OpenCV: findContours() messing with images?

[RyanCahoon]

Originally Posted by OpenCV Docs

findContours

[...]The function modifies the image while extracting the contours.[...]

http://docs.opencv.org/2.4/modules/imgproc/doc/structural_analysis_and_shape_descriptors.html?hig hlight=findcontours#findcontours

If you want to keep the unmodified image, create a copy before calling findContours:

import cv2 as cv
import numpy as np
img = cv.imread("29.jpg")#Sample image of Field
gray = cv.cvtColor(img, cv.COLOR_BGR2GRAY) #Convert to gray...just to try

edges = cv.Canny(gray, 200, 300)
#Finds the contours
scratch = edges.copy()
image, contours, hierarchy = cv.findContours(scratch,cv.RETR_EXTERNAL,cv.CHAIN_APPROX_NONE)
#Draws
cv.drawContours(img, contours, 1, (0, 255,255), 3)
#Shows
cv.imshow("edges!", edges)
cv.imshow("mask!", gray)
cv.imshow("frame!", img)

k = cv.waitKey(0) 
cv.destroyAllWindows()