JPS58195986A - Threshold value controller of character reader - Google Patents

Abstract

PURPOSE:To read character stably at a high speed by coding a picture signal into a binary-coded signal on the basis of a proper threshold value corresponding to the brightness of each character and processing the binary-coded signal at a processing part. CONSTITUTION:The content of a register 12 is supplied through a multiplexer 13 from a D/A converter 14 as the threshold value to be supplied to a binary coding comparator 11 for the binary coding of the picture signal of a television camera 10. The binary-coded picture signal is effective only in areas (h), (i), and (j) of gate circuits 18, 19, and 20 by area signals showing character ends at a left, a center, and a right end from area signal generators 15, 16 and 17, and counters 21, 22, and 23 count the number of picture element for logical operations of white in the areas (h), (i), and (j), frame by frame. Thus, the threshold values for such binary coding that 50% of picture elements in the areas corresponding to the left, center, and right ends are black are obtained in registers 28, 29, and 30 while the content of the register 12 increases by a specified value at every frame scan of the screen from an initial value to a final value.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a threshold control device that provides a threshold for stable binarization in a character reading device.

In a character reading device, an image signal containing characters obtained by an imaging device such as a television camera is compared with a certain threshold value, and the dark part is set to 11 Q I+, and the bright part is set to "1".
In many cases, characters are read by processing the binarized image obtained as a digital image, and the value to which this threshold value is set is very important. In other words, when reading the characters shown in Figure 1, the image signals in scanning lines 1, 2, and 3 for reading and reading correspond to the shading of the characters, respectively.
Obtain the value of c. The threshold value for binarization in this case may be set to the value of d, which is approximately the median value of the amplitudes of a, b, and c in FIG. 1. However, in general, when reading characters with many digits, the image signals for each digit rarely give the same output. In particular, when reading characters 6 illuminated by a light source 4 from a specific direction as shown in FIG. The brightness of the text and characters is brighter in the area closer to light source 4, and darker in areas farther from light source 4, which is the scanning line for reading. , 8.9, the image signals are e, r, g, and the threshold value for binarization cannot be uniformly set.

In conventional character reading devices, the threshold for binarization is usually controlled at the beginning of reading in order to respond to changes in character brightness, and the brightness changes for each digit of the character. It was difficult to read and compile data whose height changes.

The object of the present invention is to perform high-speed and stable reading even in such cases.

An embodiment of the present invention is shown in FIG. For convenience, in the following explanation, we will select three positions from a series of character positions, the left end, the center, and the right end, and find the corresponding threshold values for appropriate binarization. It is easy to extend this method to find the threshold value for binarization corresponding to the position of each character. In Figure 4, 1o is a television camera, 1
1 is a binarization comparator that binarizes the video signal from the television camera 10; 12 is a register that determines a threshold for binarization; 13 is a multiplexer; and 14 provides a threshold for binarization. It is a DM converter.

15, 16, and 17 apply logic "1" signals in the areas i and j shown in FIG. 18, 19, 20 are gate circuits, 21, 22, 23 are logic ``1'' within the frame of the screen of the television camera 1°;
” counter, 24!L, 24b, 240
is a comparison value generator, 25, 26.27 is a comparator, 2B,
29.

3o is a register; 31 is a switching signal generator that outputs switching signals at positions 1 between the leftmost character and the center character in FIG. 6 and l between the center character and the rightmost character in response to the sweep of the screen of the television camera 1o. 32 is a multiplexer, 33 is an arithmetic unit, and 34 is a processing unit that processes the binarized image signal and reads characters.

Next, the operation of the above embodiment will be explained. The operation of this embodiment is divided into two stages. In the first stage, a threshold value corresponding to the position of each character is determined, in which a binarization comparator is used to binarize the image signal of the television camera The threshold value provided to 11 is provided by the Dmucon Bark 14 from the contents of register 12 through multiplexer 13 . The register 12 operates in such a way that it increases by a certain value sequentially for each frame of the screen from a sufficiently low initial value given in advance, and reaches the final value. Accordingly, the binarized image signal obtained from the binarized comparator 11 is , the state changes from a state where there are many logic signals "1" representing white to a state where there are many logic signals "0" representing black. This binary image signal is generated by the area signal generator 16.
, 16.17, the gate circuits 18, 19.20 receive the sixth
h+i+] in the figure, and is further sent to counters 21, 22, and 23, which are reset every frame. That is, the counters 21, 22, and 23 each count the number of pixels that take the white logic in the area h+ i+ ] in FIG. 6 for each frame.

The contents of the counters 21, 22, 23 are determined by the constant values output by the comparison value generators 24L, 24b, 240 (usually the fifth figure, ' output a value corresponding to 50% of the number of pixels in each of the counting regions),
If it is smaller, a rewrite pulse is sent to the registers 2B and 29 and 30, which are prepared to store the contents of the register 12, respectively. By the above method, the contents of the register 12 increase from the initial value by a constant value every time the screen is scanned, until reaching the final value.

60% of the pixels in the area corresponding to the center character and the rightmost character
The threshold value for binarization at which the color becomes black is set in register 2.
You can get it on 8, 29.30.

Next, at the stage of reading each character, the multiplexer 13 is switched, and according to the switching signal generated from the switching signal generator 31, the multiplexer 32 sequentially reads out the contents of the registers 28, 29, 30 according to screen scanning, and 33, the threshold value obtained by adding a certain value or multiplying by a certain value is dynamically passed through the D mukon meter 14 to the binarization comparator 11.
give to In this way, by adding or multiplying by a certain value in the arithmetic unit 33, it is possible to provide a threshold value that allows characters to be reliably discriminated in each area.

As described above, according to the present invention, the binarized image signal obtained from the binarization comparator is binarized using an appropriate threshold value corresponding to the brightness of each character. This has the advantage that characters can be read and recorded at high speed and stably by being processed by the processing section.

[Brief explanation of drawings]

Figure 1 shows how to scan a multi-digit character with uniform brightness.
Figure 2 is a diagram showing the process of obtaining a digitized signal. Figure 2 is a perspective view schematically showing the case where a television camera reads a multi-digit character illuminated by a light source from one diagonal direction. Figure 3 is the character in Figure 2. FIG. 4 is a block diagram of an embodiment of the present invention, and FIG. 6 is a diagram showing a multi-digit counting area of the same embodiment. 10-... TV camera, 11... Binarization comparator, 12... Register, 13... Multiplexer, 14... DM converter, 15
, 16.17... Area signal generator, 18, 19
．． 20...Gate circuit, 21, 22, 23
---Counter, 24&, 24b. 240... Comparison value generator, 25, 26.27.
...Comparator, 28, 29.30...Register, 31...Switching signal generator, 32...
...Multiplexer, 33 arithmetic unit, 34...processing unit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure fIi2 Figure 3

Claims (1)

[Claims] A rusk scan type imaging device that images a part to be read with characters and symbols consisting of multiple digits, and a threshold value that sequentially changes every frame scan of the screen from a pre-given initial value. a threshold value generation procedure; a binarization comparator for generating a binarization signal by comparing an image signal from the imaging device with a threshold value from the threshold generation means; and a plurality of the read parts. Count the number of pixels of the binarization code that take a logical value of 0 or 1 in a certain area corresponding to the digit position, and store the threshold for binarization when this count becomes a constant value. It comprises a plurality of storage means, and means for reading the threshold values stored in the storage means corresponding to each of the plurality of digit positions and applying the threshold values to the binarization comparator based on the reading results. Threshold control device for character reading device.