OpenCV参数表中符号"["的含义是什么？

Hey there! Great question—those square brackets [ ] in OpenCV's parameter tables are super common but easy to overlook when you're getting familiar with the library. Let me break down their typical meanings clearly:

• Optional parameters (most common)
  This is the primary use of square brackets here. If a parameter is wrapped in [ ], it means you don’t need to explicitly pass a value for it. OpenCV will automatically use a predefined default value instead.
  For example, take the cv2.GaussianBlur function signature:
  cv2.GaussianBlur(src, ksize, sigmaX[, sigmaY[, borderType]])
  Here, sigmaY and borderType are optional. If you skip them, OpenCV sets sigmaY = sigmaX and uses the default border handling type (cv2.BORDER_DEFAULT) without you having to specify it.

• Array inputs with default options
  Sometimes [ ] indicates that a parameter accepts an array (like a Python list or NumPy array), but if you don’t provide one, it falls back to an empty array or a predefined default array.
  A common example is in contour detection functions, where a parameter like [hierarchy] lets you pass a hierarchy array if you need it, but you can omit it to use the default empty array instead.

• Value range indicators (rare)
  In a few cases, [ ] might denote the valid range of values a parameter can take. For instance, if a parameter is listed as threshold [0, 255], it means the threshold value should be between 0 and 255 (inclusive). This is less common than the first two uses, though.

Quick concrete example: When using cv2.threshold(src, thresh, maxval, type[, dst]), the dst parameter is in [ ]. You can either pass a pre-allocated destination array to store the result, or leave it out entirely—OpenCV will create and return the destination array for you automatically.

内容的提问来源于stack exchange，提问作者user9695304