How to read the first image in folder using opencv (python)

Question

I am using the following code to read and compute difference between consecutive images in a folder:

def cal_for_frames(video_path):
    frames = glob(os.path.join(video_path, '*.jpg'))
    frames.sort()


    diff = []
    prev = cv2.imread(frames[0])
    prev = cv2.cvtColor(prev, cv2.COLOR_BGR2GRAY)
    print(prev.dtype, prev.shape)
    for i, frame_curr in enumerate(frames):
        curr = cv2.imread(frame_curr)
        curr = cv2.cvtColor(curr, cv2.COLOR_BGR2GRAY)
        print(curr.dtype, curr.shape)
        tmp_diff = compute_DIFF(prev, curr)
        diff.append(tmp_diff)
        prev = curr
    
    return diff

Now I want my prev to always be the first image in the folder (i.e., to be constant). What changes do I need to make to prev = cv2.imread(frames[0]) to do this? where frame000001 is the first image in the folder.

Ahmet · Accepted Answer · 2020-10-30 17:08:43Z

1

Just remove the for-loop's last line: prev = curr and prev = cv2.imread(frames[0]).

But you can speed up your for-loop. If print function is not crucial, then you can do:

diff = [compute_DIFF(prev, cv2.cvtColor(cv2.imread(frame_curr), cv2.COLOR_BGR2GRAY)) for i, frame_curr in enumerate(frames)]

Code:

def cal_for_frames(video_path):
    frames = glob(os.path.join(video_path, '*.jpg')).sort()
    prev = cv2.cvtColor(cv2.imread(frames[0]), cv2.COLOR_BGR2GRAY)
    print(prev.dtype, prev.shape)

    diff = [compute_DIFF(prev, cv2.cvtColor(cv2.imread(frame_curr), cv2.COLOR_BGR2GRAY)) for i, frame_curr in enumerate(frames)]

    return diff

answered Oct 30, 2020 at 17:08

Ahmet

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3 Comments

SanOlans Over a year ago

Thanks! removing prev=curr did the trick. One more question, I am trying to save the images with "frame{%06d}.jpg".format(i) but I get a KeyError: '%06d'. It works fine when when I use "frame{}.jpg".format(i), I'd like to know what I am doing wrong, thanks.

SanOlans Over a year ago

Using "frame{%06d}.jpg".format(i) worked in the past, don't know why it doesn't work now.

SanOlans Over a year ago

I got it to work. I changed "frame{%06d}.jpg".format(i) to "frame{:06d}.jpg".format(i). Thanks for your help.

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