为什么skimage表示过滤器不适用于浮点数组? [英] Why skimage mean filter does not work on float array?

问题描述

例如，我将对具有window_size=3的float数组应用均值过滤器.我找到了这个图书馆:

I am going to apply a mean filter on an array of float with window_size=3 for example. I have found this library:

from skimage.filters.rank import mean
import numpy as np

x=np.array([[1,8,10],
           [5,2,9],
           [7,2,9],
           [4,7,10],
           [6,14,10]])

print(x)
print(mean(x, square(3)))


[[ 1  8 10]
 [ 5  2  9]
 [ 7  2  9]
 [ 4  7 10]
 [ 6 14 10]]
[[ 4  5  7]
 [ 4  5  6]
 [ 4  6  6]
 [ 6  7  8]
 [ 7  8 10]]

但是此函数不能在浮点数组上运行:

but this function can't run on float arrays:

from skimage.filters.rank import mean
import numpy as np

x=np.array([[1,8,10],
           [5,2,9],
           [7,2,9],
           [4,7,10],
           [6,14,10]])

print(x)
print(mean(x.astype(float), square(3)))

File "/home/pd/RSEnv/lib/python3.5/site-packages/skimage/util/dtype.py", line 236, in convert
raise ValueError("Images of type float must be between -1 and 1.")
    ValueError: Images of type float must be between -1 and 1.

如何解决这个问题?

推荐答案

通常(这对其他编程语言有效)通常可以通过两种方式表示图像:

In general (and this is valid for other programming languages), an image can be typically represented in 2 ways:

• 强度值在[0, 255]范围内.在这种情况下，值的类型为uint8-无符号整数8字节.
• 强度值在[0, 1]范围内.在这种情况下，值的类型为float.

• with intensity values in the range [0, 255]. In this case the values are of type uint8 - unsigned integer 8-bytes.
• with intensity values in the range [0, 1]. In this case the values are of type float.

根据语言和库的不同，像素强度允许的值的类型和范围或多或少是允许的.

Depending on the language and library, the types and range of values allowed for the pixels' intensity can be more or less permissive.

这里的错误告诉您图像的像素值(您的array的类型为float，但它们不在[-1, 1]范围内.由于这些值介于[0, 255]之间，因此您只需将它们全部除以255.将值转换为整数也可以.

The error here tells you that the pixels' values of your image (your array are of type float but that they are not in the range [-1, 1]. As the values are in between [0, 255], you just need to divide them all by 255. Converting the values to integers may also work.

此处是scikit-image解释支持的图像数据类型.

Here is the user-guide of scikit-image explaining the image data-types supported.

此页面上的两个句子:

• 请注意，即使数据类型本身可以超出该范围，浮动图像也应限制在-1到1范围内
• 您永远不要在图像上使用astype，因为它违反了有关dtype范围的这些假设

• Note that float images should be restricted to the range -1 to 1 even though the data type itself can exceed this range
• You should never use astype on an image, because it violates these assumptions about the dtype range

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