[gdal-dev] 4th band as ALPHA on warp

[Fernando Ribeiro]

Thank you Even for this new feature.

Hope it will be handy to many more!


On 08/08/2016 11:26 AM, Even Rouault wrote:
> Le lundi 08 août 2016 09:30:53, Daniele Romagnoli a écrit :
>> Hi Even,
>> my usual question would be: any plan to backport it? :-)
> Not really. I guess this is a new feature.
>
> As currently, our policy is to be rather conservative for what goes in stable
> branches, so people can upgrade from one micro version to another one
> blindlessly.
> Regarding that particular feature, it could potentially be backported, but
> then where to draw the limit ? At some point, one such backport will undoubtly
> cause a regression elsewhere, or will have bugs, causing more stabilization
> work in stable branches.
>
> Potential solutions:
> - More frequent major.minor.0 releases that our ~ 1 year schedule
> - Less conservative policy backport policy in regular stable branches that
> would allow some new features to be added, but within the current limits of no
> ABI change, no backward incompatibilities.
> - An extra -backport branch that would have a less conservative policy. To be
> defined what would be the limits: ABI changes allowed or not ?, backward
> incompatibilities ? Would potentially only of interest for people who can
> build from source as it would be unlikely to be widely packaged.
>
> All would need extra staffing / funding.
>
> Another option that already exists: live on the bleeding edge and build from
> trunk ;-)
>
> Even
>
>> Cheers,
>> Daniele
>>
>>
>>
>>
>>
>> On Sun, Aug 7, 2016 at 10:38 PM, Even Rouault <even.rouault at spatialys.com>
>>
>> wrote:
>>> Le dimanche 07 août 2016 19:20:05, Even Rouault a écrit :
>>>> Le samedi 06 août 2016 15:20:54, Fernando Ribeiro a écrit :
>>>>> Dear list,
>>>>>
>>>>> Currently we are working with 4 band tifs, first 3 bands as normal
>>>>> RBG and the 4th as IR. On performing a warp operation from and to a
>>>>> VRT, GDAL seems considering the 4th band as alpha, resulting in full
>>>>> black pixels if 4th band value =0.
>>>> gdalwarp will consider the 4th band as alpha... only if it is
>>>> effectively tagged as alpha in the source. You can check it with
>>>> gdalinfo
>>>>
>>>>> Some attempts were made to solve this issue, so far without success:
>>>>>
>>>>> - Using the warp creation options PHOTOMETRIC=RGB and ALPHA=NO
>>>> This will not influence the warping kernel.
>>>>
>>>>> - Manually editing the source VRT and replace Alpha color
>>> interpretation
>>>
>>>>> to Undefined
>>>> This one should work. Strange that this doesn't work for you.
>>>>
>>>>> Does anyone have more suggestions?
>>> I've just committed an improvement in trunk: "gdalwarp: add a -nosrcalpha
>>> option to wrap the alpha band as a regular band and not as the alpha
>>> band"
>>>
>>>>> Thank you
>>> --
>>> Spatialys - Geospatial professional services
>>> http://www.spatialys.com
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>>> gdal-dev at lists.osgeo.org
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-- 
Regards,
Fernando Ribeiro
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