Hi List,
I've got a 4 band raster aerial photography (RGBI) that comprises lots of
tiles. I've merged some of the tiles together with:
gdal_merge -o 1.tif -of GTiff -co TILED=YES -co BIGTIFF=YES -co
COMPRESS=JPEG -co JPEG_QUALITY=50 -co BLOCKXSIZE=512 -co BLOCKYSIZE=512
--optfile tiff_list.txt
Jonathan Moules jonathanmoules@... writes:
Hi List,
I've got a 4 band raster aerial photography (RGBI) that comprises lots of
tiles. I've merged some of the tiles together with:
gdal_merge -o 1.tif -of GTiff -co TILED=YES -co BIGTIFF=YES -co
COMPRESS=JPEG -co JPEG_QUALITY=50 -co
Hi Jonathan,
Is it possible that QGIS is using the infrared band as an alpha
channel? This might explain the whitening effect, especially in
non-vegetated areas. I would check the Layer properties
Transparency tab to see whether anything is set as the
PS. gdalwarp offers more flexibility
when mosaicing rasters, and is better at memory management. I have
just noticed that in GDAL 1.10 and above there is an gdalwarp
option -setci that 'Sets the color interpretation of the bands of
the target dataset from the
Hi Andy,
Yep, that was it. I didn't know QGIS could do that; another good example of
software trying to be smart and confusing the poor user. :-)
I didn't know gdalwarp could do mosaicing too. I'll have to test it. I'll
ask on the gdal list if I want to try the -setci parameter.
Many
I think QGIS is innocent in this - if a band is set as an alpha channel
then it should be handled as such by default in a viewer (so mark down
Arc for not using the alpha information!).
GDAL is the culprit as it is adding the alpha interpretation without
being prompted. I have just replicated
Hi Andy,
I guess that makes sense.
Relating to gdalwarp:
- Output files by default are larger than gdal_merge.
- But they can be much smaller. You have to set *both* -wm and --config
GDAL_CACHEMAX - if you only set -wm, then the file is actually larger!
- gdal_merge seems to do something that
Interesting!
Just found that you can override the GDAL behaviour of adding alpha
interpretation (this is the default as described in the GTiff format
spec here http://www.gdal.org/frmt_gtiff.html) by adding the GDAL -co
command PHOTOMETRIC=RGB. Not sure how this tallys with the YCBCR colour
Further testing indicates that the same (optimal) result can be had using a
combination of a vrt and gdal_translate without having to manually bother
with memory management.
dir /b /s *.tif tiff_list.txt
REM Builds a VRT. A VRT is basically just a XML file saying what all the
source tif
Jonathan Moules jonathanmoules@... writes:
Further testing indicates that the same (optimal) result can be had using
a combination of a vrt and gdal_translate without having to manually bother
with memory management.
Hi,
I can confirm that question is in GDAL which by default considers
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