yeah if image is there then maybe path is wrong for accessing the image . Verify that the permission in your androidManifest.xml to read from external storage is correct.

This happens when image is not there or path is incorrect. Can you verify if image is at the location or not . If yes try with absolute path . Still having issue share code and image .

I am trying to detect all the vertical lines and horizontal lines in an image . I have been able to detect all the horizontal lines successfully . But having an issue with vertical lines detection. (My first time on Opencv so don't have enough credits to upload image here ) so posting imgur link Sorry for this .

Original Image :- imgur.com/a/mZJny

After canny Edge detection

edges :- imgur.com/a/hkrve

output

o/p :- imgur.com/a/kdKwv

As you can see i have been able to detect all edges perfectly but when i am trying to detect lines with hough transform , haven't been able to do so .

Code :-

to detect vertical lines

    img = cv2.imread("sample.png")
gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)


bw = cv2.adaptiveThreshold( ~gray,255,cv2.cv.CV_ADAPTIVE_THRESH_MEAN_C,        cv2.cv.CV_THRESH_BINARY,15,-2)  

vertical = np.copy(bw)
shape = 45
verticalSize = vertical.shape[0]/shape
verticalStructure = cv2.getStructuringElement(cv2.MORPH_RECT, (1, verticalSize/2))
vertical = cv2.erode(vertical, verticalStructure)
cv2.imwrite("vertical.png", vertical)
vertical = cv2.dilate(vertical, verticalStructure)
not_vertical = cv2.bitwise_not(vertical)
cv2.imwrite("vertical.png", vertical)
edges = cv2.Canny(not_vertical,50,150,apertureSize = 3)
cv2.imwrite("edges1.png", edges)
minLineLength = 4
maxLineGap = 10
lines = cv2.HoughLinesP(edges,1,np.pi/180,100,minLineLength,maxLineGap)

I am new to opencv and i am developing a application in android and want to know how to implement Blob Extraction algorithm using openCV .