[gdal-dev] compressed GTiff large file size?

[MUTLU OZDOGAN]

Dear Developers

I have two multi-band geotiff files (each about 2 GB in size uncompressed) that I would like to mosaic using gdal_merge.py.  These files make up two halves of a single Landsat footprint so when joined should create a single mosaicked image.  I checked the corner coordinates and they seem correct.  However, when I use the gdal_merge.py command with the -co “COMPRESS=LZW” option, the final file size ends up being a ~100 GB which does not make any sense.  Any ideas about what is going on?  I checked the image dimensions and they seem to be correct and should result in a file that is about 4.5 GB in size uncompressed so the compressed version should be at least this size if not smaller.

Thank you

Mutlu...