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

[Vincent Schut]

On 12/30/2010 12:53 PM, Norman Vine wrote:
>
> 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

Well, when you call your overview file <previous overview filename).ovr, 
gdal, will automatically pick it up. I just create a complete stack of 
orig.tif, orig.tif.ovr, orig.tif.ovr.ovr, orig.tif.ovr.ovr.ovr, and so 
on with one overview level in each .ovr file, and it works like a charm. 
Running gdalinfo on orig.tif lists all overviews. Then I create expanded 
versions of each with a different basename (like orig_rgb.tif, 
orig_rgb.tif.ovr, and so on). To combine, just run "gdal_translate -co 
COPY_SRC_OVERVIEWS=YES orig_rgb.tif orig_rgb_ovr.tif", which should 
result in one output file with all overviews combined. This is the 
recipe I'm following now, and it seems to work flawlessly.

Vincent.
>
> Cheers
>
> Norman