Problem with using sparse autoencoder for recreating fingerprinting images

Hi I have a problem with using autoencoder for recreating fingerprinting images I am using MATLAB and Sparse autoencoder I am using extractHOGFeatures for extracting the features to be trained for autoencoder I got good results on the performance of training and mseError which reaching 0.0039 However when i use autoencoder with testing images i got black color on the whole Reconstructed image I followed this example in MATLAB for autoencoder but I am still facing the problem for Reconstructed images that are with black color for whole images