error: (-215) !empty() in function detectMultiScale

Python Python 2.7 Opencv Image Recognition

Python Problem Overview

I'm trying to learn cv2 in python 2.7, but when I run my code, in the specific part of it:

face_cascade = cv2.CascadeClassifier('haarcascade_frontalface_default.xml')
 eye_cascade = cv2.CascadeClassifier('haarcascade_eye.xml')


img = cv2.imread('2015-05-27-191152.jpg')
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

faces = face_cascade.detectMultiScale(gray, 1.3, 5)
for (x,y,w,h) in faces:
    img = cv2.rectangle(img,(x,y),(x+w,y+h),(255,0,0),2)

it returns this:

File "face_detection.py", line 11, in <module>
    faces = face_cascade.detectMultiScale(gray, 1.3, 5)
cv2.error: /home/arthurckl/Desktop/opencv-3.0.0-rc1/modules/objdetect/src/cascadedetect.cpp:1595: error: (-215) !empty() in function detectMultiScale

I tried to search the answer here but the best i could find is that I must be loading the face_cascade the wrong way... Any help?

Python Solutions

Solution 1 - Python

I had the same issue.

I didn't need to download anything else to solve this. CV2 had everything I needed.

Instead of trying to figure out where the .xml files are and hard coding the values, I used a property given by cv2.

From OP

face_cascade = cv2.CascadeClassifier('haarcascade_frontalface_default.xml')
eye_cascade = cv2.CascadeClassifier('haarcascade_eye.xml')

Becomes

face_cascade = cv2.CascadeClassifier(cv2.data.haarcascades + 'haarcascade_frontalface_default.xml')
eye_cascade = cv2.CascadeClassifier(cv2.data.haarcascades + 'haarcascade_eye.xml')

Solution 2 - Python

The XML or file is missing or the path to it is incorrect or the create_capture path is incorrect.

The paths in the opencv sample look like this:

cascade_fn = args.get('--cascade', "../../data/haarcascades/haarcascade_frontalface_alt.xml")
nested_fn  = args.get('--nested-cascade', "../../data/haarcascades/haarcascade_eye.xml")

cam = create_capture(video_src, fallback='synth:bg=../data/lena.jpg:noise=0.05')

Solution 3 - Python

I ran the same code. There are two things to note here.

Give the entire path of the .xml files.
Give a key press event instruction at the end.

Add this block of code at the end and run your file, worked for me:

k = cv2.waitKey(0)
if k == 27:         # wait for ESC key to exit
    cv2.destroyAllWindows()
elif k == ord('s'): # wait for 's' key to save and exit
    cv2.imwrite('messigray.png',img)
    cv2.destroyAllWindows()

For example, my code looked like

import numpy as np
import cv2

face_cascade = cv2.CascadeClassifier('C:\\opencv\\build\\etc\\haarcascades\\haarcascade_frontalface_default.xml')
eye_cascade = cv2.CascadeClassifier('C:\\opencv\\build\\etc\\haarcascades\\haarcascade_eye.xml')
 
img = cv2.imread('lena.jpg')

gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

faces = face_cascade.detectMultiScale(gray, 1.3, 5)
#faces = face_cascade.detectMultiScale(gray)

for (x,y,w,h) in faces:
    cv2.rectangle(img,(x,y),(x+w,y+h),(255,0,0),2)
    roi_gray = gray[y:y+h, x:x+w]
    roi_color = img[y:y+h, x:x+w]
    eyes = eye_cascade.detectMultiScale(roi_gray)
    for (ex,ey,ew,eh) in eyes:
        cv2.rectangle(roi_color,(ex,ey),(ex+ew,ey+eh),(0,255,0),2)

cv2.imshow('img',img)

k = cv2.waitKey(0)
if k == 27:         # wait for ESC key to exit
    cv2.destroyAllWindows()
elif k == ord('s'): # wait for 's' key to save and exit
    cv2.imwrite('messigray.png',img)
    cv2.destroyAllWindows()

My output looked like this:

ouput

Solution 4 - Python

The XML file is missing, you can get the file from the GitHub repository and place it in the same directory as your project. Link to the folder on GitHub is here. Just download the file named haarcascade_frontalface_default.xml. Actually, the file exists on your system. Just go to the site-packages folder of your python installation folder and check the cv2/data folder for the file

Solution 5 - Python

Use the entire file path and use "\" instead of "" in the xml file path.

