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Some of the images have value ranges from 0-255 i.e. the max 256 values in an 8bit raster, while others range from 1-255 - so only 255 values. So when I run my extract and want to have a NoData value - the rasters that already have a maximum number of values for 8bit (256) default to 16bit because they need to include the NoData value therefore create 257 unique values which cannot be held in an 8bit raster.