Python，Cv2，numpy可检测另一张图片中的图片

Question

I am using these codes to detect if a small picture is a part of a big picture. (or take it as, if the small picture can be found in the big picture)

this is the BIG picture

this is the SMALL picture

It works fine and give me the x_coordinate of where the small picture starts.

import cv2
import numpy as np

big_pic = cv2.imread("c:\\big.jpg")
small_pic = cv2.imread('c:\\small.jpg')
res = cv2.matchTemplate(big_pic,small_pic,cv2.TM_CCOEFF_NORMED)

threshold = 0.99
loc = np.where (res >= threshold)
x_coordinate = list(loc[0])

print x_coordinate

However, when I want to specify the detection area in the big picture – that is, if the small picture can be found in certain part of the big picture – it fails.

big_pic = cv2.imread("c:\\big.jpg")
target_area = big_pic[0:0, 238:220]

small_pic = cv2.imread('c:\\small.jpg')
res = cv2.matchTemplate(target_area,small_pic,cv2.TM_CCOEFF_NORMED)

threshold = 0.99
loc = np.where (res >= threshold)
x_coordinate = list(loc[0])

print x_coordinate

The error says:

OpenCV Error: Assertion failed (corrsize.height <= img.rows + templ.rows - 1 && corrsize.width <= img.cols + templ.cols - 1) in cv::crossCorr, file ......\\opencv-3.1.0\\modules\\imgproc\\src\\templmatch.cpp, line 658 Traceback (most recent call last): File "C:\\Python27\\finding picture.py", line 8, in res = cv2.matchTemplate(target_area,small_pic,cv2.TM_CCOEFF_NORMED) cv2.error: ......\\opencv-3.1.0\\modules\\imgproc\\src\\templmatch.cpp:658: error: (-215) corrsize.height <= img.rows + templ.rows - 1 && corrsize.width <= img.cols + templ.cols - 1 in function cv::crossCorr

What went wrong? Thank you.

Answer 1

It seems [y,y1 : x,x1] is the right format. So the credit shall go to @ZdaR.

Just to post an edited example, using a rectangle shape SMALL.

this is the BIG picture

this is the SMALL picture

The target area is,

[0,0] [300,220]. # Reading as [x, y] and [x1, y1]. 

They are the top left point and bottom right point in the BIG.

Made the code as following:

big_pic = cv2.imread("c:\\big.jpg")

target_area = big_pic[0:220, 0:300]   # [y,y1 : x,x1]   # it returns a result.
target_area = big_pic[0:300, 0:220]   # [x,x1 : y,y1]   # it doesn’t return a result.

small_pic = cv2.imread('c:\\small.jpg')
res = cv2.matchTemplate(target_area,small_pic,cv2.TM_CCOEFF_NORMED)

threshold = 0.99
loc = np.where (res >= threshold)
x_coordinate = list(loc[0])

print x_coordinate