Flips a 2D array around vertical, horizontal, or both axes

dst = cv.flip(src, flipCode)

Input

• src input array.
• flipCode a flag to specify how to flip the array:
  • 0 means flipping around the x-axis
  • positive value (for example, 1) means flipping around y-axis.
  • Negative value (for example, -1) means flipping around both axes.

Output

• dst output array of the same size and type as src.

The function cv.flip flips the array in one of three different ways (row and column indices are 0-based):

           { src(size(src,1)-i-1,j)                if flipCode = 0
dst(i,j) = { src(i,size(src,2)-j-1)                if flipCode > 0
           { src(size(src,1)-i-1,size(src,2)-j-1)  if flipCode < 0

The example scenarios of using the function are the following:

• Vertical flipping of the image (flipCode == 0) to switch between top-left and bottom-left image origin. This is a typical operation in video processing on Microsoft Windows OS.
• Horizontal flipping of the image with the subsequent horizontal shift and absolute difference calculation to check for a vertical-axis symmetry (flipCode > 0).
• Simultaneous horizontal and vertical flipping of the image with the subsequent shift and absolute difference calculation to check for a central symmetry (flipCode < 0).
• Reversing the order of point arrays (flipCode > 0 or flipCode == 0).