How do I standardize DICOM pixel values?

I am working with sets of several DICOM images from different sources. These images are plain radiographs and have pixel "values" in the thousands and are incompatible between images. I am looking for a way to standardize all values ​​in a file in order to compare two images.

Note that since these are simple X-rays, I cannot use Hounsfield units. Another possible solution is to scale all values ​​from 0-1, with 1 being the brightest pixel, but that doesn't seem very scientific. Is there any other way to do this?