[gdal-dev] Pixel remap using the warp api question

[Even Rouault]

Le vendredi 08 février 2013 23:35:26, Martin Chapman a écrit :
> I asked the following a couple of weeks ago and never got a reply.  Frank,
> can you comment on this please?
> 
> 
> 
> .
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> I am trying to remap all "0" value pixels in the source images to the
> value "1" in the output image using gdalwarp like so:
> 
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> 
> warpOptions->padfSrcNoDataReal[bandIndex] = 0;
> 
> warpOptions->padfSrcNoDataImag[bandIndex] = NULL;
> 
> warpOptions->padfDstNoDataReal[bandIndex] = 1;
> 
> warpOptions->padfDstNoDataImag[bandIndex] = NULL;
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> 
> 1. I am setting INIT_DEST=0.

That might be the issue actually. Try with INIT_DEST=1 or INIT_DEST=NO_DATA

Using the warper to do that is however a bit overkill. You could just 
RasterIO(GF_Read, ) each line/block, patch values, and then write back with 
RasterIO(GF_Write).

> 
> 2. not setting UNIFIED_SRC_NODATA.
> 
> 3. the source images have no defined nodata value.
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> 4. the output image has no defined nodata value.
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> with no luck.  My question is:  Is gdalwarp supposed to do this?  When I
> look at the pixel value of the output image the black pixels are still "0"
> and not "1".
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> My input and output are both 8-bit 3 band images.  I am using gdal 1.9.2.
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> Best regards,
> 
> Martin