colour_query.py

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# Example : displaying and interact with image from file

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

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

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import cv2

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# mouse callback function - displays or sets image colour at the click
# location of the mouse


def colour_query_mouse_callback(event, x, y, flags, param):

    # records mouse events at postion (x,y) in the image window

    # left button click prints colour information at click location to stdout

    if event == cv2.EVENT_LBUTTONDOWN:
        print("BGR colour @ position (%d,%d) = %s" %
              (x, y, ', '.join(str(i) for i in img[y, x])))

    # right button sets colour information at click location to white

    elif event == cv2.EVENT_RBUTTONDOWN:
        img[y, x] = [255, 255, 255]


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# define display window name

window_name = "Displayed Image"  # window name

# read an image from the specified file (in colour)

img = cv2.imread('example.jpg', cv2.IMREAD_COLOR)

# check it has loaded

if img is not None:

    # create a named window object

    cv2.namedWindow(window_name)

    # set the mouse call back function that will be called every time
    # the mouse is clicked inside the associated window

    cv2.setMouseCallback(window_name, colour_query_mouse_callback)

    # set a loop control flag

    keep_processing = True

    while (keep_processing):

        # display this blurred image in a named window

        cv2.imshow(window_name, img)

        # start the event loop - essential

        # cv2.waitKey() is a keyboard binding function (argument is the time in
        # ms). 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)

        # wait 40ms (i.e. 1000ms / 25 fps = 40 ms)
        key = cv2.waitKey(40) & 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

        if (key == ord('x')):
            keep_processing = False

else:
    print("No image file successfully loaded.")

# ... and finally close all windows

cv2.destroyAllWindows()

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