Gray Scale: Generally refers to a monochrome ordering of 256 shades between black and white which are assigned to raster picture elements (pixels) according to reflected light, heat, and/or other relative intensity measurements.
A gray scale USGS digital orthophoto has the following characteristics:
The data consist of an ASCII header, followed by 8-bit, binary image data.
This appears to be a 15m gray scale image. At least that is what I got when I processed it. My reference says that you are supposed to be able to produce a 12.5m natural color image but this does not make any sense to me.
11-bit digitization (up to 2,048 levels of gray scale)
Discrete non-overlapping spectral bands
Open systems ...
Geological Survey (U.S.); Gray scale
GSA
General Services Administration (U.S.); Geological Society of America; Geological Survey of Alabama ...
Color table toggle - Different types of color tables are suitable for different raster map layers. The key t flips between the following color tables: red, green, blue color ramp; gray scale; smooth changing color wave; random colors; ...
Typically, this ranges from 8 to 14 bits, corresponding to 256 levels of the gray scale and up to 16,384 intensities or "shades" of colour, in each band.
 See also: Map, Image, Cover, Digital, Information
  
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