JPH0686070A - Picture reader - Google Patents

Abstract

PURPOSE:To provide a picture reader which can be applied to a two-color facsimile, etc., and capable of easily switching gradation without deterioration of picture quality at the time of halftone processing and selectively expressing only the part of a prescribed exposure. CONSTITUTION:The picture reader is provided with a converting circuit 9 converting the signal level of a read image signal read by a reading sensor and sending the obtd. converted picture signal to a comparator and a gradation switching data storage memory 11 storing plural kinds of gradation switching data which is used in the converting circuit at the time of converting the signal level. Besides, the gradation switching data storage memory stores gradation switching data which becomes '0' in the prescribed range of the read picture signal and '2<n>-1' in another range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus capable of halftone processing, which is used in a facsimile machine or the like.

[0002]

2. Description of the Related Art FIG. 8 is a block diagram showing a conventional image reading apparatus. In the figure, 1 is a reading sensor for reading an image of a document, and 2 is an analog reading image signal output from the reading sensor 1. Reference numeral 3 is a dither generation circuit for generating a dither signal for binarizing the read image signal 2, and reference numeral 4 is a dither signal generated by the dither generation circuit 3. Reference numeral 5 is a comparator for comparing the read image signal 2 with the dither signal 4 and binarizing the same, and 6 is a binarized image signal binarized by the comparator 5.

Next, the operation will be described. Read sensor 1
Reads an image of a document to generate an analog read image signal 2 and inputs it to one input terminal of the comparator 5.
At that time, the dither signal 4 generated by the dither generation circuit 3 is input to the other input terminal of the comparator 5. The comparator 5 compares the read image signal 2 with the dither signal 4 and binarizes it, and the generated binarized image signal 6
Is output from the output terminal.

Here, FIG. 9 is an explanatory view showing the relationship between the analog read image signal 2 and the dither signal 4 for each pixel. The dither signal 4 is from the voltage "A" to the voltage "B" as shown in the figure. The range of "changes for each pixel. The comparator 5 compares the level of the read image signal 2 with such a dither signal 4, and the pixel whose level of the read image signal 2 exceeds the dither signal 4 is "H" (white), and the pixels below it are "H" (white). "L"
Binarize to (black). In the illustrated example, only the second to fourth pixels in which the level of the read image signal 2 is higher than the dither signal 4 are binarized to "H", and all the other pixels are binarized to "L".

FIG. 10 shows the relationship between the analog read image signal 2 and the dither signal 4 when the level of the dither signal 4 is lowered by "C" as compared with that shown in FIG. Therefore, the dither signal 4 changes in the range of the voltage “AC” to “BC” for each pixel, and the binarized image signal 6 output from the comparator 5 is
The "L" changes to "H" at the 8th, 10th, and 12th pixels. In this way, by changing the level of the dither signal 4, it is possible to switch the black image with many "L" shown in FIG. 9 to the white image with many "H" shown in FIG. .

In the reading sensor 1, there is a predetermined relationship between the exposure amount and the output level of the analog read image signal to be output, and FIG. 11 shows its general characteristic. In the illustrated example, the output level of the read image signal 2 at the maximum exposure amount g is G, the output level of the read image signal 2 at the exposure amount “0” is α, and the sensitivity of the reading sensor 1 is k. In this case, the following equation holds between the exposure amount I and the output level V of the read image signal 2.

[0007]

[Equation 1]

At this time, when the exposure amount changes from "0" to "d", the output level of the read image signal 2 is "α".
From "e" to "e"
When it changes to + d ”, it greatly changes from“ E ”to“ F. ”Thus, when the exposure amount is small, the change in the output level of the read image signal 2 with respect to the change in the exposure amount is small, and the exposure amount is small. Becomes larger, the change in the output level of the read image signal 2 with respect to the change in the exposure becomes larger.

Here, the relationship between the dither and the dither signal 4 is shown in FIG. 12 by taking the case of 16 gradations as an example. In this case, the maximum level of the dither signal 4 is "A" which is slightly smaller than "G" shown in FIG. 11, and the minimum level is "B" which is slightly larger than "α" in FIG. Since the relationship between the dither and the dither signal 4 also corresponds to the characteristic of the reading sensor 1 shown in FIG. 11, the dither “9” is more than the voltage range of the dither signal 4 for the dithers “1” to “8”. ~
The voltage range of the dither signal 4 with respect to "16" is larger. Therefore, in an area where the signal level of the dither signal 4 is also small, the number of gradations of the dither is large, and an image quality faithful to the image of the original document is to be reproduced.

Further, in FIG. 12, the dither indicated by black dots is due to the dither signal 4 changing in the voltage range from "A" to "B" shown in FIG. Also,
The dither shown by the white dots is due to the dither signal 4 changing in the voltage range lower by “C” than that shown in FIG. 10, and therefore, in this case, it is more than the case of the dither shown by the black dots. The image quality is pale. In this way, the grayscale switching of the image quality is realized by changing the dither signal 4.

