How many USB cameras can be accessed by one PC

Question

I am just wondering how many USB cameras can be accessed by one desktop PC? Is there any limit? I am planning to create my own Windows application (using .NET) to capture ar

Answer 1

a bit late sorry :) What i found out is that a single USB card is limited by the USB bandwidth. but.. if you add USB cards on the PCI you can get more cameras but... most vendors do not bother to alter the USB card address the computer see so you need to buy USB to PCI cards from different vendors and try your luck. I had the same problem with firewire. here is my code for python. (thank other programmers on stackoverflow)

# show multiple usb cameras

import os
import cv2
import threading
import time
import datetime

#font for image writing
font = cv2.FONT_HERSHEY_SIMPLEX
fontScale = 1
fontColor = (255,180,180)
lineType = 2

SaveImage = True # if true save images
duration = [100,100,100,10,10] # time between image saves in sec
IMAGESAVEPATH = "C:/tmp/pix" # path for camera to store image to

ShowText = True #Show text on image - text will be  saved with the image

#camera thread. here me make a thread and its functions
class camThread(threading.Thread):
def __init__(self, previewName, camID):
    threading.Thread.__init__(self)
    self.previewName = previewName
    self.camID = camID
def run(self):
    print ("Starting " + self.previewName)
    camPreview(self.previewName, self.camID)

#camera main loop - here we init the specific camera and start it then have a             window to show the image and we store the image to the right directory
def camPreview(previewName, camID):
    cv2.namedWindow(previewName)
cam = cv2.VideoCapture(camID) #start the camera (the cameras are numbered by the         order they are connected to the computer)
if cam.isOpened():  # try to get the first frame
    cam.set(3,4000)    #this will bring the largest frame set    
    cam.set(4,4000)
    cam.set(5,1) #fps
    time.sleep(2)
    cam.set(15, -1.0)
    rval, frame = cam.read() #read the image
else:
    rval = False

TStart = time.time() # time  for next image
mpath = os.path.join(IMAGESAVEPATH, str(camID)) #make sure the directory we save in exists, otherwise make it
print("try to make dir ", mpath, " T " , time.time())
if not os.path.exists(mpath):
    os.makedirs(mpath)
    
    cv2.namedWindow(previewName, cv2.WINDOW_NORMAL)

while rval: #if we get an image
    height, width, channels = frame.shape
    if ShowText: # write text on the image
        caption = str(camID) + " - " + str(height) + " " + str(width) + " "
        cv2.putText(frame,str(caption),(20,20),font, fontScale, fontColor, lineType)
    cv2.imshow(previewName, frame) # show image in its window
    #cv2.resizeWindow(previewName, 1280,960) # resize all windows removed ofer
    rval, frame = cam.read() #raed next image
    key = cv2.waitKey(20) 
    if key == 27:  # exit on ESC
        print("key pressed ", camID)
        break
    
    TDiff = int(time.time() - TStart) # time difference from last image
    if (SaveImage and TDiff > duration[camID]): # Save if time passed
        file_name = os.path.join(mpath, "T{:%Y.%m.%d %H-%M-%S}.jpg".format(datetime.datetime.now())) # make file name string
        cv2.imwrite(file_name, frame) 
        print("\rsaved to : ", file_name)
        TStart = time.time() #reset time to next image
        
    cv2.destroyWindow(previewName)

# Create 5 threads as follows
thread1 = camThread("Camera 1", 0)
thread2 = camThread("Camera 2", 1)
thread3 = camThread("Camera 3", 2)
thread4 = camThread("Camera 4", 3)
thread5 = camThread("Camera 5", 4)
thread1.start()
thread2.start()
thread3.start()
thread4.start()
thread5.start()