一、skimage.util.random_noise用法
可以實現的噪聲類型包括：高斯白噪聲、泊松噪聲、椒鹽噪聲、鹽噪聲、椒噪聲、乘性噪聲等等。
具體用法文檔如下介紹：
random_noise(image, mode='gaussian', seed=None, clip=True, **kwargs)
Function to add random noise of various types to a floating-point image.
Parameters
----------
image : ndarray
Input image data. Will be converted to float.
mode : str, optional
One of the following strings, selecting the type of noise to add:
- 'gaussian' Gaussian-distributed additive noise.
- 'localvar' Gaussian-distributed additive noise, with specified
local variance at each point of `image`.
- 'poisson' Poisson-distributed noise generated from the data.
- 'salt' Replaces random pixels with 1.
- 'pepper' Replaces random pixels with 0 (for unsigned images) or
-1 (for signed images).
- 's&p' Replaces random pixels with either 1 or `low_val`, where
`low_val` is 0 for unsigned images or -1 for signed
images.
- 'speckle' Multiplicative noise using out = image + n*image, where
n is uniform noise with specified mean & variance.
seed : int, optional
If provided, this will set the random seed before generating noise,
for valid pseudo-random comparisons.
clip : bool, optional
If True (default), the output will be clipped after noise applied
for modes `'speckle'`, `'poisson'`, and `'gaussian'`. This is
needed to maintain the proper image data range. If False, clipping
is not applied, and the output may extend beyond the range [-1, 1].
mean : float, optional
Mean of random distribution. Used in 'gaussian' and 'speckle'.
Default : 0.
var : float, optional
Variance of random distribution. Used in 'gaussian' and 'speckle'.
Note: variance = (standard deviation) ** 2. Default : 0.01
local_vars : ndarray, optional
Array of positive floats, same shape as `image`, defining the local
variance at every image point. Used in 'localvar'.
amount : float, optional
Proportion of image pixels to replace with noise on range [0, 1].
Used in 'salt', 'pepper', and 'salt & pepper'. Default : 0.05
salt_vs_pepper : float, optional
Proportion of salt vs. pepper noise for 's&p' on range [0, 1].
Higher values represent more salt. Default : 0.5 (equal amounts)
Returns
-------
out : ndarray
Output floating-point image data on range [0, 1] or [-1, 1] if the
input `image` was unsigned or signed, respectively.
Notes
-----
Speckle, Poisson, Localvar, and Gaussian noise may generate noise outside
the valid image range. The default is to clip (not alias) these values,
but they may be preserved by setting `clip=False`. Note that in this case
the output may contain values outside the ranges [0, 1] or [-1, 1].
Use this option with care.
Because of the prevalence of exclusively positive floating-point images in
intermediate calculations, it is not possible to intuit if an input is
signed based on dtype alone. Instead, negative values are explicitly
searched for. Only if found does this function assume signed input.
Unexpected results only occur in rare, poorly exposes cases (e.g. if all
values are above 50 percent gray in a signed `image`). In this event,
manually scaling the input to the positive domain will solve the problem.
The Poisson distribution is only defined for positive integers. To apply
this noise type, the number of unique values in the image is found and
the next round power of two is used to scale up the floating-point result,
after which it is scaled back down to the floating-point image range.
To generate Poisson noise against a signed image, the signed image is
temporarily converted to an unsigned image in the floating point domain,
Poisson noise is generated, then it is returned to the original range.