问题
I want to use my raspi cam modul to scan QR codes. For detecting and decoding qr codes I want to use zbar. My current code:
import io
import time
import picamera
import zbar
import Image
if len(argv) < 2: exit(1)
# Create an in-memory stream
my_stream = io.BytesIO()
with picamera.PiCamera() as camera:
camera.start_preview()
# Camera warm-up time
time.sleep(2)
camera.capture(my_stream, 'jpeg')
scanner = zbar.ImageScanner()
scanner.parse_config('enable')
pil = Image.open(argv[1]).convert('L')
width, height = pil.size
raw = pil.tostring()
my_stream = zbar.Image(width, height, 'Y800', raw)
scanner.scan(image)
for symbol in image:
print 'decoded', symbol.type, 'symbol', '"%s"' % symbol.data
As you may see, I want to create a picture stream, send this stream to zbar to check if a qr code is contained in the picture. I am not able to run this code, this error is the result:
Segmentation fault
------------------ (program exited with code: 139) Press return to continue
I don't find any solution how to fixx this bug, any idea?
Kind regards;
回答1:
The shortage of all the other answers is that they have a large amount of DELAY - for example, what they are scanning and displaying to the screen was actually a frame taken several seconds ago and so on.
This is due to the slow CPU of Raspberry Pi. So the frame-rate is much bigger than the rate our software can read and scan.
With lots of effort, I finally made this code, which have LITTLE DELAY. So when you give it a QRCode/BarCode, it will give you a result in less than a second.
The trick I use is explained in the code.
import cv2
import cv2.cv as cv
import numpy
import zbar
import time
import threading
'''
LITTLE-DELAY BarCodeScanner
Author: Chen Jingyi (From FZYZ Junior High School, China)
PS. If your pi's V4L is not available, the cv-Window may have some error sometimes, but other parts of this code works fine.
'''
class BarCodeScanner(threading.Thread):
def __init__(self):
threading.Thread.__init__(self)
self.WINDOW_NAME = 'Camera'
self.CV_SYSTEM_CACHE_CNT = 5 # Cv has 5-frame cache
self.LOOP_INTERVAL_TIME = 0.2
cv.NamedWindow(self.WINDOW_NAME, cv.CV_WINDOW_NORMAL)
self.cam = cv2.VideoCapture(-1)
def scan(self, aframe):
imgray = cv2.cvtColor(aframe, cv2.COLOR_BGR2GRAY)
raw = str(imgray.data)
scanner = zbar.ImageScanner()
scanner.parse_config('enable')
#print 'ScanZbar', time.time()
width = int(self.cam.get(cv.CV_CAP_PROP_FRAME_WIDTH))
height = int(self.cam.get(cv.CV_CAP_PROP_FRAME_HEIGHT))
imageZbar = zbar.Image(width, height,'Y800', raw)
scanner.scan(imageZbar)
#print 'ScanEnd', time.time()
for symbol in imageZbar:
print 'decoded', symbol.type, 'symbol', '"%s"' % symbol.data
def run(self):
#print 'BarCodeScanner run', time.time()
while True:
#print time.time()
''' Why reading several times and throw the data away: I guess OpenCV has a `cache-queue` whose length is 5.
`read()` will *dequeue* a frame from it if it is not null, otherwise wait until have one.
When the camera has a new frame, if the queue is not full, the frame will be *enqueue*, otherwise be thrown away.
So in this case, the frame rate is far bigger than the times the while loop is executed. So when the code comes to here, the queue is full.
Therefore, if we want the newest frame, we need to dequeue the 5 frames in the queue, which is useless because it is old. That's why.
'''
for i in range(0,self.CV_SYSTEM_CACHE_CNT):
#print 'Read2Throw', time.time()
self.cam.read()
#print 'Read2Use', time.time()
img = self.cam.read()
self.scan(img[1])
cv2.imshow(self.WINDOW_NAME, img[1])
cv.WaitKey(1)
#print 'Sleep', time.time()
time.sleep(self.LOOP_INTERVAL_TIME)
cam.release()
scanner = BarCodeScanner()
scanner.start()
回答2:
In the line
scanner.scan(image)
you're using a variable that hasn't appeared in the code before. Because zbar is written in C, it doesn't catch that the variable is undefined, and the library tries to read garbage data as if it were an image. Hence, the segfault. I'm guessing you meant my_stream instead of image.
