Problem to retain original grayscale values, if process PNG image with Python.

I need to process a 12-bit grayscale image saved in png format with Python. A monochromatic 12-bit camera was used as the signal source. The image file was created with  IMAQ Write File2.vi. The maximum pixel value is 419 counts.
When I load the image with Python3 imageio-2.32.0imageio.imread("testimagefile"), it seems that the image is scaled automatically, the maximum value is now 55019 counts. Does IMAQ Write File2.vi store PNG Files with some kind of scaled flag? Does anyone have any ideas on how to get the original values?