[GRASS-dev] Re: [GRASS GIS] #73: r.out.gdal tiff output does not work

[Glynn Clements]

GRASS GIS wrote:

> #73: r.out.gdal tiff output does not work
> ----------------------+-----------------------------------------------------
>   Reporter:  helena   |       Owner:  grass-dev at lists.osgeo.org
>       Type:  defect   |      Status:  new                      
>   Priority:  major    |   Milestone:  6.4.0                    
>  Component:  default  |     Version:  svn-trunk                
> Resolution:           |    Keywords:  r.out.gdal, tiff         
> ----------------------+-----------------------------------------------------
> Comment (by hamish):
> 
>  (I see the same with 6.2.1's old script version of r.out.gdal)
> 
>  it works if the values are in the range of 0-255:
>  {{{
>    #spearfish
>    r.out.gdal in=fields out=fields.tif type=Byte
>    qiv fields.tif   # qiv is a quick image viewer
>  }}}
> 
>  but not if all values are out of range:
>  {{{
>    r.info -r elevation.dem
>      min=1066
>      max=1840
>    r.info -t elevation.dem
>      datatype=CELL
>    r.out.gdal in=elevation.dem out=elv.tif type=Byte
> 
>    gdalinfo -stats elv.tif | grep STATISTIC
>      STATISTICS_MINIMUM=255
>      STATISTICS_MAXIMUM=255
>      STATISTICS_MEAN=255
>      STATISTICS_STDDEV=0
> 
>    r.in.gdal in=elv.tif out=elv2
>    r.info -r elv2
>      min=255
>      max=255
>  }}}
> 
> 
>  we can try with half the raster in range:
>  {{{
>    r.mapcalc "elev_0 = elevation.dem - 1066"
>    r.info -r elev_0
>      min=0
>      max=774
>    r.out.gdal in=elev_0 out=elv0.tif type=Byte
>    gdalinfo -stats elv0.tif | grep STATISTIC
>      STATISTICS_MINIMUM=0
>      STATISTICS_MAXIMUM=254
>      STATISTICS_MEAN=138.68943338231
>      STATISTICS_STDDEV=56.526296226099
>  }}}
> 
>  If I load elv0.tif into an image viewer it comes out as all black. But in
>  Gimp if you use the eyedropper you can see the index number changes, but
>  the palette is black for all 256 index entries.
> 
>  gdalinfo confirms palette info was not written to file:

I have noticed that r.out.gdal only generates the palette if
G_read_colors() returns 1, i.e. if the map has its own colour table. 
If G_read_colors() falls back to a default rainbow colour table, you
don't get a palette.

I suggest:

--- raster/r.out.gdal/main.c	(revision 30389)
+++ raster/r.out.gdal/main.c	(working copy)
@@ -125,7 +125,7 @@
     GDALSetRasterColorInterpretation(hBand, GPI_RGB);
     CPLPopErrorHandler();
 
-    if( G_read_colors(name, mapset, &sGrassColors ) == 1 )
+    if( G_read_colors(name, mapset, &sGrassColors ) >= 0 )
     {
 	int maxcolor, i;
 	CELL min, max;

G_read_colors() returns -1 on error (e.g. the map doesn't exist), 0 if
a default rainbow colour table was generated, and 1 if the map has its
own colour table.

AFAICT, the UInt16 case actually works, insofar as the debug output
with DEBUG=3 and the output from gdalinfo look just like they do for
an 8-bit TIFF which works fine in various viewers.

I wouldn't rule out the possibility that popular image viewers can't
handle 16-bit indexed-colour images. 

TIFF's strong-point is that it supports so many different formats. 
It's weak point is also that it supports so many different formats. I
doubt that there is a program in existence which can correctly handle
every possible valid TIFF file.

-- 
Glynn Clements <glynn at gclements.plus.com>