[gdal-dev] convert USGS Topo GeoPDF to GeoTiff, file size

[Jukka Rahkonen]

Liu, Jian <JLiu <at> eris.ca> writes:

> 
> 
> Hello, 
>  
> I try to use GDAL to convert USGS Topo geopdfs to Geotiff format. I have
the following command:  
>  
> gdalwarp geo.pdf geo.tif -crop_to_cutline -cutline
C:\JIANTestFolder\cutline.csv -overwrite --config GDAL_CACHEMAX 500 -wm 500
--config GDAL_PDF_LAYERS_OFF Projection_and_Grids --config GDAL_PDF_DPI 508
-co "TILED=YES" -co "TFW=YES" -co "COMPRESS=JPEG" –co "PHOTOMETRIC=YCBCR"
>  
> I want to maintain the image quality while keeping the file to a minimal
size. But my output .tif is about twice as big as the input pdf (19.5M vs.
11.9M)  -- the output dpi (GDAL_PDF_DPI=508) is set based on the metadata
information in the geopdf. I read somewhere that pdf just stores image “as
it is”, and I am wondering how come my geotiff is twice as big, even with
the jpeg compression with the YCBCR option? Is it still possible to reduce
its size? 
>  
> Here is the geopdf I use:
   http://ims.er.usgs.gov/gda_services/download?item_id=5998960
>  
> I’ve searched the mail archive and couldn’t find anything relevant. I
appreciate any answers or suggestions about converting geopdf to geotiffs.
Thank you! 


Hi,

Judged by the compression artifacts I believe that the image in the PDF if
already JPEG compressed. When this image is compressed again with JPEG the
algorithm tries to save also the new details of the artifacts and therefore
the compression ratio is not as good. 

For minimum size your could try to write the map first into an uncompressed
tiff file. Next you can try to remove the noise that is caused by the
previous compression with for example GIMP or Photoshop. Once the image is
clean it may be possible to compress it with better compression ratio into
JPEG. And if you can get it very clean it is possible that compression with
LZW or deflate method could compress it even more and without further
degradation of quality.

-Jukka Rahkonen-
 
> Best regards, 
> Jian 
>  
>  
> 
> 
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