回答3:
i'm using QR decoding on raspberry for my project. I solved it by using subprocces module. Here is my function for QR decoding:
import subprocess
def detect():
"""Detects qr code from camera and returns string that represents that code.
return -- qr code from image as string
"""
subprocess.call(["raspistill -n -t 1 -w 120 -h 120 -o cam.png"],shell=True)
process = subprocess.Popen(["zbarimg -D cam.png"], stdout=subprocess.PIPE, shell=True)
(out, err) = process.communicate()
qr_code = None
# out looks like "QR-code: Xuz213asdY" so you need
# to remove first 8 characters plus whitespaces
if len(out) > 8:
qr_code = out[8:].strip()
return qr_code
You can easy add parameters to function such as img_widt and img_height and change this part of code
"raspistill -n -t 1 -w 120 -h 120 -o cam.png"
to
"raspistill -n -t 1 -w %d -h %d -o cam.png" % (img_width, img_height)
if you want different size of image for decoding.
回答4:
After reading this, I was able to come up with a pythonic solution involving OpenCV.
First, you build OpenCV on the Pi by following these instructions. That will probably take several hours to complete.
Now reboot the Pi and use the following script (assuming you have python-zbar installed) to get the QR/barcode data:
import cv2
import cv2.cv as cv
import numpy
import zbar
class test():
def __init__(self):
cv.NamedWindow("w1", cv.CV_WINDOW_NORMAL)
# self.capture = cv.CaptureFromCAM(camera_index) #for some reason, this doesn't work
self.capture = cv.CreateCameraCapture(-1)
self.vid_contour_selection()
def vid_contour_selection(self):
while True:
self.frame = cv.QueryFrame(self.capture)
aframe = numpy.asarray(self.frame[:,:])
g = cv.fromarray(aframe)
g = numpy.asarray(g)
imgray = cv2.cvtColor(g,cv2.COLOR_BGR2GRAY)
raw = str(imgray.data)
scanner = zbar.ImageScanner()
scanner.parse_config('enable')
imageZbar = zbar.Image( self.frame.width, self.frame.height,'Y800', raw)
scanner.scan(imageZbar)
for symbol in imageZbar:
print 'decoded', symbol.type, 'symbol', '"%s"' % symbol.data
cv2.imshow("w1", aframe)
c = cv.WaitKey(5)
if c == 110: #pressing the 'n' key will cause the program to exit
exit()
#
p = test()
Note: I had to turn the Raspi Camera's lens counterclockwise about 1/4 - 1/3 of a turn before zbar was able to detect the QR/barcodes.
With the above code, whenever zbar detects a QR/barcode, the decoded data is printed in the console. It runs continuously, only stopping if the n key is pressed
回答5:
For anyone that is still looking for a solutions to this... This code is ugly but it works from a regular webcam pretty well, haven't tried the Pi camera yet. I'm new to python so this is the best I could come up with that worked in both Python2 and 3.
Make a bash script called kill.sh and make it executable... (chmod -x)
#kill all running zbar tasks ... call from python
ps -face | grep zbar | awk '{print $2}' | xargs kill -s KILL
Then do a system call from python like so...
import sys
import os
def start_cam():
while True:
#Initializes an instance of Zbar to the commandline to detect barcode data-strings.
p=os.popen('/usr/bin/zbarcam --prescale=300x200','r')
#Barcode variable read by Python from the commandline.
print("Please Scan a QRcode to begin...")
barcode = p.readline()
barcodedata = str(barcode)[8:]
if barcodedata:
print("{0}".format(barcodedata))
#Kills the webcam window by executing the bash file
os.system("/home/pi/Desktop/kill.sh")
start_cam()
Hopefully this helps people with the same questions in the future!
回答6:
Quite a late response, but I ran into a number of issues while trying to get Zbar working. Though I was using a USB webcam, but I had to install multiple libraries before i could get to install zbar. I installed fswebcam, python-zbar, libzbar-dev and finally ran setup.py.
More importantly, the zbar from sourceforge did not work for me, but the one from github, which has a Python wrapper worked for me.
I documented my steps by steps at http://techblog.saurabhkumar.com/2015/09/scanning-barcodes-using-raspberry-pi.html if it might help
回答7:
Just a small modified from Dan2theR, because I don't want to create another shell file.
import sys
import os
p = os.popen('/usr/bin/zbarcam --prescale=300x300 --Sdisable -Sqrcode.enable', 'r')
def start_scan():
global p
while True:
print('Scanning')
data = p.readline()
qrcode = str(data)[8:]
if(qrcode):
print(qrcode)
try:
start_scan()
except KeyboardInterrupt:
print('Stop scanning')
finally:
p.close()
来源：https://stackoverflow.com/questions/23538522/scanning-qr-code-via-zbar-and-raspicam-module