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The Output Layer

 

You do not have to read or understand this section unless you want to!

 

When it is being trained to recognize a font a Scan2CAD neural network is made up of three parts called “layers” – the Input Layer, the Hidden Layer and the Output Layer. See Advanced neural network information for a diagram.

The Output Layer is the set of characters that you are training the neural network to recognize.  Each character you want to recognize is termed a “node”.

 

The number of nodes in the Output Layer

There are 256 characters numbered from 0 to 255 in the complete ASCII character range. Of these, there are 192 that are likely to appear on a drawing. The maximum number of nodes in the Output Layer is therefore 192.

By default the number of nodes in the Output Layer equals the number of characters represented in the training set. So, if you have entered examples of all the alphanumeric characters into the training set – A-Z, a-z and 0-9 – the number of nodes in the Output Layer will be 62 – one for each character.

You may want to train the neural network to recognize only a subset of the characters in the training set. For example, the training set may contain examples of all alphanumeric characters and you may only want to train the neural network to recognize upper case letters. In this case you need to restrict the number of nodes in the Output Layer to the letters A to Z only.

 

Restrict the number of nodes in the Output Layer

You can restrict the number of  nodes in the Output Layer when you initialize a neural network.

 

1. Select Train Menu > Initialize Neural Net.
2. Click on the Advanced button.

The Initialize New Training Net dialog appears.

3. Type the number of output nodes that you want into the Output box. For example if you only want to train the neural network to recognize the letters A to Z, the number of output nodes is 26.

 

 

4. Once you have restricted the number of output nodes, you need to specify which character each output node represents.

You can either set the value of each output node individually – e.g. node 1=A, node 2=B etc. or set the values of a range of nodes to a range of characters – e.g. nodes 1 to 26 = characters A to Z.

To specify output nodes individually:

 

 

To specify output nodes as a range of characters:

 

 

The first node in the range can be any node. For example if you wanted to train the neural network to recognize the characters a, b and c plus the characters A to Z, you could set the value of node 1 to a,  the value of node 2 to b and the value of node 3 to c individually. You could then enter the range A to Z into node positions 4 to 29.

5. Click OK.

 

View the number of nodes in the Output Layer

To view the number of nodes in the Output Layer select Train Menu > Inspect Neural Net.

 

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