Randy,
with JPEG (and mainly also ECW) you will not completely get rid of the
black borders because, as you mention, their 'black' is not fully black.
But you can get get most parts of the black transparent by applying a
PROCESSING "SCALE..." tag, eg.
PROCESSING "SCALE_1=3,255"
PROCESSING "SCALE_2=3,255"
PROCESSING "SCALE_3=3,255"
OFFSITE 0 0 0
All pixel values from 0 to 3 will be mapped to 0 and then set
transparent by the OFFSITE tag. It has the slight drawback that some
very dark parts inside the image will also be touched by this and become
transparent. It works quite well though for multispectral images, a bit
less nicely on panchromatic.
Armin
Randy How wrote:
My question is in regards to using the OFFSITE setting for a JPEG data
source to remove the "black/NoData" areas. Does it work at all? I've
attempted this but it made no difference (mapserver 4.7).
It will work with Tiff's (that have internal JPEG compression) and
poorly with ECW's due to the variability in "black".
Randy
