gamma.py

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# Example : gamma correction /power-law transform on an image
# from an attached web camera (or video file specified on command line)

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

# Copyright (c) 2015 School of Engineering & Computing Science,
# Copyright (c) 2019 Dept Computer Science,
#                    Durham University, UK
# License : LGPL - http://www.gnu.org/licenses/lgpl.html

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import cv2
import argparse
import sys
import numpy as np

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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(
    "-r",
    "--rescale",
    type=float,
    help="rescale image by this factor",
    default=1.0)
parser.add_argument(
    'video_file',
    metavar='video_file',
    type=str,
    nargs='?',
    help='specify optional video file')
args = parser.parse_args()


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# this function is called as a call-back everytime the trackbar is moved
# (here we just do nothing)

def nothing(x):
    pass

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# power law transform
# image - colour image
# gamma - "gradient" co-efficient of gamma function


def powerlaw_transform(image, gamma):

    # compute power-law transform
    # remembering not defined for pixel = 0 (!)

    # handle any overflow in a quick and dirty way using 0-255 clipping

    image = np.clip(np.power(image, gamma), 0, 255).astype('uint8')

    return image

#####################################################################

# define video capture object


cap = cv2.VideoCapture()

# define display window name

window_name = "Live Camera Input"  # window name
window_name2 = "Gamma Corrected (Power-Law Transform)"  # window name

# if command line arguments are provided try to read video_file
# otherwise default to capture from attached H/W 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(window_name, cv2.WINDOW_AUTOSIZE)
    cv2.namedWindow(window_name2, cv2.WINDOW_AUTOSIZE)

    # add some track bar controllers for settings

    gamma = 100  # default gamma - no change

    cv2.createTrackbar("gamma, (* 0.01)", window_name2, gamma, 500, nothing)

    while (keep_processing):

        # if video file or camera successfully open then read frame from video

        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

            # rescale if specified

            if (args.rescale != 1.0):
                frame = cv2.resize(
                    frame, (0, 0), fx=args.rescale, fy=args.rescale)

        # get parameters from track bars

        gamma = cv2.getTrackbarPos("gamma, (* 0.01)", window_name2) * 0.01

        # make a copy

        gamma_img = frame.copy()

        # use power-law function to perform gamma correction

        gamma_img = powerlaw_transform(gamma_img, gamma)

        # display image

        cv2.imshow(window_name, frame)
        cv2.imshow(window_name2, gamma_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

    # close all windows

    cv2.destroyAllWindows()

else:
    print("No usable camera connected.")


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