Terrain from IMG, JP2, or Tiff File

Hi, I need to plot high resolution lunar terrain mostly as contour plots and using meshm from the mapping toolbox. I have access to .tiff, .IMG, or .JP2 files:

• IMG and JP2: http://imbrium.mit.edu/BROWSE/LOLA_GDR/POLAR/SOUTH_POLE/
• IMG and JP2: https://pds-geosciences.wustl.edu/missions/lro/lola.htm
• tiff: http://wms.lroc.asu.edu/lroc/view_rdr/NAC_POLE_SOUTH

Topographic maps, see link below, have been produced from this data previously and this is what I've been comparing my results to.

• https://www.lpi.usra.edu/lunar/lunar-south-pole-atlas/

My primary issue is how to get elevation information from these files. I've tried geotiffread but I don't know how to translate the grayscale image information I get from the function into actual elevations after reading the tiff file. I've tried using geotiffinterp from the file exchange (https://www.mathworks.com/matlabcentral/fileexchange/47899-geotiffinterp) to do this but I wasn't getting elevations that were close to the known values (all the values were from 0 to 256 so I think this was just color information and not elevation info I was getting). For the IMG files I've used fread to read in the image but after that I'm again stuck with how to get elevation information from what I've read in.

To summarize, how can I get elevation information to plot the terrain from tiff, IMG, or JP2 files like those from the links above?

Thank you for your help!