[gdal-dev] gdal_translate -expand rgb incompatible with geotiff COPY_SRC_OVERVIEWS

[Norman Vine]

On Dec 30, 2010, at 6:18 AM, Vincent Schut wrote:

> 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.


The Ossim utility ossim-icp has a  --res-level  option that will extract an overview level from a file
something similar might be a useful addition to gdal functionality


pseudo code

for level in overviews
  ossim-icp -r level tiff_tiled  $SRC tmp$SRC_%level
  gdal_translate -expand tmp$SRC_%level $SRC_%level
  ?? how best to recombine overviews ?? 

I don't know how best to do step 3

Cheers

Norman
 
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