What does this thing returns : frame[:, :, ::-1]

Question

I cant sort out what this section of code is returning frame[:, :, ::-1]

success, frame = video_capture.read()
rgb_image = frame[:, :, ::-1]
results = model.detect([rgb_image], verbose=0)

Use `print(rgb_image)` to see what it returns. You should add `opencv` tag as question is related to it. — Sociopath, Mar 27 '19 at 05:09

ndrwnaguib · Answer 1 · 2019-03-27T05:22:05.660

2

The first : returns all rows, second : returns all columns, ::-1 returns the frame channels in a reversed way. Read more about slicing notation.

edited Mar 27 '19 at 05:22

answered Mar 27 '19 at 05:10

ndrwnaguib

4,539
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score 1 · Answer 2 · answered Mar 27 '19 at 13:39

1

OpenCV cv2.VideoCapture.read() returns frame in BGR format so frame[:, :, ::-1] converts it into RGB format. This is similar to using cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)

answered Mar 27 '19 at 13:39

pankaj Kang

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score 0 · Answer 3 · answered Mar 27 '19 at 05:21

Here you are assigning all rows and all columns in reverse order to rgb_image variable.

-1 here significant's that, reverse the list using last index of columns.

It's is also the shortcut way to slice the lists or tuples. In short it's a pythonic way to slice the non linear data structures in Python.

What does this thing returns : frame[:, :, ::-1]

3 Answers3