我想计算I（x，y）/Io（x，y）的强度。
首先，我使用rawpy读取图像，因为我有.nef文件（Nikon raw）。然后我使用opencv将图像转换为灰度，并计算I（x，y）/Io（x，y）。其中I（x，y）是“brut”，Io（x，y）是“init”。
但是在划分两个图像（cv2.divide）之后，我使用cv2.meanStdDev（test），我有一个“Nan”值。
当我使用matplotlib绘制“test”时，我得到了这个：

当我从cv 2中使用imshow时，我得到了我想要的：

我不明白为什么我从cv2.meanStdDev（test）中得到nan，以及两个图之间的差异？

import numpy as np
import cv2
import rawpy
import rawpy.enhance
import matplotlib.pyplot as plt

####################
# Reading a Nikon RAW (NEF) image
init="/media/alexandre/Transcend/Expérience/Ombroscopie/eau/initialisation/2023-09-19_19-02-33.473.nef"
brut="/media/alexandre/Transcend/Expérience/Ombroscopie/eau/DT0.2/2023-09-20_10-34-27.646.nef"
bruit="/media/alexandre/Transcend/Expérience/Ombroscopie/eau/bruit-electronique/2023-09-18_18-59-34.994.nef"

####################
# This uses rawpy library
print("reading init file using rawpy.")
raw_init = rawpy.imread(init)
image_init = raw_init.postprocess(use_camera_wb=True, output_bps=16)
print("Size of init image read:" + str(image_init.shape))

print("reading brut file using rawpy.")
raw_brut = rawpy.imread(brut)
image_brut = raw_brut.postprocess(use_camera_wb=True, output_bps=16)
print("Size of brut image read:" + str(image_brut.shape))

print("reading bruit file using rawpy.")
raw_bruit = rawpy.imread(bruit)
image_bruit = raw_bruit.postprocess(use_camera_wb=True, output_bps=16)
print("Size of bruit image read:" + str(image_bruit.shape))

####################
# (grayscale) OpenCV
print(image_init.dtype)
init_grayscale = cv2.cvtColor(image_init, cv2.COLOR_RGB2GRAY).astype(float)
brut_grayscale = cv2.cvtColor(image_brut, cv2.COLOR_RGB2GRAY).astype(float)
bruit_grayscale = cv2.cvtColor(image_bruit, cv2.COLOR_RGB2GRAY).astype(float)

print(np.max(brut_grayscale))
print(init_grayscale.dtype)

"test = (brut_grayscale)/(init_grayscale)"
init = init_grayscale-bruit_grayscale
test = cv2.divide((brut_grayscale),(init_grayscale))

print(test.shape)
print(test.dtype)
print(type(test))

print(test.max())
print(test.min())

####################
# Irms
mean, std_dev = cv2.meanStdDev(test)
intensite_rms = std_dev[0][0]
print("Intensité RMS de l'image :", intensite_rms)

####################
# Matplotlib
import matplotlib.pyplot as plt
plt.imshow(test, cmap='gray')
plt.show()

# Show using OpenCV
import imutils
image_rawpy = imutils.resize(test, width=1080)
cv2.imshow("image_rawpy read file: ", image_rawpy)
cv2.waitKey(0)
cv2.destroyAllWindows("image_rawpy read file: " , image_rawpy)

产出：

reading init file using rawpy.
Size of init image read:(5520, 8288, 3)
reading brut file using rawpy.
Size of brut image read:(5520, 8288, 3)
reading bruit file using rawpy.
Size of bruit image read:(5520, 8288, 3)
uint16
37977.0
float64
(5520, 8288)
float64
<class 'numpy.ndarray'>
nan
nan
Intensité RMS de l'image : nan
^CTraceback (most recent call last):
  File "ombro.py", line 62, in <module>
    plt.show()
  File "/home/alexandre/.local/lib/python3.8/site-packages/matplotlib/pyplot.py", line 368, in show
    return _backend_mod.show(*args, **kwargs)
  File "/home/alexandre/.local/lib/python3.8/site-packages/matplotlib/backend_bases.py", line 3544, in show
    cls.mainloop()
  File "/home/alexandre/.local/lib/python3.8/site-packages/matplotlib/backends/backend_qt.py", line 1023, in mainloop
    qt_compat._exec(qApp)
  File "/usr/lib/python3.8/contextlib.py", line 120, in __exit__
    next(self.gen)
  File "/home/alexandre/.local/lib/python3.8/site-packages/matplotlib/backends/qt_compat.py", line 262, in _maybe_allow_interrupt
    old_sigint_handler(*handler_args)