Python OpenCV Template Matching error

Question

I've been messing around with the OpenCV bindings for python for a while now and i wanted to try template matching, i get this error and i have no idea why

C:\builds\master_PackSlaveAddon-win64-vc12-static\opencv\modules\imgproc\src\templmatch.cpp:910: error: (-215) (depth == CV_8U || depth == CV_32F) && type == _templ.type() && _img.dims() <= 2 in function cv::matchTemplate

Anyone have any clues as to why this might be happening?

Source code:

import win32gui
from PIL import ImageGrab
import win32api, win32con
import numpy
deckVar = "deck.png" # Temporary

def click(x,y):
    win32api.SetCursorPos((x,y))
    win32api.mouse_event(win32con.MOUSEEVENTF_LEFTDOWN,x,y,0,0)
    win32api.mouse_event(win32con.MOUSEEVENTF_LEFTUP,x,y,0,0)

margin = 10

def OOO(): # Order Of Operations
    print None

def main():
    deck = "test"

    img = ImageGrab.grab()

    HWNDHandle = win32gui.FindWindow(None, "Hearthstone");
    x,y,x2,y2 = win32gui.GetWindowRect(HWNDHandle)
    print x,y,x2,y2
    l = x2-x
    h = y2-y
    print l,h

    img_recog(img,"imgs/my_collection.png")

def img_recog(img,templ):
    import cv2
    import numpy as np
    from matplotlib import pyplot as plt


    img2 = numpy.array(img.getdata()).reshape(img.size[0], img.size[1], 3)
    template = cv2.imread(templ,0)
    w, h = template.shape[::-1]

    # All the 6 methods for comparison in a list
    methods = ['cv2.TM_CCOEFF', 'cv2.TM_CCOEFF_NORMED', 'cv2.TM_CCORR',
                'cv2.TM_CCORR_NORMED', 'cv2.TM_SQDIFF', 'cv2.TM_SQDIFF_NORMED']


    img = img2.copy()
    method = eval(methods[1])

    # Apply template Matching
    try:
        res = cv2.matchTemplate(img,template,method)
    except Exception as e:
        print str(e)
        raw_input()
    min_val, max_val, min_loc, max_loc = cv2.minMaxLoc(res)


    # If the method is TM_SQDIFF or TM_SQDIFF_NORMED, take minimum
    if method in [cv2.TM_SQDIFF, cv2.TM_SQDIFF_NORMED]:
        top_left = min_loc
    else:
        top_left = max_loc
    bottom_right = (top_left[0] + w, top_left[1] + h)

    return cv2.rectangle(img,top_left, bottom_right, 255, 2)


main()  

Answer 1

Pay attention to the error message:

error: (-215) (depth == CV_8U || depth == CV_32F) && type == _templ.type() && _img.dims() <= 2 in function cv::matchTemplate

It means the data type of the image should be CV_8U or CV_32F, and it should have 3 or less channels.

If you don't know what CV_8U, CV_32F means, see this list.

Probably you are passing numpy objects other than np.uint8 or np.float32. you can easily convert numpy dtype to 8-bit or 32-bit using:

img.astype(np.float32)
img.astype(np.uint8)

Just pay attention that OpenCV expect CV_8U 8-bit data to be in the range 0..255 and CV_32F can be in any range.