As a document describing a technique related to such a conventional image reading apparatus, for example, Japanese Patent Laid-Open No.
There are JP-A-284175, JP-A-2-279071, JP-A-63-252067 and the like.

[0012]

Since the conventional image reading apparatus is configured as described above, the change amount of the read image signal 2 with respect to the change amount of the exposure amount when the exposure amount is small is small, and therefore, When the read image signal 2 is compared and binarized by the dither signal 4 of gradation from several tens of gradations, the accuracy is poor and the reproducibility of the image quality is deteriorated.
In order to lower the image quality by lowering the level, the lower level of the read image signal 2 is compared and binarized, which further deteriorates the accuracy.

The invention described in claim 1 is made to solve the above-mentioned problems, and an image in which the gradation can be easily switched during halftone processing without deteriorating the reproducibility of the image quality. The purpose is to obtain a reader.

[0014]

According to another aspect of the present invention, there is provided an image reading apparatus which performs signal level conversion of a read image signal read by a reading sensor and sends the obtained converted image signal to a comparator. A conversion circuit and a gradation switching data storage memory that stores a plurality of types of gradation switching data used in the conversion circuit at the time of signal level conversion are provided.

In the image reading device according to the second aspect of the present invention, the grayscale switching data that is "0" in a predetermined range of the read image signal and "2 ⁿ -1" in the other range is grayscale switched. It is stored in the data storage memory.

[0016]

According to another aspect of the invention, in the conversion circuit, the signal level of the read image signal read by the reading sensor is selected by using one of a plurality of types of gray level switching data stored in the gray level switching data storage memory. By converting the image data and transmitting the generated converted image signal to the comparator, it is possible to realize an image reading apparatus that can easily perform the grayscale switching during the halftone processing without degrading the reproducibility of the image quality.

Further, the grayscale switching data storage memory according to the second aspect of the present invention stores the grayscale switching data which is "0" in a predetermined range of the read image signal and "2 ⁿ -1" in other ranges. This makes it possible to selectively take out only a portion having a predetermined exposure amount and express it.

[0018]

EXAMPLES Example 1. Embodiment 1 of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the invention described in claim 1. In the figure, 1 is a reading sensor, 2 is an analog read image signal, and 6 is a binarized image signal, which are the same as those of the conventional one denoted by the same reference numeral in FIG. Further, 7 is an analog-digital converter (hereinafter referred to as A / D converter) for digitizing the analog read image signal 2, and 8 is a digital read image signal converted by the A / D converter 7. is there. Hereinafter, the analog read image signal 2 before conversion will be referred to as an analog image signal,
The digital read image signal 8 after conversion is called a digital image signal.

Reference numeral 9 denotes a conversion circuit for performing gamma (hereinafter referred to as γ) conversion of the characteristic of the digital image signal 8 input from the A / D converter 7 using the grayscale switching data.
Is a converted image signal that has been γ-converted by the conversion circuit 9. Reference numeral 11 denotes a grayscale switching data storage memory that stores a plurality of grayscale switching data used in the conversion circuit 9 in accordance with the grayscale. Reference numeral 12 is a dither generation circuit different from that denoted by reference numeral 3 in FIG. 8 in that the dither signal is generated digitally, and 13 is the digital dither signal. Reference numeral 14 is a comparator different from the one denoted by reference numeral 5 in FIG. 8 in that the digital dither signal 13 and the converted image signal 10 are compared to generate a binarized image signal 6.

Next, the operation will be described. The analog image signal 2 from the reading sensor 1 that has read the image of the original is
The digital image signal 8 is converted by the A / D converter 7 and sent to the conversion circuit 9. Here, FIG. 2 shows the reading sensor 1
Is a characteristic diagram showing the relationship between the exposure amount I of the digital image signal 8 and the digital image signal 8, and the value of the digital image signal 8 with respect to the maximum exposure amount g when A / D conversion is performed with n bits is "2 ⁿ -1".
Has become. Upon receiving the digital image signal 8 as described above, the conversion circuit 9 receives the digital image signal 8 corresponding to the exposure amount.
Is subjected to γ conversion using one of the grayscale switching data stored in the grayscale switching data storage memory 11.

FIG. 3 is a characteristic diagram showing the gradation switching data. In the range from "0" to "A", the digital image signal 8 is "0", and in the range from "B" to "2 ⁿ -1". A value of “2 ⁿ −1” is given, and in the range from “A” to “B”, contrary to the characteristic shown in FIG. 2, “0” to “2 ⁿ -1” along a convex curve is obtained. The values up to are given respectively. When .gamma.-converted the digital image signal 8 having the characteristic shown in FIG. 2 using the grayscale switching data having such characteristics, the digital image signal 8 has an exposure amount I as shown in FIG.
Is "0" from "0" to "f", "2 ⁿ -1" from "h" to "g", and "0" to "2 ⁿ -1" from "f" to "h". Is converted into a converted image signal 10 that increases linearly.

