Thanks @takashi.It was the ECW format.I changed it to save to GeoTIFF and did not get this issue.(Although it did consume a lot of diskspace!) I'm going to see if I get the same results with JPEG2000.Thank you for your help.
Hi@rclarkenz,as far as I know,the ECW format adopts a lossy compression method.I suspect that the slight change could be caused through the compression process.
What happens if you save the resulting rasters with other format (e.g.GeoTIFF) that uses lossless compression method?