16-bit gray scale images flattened by WCB. Flattening involved:
  - cropping of each image to an area of interest and filling the surround with pixels of 0 intensity;
  - division of each numerator image by a corresponding flats image;
  - restoration of the original mean pixel value of the numerator image.

The flats images used were those for Spectralon at the 00 position (Spec-00) recorded at the time the images of interest were captured.

Flats images were first median filtered (r = 20), and Gaussian blurred (r = 2) to reduce noise due to small imperfections and contaminants of the Spectralon reference material.

Resulting quotient images were normalized to a 16 bit range.