Converting hand radiograph DICOM to PNG returns white/bright image-CodePudding

I am converting hand X-rays in DICOM format to PNG format. The code below does this:

import os
import cv2
import pydicom
import numpy as np
from PIL import Image

inputdir = "P:/BoneDataset/DICOM-File/0-RefinedDICOM/"
outdir = 'P:/BoneDataset/DICOM-File/1-ConvertedPics/'

test_list = [f for f in os.listdir(inputdir)]

for f in test_list[:10]:
    ds = pydicom.read_file(inputdir   f) # read dicom image
    img = ds.pixel_array # get image array
    scaled_img = (np.maximum(img,0) / img.max()) * 255.0
    img = scaled_img.astype(np.uint8)
    cv2.imwrite(outdir   f.replace('.dcm','.png'),img)

The image below shows some of the result (Input (DICOM) --> Output (PNG)):

Output of above sample code:

Output of img = lin_stretch_img(img, 0.01, 99.99) (may give better result):

Update

The polarity of the sample DICOM images is inverted.
The minimum value is intended to be displayed as white, and the maximum as black.

For correcting the polarity, we may execute img = 255-img (after converting to uint8).

Checking if the polarity is inverted:
According to the