Multilayer feedforward networks are commonly used in handwritten character
recognition tasks. However, it has been observed that feature extraction and
feature mapping are common issues which have an important influence in the
results of the classifier. In most cases, a hand-crafted feature extractor is often
designed, specifically adapted to the problem. This is a hard task, which must
be redone for each new problem. Therefore, in this work a type of multilayer
perceptron called Convolutional Network (CNN), firstly described in LeCun et
al.[9], is presented. It is specifically designed to recognize two-dimensional shapes
with a high degree of invariance to translation, scaling, skewing, and other forms
of distortion [5]. This network includes in its structure some forms of constraints:
feature extraction, feature mapping and subsampling. In these experiments, the
network architecture is composed by an input layer, five hidden layers and an
output layer. The topology of a typical CNN contains two types of hidden layers.
Some of them perform convolution, i.e., each layer is composed by some feature
maps which are used for local feature extraction. This is achieved by an operation