Setting pixels at edge of raster to NoData in FME

Question

I am trying to generate GeoTiff rasters using FME Desktop 2015.1. My input is an 8 bit raster that has areas with pixel values of 0 around its edges. I want to set these to NoData.

I tried using the RasterBandNodataSetter to set the values to NoData. This was technically successful but pixels with a value of 0 in the middle of my raster were set to NoData as well which is not what I want.

I have also experimented with using the clipper to extract the areas I want hoping that the areas I do not extract would be set to NoData. However the clipper transformer uses the rectangular extent of my clipper feature to clip while I need it to be tapered to the extent of my study area.

I have also tried to write an alpha8 band to the GeoTiff in addition to my main Gray8 band. I was hoping to set the alpha8 to 0 where there is no data so nothing would be displayed. However the GeoTiff writer seems to insist on turning by alpha8 band into a UINT8.

What is the best approach to achieve this?

Answer 1

I believe the solution lies in using the RasterCellColorReplacer tool only after you apply a Perimeter polygon. Specifically, you apply a perimeter by thresholding the 0-value pixels on the exterior only. The perimeter polygon should be "inside" this exclusion area (so that the 0-value pixels are "outside" the perimeter.) Next, apply the RCCR tool to only the ClippedOutside result set from the perimeter clipper...use the RCCR to change the 0-pixels to NoData values only outside. This should give you a full-sized image with NoData mask pixels on the outside and 0-valued pixels un-effected within.

For more details, check out this FME blog post which uses a similar (but not exactly the same approach.)