python - How does [...,::-1] work in slice notation? -


opencv uses bgr encoding, , img[...,::-1] swaps red , blue axes of img when image needs in more common rgb. i've been using several months still don't understand how works.

the slice operator works 3 params. start(inclusive), end(exclusive) , step. if start not specified gets start of array, same end last element. if step not specified default 1.

this way, if [1, 2, 3, 4][0:2] return [1, 2]

if [1, 2, 3, 4][1:] return [2, 3, 4]

if [1, 2, 3, 4][1::2] return [2, 4]

for negative indexes, means iterate backwards [1, 2, 3, 4][::-1] says, starting element until last element iterate list backwards 1 element @ time, returning [4, 3, 2, 1].

as question not entirely clear hope clears functioning , make answer.


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