Ciao a tutti,
addign a bit to this, I would not use band interleaving as we have seen bad
performance in the past wrt pixel interleaving.
Simone.
On Wednesday, November 20, 2013, Even Rouault wrote:
> 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 <javascript:;>> 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 <javascript:;>>:
> > >> > On Tue, Nov 12, 2013 at 12:45 PM, Simone Giannecchini <
> > >> >
> > >> > simone.giannecch...@geo-solutions.it <javascript:;>> 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
> > >> >
> > >> > --
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