Patent GB-1463888-A (GB)
Title: Methods of and systems for generating sets of digital signals representative of handwritten characters
IPC: G06K9/68
Filed: 1974-07-09
Abstract: 1463888 Character recognition systems STANFORD RESEARCH INSTITUTE 9 July 1974 [31 Jan 1974] 30402/74 Heading G4R A system for recognizing a hand-written character employs a pen which provides a succession of signals indicative of the successive directions of motion of the pen in writing the character. Certain of the direction signals are ignored since certain sequences of directions are not permitted. Each of the remaining signals of the succession is used in turn as part of the address of a location in a memory. The other part of the address is obtained from the location addressed previously, the presently addressed location providing part of the address of the next location, and so on in the manner of a decision tree until a final location is addressed, the final location containing a signal representing the character. The pen disclosed (Fig. 12, not shown), has an angularly movable stylus whose instantaneous angular direction is indicative of the instantaneous direction of movement of the pen and is detected by four quadrantally arranged photocells. The photocell outputs are combined to resolve the angular direction into X and Y components which are used to provide U (up), D (down), L (left) and R (right) signals. If the photocell outputs cannot be clearly resolved to a U, D, L, or R signal, e.g. when the pen is moved diagonally it is assumed that the last clear signal persists. In addition a signal (.) is given indicating that the pen is not pressing on the writing surface. The signals U, D, L, R and . are each represented as a 3-bit word called a branch address. A read-only memory provides an initial node address from an initial location. A node address is a 7-bit word which defines part of the address of the next location to be addressed. Thus the initial node address together with the first branch address define the address of the root node location of a logic tree. For example if the first branch address is U, which it will be only if the character written is A, P, V, or 1, the logic tree which has a root node U will be selected, Fig. 7. The root node location contains a node address defining, in the case of Fig. 7, three possible locations, one of which is selected by the next branch address. For example, if the next branch address is D the centre branch is selected, and so on, successive memory locations being addressed until a final location is reached, the final location providing a character-representing signal to an output device. If a direction signal sequence begins UL the decision tree chooses the left hand branch. This has the effect of disregarding the initial U and starting the sequence at L by passing to the decision tree having a root node L. The disregarded U represents a flourish at the start of formation of a character. The initial R of a sequence beginning RU is similarly disregarded. Certain characters cannot be reliably recognized until either it has been ascertained by a timing unit that no further character follows or the next character is begun. For example, in the case of the centre branch of Fig. 7 numeral 1 cannot be distinguished from character A until it is determined that UD. is not followed by R. This will be so only if the next pen movements (if any) relate to the following character, since no character begins with this sequence.