[gdal-dev] Question about r27234

[Even Rouault]

Hi Jukka,

I blogged about it :

http://erouault.blogspot.fr/2014/04/advanced-jpeg-in-tiff-uses-in-gdal.html

This can be definitely usefull when you need subsampling of JPEG-in-TIFF that
don't have any internal or external overviews. But if you have storage space
available and some CPU time in advance, I'd still recommand generating
precomputed overviews.

Those "implicit" overviews will be faster than the previous way GDAL was doing
subsampling if you have relatively fast I/O compared to CPU.

But by nature of the JPEG codestream, JPEG implicit overviews will remain far
less powerfull than, let's say, JPEG2000 ones (or other similar wavelet-based
technologies). In wavelets, you can have frequency coefficients for the whole
image, whereas in JPEG, there are only for small 8x8 or 16x16 blocks, so in JPEG
you still need to read the whole set of coefficients, even if you only use 1/4,
1/16 or 1/64 of them.

Even

> Hi Even,
>
> I noticed that you have implemented into GDAL the new Rasterlite 2 feature
> of fast JPEG subsampling to levels 2, 4, and 8 in
> http://trac.osgeo.org/gdal/changeset/27234.
>
> I am curious to know how cool you consider this stuff is.
>
> -Jukka Rahkonen-
>
>
>
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