ENVI 5.1 - ANN Classification - Background was classified into one of the class

Question

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

Answer 1

It has been long time since I used ENVI, but I remember that you can draw a region of interest (ROI) covering only the image data without the black background, and then use the ROI to subset the image. This is the simplest way to get rid of the background.

Here is a YouTube video showing how to subset an image using ROI: Lesson 5, Cut using roi tool, Envi 5.0 lessons