Continuous image capture from webcam

As part of an online course, I currently take “Computer Vision with Embedded Machine Learning” where is need to collect images to make the dataset. I modified the original code so I can use my regular Linux box and webcam, not Raspberry Pi. The programme counts down and saves images every 7 seconds. That is enough time to change the object position. It also crops and resizes images to 96×96 px size as needed.

This is my setup:

Example images from created dataset:

And my code:

#!/usr/bin/env python3
"""
Image Capture

Displays image preview on screen.
Counts down and saves image 96*96px.
Restarts count down.
To exit press "q".

06.09.2021 Tauno Erik
"""

import cv2
import numpy as np

# Settings
file_num = 0
save_path = "./"      # Save images to current directory
file_suffix = ".png"  # Extension for image file
SECONDS_TO_COUNTDOWN = 7


def file_exists(filepath):
    """
    Returns true if file exists, false otherwise.
    """
    try:
        f = open(filepath, 'r')
        exists = True
        f.close()
    except:
        exists = False
    return exists

def get_filepath():
    """
    Returns the next available full path to image file
    """
    global file_num
    # Loop through possible file numbers to see if that file already exists
    filepath = save_path + str(file_num) + file_suffix
    while file_exists(filepath):
        file_num += 1
        filepath = save_path + str(file_num) + file_suffix

    return filepath

def main():
    countdown = SECONDS_TO_COUNTDOWN

    # Figure out the name of the output image filename
    filepath = get_filepath()

    cam = cv2.VideoCapture(0)

    # Set smaller resolution
    #cam.set(cv2.CAP_PROP_FRAME_WIDTH, 160) # 640
    #cam.set(cv2.CAP_PROP_FRAME_HEIGHT, 120) # 480

    # Initial countdown timestamp
    countdown_timestamp = cv2.getTickCount()

    while cam.isOpened():
        # Read camera
        ret, frame = cam.read()

        # Get timestamp for calculating actual framerate
        timestamp = cv2.getTickCount()

        # Each second, decrement countdown
        if (timestamp - countdown_timestamp) / cv2.getTickFrequency() > 1.0:
            countdown_timestamp = cv2.getTickCount()
            countdown -= 1
            
            # When countdown reaches 0, break out of loop to save image
            if countdown <= 0:
                # Get new image file name
                filepath = get_filepath()
                # Save image
                cv2.imwrite(filepath, resized)
                # Start new count down
                countdown = SECONDS_TO_COUNTDOWN
                #break

        # Frame resolution
        frame_height = frame.shape[0]
        frame_width = frame.shape[1]

        # Crop center of image
        new_size = 98
        start_y = int(frame_height/2 - new_size/2)
        end_y = int(frame_height/2 + new_size/2)
        start_x = int(frame_width/2 - new_size/2)
        end_x = int(frame_width/2 + new_size/2)
        # Crop
        cropped = frame[start_y:end_y, start_x:end_x]

        # Rezise to 96*96
        resized = cv2.resize(cropped, (96,96), interpolation=cv2.INTER_CUBIC)

        # Put text only on copied image
        copy = resized.copy()
        # Draw countdown on image
        cv2.putText(copy, 
                    str(countdown),
                    (round(resized.shape[1] / 2) - 15, round(resized.shape[0] / 2)+10),
                    cv2.FONT_HERSHEY_PLAIN,
                    4,
                    (255, 255, 255))

        # Display raw camera image
        cv2.imshow('Kaamera', copy)

        # Press 'q' to exit
        if cv2.waitKey(10) == ord('q'):
            break

    # Clean up
    cam.release()
    cv2.destroyAllWindows()

if __name__ == "__main__":
    print('To exit press "q"')
    main()

Original code: https://github.com/ShawnHymel/computer-vision-with-embedded-machine-learning/blob/master/1.1.3%20-%20Data%20Collection/Raspberry%20Pi/pi-cam-capture.py