# Feature set out of grayscale Images for training a neural network?

Previously I had trained a Neural Networkupon 20,000 character images. This Neural Net generally works well, it uses RGB- Hue, Saturation, Intensity feature set for training. However, there can be certain character images which have RGB-HSI values that this neural net has not seen before. Therefore I am looking forward to converting training data to grayscale and use some feature set well suited for grayscale images.

So are there any good suggestion for extracting a feature set out of grayscale images.