Transformation Invariant Autoassociation with Application to Handwritten Character Recognition

When training neural networks by the classical backpropagation algo(cid:173) rithm the whole problem to learn must be expressed by a set of inputs and desired outputs. However, we often have high-level knowledge about the learning problem. In optical character recognition (OCR), for in(cid:173) stance, we know that the classification should be invariant under a set of transformations like rotation or translation. We propose a new modular classification system based on several autoassociative multilayer percep(cid:173) trons which allows the efficient incorporation of such knowledge. Results are reported on the NIST database of upper case handwritten letters and compared to other approaches to the invariance problem.