JPEG compression, by the xv program, at the default
parameter setting of 75%, gives a 14,798 byte file. (The JPEG parameter
scale is arbitrary, and does not mean, say, 75% accuracy.)
Parameters of 50 and 25 give files of 10,408 and 7,275 bytes respectively.
The
compression is quite impressive, if you can tolerate the errors.
Table t:jpeg5025 shows a histogram of the errors for three JPEG
parameter setting. For the 75 parameter, 
of the elevations
were not changed by JPEG compression, the average elevation was
changed by 
scaled units, which is 4 original units
(meters), and the worst change was 8 scaled units. The RMS
error is 
scaled units, 
original units.
xv also has a smoothing parameter for JPEG compression. However it doesn't have much effect; setting it to the high value of 50% reduced the compressed files by about 2%.