方法#1使用Scipy's 2D max filter
-
from scipy.ndimage.filters import maximum_filter as maxf2D
# Store shapes of inputs
N,M = window_size
P,Q = a.shape
# Use 2D max filter and slice out elements not affected by boundary conditions
maxs = maxf2D(a, size=(M,N))
max_Map_Out = maxs[M//2:(M//2)+P-M+1, N//2:(N//2)+Q-N+1]
方法2使用Scikit's 2D sliding window views
- 在窗口的大小和它的使用
from skimage.util.shape import view_as_windows
N,M = window_size
max_Map_Out = view_as_windows(a, (M,N)).max(axis=(-2,-1))
注:原来的做法有窗口大小以翻转方式对齐,即的第一个形状参数沿着第二轴滑动,而第二形状参数决定窗沿着第一轴滑动的方式。对于滑动最大值过滤的其他问题可能不是这种情况,我们通常对2D
数组的第一个轴使用第一个形状参数,对于第二个形状参数也使用类似的方法。因此,要解决这些情况,只需使用:M,N = window_size
并按原样使用其余代码。
运行测试
途径 -
def org_app(a, window_size):
shape = a.shape[1], a.shape[0]
max_Map=np.full((shape[1]-window_size[1]+1,
shape[0]-window_size[0]+1),0,dtype=a.dtype)
for i in range(shape[1]-window_size[1]+1):
for j in range(shape[0]-window_size[0]+1):
window_max=np.max(a[i:i+window_size[1],j:j+window_size[0]])
max_Map[i][j]=window_max
return max_Map
def maxf2D_app(a, window_size):
N,M = window_size
P,Q = a.shape
maxs = maxf2D(a, size=(M,N))
return maxs[M//2:(M//2)+P-M+1, N//2:(N//2)+Q-N+1]
def view_window_app(a, window_size):
N,M = window_size
return view_as_windows(a, (M,N)).max(axis=(-2,-1))
时序和验证 -
In [573]: # Setup inputs
...: shape=(1050,300)
...: window_size=(120,60)
...: a = np.arange(shape[1]*shape[0]).reshape(shape[1],shape[0])
...:
In [574]: np.allclose(org_app(a, window_size), maxf2D_app(a, window_size))
Out[574]: True
In [575]: np.allclose(org_app(a, window_size), view_window_app(a, window_size))
Out[575]: True
In [576]: %timeit org_app(a, window_size)
1 loops, best of 3: 2.11 s per loop
In [577]: %timeit view_window_app(a, window_size)
1 loops, best of 3: 1.14 s per loop
In [578]: %timeit maxf2D_app(a, window_size)
100 loops, best of 3: 3.09 ms per loop
In [579]: 2110/3.09 # Speedup using Scipy's 2D max filter over original approach
Out[579]: 682.8478964401295
我认为它应该是:'max_Map = np.full((形状[1] - 对于范围内的形状(形状[1] -window_size [1] +1):'和'对于范围为j的window_size [1] + 1,shape [0] -window_size [0] +1) (shape [0] -window_size [0] +1):'覆盖所有元素。 – Divakar
@Divaka你是绝对正确的,我编辑了我的文章。谢谢! – Susie