Hi Micheal,
I'm afraid I misadvised you. Nearblack and gdal_rasterize can't write to
file formats which don't allow updating in place. Is using jp2 a hard
requirement? Have you tried the available geotiff compressions
(http://www.gdal.org/frmt_gtiff.html look at Creation Options)? Black
and white images should compress pretty well.
matt wilkie
--------------------------------------------
Geographic Information,
Information Management and Technology,
Yukon Department of Environment
10 Burns Road * Whitehorse, Yukon * Y1A 4Y9
867-667-8133 Tel * 867-393-7003 Fax
http://environmentyukon.gov.yk.ca/geomatics/
--------------------------------------------
Smith, Michael wrote:
I tried that but it doesn't seem to write to JP2KAK. If I do this:
nearblack mosaic_jp2.jp2
I get this error:
0...10..ERROR 6: WriteBlock() not supported for this dataset.
ERROR 1: GetBlockRef failed at X block offset 1, Y block offset 19
ERROR 6: WriteBlock() not supported for this dataset.
ERROR 6: WriteBlock() not supported for this dataset.
ERROR 6: WriteBlock() not supported for this dataset.
ERROR 6: WriteBlock() not supported for this dataset.
I have also tried creating an alpha channel with this:
gdalwarp -srcnodata 0 -dstalpha *.tif mosaic.tif
gdal_translate -ot Byte -of JP2KAK mosaic.tif mosaic_jp2.jp2
That works, but provides a JP2 that is twice the size since it has a
second band (these are black-and-white images, so one 8-bit band). I
tried converting that to a single-band image, hoping it would interpret
the alpha channel correctly, with this:
gdal_translate -ot Byte -of JP2KAK -b 1 -a_nodata 0 mosaic_jp2.jp2
mosaic2_jp2.jp2
But the output again has a bunch of pixels on the edge which are now not
value 0.
I cannot gdal_rasterize -burn the JP2 because gdal_rasterize does not
write JP2KAK (why is that? gdal_translate will but not gdal_rasterize)?
It seems like all the functions I need to work only do so on TIFFs, but
it's the JP2s I need it to work on.
Any other suggestions? Some trick involving alpha channels I don't
know? A way to get gdal_rasterize to write JP2KAK?
**********
Michael Smith
State GIS Manager
Maine Office of GIS
-----Original Message-----
From: Matt Wilkie [mailto:matt.wil...@gov.yk.ca]
Sent: Tuesday, December 16, 2008 1:50 PM
To: Smith, Michael
Cc: gdal-dev@lists.osgeo.org
Subject: Re: [gdal-dev] Border slivers and JPEG2000 compression
Hi Micheal, try the nearblack utility (which is a relatively new
addition): http://www.gdal.org/nearblack.html
"This utility will scan an image and try to set all pixels that are
nearly black (or nearly white) around the collar to exactly black (or
white). This is often used to "fix up" lossy compressed airphotos so
that color pixels can be treated as transparent when mosaicing."
cheers,
matt wilkie
--------------------------------------------
Geographic Information,
Information Management and Technology,
Yukon Department of Environment
10 Burns Road * Whitehorse, Yukon * Y1A 4Y9
867-667-8133 Tel * 867-393-7003 Fax
http://environmentyukon.gov.yk.ca/geomatics/
--------------------------------------------
Smith, Michael wrote:
I have several orthophotos which are TIFFs, and they align with the
USGS
quadrangle corners, which means they are rotated slightly, leaving
small
uneven slivers along the edges where pixel value is 0 (the data for
these are available from adjacent tiles). All the pixels inside the
'real' area of the photo are value > 0.
This is no problem with TIFFs, as the 0 can be turned off in
applications such as ArcGIS or serving them out via MapServer WMS.
But
when I convert to JPEG2000 (using Kakadu), the edge pixels are
interpolated to different values, typically something like 0, 1, 2, or
3. Thus I can't just filter them out. Also inside the photo,
sometimes
very dark pixels (which should really be value 2, 3, etc) are
converted
to value 0. Thus they show up as 'holes' in applications when pixel
value 0 is filtered out.
What I want to do is simply show a bunch of JP2 tiles, with the border
pixels staying as value 0, and no other pixels having value 0.
I have tried a couple approaches, including
gdal_translate -a_nodata 0 (the border pixels still have values > 0)
gdal_rasterize -i -burn 0 (won't write JP2KAK)
Surely I'm not the first to try this, but I can't find the right steps
on the web. Any suggestions would be appreciated.
**********
Michael Smith
State GIS Manager
Maine Office of GIS
------------------------------------------------------------------------
_______________________________________________
gdal-dev mailing list
gdal-dev@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/gdal-dev
_______________________________________________
gdal-dev mailing list
gdal-dev@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/gdal-dev
