Maybe i'm missing a basic concept when it comes to manipulating/removing values from an RGB orthophoto mosaic. Is it possible to completely eliminate the collar (black background) from an orthophoto mosaic that is in an ECW format. I was able to do in a TIFF format but the file needs to be in an ECW format as it is very large. I've had limited success, using FME, to accomplish this but the resultant file always has areas that are not removed. Hope all this make sense.
I'm open to other formats that will work, but as long as it performes to the same level as an ECW.
I have access to FME and ArcInfo.
Answer
This is a limitation of early versions (<= 3.3) of the ECW format which didn't support NoData values or Alpha transparency. The lossy compression makes it even harder to remove the collars as the black values aren't exactly RGB 0,0,0 but vary.
To get rid of the collar you'll need to mask/clip the collar and convert the image to another format that does support NoData values, mask bands or Alpha transparency. You can use ECWs compressed using version 4 or later of the ERDAS ECW/JP2 SDK, JPEG2000 or Geotiff.
There are a few ways to remove the collar, I tend to either draw a polygon around the "good" data and clip with that or use the GDAL nearblack utility.
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