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
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