My dataset consists of about 500k .png images, each with dimension 250x250x3 (CASIA Webface, which I aligned using https://github.com/davidsandberg/facenet/tree/master/src/align 46). Each epoch it takes 20k triplets of images from this dataset, 10k for training and 10k for validation.
I will try to iterate over the dataset directly and post a response once I am done.