Anyone use the Python ( got the problem with TypeError?

asked 2014-04-25 16:41:31 -0600

ianymu gravatar image

updated 2014-04-26 00:12:11 -0600

berak gravatar image

Recently, I use the python example (

But I get the problem with that

File "", line 63, in (module)

cascade = cv.Load(options.cascade)

TypeError: OpenCV returned Null

I am really confused with that problem, and really want solve that problem as soon as possible, anyone can help me, please?

the Code is

The program finds faces in a camera image or video stream and displays a red box around them.
import sys
import as cv
from optparse import OptionParser
The program finds faces in a camera image or video stream and displays a red box around them.

import sys
import as cv
from optparse import OptionParser     
min_size = (20, 20)
image_scale = 2
haar_scale = 1.2
min_neighbors = 2
haar_flags = 0
def detect_and_draw(img, cascade):
# allocate temporary images
    gray = cv.CreateImage((img.width,img.height), 8, 1)
    small_img = cv.CreateImage((cv.Round(img.width / image_scale),
                   cv.Round (img.height / image_scale)), 8, 1)

    # convert color input image to grayscale
    cv.CvtColor(img, gray, cv.CV_BGR2GRAY)
    # scale input image for faster processing
    cv.Resize(gray, small_img, cv.CV_INTER_LINEAR)
    cv.EqualizeHist(small_img, small_img)

        t = cv.GetTickCount()
        faces = cv.HaarDetectObjects(small_img, cascade, cv.CreateMemStorage(0),
                                     haar_scale, min_neighbors, haar_flags, min_size)
        t = cv.GetTickCount() - t
        print "time taken for detection = %gms" % (t/(cv.GetTickFrequency()*1000.))
        if faces:
            for ((x, y, w, h), n) in faces:
                # the input to cv.HaarDetectObjects was resized, so scale the
                # bounding box of each face and convert it to two CvPoints
                pt1 = (int(x * image_scale), int(y * image_scale))
                pt2 = (int((x + w) * image_scale), int((y + h) * image_scale))
                cv.Rectangle(img, pt1, pt2, cv.RGB(255, 0, 0), 3, 8, 0)

    cv.ShowImage("video", img)

if __name__ == '__main__':
    parser = OptionParser(usage = "usage: %prog [options] [filename|camera_index]")
    parser.add_option("-c", "--cascade", action="store", dest="cascade", type="str", help="Haar cascade file, default %default", default = "../data/haarcascades/haarcascade_frontalface_alt.xml")
    (options, args) = parser.parse_args()

    cascade = cv.Load(options.cascade)
    if len(args) != 1:
    input_name = args[0]
    if input_name.isdigit():
        capture = cv.CreateCameraCapture(int(input_name))
        capture = None

    cv.NamedWindow("video", 1)

    #size of the video
    width = 160
    height = 120

    if width is None:
        width = int(cv.GetCaptureProperty(capture, cv.CV_CAP_PROP_FRAME_WIDTH))

    if height is None:
    height = int(cv.GetCaptureProperty(capture, cv.CV_CAP_PROP_FRAME_HEIGHT))

    if capture:
        frame_copy = None
        while True:

            frame = cv.QueryFrame(capture)
            if not frame:
            if not frame_copy:
                frame_copy = cv.CreateImage((frame.width,frame.height),
                                            cv.IPL_DEPTH_8U, frame.nChannels)

            if frame.origin == cv.IPL_ORIGIN_TL:
               cv.Copy(frame, frame_copy)
                cv.Flip(frame, frame_copy, 0)

            detect_and_draw(frame_copy, cascade)

            if cv.WaitKey(10) >= 0:
        image = cv.LoadImage(input_name, 1)
            detect_and_draw(image, cascade)

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please don't use the outdated api, it will be gone in the next opencv version.

use cv2 instead.

(and it seems, that it did not find your cascade file. wrong path ?)

berak gravatar imageberak ( 2014-04-26 00:15:39 -0600 )edit