The file path should be as follows:

face_cascade = cv2.CascadeClassifier('C:\\opencv\\build\\etc\\haarcascades\\haarcascade_frontalface_default.xml')

instead of:

cascade_fn = args.get('--cascade', "..\..\data\haarcascades\haarcascade_frontalface_alt.xml")

Solution 6 - Python

You just need to add proper path of the haarcascade_frontalface_default.xml file i.e. you only have to add prefix (cv2.data.haarcascades)

face_cascade = cv2.CascadeClassifier(cv2.data.haarcascades + 'haarcascade_frontalface_default.xml')
eye_cascade = cv2.CascadeClassifier(cv2.data.haarcascades + 'haarcascade_eye.xml')

Solution 7 - Python

no need to change the code

download that .xml file , then put the path of that file

it will solve the error (100%)

Solution 8 - Python

If you are using Anaconda you should add the Anaconda path.

new_path = 'C:/Users/.../Anaconda/Library/etc/haarcascades/'

face_cascade = cv2.CascadeClassifier(new_path + 'haarcascade_frontalface_default.xml')

Solution 9 - Python

This error means that the XML file could not be found. The library needs you to pass it the full path, even though you’re probably just using a file that came with the OpenCV library.

You can use the built-in pkg_resources module to automatically determine this for you. The following code looks up the full path to a file inside wherever the cv2 module was loaded from:

import pkg_resources
haar_xml = pkg_resources.resource_filename(
    'cv2', 'data/haarcascade_frontalface_default.xml')

For me this was '/Users/andrew/.local/share/virtualenvs/foo-_b9W43ee/lib/python3.7/site-packages/cv2/data/haarcascade_frontalface_default.xml'; yours is guaranteed to be different. Just let python’s pkg_resources library figure it out.

classifier = cv2.CascadeClassifier(haar_xml)
faces = classifier.detectMultiScale(frame)

Success!

Solution 10 - Python

On OSX with a homebrew install the full path to the opencv folder should work:

face_cascade = cv2.CascadeClassifier('/usr/local/Cellar/opencv/3.4.0_1/share/OpenCV/haarcascades/haarcascade_frontalface_default.xml')
eye_cascade = cv2.CascadeClassifier('/usr/local/Cellar/opencv/3.4.0_1/share/OpenCV/haarcascades/haarcascade_eye.xml')

Take care of the version number in the path.

Solution 11 - Python

Probably the face_cascade is empty. You can check if the variable is empty or not by typing following command:

face_cascade.empty()

If it is empty you will get True and this means your file is not available in the path you mentioned. Try to add complete path of xml file as follows:

r'D:\folder Name\haarcascade_frontalface_default.xml'

Solution 12 - Python

"\Anaconda3\Lib\site-packages\cv2\data" I found the xml file in this path for Anaconda

Solution 13 - Python

You can solve this problem by placing XML in the same directory in which your main python file (from where you tried to include this file) was placed. Now the next step is to use full path. For example

This will not work

front_cascade = cv2.CascadeClassifier('./haarcascade_eye.xml')

Use full path, now it will work fine

front_cascade = cv2.CascadeClassifier('/Users/xyz/Documents/project/haarcascade_eye.xml')

Solution 14 - Python

You may find such kind of errors when you did not define the complete path of your XML file. Try this one if you are using opencv3.1.0 in raspberrypi 3:

faceCascade = cv2.CascadeClassifier('/home/pi/opencv-3.1.0/data/haarcascades/haarcascade_frontalface_default.xml')

Solution 15 - Python

I found this in some other answer but eventually worked for me when I added the two answers.

import cv2
from matplotlib import pyplot as plt
import numpy as np
face_cascade = cv2.CascadeClassifier(cv2.data.haarcascades + "haarcascade_frontalface_default.xml")
eye_cascade = cv2.CascadeClassifier(cv2.data.haarcascades + "haarcascade_eye.xml")

img = cv2.imread('image1.jpg')
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
faces = face_cascade.detectMultiScale(gray, 1.3, 5)

Solution 16 - Python

Your XML file was not found. Try using absolute paths like:

/path/to/my/file (Mac, Linux)
C:\\path\\to\\my\\file (Windows)

Solution 17 - Python

the error may be due to, the required xml files has not been loaded properly. Search for the file haarcascade_frontalface_default.xml by using the search engine of ur OS get the full path and put it as the argument to cv2.CascadeClassifier as string

Solution 18 - Python

Please do not copy paste the content of xml file, because once you paste it to notepad it will be saved a s text file. So directly download the file from the given source.

Solution 19 - Python

I ran into the same problem. but wrote the correct location.

face_cascade = cv2.CascadeClassifier('./model/haarcascade_frontalface_default.xml')

I figured out that i need to declare the full path to remove the error.

face_cascade = cv2.CascadeClassifier('C:/pythonScript/Facial-Emotion-Detection/model/haarcascade_frontalface_default.xml')

Solution 20 - Python

The error occurs due to missing of xml files or incorrect path of xml file.

