3. The method of claim 1 , wherein generating the merged node further comprising determining an updated set of letter properties representing letter properties of letters in the merged node.
1. A method comprising: receiving an image file representing an image comprising text, the text comprising a plurality of letters including a first letter, wherein the first letter is an instance of an unknown first letterform and wherein the first letter is associated with a known first set of letter properties; classifying the first letter into a first initial letterform class of a plurality of initial letterform classes based on the known first set of letter properties, wherein the first initial letterform class represents letter properties of letters in the first initial letterform class; determining a set of final letterform classes, including a first final letterform class representing the unknown first letterform, wherein determining the first final letterform class comprises: generating a hierarchical tree structure comprising a plurality of terminal nodes representing the initial letterform classes including a first terminal node representing the first initial letterform class and a plurality of parent nodes representing an initial letterform class group; generating a plurality of first similarity metrics by comparing a first parent node the plurality of parent nodes to other parent nodes of the plurality of parent nodes the hierarchical tree structure, wherein a first initial letterform class group represented by the first parent node is associated with a plurality of initial letterform classes of different letters having common letter properties; and if one of the plurality of first similarity metrics is above a threshold, generating a merged node by merging the first parent node with a second parent node associated with the one of the plurality of metrics; and determining, for the first letter, the unknown first letterform based on the first final letterform class.