Here, as described above, the grayscale switching data storage memory 11 stores a plurality of types of grayscale switching data. FIG. 5 is a characteristic diagram showing three types of such grayscale switching data. The grayscale switching data shown in FIG. Larger shade switching data is indicated by a broken line with reference numeral (b), and smaller shade switching data is indicated by a dashed line with reference numeral (c).

Further, by using each of these gradation switching data,
FIG. 6 shows the characteristics of each converted image signal 10 when the digital image signal 8 having the characteristics shown in FIG. 2 is γ-converted. In the figure,
The solid line with the reference sign (A) is the characteristic shown in FIG. 4 converted using the grayscale switching data of (a), and when the grayscale switching data of (b) is used, it is a larger value overall than that. When the grayscale switching data of (c) is used, it becomes a dashed line with a code (C) that has a smaller value as a whole.

The converted image signal 10 output from the conversion circuit 9 is sent to the comparator 14 and compared with the dither signal 13 generated by the dither generation circuit 12, and the binarized image signal 6
Is output to the outside as. At this time, when the comparison and binarization are performed using the dither signal 13 having the characteristics shown by the black dots in FIG.
Comparing the converted image signal with the symbol (A) and the converted image signal with the symbol (B) shown in FIG.
The converted image signal of the code (B) has a darker halftone image quality than that of the converted image signal of No., and if the converted image signal with the code (A) is compared with the converted image signal with the code (C), the code ( The converted image signal of code (C) has a lighter halftone image quality than the converted image signal of A).

As described above, by using a plurality of types of grayscale switching data, it becomes possible to switch the grayscale of the read image even if the dither signal 13 is one type. Also,
At the same time, the digital image signal 8 in the area where the exposure amount is small is raised by the γ conversion by the conversion circuit 9, and therefore, when binarized by comparison with the dither signal 13, the reproducibility of the image quality is improved. Therefore, the accuracy is improved.

Example 2. Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 7 is a characteristic diagram showing the grayscale switching data stored in the grayscale switching data storage memory 11 in the embodiment of the invention described in claim 2. In the above embodiment, the case of halftone processing has been described. However, using the grayscale switching data shown in FIG. 7, only "0" in the range from "M" to "N" of the digital image signal and "0" in other areas. Two
By converting into ^n- 1 ", it is possible to express only a part of a certain exposure amount as black and the other part as white. For example, an image signal corresponding to a red character in a range from" M "to" N ". If the image signal corresponding to the black character is "M" or less and the white information is "N" or more, only the image signal of the red character can be extracted and represented by the black image.

Further, by preparing a plurality of types of such grayscale switching data and combining the range to be extracted with the blue part, the yellow part, etc., it is possible to apply to a two-color facsimile or the like.

[0028]

As described above, according to the first aspect of the present invention, a plurality of types of gray level switching data are stored in the gray level switching data storage memory, and one of them is used as a reading sensor. Since the signal level of the read read image signal is converted and sent to the comparator, the image quality can be accurately reproduced at the time of halftone expression, and the image density can be switched easily. There is an effect that can be obtained.

According to the second aspect of the invention, "0" is set in the predetermined range of the read image signal, and "2" is set in the other range.
^Since it is configured to use the gray level switching data of " ⁿ -1", it is possible to selectively extract and express only a portion having a predetermined exposure amount, and thus it is possible to apply to a two-color facsimile or the like. .

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a digital image signal of the above embodiment.

FIG. 3 is a characteristic diagram showing the grayscale switching data of the above embodiment.

FIG. 4 is a characteristic diagram showing a converted image signal of the above embodiment.

FIG. 5 is a characteristic diagram showing a plurality of types of grayscale switching data according to the above embodiment.

FIG. 6 is a characteristic diagram showing a plurality of types of converted image signals of the above embodiment.

FIG. 7 is a characteristic diagram showing grayscale switching data according to the second embodiment of the present invention.

FIG. 8 is a block diagram showing a conventional image reading device.

FIG. 9 is an explanatory diagram showing a relationship between a conventional read image signal and a dither signal.

FIG. 10 is an explanatory diagram showing a relationship between a conventional read image signal and a level-shifted dither signal.

FIG. 11 is a characteristic diagram showing a conventional read image signal.

FIG. 12 is a characteristic diagram showing a relationship between conventional dither and a dither signal.

[Explanation of symbols]

 1 Reading Sensor 9 Conversion Circuit 11 Gray Scale Data Storage Memory 12 Dither Generation Circuit 14 Comparator

Claims (2)

[Claims] 1. A reading sensor for reading an image of a document to generate a read image signal, a grayscale switching data storage memory for storing a plurality of types of grayscale switching data used for signal level conversion of the read image signal, and the grayscale. One of the plurality of types of grayscale switching data stored in the switching data storage memory
A conversion circuit for converting the signal level of the read image signal, a dither generation circuit for generating a dither signal for binarizing the conversion image signal output from the conversion circuit, and the conversion image signal. Is compared with the dither signal and 2
An image reading apparatus provided with a comparator for digitizing. 2. The density switching data storage memory stores density switching data which is “0” in a predetermined range of the read image signal and “2 ⁿ −1” in other ranges. The image reading apparatus according to claim 1.