generic_interface.py

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# Example : perform generic live display from a video file
# specified on the command line (e.g. python FILE.py video_file) or from an
# attached web camera

# Author : Toby Breckon, toby.breckon@durham.ac.uk

# Copyright (c) 2015 - 2018 Toby Breckon, Engineering & Computing Science,
#                           Durham University, UK
# License : LGPL - http://www.gnu.org/licenses/lgpl.html

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import cv2
import argparse
import sys
import math

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keep_processing = True;

# parse command line arguments for camera ID or video file

parser = argparse.ArgumentParser(description='Perform ' + sys.argv[0] + ' example operation on incoming camera/video image')
parser.add_argument("-c", "--camera_to_use", type=int, help="specify camera to use", default=0)
parser.add_argument("-fs", "--fullscreen", action='store_true', help="run in full screen mode");
parser.add_argument('video_file', metavar='video_file', type=str, nargs='?', help='specify optional video file')
args = parser.parse_args()

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# define video capture object

cap = cv2.VideoCapture();

# define display window name

windowName = "Live Camera Input"; # window name

# if command line arguments are provided try to read video_name
# otherwise default to capture from attached camera

if (((args.video_file) and (cap.open(str(args.video_file))))
    or (cap.open(args.camera_to_use))):

    # create window by name (as resizable)

    cv2.namedWindow(windowName, cv2.WINDOW_NORMAL);

    while (keep_processing):

        # start a timer (to see how long processing and display takes)

        start_t = cv2.getTickCount();

        # if camera /video file successfully open then read frame

        if (cap.isOpened):
            ret, frame = cap.read();

            # when we reach the end of the video (file) exit cleanly

            if (ret == 0):
                keep_processing = False;
                continue;

        # ***
        # *** do any processing here ****
        # ***

        # display image

        cv2.imshow(windowName,frame);
        cv2.setWindowProperty(windowName, cv2.WND_PROP_FULLSCREEN,
                                cv2.WINDOW_FULLSCREEN & args.fullscreen);

        # stop the timer and convert to ms. (to see how long processing and display takes)

        stop_t = ((cv2.getTickCount() - start_t)/cv2.getTickFrequency()) * 1000;

        # start the event loop - essential

        # cv2.waitKey() is a keyboard binding function (argument is the time in milliseconds).
        # It waits for specified milliseconds for any keyboard event.
        # If you press any key in that time, the program continues.
        # If 0 is passed, it waits indefinitely for a key stroke.
        # (bitwise and with 0xFF to extract least significant byte of multi-byte response)
        # here we use a wait time in ms. that takes account of processing time already used in the loop

        # wait 40ms or less depending on processing time taken (i.e. 1000ms / 25 fps = 40 ms)

        key = cv2.waitKey(max(2, 40 - int(math.ceil(stop_t)))) & 0xFF;

        # It can also be set to detect specific key strokes by recording which key is pressed

        # e.g. if user presses "x" then exit  / press "f" for fullscreen display

        if (key == ord('x')):
            keep_processing = False;
        elif (key == ord('f')):
            args.fullscreen = not(args.fullscreen);

    # close all windows

    cv2.destroyAllWindows()

else:
    print("No video file specified or camera connected.");

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