I want to use Stacked Autoencoders for colour image classification. The example given on matlab site for image classification of MNIST dataset is only for black and white images which has only one colour channel. But for colour images, it has 3 colour channels, RGB. So what pre processing should i do to the colour images since colour images are matrix in 3 dimensions, for the stacked autoencoders to work. I just need the concept, not specific detailed answer.
URL for matlab example - https://in.mathworks.com/help/nnet/examples/training-a-deep-neural-network-for-digit-classification.html