Transparent raster layer (with Jpegs source rasters)

[Pedro Mendes]

Frank,

Thanks! it was just what I needed! 
I only have to set the expression to a higher value - [pixel] < 150 - to
render all the pixels I want.

Thanks again!

Cumps, Pedro


Frank Warmerdam-2 wrote:
> 
> On 10/1/07, Pedro Mendes <mendes at gaveta.net> wrote:
>> Hi people,
>>
>> I´m trying to display a raster layer from a tileindex file (.shp). The
>> source rasters for this shapefile are jpeg with the following info:
> ...
>> My prob is that i can´t force mapserver only to render the black color in
>> the rasters (i tried changing several parameters in the layer object, and
>> using different output declarations). If it´s possible can u show it to
>> me?
>>
>> The output format isn´t important, just wanna get fully transparent
>> layers
>> (in colors grey and white, keeping black).
> 
> Pedro,
> 
> My understanding is that you want black (0,0,0) in your
> source raster to be rendered, and all other values to be
> treated as transparent ... is that right?
> 
> The only mechanism that comes to mind to accomplish
> this is to define a class for pixel value 0 with a color
> of 0,0,0 and no other classes so all other values will
> appear as transparent.  Something like:
> 
>   CLASS
>     EXPRESSION ([pixel]  = 0)
>     COLOR 0 0 0
>   END
> 
> You may find that the source jpeg file has corrupted some
> black pixels causing them to have values near zero but not
> quite equal to zero.  to capture these too, you might change
> your expression to be something like [pixel] < 5.
> 
> Good luck,
> -- 
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam,
> warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush    | Geospatial Programmer for Rent
> 
> 

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