Numpy：避免嵌套循环操作矩阵值图像

我是python和numpy的初学者，我需要计算矩阵值图像的每个“像素”（即x，y位置）的矩阵对数尺寸NxMx3x3。 3×3是每个像素处的矩阵的尺寸。Numpy：避免嵌套循环操作矩阵值图像

到目前为止，我已经写的功能如下：

def logm_img(im): 
    from scipy import linalg 
    dimx = im.shape[0] 
    dimy = im.shape[1] 
    res = zeros_like(im) 
    for x in range(dimx): 
     for y in range(dimy): 
      res[x, y, :, :] = linalg.logm(asmatrix(im[x,y,:,:])) 
    return res

是否确定？有没有办法避免两个嵌套循环？

来源

2012-03-14 Tyler Durden

-2

Numpy可以做到这一点。只需拨打numpy.log：

>>> import numpy 
>>> a = numpy.array(range(100)).reshape(10, 10) 
>>> b = numpy.log(a) 
__main__:1: RuntimeWarning: divide by zero encountered in log 
>>> b 
array([[  -inf, 0.  , 0.69314718, 1.09861229, 1.38629436, 
     1.60943791, 1.79175947, 1.94591015, 2.07944154, 2.19722458], 
     [ 2.30258509, 2.39789527, 2.48490665, 2.56494936, 2.63905733, 
     2.7080502 , 2.77258872, 2.83321334, 2.89037176, 2.94443898], 
     [ 2.99573227, 3.04452244, 3.09104245, 3.13549422, 3.17805383, 
     3.21887582, 3.25809654, 3.29583687, 3.33220451, 3.36729583], 
     [ 3.40119738, 3.4339872 , 3.4657359 , 3.49650756, 3.52636052, 
     3.55534806, 3.58351894, 3.61091791, 3.63758616, 3.66356165], 
     [ 3.68887945, 3.71357207, 3.73766962, 3.76120012, 3.78418963, 
     3.80666249, 3.8286414 , 3.8501476 , 3.87120101, 3.8918203 ], 
     [ 3.91202301, 3.93182563, 3.95124372, 3.97029191, 3.98898405, 
     4.00733319, 4.02535169, 4.04305127, 4.06044301, 4.07753744], 
     [ 4.09434456, 4.11087386, 4.12713439, 4.14313473, 4.15888308, 
     4.17438727, 4.18965474, 4.20469262, 4.21950771, 4.2341065 ], 
     [ 4.24849524, 4.26267988, 4.27666612, 4.29045944, 4.30406509, 
     4.31748811, 4.33073334, 4.34380542, 4.35670883, 4.36944785], 
     [ 4.38202663, 4.39444915, 4.40671925, 4.41884061, 4.4308168 , 
     4.44265126, 4.4543473 , 4.46590812, 4.47733681, 4.48863637], 
     [ 4.49980967, 4.51085951, 4.52178858, 4.53259949, 4.54329478, 
     4.55387689, 4.56434819, 4.57471098, 4.58496748, 4.59511985]])

来源

2012-03-14 16:46:55 Bogdan

其实我不想计算逐元素对数，但包含在我的M×N的图像的每个3x3矩阵的矩阵数http://en.wikipedia.org/wiki/Logarithm_of_a_matrix。这就是为什么我使用logm（）而不是日志。 – 2012-03-14 16:55:08

Numpy：避免嵌套循环操作矩阵值图像

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