#1071: histogram equalized color rules for raster takes inordinately long to
display
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Reporter: isaacullah | Owner: grass-dev@lists.osgeo.org
Type: defect | Status: new
Priority: major | Milestone: 6.4.0
Component: Display | Version: 6.4.0 RCs
Keywords: histogram equalization, display, r.colors | Platform: Linux
Cpu: Unspecified |
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Recently, I have discovered that displaying a map that has been recolored
using the histogram equalization option (-e) in r.color takes much much
much longer than displaying the same map colored without the histogram
equalization option. With a histogram equalized raster, every redisplay
takes about 5 minutes, whereas with a normally colored raster, redisplay
takes a second. This means that every little action you do that causes a
need to redisplay (ie. even just moving the scale bar) leads to a 5 minute
wait. I've tested this with 6.4 RC5 and 6.5SVN, and both have the same
behavior. I'm using a single ASTER tile as a test raster. The tile
displays normally (fast) when given normal color rules, but when the
histogram equalization option is checked, it takes about 5 minutes to
display it (or even just a small portion of it).
I'm using a brand new 64bit core-i5 laptop with 4 gigs of RAM running
Ubuntu 10.04. My system is blazing fast, so this is definitely NOT a
hardware issue. I don't know if this is a known issue with the -e option
of r.color, or perhaps a known issue with installation on Ubuntu 10.04,
but I don't remember experiencing this problem in the past (with other
versions of 6.4RC's or 6.5SVN on Ubuntu 9.10 or Windows), and I can't find
any other open bug tickets that report this problem. If this is indeed a
bug, this seems like a pretty major issue that would need to be addressed
before the 6.4 stable is released?
#1071: histogram equalized color rules for raster takes inordinately long to
display
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Reporter: isaacullah | Owner: grass-dev@lists.osgeo.org
Type: defect | Status: new
Priority: major | Milestone: 6.4.0
Component: Display | Version: 6.4.0 RCs
Resolution: | Keywords: histogram equalization, display, r.colors
Platform: Linux | Cpu: Unspecified
-------------------------+--------------------------------------------------
Comment (by glynn):
Replying to [ticket:1071 isaacullah]:
> Recently, I have discovered that displaying a map that has been
recolored using the histogram equalization option (-e) in r.color takes
much much much longer than displaying the same map colored without the
histogram equalization option. With a histogram equalized raster, every
redisplay takes about 5 minutes,
If you use -e on an integer map, it will create one rule for each value
which occurs in the map, which can result in an excessively large colour
table.
I'm sure that this very issue has been addressed before, but I don't
remember the details.
The quick fix would be to use the same code as for floating point (which
just splits the range into 1000 bins, and always generates 1000 rules). A
better fix is to coalesce a run with a constant colour into a single rule.