I have an image I need to draw a bounding box around and I'm trying to use the code at bottom of this post. The issue I have is that I have tried to blur the blue box shape to remove its details e.g.
cv2.blur(img,(20,20))
but the blurred image doesnt seem to have a good enough edge to produce a bounding box.
I have found that if I use my code below with a plain blue square with sharp edges of the same size as the image below, it works just fine. It seems the detail within the blue area stops a boundary box being drawn.
I was hoping someone could tell me how to get this to work please.
import cv2
# Load the image - container completely blurred out so no hinges,locking bars , writing etc are visible, just a blank blue square
img = cv2.imread('blue_object.jpg')
# convert to grayscale
gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
edged = cv2.Canny(img, 120,890)
# Apply adaptive threshold
thresh = cv2.adaptiveThreshold(edged, 255, 1, 1, 11, 2)
thresh_color = cv2.cvtColor(thresh, cv2.COLOR_GRAY2BGR)
# apply some dilation and erosion to join the gaps - change iteration to detect more or less area's
thresh = cv2.dilate(thresh,None,iterations = 50)
thresh = cv2.erode(thresh,None,iterations = 50)
# Find the contours
contours,hierarchy = cv2.findContours(thresh,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)
# For each contour, find the bounding rectangle and draw it
for cnt in contours:
area = cv2.contourArea(cnt)
if area > 50000:
x,y,w,h = cv2.boundingRect(cnt)
cv2.rectangle(img,(x,y),(x w,y h),(0,255,0),2)
cv2.imshow('img',img)
cv2.waitKey(0)
cv2.destroyAllWindows()
CodePudding user response:
You're converting to gray, throwing all that valuable color information away. You're also Canny-ing, which is generally a bad idea. Beginners don't have the judgment to apply Canny sensibly. Best stay away from it.
This can be solved with the usual approach:
- transform colorspace into something useful, say HSV
inRange
on well-saturated blue- some morphology operations to clean up debris
- bounding box
That is assuming you are looking for a blue container, or any well-saturated color really.
im = cv.imread("i4nPk.jpg")
hsv = cv.cvtColor(im, cv.COLOR_BGR2HSV)
lower = (90, 84, 0)
upper = (180, 255, 255)
mask1 = cv.inRange(hsv, lower, upper)
mask2 = cv.erode(mask1, kernel=None, iterations=2)
(x, y, w, h) = cv.boundingRect(mask2) # yes that works on masks too
canvas = cv.cvtColor(mask2, cv.COLOR_GRAY2BGR)
cv.rectangle(canvas, (x,y), (x w, y h), color=(0,0,255), thickness=3)