Jacob Rabinow, Takoma Park, and Arthur W. Holt, Silver
Spring, MM., assignors to Rabinow Engineering Co.,
Inc., Takoma Park, Md.
Filed Feb. 2,1961, Ser. No. 86,817
12 Claims. (CI. 340—146.3)
This invention relates to character reading. machines and particularly to methods and means for enabling them to function more efficiently with imperfect characters and/or characters accompanied by appreciable background noise.
This application is a continuation-in-part of copending application Serial No. 32,911 which was filed on May 31, 1960, and having a common assignee.
The term "character" used herein signifies letters, numerals, symbols, marks and other forms of intelligence. For brevity, the term "character" is used throughout the description and claims. Further, the principle of the invention is described in terms of optical reading machines having scanners which provide outputs that vary in accordance with the absorption of light falling on the character. However, it is not essential that the scanner outputs result from optical investigation. For instance, the invention is equally well suited for recognition equipment providing output signals from magnetic intelligence or others.
Considering a few of the problems encountered by reading machines, a given character may have some parts approaching total black and other parts of the same character may be dark gray and/or light gray. This is especially true if the characters are formed by a typewriter. Another difficulty is that the characters of a single typed line are often different shades of gray and black. Sometimes characters are wholly or partially smudged. This often happens when making carbon copies.
The human intellect automatically distinguishes smudges, i.e. background noise, from the significant portions of the character. Normally, when typewritten material is read, a human being does not consciously notice the different shades of gray and black of the characters.
Since machines are incapable of mental processes such as discussed above, character recognition machines pick up the different levels of reflected light 'and background noise, complicating the character recognition procedure of the machine. An object of this invention is to provide means and methods for overcoming the above difficulties in a machine such as disclosed in the copending application or in other character recognition machines.
A more specific object of the invention is to provide a system of quantizing the scanner outputs at a number of different thresholds to represent not only "black" and "white" but also to represent intermediate shades of "gray." We then select the quantized output which possesses the most 'significant information regarding the unknown character in order to make available a character identification signal which may be processed by any type of recognition circuit or circuits or systems.
Another object of the invention is to provide a pluralthreshold or multilevel quantizing system which obtains the desired results by considerably fewer circuit components than would ordinarily be expected. In one embodiment, we code the scanner outputs to indicate the optical density of the elemental areas, 'and store the code in the temporary storage of the reading machine. Then we convert the code to analog signals proportional to the density of the area elements, making character identification input signals available for the decision section of the
reading machine. By coding the signals, we are able to use a smaller capacity memory than would be the case of separate memories for each quantize level. The general concept of quantizing is not new. Most
5 reading machines quantize the scanner output signals at a single threshold to (a) provide a quantized signal representing "black" if the scanner signal is at or above the threshold, or (b) provide a different quantized signal (or no signal) representing "white" if the same scanner
10 signal is below the threshold. In contrast, our invention takes intermediate shades of "gray" into consideration by quantizing the scanner output signals at more than one threshold. Thus, for a single scanner signal, we have at least three quantized signals to correspond to at least
15 three levels of optical density of the scanned point from which the scanner output originated.
We are aware of another prior quantizing system which requires that a character, or fine of characters, etc., be scanned a second time at a different sensitivity, if the first
20 scanning attempt failed to provide a satisfactory output. Such a solution to the problem is not nearly so satisfactory as the solution presented herein for the following reasons:
The electronic circuits (and optics) of character recog25 nition machines are very much f aster than the scanning in mahines in which the scanning speed is a function of the "paper moving" equipment. In other words, the speed of modern character recognition machines is h'mited by the capabilities of the mechanisms and techniques of 30 presenting the 'Character or characters to the scanner (or vice versa), and not the electronic data processing of the information 'available at the scanner. By requiring a separate scan operation or even a repetition of a previous scan and/or paper handling step to obtain quantizing, the 35 slowest part of the machine must be reused.
One of the features of our invention is that the various embodiments are capable of quantizing at any number of levels in parallel, completely independent of the act of scanning, i.e. the relative movement of the scanner and 4° paper handling, so that the speed of the character recognition machine is not significantly reduced. Even though we may quantize serially to any number of levels, the faster system comprehended by the invention is to quantize to various levels in parallel so that the quantizing 4j itself is fast.
Other objects and features of importance will become apparent in describing the illustrated forms of the invention which are given by way of example only.
FIGURE 1 is a diagrammatic view showing one system for the practice of the invention.
FIGURE 2 is a fragmentary diagrammatic view showing in additional detail, one possible construction of portions of the system shown in FIGURE 1. gg FIGURE 3 is a fight 'absorption table showing arbitrarily selected quantizing ranges for different optical gradations of black, gray 'and white.
FIGURE 4 is a circuit diagram showing storage means by an analog procedure.
FIGURE 5 is a schematic view showing a form of our invention using a binary coding system to represent the various quantized signals.
FIGURE 5a is a fragmentary view showing one point in the shift register memory and the part of the summing 65 network for deriving one quantized signal.
FIGURE 6 is a truth table for one possible binary coding sj'Stem which may be used in the embodiment of FIGURE 5.
In the accompanying drawings FIGURE 1 shows the ^0 character "O" on a white background 1®. Although the character is nominally called "black," in practice, characters are usually very dark gray and vary to light gray in