Save float array to image (with EXR format)

Question

The following code does not work, it converts values to np.uint8 before writing image to disk.

import cv2
import numpy as np
# Generate dummy gradient with float values
arr = np.arange(0,10,0.02)
arr = np.repeat(arr, arr.shape[0])
arr.reshape((500,500))
cv2.imwrite('output.exr',arr)
# At this point, returns True. Opening the image with OpenEXR 1.4 shows values have become UINT8 instead of Float
arr = cv2.imread('output.exr')
# Shape is (1000, 1000, 3)
print(arr[10,10])
array([0, 0, 0], dtype=uint8) # All float data is lost

As a little bonus, the documentation is very not helpful

$ pydoc cv2.imwrite
Help on built-in function imwrite in cv2:

cv2.imwrite = imwrite(...)
    imwrite(filename, img[, params]) -> retval

Doesn't say what the params should be...

How can I save an array with floating point values to EXR format ? (using OpenCV)

Answer 1

imageio can save EXR files in any data format, (and it also supports a large amount of other image formats).

Pretty much a life saver for reading and writing most images:

import numpy as np
import imageio

# Generate dummy random image with float values
arr = np.random.uniform(0.0, 1.0, size=(500,500))

# freeimage lib only supports float32 not float64 arrays
arr = arr.astype("float32")

# Write to disk
imageio.imwrite('float_img.exr', arr)

# Read created exr from disk
img = imageio.imread('float_img.exr')

assert img.dtype == np.float32