Le mercredi 20 novembre 2013 18:21:06, Jonathan Moules a écrit : > Hi List, > One thing I'm noticing with PHOTOMETRIC=YCBCR - I'm losing a lot of > sharpness. > > In fact, a 50% without YCBCR looks better than a 85% that also has YCBCR > enabled. > > This is very noticeable at the native resolution, but once you're about > double it or further, it's effectively invisible.
YCbCr comes with a oversampling by a factor of 2 of the Cb and Cr channels, hence the extra compression and quality loss. Although than this oversampling is done because the human eye is less sensible to chromatic than luminance. > > On the other hand, the YCBCR is about 25% the size of > a equivalently compressed JPEG. I guess I'm going to have to choose which > way to go. > > ============ > > I've also been testing a lot of other variables and for some reason DEFLATE > compression seems to make the file *larger* in all circumstances. It > doesn't matter what the Z level is (even 9), or "predictor", in all > instances the resultant file is larger than an uncompressed version. That's > with four band data. > Anyone know why? It is not completely surprising. If there are no repeateable patterns in the uncompressed stream, deflate can result in (a bit) larger files. You might want to try with -co INTERLEAVE=BAND added to see if it improves things. But generally DEFLATE is not appropriate for aerial imagery. > > Cheers, > Jonathan > > > > On 12 November 2013 14:24, Jonathan Moules < > > jonathanmou...@warwickshire.gov.uk> wrote: > > HI All, > > Many thanks for the all the responses. Interesting discussion; I've > > learnt a lot. > > > > I think my next step is to do some testing; I've not tried the four band > > - RGBI imagery yet. When I do I'll post back here with whatever seems to > > work best. > > > > Cheers, > > Jonathan > > > > On 12 November 2013 13:45, Even Rouault <even.rouault@mines- paris.org>wrote: > >> Selon Andrea Aime <andrea.a...@geo-solutions.it>: > >> > On Tue, Nov 12, 2013 at 12:45 PM, Simone Giannecchini < > >> > > >> > simone.giannecch...@geo-solutions.it> wrote: > >> > > > Will the PHOTOMETRIC= YCBCR work with a four band RGBI? > >> > > > >> > > It should not. > >> > > >> > Actually... JPEG itself is not defined on 4 bands images as far as I > >> > >> know? > >> > >> > Maybe GDAL is dropping the 4th band during the JPEG compression? > >> > >> The YCbCR JPEG profile of TIFF is indeed limited to 3 bands. So if you > >> pass a 4 > >> band image, gdal_translate should refuse to process it. > >> You can JPEG compress a 4 band image, but it will use a JPEG codestream > >> for each > >> band independantly, so the resulting size will be bigger. > >> A possible option would be to generate 2 GeoTIFFs for each input file : > >> one > >> YCbCR JPEG compressed with the RGB components, and one JPEG compressed > >> with the > >> I component. But that might complicate the overall workflow. > >> > >> Even > >> > >> > Cheers > >> > Andrea > >> > > >> > -- > >> > == > >> > Our support, Your Success! Visit http://opensdi.geo-solutions.it for > >> > >> more > >> > >> > information. > >> > == > >> > > >> > Ing. Andrea Aime > >> > @geowolf > >> > Technical Lead > >> > > >> > GeoSolutions S.A.S. > >> > Via Poggio alle Viti 1187 > >> > 55054 Massarosa (LU) > >> > Italy > >> > phone: +39 0584 962313 > >> > fax: +39 0584 1660272 > >> > mob: +39 339 8844549 > >> > > >> > http://www.geo-solutions.it > >> > http://twitter.com/geosolutions_it > >> > > >> > ------------------------------------------------------- > >> > >> ------------------------------------------------------------------------ > >> ------ November Webinars for C, C++, Fortran Developers > >> Accelerate application performance with scalable programming models. > >> Explore > >> techniques for threading, error checking, porting, and tuning. Get the > >> most > >> from the latest Intel processors and coprocessors. See abstracts and > >> register > >> > >> http://pubads.g.doubleclick.net/gampad/clk?id=60136231&iu=/4140/ostg.clk > >> trk _______________________________________________ > >> Geoserver-users mailing list > >> Geoserver-users@lists.sourceforge.net > >> https://lists.sourceforge.net/lists/listinfo/geoserver-users -- Geospatial professional services http://even.rouault.free.fr/services.html ------------------------------------------------------------------------------ Shape the Mobile Experience: Free Subscription Software experts and developers: Be at the forefront of tech innovation. Intel(R) Software Adrenaline delivers strategic insight and game-changing conversations that shape the rapidly evolving mobile landscape. Sign up now. http://pubads.g.doubleclick.net/gampad/clk?id=63431311&iu=/4140/ostg.clktrk _______________________________________________ Geoserver-users mailing list Geoserver-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/geoserver-users
