On 12/30/2010 12:07 PM, Even Rouault wrote:
Le jeudi 30 décembre 2010 11:52:34, Vincent Schut a écrit :
Hi all,
Kind of a corner case, but i was hoping that gdal_translate's -expand
option (to expand colorindexed 1-band files into 3-band rgb files) would
also copy and expand the overviews when run with the (geotiff specific,
I know) create option "-co COPY_SRC_OVERVIEWS=YES". It appears to not do
so, and just discards the overviews. Would this be a bug, or maybe a
feature to add?
When you use -expand, an intermediate VRT file is created to do the color
expension, but it doesn't retain the source overviews, so when the GeoTIFF
driver copies the VRT into the final TIFF, there are no more source overviews
from its point of view. "-co COPY_SRC_OVERVIEWS=YES" will only work if no
intermediate VRT is used, so basically when you don't use any gdal_translate
options, except creation options of the target driver.
Use case: for a classified, indexed image, I have built overviews using
the 'mode' operator, which is obviously the most usefull for this kind
of image, and only applicable on 1-band indexed data. I want to have a
rgb version of this, but with those overviews, so the overviews should
be an rgb version of the 'mode' overviews of the original. It is
impossible to create the same overviews once the image has been expanded
into rgb; mode will result in wrong, and sometimes even weird results (I
presume mode works band-wise),
yes, mode works band per band
and average and partners will result in
colors that are not defined in the original colorindex (which I want to
avoid, we are talking maps and legends here).
I think I can work around this by creating a separate file for each
overview level (bla.ovr, bla.ovr.ovr, and so on), expanding those, and
than using copy_src_overviews to create one file with internal overviews
again, but this feels kind of awkward, and the above seemed so elegant...
yes that's a plausible way of proceeding. Making what you wish work would
require :
1) add support for using/exposing source overviews in the VRT
2) add support for doing color expansion on overviews of the VRT
which I feel would be rather complicated to implement
Which I understand. I didn't know it worked through vrt, though now that
sounds very plausible.
I'll script my workaround, no problem.
Thanks for the info.
Vincent.
Vincent.
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