[GRASS-dev] [GRASS GIS] #3210: r.texture: bug when non continuous series of values

[GRASS GIS]

#3210: r.texture: bug when non continuous series of values
--------------------------+-------------------------
  Reporter:  mlennert     |      Owner:  grass-dev@…
      Type:  defect       |     Status:  new
  Priority:  normal       |  Milestone:  7.2.0
 Component:  Raster       |    Version:  svn-trunk
Resolution:               |   Keywords:  r.texture
       CPU:  Unspecified  |   Platform:  Unspecified
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Comment (by mmetz):

 Replying to [comment:4 mlennert]:
 > Replying to [comment:3 mlennert]:
 > > Just one question:
 > >
 > >
 > > The manual says:
 > >
 > > r.texture  assumes  grey levels ranging from 0 to 255 as input.  The
 input is automatically rescaled to 0 to 255 if the input map
 > >        range is outside of this range.
 > >
 > >
 > > But when I rescale the above (second) matrix to 0,255 I get a
 different result:
 > >
 > >
 > > {{{
 > > r.in.ascii --o in=- out=test_matrix <<EOF
 > > north: 3
 > > south: 0
 > > east: 3
 > > west: 0
 > > rows: 3
 > > cols: 3
 > > 1 1 1
 > > 3 0 0
 > > 0 0 3
 > > EOF
 > > r.texture -s test_matrix out=text method=idm --o
 > > r.stats -1n text_IDM_90
 > > 0.40000007
 > >
 > > r.rescale test_matrix out=test_matrix_rescaled to=0,255
 > > r.texture -s test_matrix_rescaled out=text_rescaled method=idm --o
 > > r.stats -1n text_rescaled_IDM_90
 > > 0.16672371
 > > }}}
 > >
 > > I would have thought that the result should be the same ?

 No, because the differences become larger, therefore IDM becomes smaller.

 There are other measurements that are also possibly affected: Contrast,
 Correlation, Variance, Sum Average, Sum Variance.

 IMHO, there is also a bug in all the entropy and information measures
 because p * log(p) is zero for p = 0 while the code uses p * log(p +
 EPSILON) as a workaround which provides slightly different results for p
 != 0.

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Ticket URL: <https://trac.osgeo.org/grass/ticket/3210#comment:5>
GRASS GIS <https://grass.osgeo.org>