Mike Flannigan <mikeflan <at> att.net> writes: > > > > Thank you all. I got it to work with the following > command: > gdal_translate -of GTiff -co "TILED=YES" -co "TFW=YES" > C:\Copy\wp.pdf C:\Copy\wpt.tif --config GDAL_PDF_DPI 300 > It works pretty good. It converts a 11.1 MB PDF into a > 96MB Tiff file that zips up into a 57 MB file. These files > are about 15 times bigger than the ones I am used to, but > they do have quite a bit of detail and don't have the > blank white space that a 7.5 minute topo has. > These Tiffs are very well georeferenced. I am pleased.
Hi, You should not be pleased yet because you can get better. Start by reading creation options - compress from http://www.gdal.org/frmt_gtiff.html. Zipping tiff files is mostly not necessary because you can compress the image data that is stored into a tiff. That reduces the file size and removes the need for zipping-unzipping. Some hints about how and when to compress. Natural images like aeriel and satellite photos compress best with JPEG compression. Use parameters -co COMPRESS=JPEG -co PHOTOMETRIC=YCBCR For b/w images just -co COMPRESS=JPEG Your originals seem to be topo maps. For those JPEG compression may not be optimal because JPEG compression is blurring sharp edges and topo maps are full of those because of texts and line drawings. Adding -co JPEG_QUALITY= with a higher value than the default value 75 makes better quality, test it and look at the results. However, generally LZW and deflate compression methods are better for topo maps. Both methods are lossless and keep texts sharp. At the same time the compression ratio can be very good. The parameters to use are -co COMPRESS=LZW of -CO COMPRESS=DEFLATE With deflate you can also use parameter -co ZLEVEL= Big ZLEVEL value gives smaller files but compression is slower. Quality is the same, lossless. Scanned old maps are somehow in the middle of computer made topo maps and aerial images. The old paper gives non-uniform colour to the whole background and LZW of deflate compression may not give good compression ratio. Make some tests and consider what suits you best. There is still one drawback with compressed tiffs: all applications cannot open all kind of compressed tiffs. If images are for your own use or your users will use GDAL based applications then all compression alternatives should be as usable. If you know that some other viewers will be used and you know what they are then you can make a test and feel relaxed. If you want the widest possible audience then zipping the uncompressed tiffs is an option but perhaps I wouldn't go for that myself. Being forced to unzip images before viewing them is not a pleasure. -Jukka Rahkonen- _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
