JPS5939791B2 - optical character reader - Google Patents

Description

[Detailed description of the invention] The present invention relates to an optical character reading device.

Conventional character reading devices that have the ability to quantize using multiple thresholds have used a method of integrating analog signals obtained by scanning characters and switching from a lower threshold to a higher threshold as the value increases. There is. However, this method has a fatal drawback when the characters have significant uneven shading. In other words, since the threshold value is determined by the dark part of the character, information in the light part is lost during quantization. Another method that has been used is to select a plurality of threshold values in a predetermined order. The disadvantage of this method is that if there is a large deviation in shading in a group of media with characters written on them, for example, when the ribbon of a line printer, etc. is new, the ribbon is printed with many lines, and the ribbon is printed with many lines and then printed. It is generally recognized that there is a large deviation in shading between printed and written forms, but while it is advantageous for one type of form, it is extremely disadvantageous for the other. That's what it means. That is,
This means that a threshold selection order that is advantageous for dark characters is often disadvantageous for light characters. Naturally, the degree of inconvenience depends on the degree of shading, the number of threshold values, and the difference between the threshold values. The object of the present invention is to improve these conventional drawbacks.

The feature of this invention is that it uses a learning method that determines the order in which to select the threshold value for quantizing the next character, based on the statistical results that have been discriminated up to that point while discriminating characters.

Embodiments of the present invention will be described in detail below with reference to the drawings.

In Fig. 1, the photoelectric converter 1 optically scans a character and converts it into an electrical signal (for example, when the character ``8'' shown in Fig. 2 is scanned in the direction of the arrow, the waveform ws shown in Fig. 3 is obtained). )
and input to the quantization circuit 2. The quantization circuit 2 is a circuit that can perform quantization using multiple threshold values (in the example shown in FIG. 3, three slice levels: SLA, SLB, and SLC), and its output is controlled by the slice level selection circuit 4 and input to the discrimination circuit 3. has been done. The slice level selection circuit 4 is the quantization circuit 2
The discrimination circuit 3 counts and holds the number of unidentifiable characters for each threshold value, calculates the rank with the lowest unidentifiable rate, and based on the result, the quantization circuit 2 selects the threshold with the lowest unidentifiable rate. send a control signal to. If it becomes indistinguishable at that threshold, a control signal is sent from the slice level selection circuit 4 to the quantization circuit 2 to select the threshold with the second lowest indistinguishability ratio, rescan, and re-determine. be done. In this way, threshold values are selected in order of decreasing indistinguishability ratio. An embodiment of the slice level selection circuit will be described in detail with reference to FIGS. 3 and 4.

The DSLA in FIG. 4, which is the result of selecting and determining the slice level SLA in FIG. 3, is sequentially stored in the memory 6 from A1 to An. When the capacity n of the memory 6 is exceeded, the data is written again starting from A1. In this case, ``1'' indicates that it cannot be determined, and ``0'' is stored in the memory 6 when it can be determined. Furthermore, the total number of read characters is set to a predetermined value, for example 1000.
An indiscernible number of A1 to An in memory 6 for each character, that is, "
Count the number of 1゛ and send the result to the counter (URC-
A) Keep it at 9. Similarly, slice level SL
For B and SLc, the number of unidentifiable numbers is counted from the contents of memory 7 (B1 to Bn) and memory 8 (C, to Cn), which respectively hold the determination results, and the corresponding counter (U
RC-B) 10 and counter (URC-C) 11. When the total number of read characters reaches 1000 characters, the output of each counter is inputted to a ranking determination holding circuit 12 which compares the magnitudes of counters 9, 10, and 11 and holds the ranking with the lowest number. It is clear that the ranking can be determined. Although the logic for determining the ranking is omitted, the content of the counter that first reaches 10 after subtracting 1 from each of counters 9, 10, and 11 ranks first.
It is clear that the contents of the counter that reached 60゛5 will be in second place, and the rest will be in third place. Also, if the slice levels become 60 degrees at the same time, this means that the rankings are the same, and in that case, it may be determined in advance that the slice levels are ranked in descending order of slice level, ie, SLO, SLB, and SLA. Memory 6,7
, 8 has a capacity n of 1,000 to 10,000 bits, which is practically acceptable. Further, although not shown in the drawing, slice levels may be selected in the order of the rankings SLc, SLB, and SLA until the total number of read characters reaches a predetermined value (1000 characters in the embodiment). Also, counters 9, 10, 1
The contents of 1 are cleared when the order of size is determined and retained, and when the total number of read characters reaches 1000 characters again, the unidentifiable numbers in memories 6, 7, and 8 are counted. . During that time, each memory 6 (A1 to An), 7
The contents of (B1 to Bn) and 8 (C1 to Cn) are only updated based on the discrimination results based on each slice level, so slice levels with less indistinguishability are often used. It is clear that the memory contents are also frequently updated. According to this invention, since the threshold values are selected in order of decreasing indistinguishability ratio, it has the advantage that the average speed of characters is high.

Also, even if the shading quality of input characters changes constantly, the threshold selection order is determined every time a predetermined number of characters are determined.
Another great advantage is that it has a learning effect that automatically follows character quality. Although this embodiment has been described with three slice levels, it is clear that it is also possible to implement a system with two or four or more slice levels.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the block configuration of the present invention, Fig. 2 is an explanatory diagram showing the scanning position of characters written on a document, and Fig. 3 is an illustration showing the relationship between the character scanning waveform and a plurality of slice levels. FIG. 4 is an explanatory diagram showing details of the slice level selection circuit. 1...Photoelectric conversion unit, 2...Quantization circuit, 3...Discrimination circuit, 4...Slice level selection circuit, 6, 7, 8... ...Memory, 9,1
0, 11... Counter, 12... Rank determination holding circuit.

Claims (1)

[Claims] 1. Quantize the gray level signal obtained by optically scanning the characters at a selected slice level, distinguish the quantized character pattern, and if there is an undiscernible character in the discrimination result, switch the slice level and try again. In an optical character reading device that performs discrimination, the discrimination results of the character pattern are retained for each slice level, and when the number of retained discrimination results reaches a predetermined value, the indistinguishability rate is calculated, and subsequent character quantization is performed. The optical character reading device is characterized in that the above-mentioned slicing level is selected and the indistinguishability ratio is small.