Alister Hood <alister.hood@...> writes: > > > Date: Mon, 05 Dec 2011 10:40:32 +0000 > > From: Giovanni Manghi <giovanni.manghi@...> > > Subject: Re: [Qgis-developer] Re: [Qgis-user] Re: ecw problems > > To: pieri70 <pietro.rossin@...> > > Cc: qgis-user@... > > Message-ID: <1323081632.2277.19.camel <at> sibirica> > > Content-Type: text/plain; charset="UTF-8" > > > > On Mon, 2011-12-05 at 01:15 -0800, pieri70 wrote: > > > Hello Jürgen > > > which kind of compressed raster do you use instead of ECW (if you use > > > any..?? > > Personally I'd try JPEG2000 (using openjpeg). But you might need to build openjpeg and gdal yourself :( > > > try > > > > GeoTIFF TILED=YES COMPRESS=JPEG QUALITY=75 and overviews. > > Do you use JPEG compression for maximum compatibility? I would have thought you'd get much better results > with something else.
JPEG-in-TIFF is by no means maximally compatible but it suits very well for GDAL based systems, especially Mapserver. The result is not a JPEG image, it is a TIFF image but the image data inside TIFF is compressed with JPEG algorithm. It is not uncommon that tiff drivers cannot open such images but GDAL has no problems. It is essential to use JPEG compression with tiling. JPEG must be decompressed totally but if tiff file is split into tiles GDAL can pick just a correct set of tiles to be decompressed. Jpeg compressed tiffs have about same file size as ECW and JPEG2000 with about the same visual quality but the artifacts are different. GDAL is handling jpeg-in-tiff images at least as fast as ECW images and much faster than JPEG2000 images even with the fastest JPEG2000 driver which is usually JP2KAK (Kakadu)or JP2ECW (ERDAS). They are not free. JP2MrSID a third non-free driver but I have not used it. OpenJPEG driver JP2OpenJPEG is much better than Jasper driver JPEG2000 at least with big images. For a desktop use I would guess that JPEG2000 with OpenJPEG driver is fast enough. For a busy WMS server it is not so good choice. I do not mean that JPEG2000 is slow by the nature. If used, for example, with native Kakadu tools it is flaming fast. The problem is that JPEG2000 is very complicated format and open source libraries are not yet as good as the best commercial ones. -Jukka Rahkonen- _______________________________________________ Qgis-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/qgis-user