Please try the following code,

import numpy as np
import cv2

face_cascade = cv2.CascadeClassifier('haarcascade_frontalface_default.xml')
eye_cascade = cv2.CascadeClassifier('haarcascade_eye.xml')

cap = cv2.VideoCapture(0)

while 1:
    ret, img = cap.read()
    gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
    faces = face_cascade.detectMultiScale(gray, 1.3, 5)

    for (x,y,w,h) in faces:
        cv2.rectangle(img,(x,y),(x+w,y+h),(255,0,0),2)
        roi_gray = gray[y:y+h, x:x+w]
        roi_color = img[y:y+h, x:x+w]
        
        eyes = eye_cascade.detectMultiScale(roi_gray)
        for (ex,ey,ew,eh) in eyes:
            cv2.rectangle(roi_color,(ex,ey),(ex+ew,ey+eh),(0,255,0),2)

    cv2.imshow('img',img)
    k = cv2.waitKey(30) & 0xff
    if k == 27:
        break

cap.release()
cv2.destroyAllWindows()

Solution 21 - Python

I had the same problem with opencv-python and I used a virtual environment. If it's your case, you should find the xml files at:

/home/username/virtual_environment/lib/python3.5/site-packages/cv2/data/haarcascade_frontalface_default.xml

/home/username/virtual_environment/lib/python3.5/site-packages/cv2/data/haarcascade_eye.xml

Please be sure that you're using the absolute path. Otherwise, it won't work.

Solution 22 - Python

The main idea of the solution as above mentioned: find the right path of the .xml file and use it to access the file correctly.

In my case, I installed the opencv in anoconda env, first direct to path of Anoconda, then

find the path of .xml file by using:

$ find . -name 'haarcascade_eye.xml' (for example search the haarcascade_eye.xml file in current dir (.))
Then use the return path:

eye_cascade = cv2.CascadeClassifier(path + 'haarcascade_eye.xml')

Solution 23 - Python

I faced a similar issue. It seems correcting the path to XML makes this error to go away.

Solution 24 - Python

It seems to be file path issue. I changed code like this and it worked.

haar_face_filename = "D:\Sandbox\Github\Faces\haar_face.xml"
haar_cascade = cv.CascadeClassifier(haar_face_filename)

Solution 25 - Python

I had the same issue and was trying to use open cv in a springboot application where my xml files and images are in resources folder. Trying to give path starting from src or a absolute path like C:\a\b.xml did not work.

Creating the file path dynamically with project root path worked.

String classifierPath = System.getProperty("user.dir") + "/src/main/resources/haarcascades/haarcascade_frontalface.xml";

// similarly for image paths

Solution 26 - Python

Path needs to start with /, eg. /file.xml.

Content Type	Original Author	Original Content on Stackoverflow
Question	arthurckl	View Question on Stackoverflow
Solution 1 - Python	Mandelbrotter	View Answer on Stackoverflow
Solution 2 - Python	Person	View Answer on Stackoverflow
Solution 3 - Python	Keerthana Gopalakrishnan	View Answer on Stackoverflow
Solution 4 - Python	Avneesh Mishra	View Answer on Stackoverflow
Solution 5 - Python	Anubhav	View Answer on Stackoverflow
Solution 6 - Python	MashukKhan	View Answer on Stackoverflow
Solution 7 - Python	Coder	View Answer on Stackoverflow
Solution 8 - Python	Ale	View Answer on Stackoverflow
Solution 9 - Python	andrewdotn	View Answer on Stackoverflow
Solution 10 - Python	Master Bee	View Answer on Stackoverflow
Solution 11 - Python	Vaibhav K	View Answer on Stackoverflow
Solution 12 - Python	My3	View Answer on Stackoverflow
Solution 13 - Python	am2505	View Answer on Stackoverflow
Solution 14 - Python	Sahil Sharma	View Answer on Stackoverflow
Solution 15 - Python	Dipak	View Answer on Stackoverflow
Solution 16 - Python	Clyde McQueen	View Answer on Stackoverflow
Solution 17 - Python	Niharranjan Pradhan	View Answer on Stackoverflow
Solution 18 - Python	Nagesh Singh Chauhan	View Answer on Stackoverflow
Solution 19 - Python	kiLLua	View Answer on Stackoverflow
Solution 20 - Python	Codemaker	View Answer on Stackoverflow
Solution 21 - Python	lenhhoxung	View Answer on Stackoverflow
Solution 22 - Python	Xiaoyan Zhuo	View Answer on Stackoverflow
Solution 23 - Python	Sagar Singh	View Answer on Stackoverflow
Solution 24 - Python	Syed Amir Raza	View Answer on Stackoverflow
Solution 25 - Python	saivishnu tammineni	View Answer on Stackoverflow
Solution 26 - Python	Jacek Góraj	View Answer on Stackoverflow