I am trying to extract JPEGs from SID images using GDAL. I ran into a an issue where black lines were present and figured out that it was a nodata issue, so I added -src/dst/vrt nodata arguments and it stitched together properly but there are color distortions where the black lines used to be.
Here is what I am doing, using GDAL 10.1.1 packaged with QGIS:
Building the VRT from SID files
gdalbuildvrt -overwrite -srcnodata 0 -vrtnodata 0 -input_file_list C:\imaging_test\pa18.txt pa18.vrt
Warping into latlong projection (from NAD83 utm18)
gdalwarp -t_srs "+proj=latlong +datum=WGS84" -srcnodata 0 -dstnodata 0 -of vrt -overwrite pa18.vrt pa18_ll.vrt
Extracting the JPEG (subsection) from the VRT
gdal_translate -of jpeg -projwin -74.957684 40.176146 -74.880596 40.147794 pa18_ll.vrt pa_test_discol.jpeg
Here is what I am observing:
I am a programmer, and have limited experience with GIS issues.