Question

Not quite sure where I’m going wrong – I’m trying to train OpenCV for object detection with +/- images that I’ve taken myself. All the steps work ok, but ultimately my Python script won’t read my XML cascade file (but will load one of the built-in face detection files).

For what it’s worth, I’m on Mac Lion running Python 2.7.3.

My process:

1. Create a collection file with bounding boxes on the positive images
2. Create a list of negative images
3. Use opencv_createsamples using the following command: opencv_createsamples -info collection.txt -bg negativeImages.txt -vec positiveVectorFile.vec -num 20 -w 32 -h 24
4. Check vector file: images are a bit squished but look ok
5. Run traincascade program using the following command: opencv_traincascade -data directoryToStoreFiles -vec positiveVectorFile.vec -bg negativeImageList.txt -numPos 16 -numNeg 20 -numStages 5 -mem 1000 -maxHitRate 0.95 -w 32 -h 24

Then I run the following Python script (which works with the usual face-detection XML):

import cv
img = cv.LoadImage("test.jpg", 0)

# load detection file (various files for different views and uses)
cascade = cv.Load("cascade.xml")        # doesn't work
#cascade = cv.Load("frontalface.xml")   # works

# detect faces, return as list
detected = cv.HaarDetectObjects(img, cascade, cv.CreateMemStorage())

# iterate detected objects, drawing a rectangle around each
for (x,y, w,h), n in detected:
    cv.Rectangle(img, (x,y), (x+w, y+h), 255)

# create a window to display the results
windowTitle = "Test Cascade"
cv.NamedWindow(windowTitle, cv.CV_WINDOW_AUTOSIZE)

# display tested image until the escape key is pressed
while True:
    cv.ShowImage(windowTitle, img)

    # watch for escape key (ASCII 20)
    key = cv.WaitKey(20)
    if key == 27:

        # save the image to file is specified
        if saveIt == True:
            cv.SaveImage("detected.png", img)

        # ... and quit
        exit()

The result is the error:
cv2.error: The node does not represent a user object (unknown type?)

I’ve uploaded the cascade file here: http://pastebin.com/w7uRjyN7. Not sure if it’s my cascade file, some other problem along the way, or something obvious?

Answer 1

Well, it appears that cyberdecker’s suggestion was one of a few problems: that cv2 has entirely different commands for everything and is required when using opencv_traincascade. My code, which now works (though my cascade doesn’t quite yet):

#import library - MUST use cv2 if using opencv_traincascade
import cv2

# rectangle color and stroke
color = (0,0,255)       # reverse of RGB (B,G,R) - weird
strokeWeight = 1        # thickness of outline

# set window name
windowName = "Object Detection"

# load an image to search for faces
img = cv2.imread("test.jpg")

# load detection file (various files for different views and uses)
cascade = cv2.CascadeClassifier("cascade.xml")

# preprocessing, as suggested by: http://www.bytefish.de/wiki/opencv/object_detection
# img_copy = cv2.resize(img, (img.shape[1]/2, img.shape[0]/2))
# gray = cv2.cvtColor(img_copy, cv2.COLOR_BGR2GRAY)
# gray = cv2.equalizeHist(gray)

# detect objects, return as list
rects = cascade.detectMultiScale(img)

# display until escape key is hit
while True:

    # get a list of rectangles
    for x,y, width,height in rects:
        cv2.rectangle(img, (x,y), (x+width, y+height), color, strokeWeight)

    # display!
    cv2.imshow(windowName, img)

    # escape key (ASCII 27) closes window
    if cv2.waitKey(20) == 27:
        break

# if esc key is hit, quit!
exit()