[mapserver-users] Specify NODATA for 3 bands?

[Mark Korver]

I think your "halos" are blacks that are not pure black. Not 0/0/0,
just close.  This is a compression artifact. I think the same thing
also happens with jp2 CCMs.
The NAIP CCMs/or County Compressed Mosaics were never meant to be
mosaicked together like this.  They are a deliverable at the county
level, not the state.

MapServer as far as I know will only do 0/0/0 and does not have a
feature to make that fuzzy.

You may have seen page, written some time ago, that speaks to this
problem -  http://sites.google.com/site/bpederse/caliwms

The vertical and horizontal banding in the California case is related
but diff from the halo effect. That is because with the large counties
are cut into smaller sids in order to keep file sizes under control.
That in combination with re-projecting the data causes issues with
no-data areas.





On Fri, Sep 17, 2010 at 11:28 PM, Gregor at HostGIS <gregor at hostgis.com> wrote:
> Hey guys.
>
> I have some NAIP imagery in MrSID format. It displays, but the black area
> where counties meet is really ugly. The MrSIDs are 3 one-byte bands: R/G/B
> The bands do not specify a NODATA but I figure that 0/0/0 (all black) may be
> usable as a NODATA value, via a PROCESSING directive.
>
> It works nicely, suppressing the black halos and making the almost-seamless
> effect where the counties intersect. BUT... it only does so if I don't show
> all 3 bands. If I specify any combination of BAND directives, I get a
> greyscale image (of course) and the NODATA works (black halos are gone, so
> counties are near seamless).
>   PROCESSING "NODATA=0"
>   PROCESSING "BANDS="1,2"
>   #PROCESSING "BANDS="3"
>   #PROCESSING "BANDS="1,3"
>
> But, if I do not specify the BAND or if I specify all 3 bands, I get the
> black halos as if the NODATA were not specified. What gives? Is there
> something special I must do to have the NODATA take effect for 3 or more
> bands?
>
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