[gdal-dev] VRT image definition and LUT stretch

[Tamas Szekeres]

Armin,

The LUT capability in the VRT driver have been added a couple of weeks
ago, so you'll have to checkout and compile the latest SVN trunk to
get it work.

Best regards,

Tamas



2008/4/20, Armin Burger <armin.burger at gmx.net>:
> Tamas
>
>  thanks a lot for the quick help. The first option was the one I had tried
> before and it had no effect (so I thought the range definition has probably
> to be different). But the second option using ScaleRatio/Offset works well.
>
>  Armin
>
>
>  On 20/04/2008 22:45, Tamas Szekeres wrote:
>
> > Armin,
> >
> > As far as I know mapserver transforms the scale min/max values to the
> > 0-255 range of the values. So by using the VRT ComplexSource the
> > following 2 options can possibly be used:
> >
> > Option 1:
> >
> >  <VRTRasterBand dataType="Byte" band="1">
> >    <ColorInterp>Red</ColorInterp>
> >    <ComplexSource>
> >      <LUT>117:0,339:255</LUT>
> >      <SourceFilename>src.tif</SourceFilename>
> >      <SourceBand>1</SourceBand>
> >    </ComplexSource>
> >  </VRTRasterBand>
> >
> > Option 2:
> >
> > <VRTRasterBand dataType="Byte" band="1">
> >    <ColorInterp>Red</ColorInterp>
> >    <ComplexSource>
> >      <ScaleOffset>-134.919</ScaleOffset>
> >      <ScaleRatio>1.153</ScaleRatio>
> >      <SourceFilename>src.tif</SourceFilename>
> >      <SourceBand>1</SourceBand>
> >    </ComplexSource>
> >  </VRTRasterBand>
> >
> > Where:
> >
> > ScaleRatio = 256/(scaleMax-scaleMin)
> > ScaleOffset = -ScaleRatio*scaleMin
> >
> > Best regards,
> >
> > Tamas
> >
> >
> >
> > 2008/4/20, Armin Burger <armin.burger at gmx.net>:
> >
> > > Hello
> > >  Mapserver has the nice functionality for a histogram stretch of images
> > > using the tag PROCESSING "SCALE=x,y". I would like know to predefine
> TIFF
> > > images as a Virtual Format (VRT) and define the parameters for the
> linear
> > > stretch in the VRT file instead of the layer definition via PROCESSING
> > > SCALE=...
> > >
> > >  Is this possible? There is the <LUT> tag but I have not understood how
> to
> > > convert from the PROCESSING definition to the required values there.
> What
> > > would I need for example in the LUT that corresponds to
> > >  PROCESSING "SCALE_1=117,339"
> > >  for an image of type UInt16?
> > >
> > >  Thanks for any help
> > >
> > >  Armin
> > >  _______________________________________________
> > >  gdal-dev mailing list
> > >  gdal-dev at lists.osgeo.org
> > >  http://lists.osgeo.org/mailman/listinfo/gdal-dev
> > >
> > >
> >
> >
>