[gdal-dev] gdalbuildvrt and nulls again - now from Photoshop

[Even Rouault]

Le Friday 10 July 2009 21:14:18 William Kyngesburye, vous avez écrit :
> This time I'm taking some Photoshop-created tiffs that I georeference
> with a TFW.  These tiffs I save with transparency mask (not layers) to
> handle nulls.
>
> Reported by gdalinfo, they appear as:
>
> Band 1 Block=12775x5 Type=Byte, ColorInterp=Red
>    Mask Flags: PER_DATASET ALPHA
> Band 2 Block=12775x5 Type=Byte, ColorInterp=Green
>    Mask Flags: PER_DATASET ALPHA
> Band 3 Block=12775x5 Type=Byte, ColorInterp=Blue
>    Mask Flags: PER_DATASET ALPHA
> Band 4 Block=12775x5 Type=Byte, ColorInterp=Alpha
>
> But when I run gdalbuildvrt on them, they are skipped:
>
> gdalbuildvrt does not support heterogenous band numbers. Skipping
> [sometiff].

This warning means that you are giving a list of datasets that don't have the 
same number of bands. For example, if the first dataset examined by 
gdalbuildvrt has only 3 bands, it will ignore any further dataset whose band 
number is not 3. (if the error message isn't clear, you're welcome to suggest 
a better one)

>
> If I save it with layers instead of transparency, GDAL doesn't see the
> alpha mask on the layer:
>
> Band 1 Block=12775x6 Type=Byte, ColorInterp=Red
> Band 2 Block=12775x6 Type=Byte, ColorInterp=Green
> Band 3 Block=12775x6 Type=Byte, ColorInterp=Blue

I'm not sure what a 'layer' is for photoshop, but it is something apparently 
ignored by GDAL. Would 'tiffdump' show something interesting on those files ?

>
>
> Is there a way I can get gdalbuildvrt to recognize the transparency as
> null, without converting them with gdal_translate first?  Maybe a
> different way to save the tiff with a mask from Photoshop?

Just run gdalbuildvrt on a list of datasets that have all 4 bands.

>
> Does the vrt format support a tiff transparency mask as null (and it's
> just gdalbuildvrt that doesn't)?
>
> -----
> William Kyngesburye <kyngchaos*at*kyngchaos*dot*com>
> http://www.kyngchaos.com/
>
> "History is an illusion caused by the passage of time, and time is an
> illusion caused by the passage of history."
>
> - Hitchhiker's Guide to the Galaxy
>
>
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