I think you probably need to learn about raster data.I am looking for something to send you that will help, haven't quite figured out how or what to send. My attempt to paste a screenshot form ESRI ArcMap help didnt work, but there must be something equal in Autcad Map Help as well.
You can use raster cell values to perform map algebra. I am not sure why the max cell size in your example is so large...are there really so many values between white and black? Amazing! Thats infinity for you, I guess.
I can at least give you the book answer...
Changing Brightness, Color, or Transparency for Raster Images
To display your image in color or grayscale
4. If you select grayscale, adjust the range for grayscale mapping with the Cell Minimum and Cell Maximum values.
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