[Gdal-dev] gdal_merge: merge/mosaic NITF files

[Frank Warmerdam]

Charles Chung wrote:
> Hi all, I am new using GDAL and raster format. Here is my situation.
> 
> With GDAL 1.6.0dev, I want to merge or mosaic many NITF files into one NITF
> or GeoTIFF file.
> 
> Each NITF file is about 284 KB and its characterists are:
> 
> Driver: NITF/National Imagery Transmission Format
> Files: ???????.???
> Size is 1536, 1536
> ...
> Pixel Size = (0.000059486040609,-0.000044956841432)
> ...
> Band 1 Block=256x256 Type=Byte, ColorInterp=Palette
> 
> If I use "gdal_merge" with one NITF input file and default settings, the
> default output is GeoTIFF and the size is 2,316 KB.  That's 8 times bigger
> in size even though I used only one input file.  If I output to NITF format,
> the size is also 8 times bigger.  If I merge two NITF files the output is
> about 16 times bigger.
> 
> Why the output file size is so much bigger than the input file?  Is there
> settings to make it smaller?
> Basically I want the size of merged files to be about the same size as the
> sum of input file size.

Charles,

I suspect the input NITF files are compressed, and for the most part GDAL
does not support producing compressed files.  If you run gdalinfo on the
input file, and check the IC (compression) field, I presume it will be
set.

If you were to convert ultimately to a compressed format like PNG or
Deflate compressed TIFF you should get similar or better results.

Best regards,
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