使用numpy实现矩阵的翻转(flip)与旋转_Python

numpy.flip(m, axis=None)

Reverse the order of elements in an array along the given axis.

The shape of the array is preserved, but the elements are reordered.

把m在axis维度进行切片，并把这个维度的index进行颠倒

示例

随机生成一个二维数组

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									import  numpy as np

									a=np.random.randint(1,9,size=9).reshape((3,3))

[[5 8 6]
[3 1 7]
[8 7 8]]

axis=0：上下翻转，意味着把行看成整体，行的顺序发生颠倒，每一行的元素不发生改变

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									print(np.flip(a,axis=0))

[[8 7 8]
[3 1 7]
[5 8 6]]

axis=1：左右翻转，意味着把列看成整体，列的顺序发生颠倒，每一列的元素不发生改变

				?

									print(np.flip(a,axis=1))

[[6 8 5]
[7 1 3]
[8 7 8]]

Numpy矩阵的旋转

使用skimage.io读出来的图片是numpy.darray格式，掌握numpy矩阵的旋转与翻转，可实现数据增广（data augmentation）。

可用rot90函数实现，例子如下：

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									import numpy as np

									mat = np.array([[1,3,5],

									                [2,4,6],

									                [7,8,9]

									                ])

									print mat, "# orignal"

									mat90 = np.rot90(mat, 1)

									print mat90, "# rorate 90 <left> anti-clockwise"

									mat90 = np.rot90(mat, -1)

									print mat90, "# rorate 90 <right> clockwise"

									mat180 = np.rot90(mat, 2)

									print mat180, "# rorate 180 <left> anti-clockwise"

									mat270 = np.rot90(mat, 3)

									print mat270, "# rorate 270 <left> anti-clockwise"