On Wed, 2008-08-06 at 01:14 +0100, Glynn Clements wrote: > Nikos Alexandris wrote: > > > > The -g and -e switches make grey.log and grey.eq redundant > > > > By the way, something I don't understand (copy-paste from the manual): > > > > The -e flag equalizes the original raster's color table. It can preclude > > the need for grey.eq rule, when used as -e color=grey. Note however, > > that this will not yield a color table identical to color=grey.eq, > > because grey.eq scales the fraction by 256 to get a grey level, while -e > > uses it to interpolate the original colour table. > > It then goes on to say: > > If the original colour table is a 0-255 grey scale, -e is > effectively scaling the fraction by 255. Different algorithms > are used. -e is designed to work with any color table, both > the floating point and the integer raster maps. > > Essentially the only difference is in how a floating-point value > between 0 and 1 is converted to an integer between 0 and 255. In > practice, the difference will be invisible to the eye. > > Here's a concrete example: > > $ r.colors elevation.dem -e color=grey > Reading elevation.dem ... > Color table for <elevation.dem> set to grey > $ r.mapcalc 'tmp1 = r#elevation.dem' > $ r.colors elevation.dem color=grey.eq > Reading elevation.dem ... > Color table for <elevation.dem> set to grey.eq > $ r.mapcalc 'tmp2 = r#elevation.dem' > $ r.mapcalc 'diff = tmp1 - tmp2' > $ r.stats -c diff > -1 155417 > 0 147001 > r.stats complete. > > So, roughly half the cells are identical between the two, while half > differ by one intensity level.
Thank you for your time and the concrete example. Nikos _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
