Plot a histogram of the image:
w,0 plot,histogram(meteosat) tv,bytscl(meteosat) ;OR tvscl(meteosat) plot,histogram(bytscl(meteosat))
bytscl will rescale any array to 0-255.
Contrast in some areas can be improved using,
tv,hist_equal(meteosat) plot,histogram(hist_equal(meteosat))