Frank
the original images showed
...
Metadata:
AREA_OR_POINT=Area
Image Structure Metadata:
INTERLEAVE=PIXEL
...
Band 1 Block=3000x1 Type=Byte, ColorInterp=Red
Band 2 Block=3000x1 Type=Byte, ColorInterp=Green
Band 3 Block=3000x1 Type=Byte, ColorInterp=Blue
Then I tried to set the NODATA value to 0 using Gdal-Python, and
afterwards they had
Band 1 Block=3000x1 Type=Byte, ColorInterp=Red
NoData Value=0
Band 2 Block=3000x1 Type=Byte, ColorInterp=Green
NoData Value=0
Band 3 Block=3000x1 Type=Byte, ColorInterp=Blue
NoData Value=0
But the result was the same, when using "-r average" a 1-2 pixel area of
the original NODATA values along the border to the DATA areas seem to
have got pixels with higher values than 0 (at least in Mapserver they
cannot any more be "hidden" with OFFSITE). Is there a simple way to
write out the overviews to separate Tiff files so that I can check them
directly?
Armin
On 21/02/2012 21:48, Frank Warmerdam wrote:
Armin,
Reviewing the overview building code in gdal/gcore/overview.cpp
it clearly tries to exclude nodata values from the averaging calculation.
What does the gdalinfo report look like for the file before you run
gdaladdo?
Best regards,
On Tue, Feb 21, 2012 at 12:36 PM, Armin Burger<[email protected]> wrote:
Hi all
I have a question regarding the gdaladdo tool and NODATA pixels:
When using resampling like "average" it seems that along the border of DATA
and NODATA pixels there happens an averaging also of some of the original
NODATA pixels (looks like 1-2 pixel width). This way in the overviews they
get values higher than 0 (0 is defined as NODATA). Using this type of data
in mapserver leads to small black borders when the overviews are taken since
the tag
OFFSITE 0 0 0
does not work anymore for the small border of now only "nearly-black"
pixels.
I tried to set the metadata NODATA of the images to 0 for each band but it
had no effect. Only when I use resampling "nearest" then every NODATA pixel
of the overviews retains the full black 0 0 0.
Is there a way to force to exclude NODATA pixels during the "average"
resampling so that they retain their NODATA values?
Thanks
Armin
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