I'm new to Remote Sensing and I'm having trouble in ENVI 5.1 where the background was classified as one of the classes in the ROI I used, which is not right. How can I exclude the background or at least make it classified as "unclassified". I've tried the trick in here, but it doesn't work. I've also tried to make and apply a mask into it, but it also doesn't work.

I'm using Landsat 8 OLI as my raster data and classic Neural Network as my classifier, here are the parameters I'm using:

• Activation Method: Logistic (Sigmoid Function)
• Training Threshold Contribution: 0.05
• Training Rate: 0.1
• Training Momentum: 0.05
• Training RMS Exit Criteria: 0.001
• Hidden Layer: 1
• Iterations: 5000
• Min Output Activation Threshold: 0.5