cv2.cvtColor(res, cv2.COLOR_BGR2GRAY)
trash, bin = cv2.threshold(gray, 227, 255, 1, cv2.THRESH_BINARY)

完整代码：

import cv2
import numpy as np


def nothing(x):
    pass


cv2.namedWindow("Tracking")
cv2.createTrackbar("LH", "Tracking", 0, 255, nothing)
cv2.createTrackbar("LS", "Tracking", 0, 255, nothing)
cv2.createTrackbar("LV", "Tracking", 0, 255, nothing)
cv2.createTrackbar("UH", "Tracking", 255, 255, nothing)
cv2.createTrackbar("US", "Tracking", 255, 255, nothing)
cv2.createTrackbar("UV", "Tracking", 255, 255, nothing)

while True:
    frame = cv2.imread('3Blobs.jpg', 1)
    font = cv2.FONT_HERSHEY_COMPLEX
    hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)

    l_h = cv2.getTrackbarPos("LH", "Tracking")
    l_s = cv2.getTrackbarPos("LS", "Tracking")
    l_v = cv2.getTrackbarPos("LV", "Tracking")

    u_h = cv2.getTrackbarPos("UH", "Tracking")
    u_s = cv2.getTrackbarPos("US", "Tracking")
    u_v = cv2.getTrackbarPos("UV", "Tracking")

    l_b = np.array([l_h, l_s, l_v])
    u_b = np.array([u_h, u_s, u_v])

    mask = cv2.inRange(hsv, l_b, u_b)

    res = cv2.bitwise_and(frame, frame, mask=mask)
    gray = cv2.cvtColor(res, cv2.COLOR_BGR2GRAY)
    trash, bin = cv2.threshold(gray, 227, 255, 1, cv2.THRESH_BINARY)

    # Detecting contours in image.
    contours, _ = cv2.findContours(bin, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

    # Going through every contours found in the image.
    for cnt in contours:

        approx = cv2.approxPolyDP(cnt, 0.009 * cv2.arcLength(cnt, True), True)

        # draws boundary of contours.
        cv2.drawContours(frame, [approx], 0, (0, 0, 255), 2)

        # Used to flatted the array containing
        # the co-ordinates of the vertices.
        n = approx.ravel()
        i = 0

        for j in n:
            if (i % 2 == 0):
                x = n[i]
                y = n[i + 1]

                # String containing the co-ordinates.
                string = str(x) + " " + str(y)

                if (i == 0):
                    # text on topmost co-ordinate.
                    cv2.putText(frame, "Arrow tip", (x, y),
                                font, 0.5, (255, 0, 0))
                else:
                    # text on remaining co-ordinates.
                    cv2.putText(frame, string, (x, y),
                                font, 0.5, (0, 255, 0))
            i += 1

    # cv2.imshow("frame", frame)
    # cv2.imshow("mask", mask)

    cv2.namedWindow('res', cv2.WINDOW_NORMAL)
    cv2.namedWindow('bin', cv2.WINDOW_NORMAL)
    cv2.imshow("res", res)
    cv2.imshow("bin", bin)

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

cv2.destroyAllWindows()

结果：