Python cv2 not matching template with main image

Question

I have my main image:

And my template:

However, the cv2 code that i am using is not generating the rectangle to show that there is a match, but I am also receiving 0 errors.

Here is the code:

# Read the main image 
img_rgb = cv2.imread('main.png')

# Convert it to grayscale 
img_gray = cv2.cvtColor(img_rgb, cv2.COLOR_BGR2GRAY) 

# Read the template 
template = cv2.imread('temp.png',0) 
template = np.array(template[:,::-1])

# Store width and height of template in w and h 
w, h = template.shape[::-1] 

# Perform match operations. 
res = cv2.matchTemplate(img_gray, template, cv2.TM_CCOEFF_NORMED) 

# Specify a threshold 
threshold = 0.8

# Store the coordinates of matched area in a numpy array 
loc = np.where( res >= threshold)  

# Draw a rectangle around the matched region. 
for pt in zip(*loc[::-1]): 
    cv2.rectangle(img_rgb, pt, (pt[0] + w, pt[1] + h), (0,255,255), 2) 

# Show the final image with the matched area. 
cv2.imshow('Detected',img_rgb) 
cv2.waitKey()
cv2.destroyAllWindows()

My initial thoughts are that the template image is too large to match with the main, however this is my first go with cv2 and I am unsure how to fix it.

Answer 1

The template matching code I have always matches the dimensions of the template to the dimensions of the image. In your case, where you've already converted the source images to grayscale, change

template = np.array(template[:,::-1])
w, h = template.shape[::-1] 

(which might not be doing what you intend anyway) to

template = cv2.cvtColor(template, cv2.COLOR_BGR2GRAY)
w, h = template.shape