JPS62230165A - Two-color original reader - Google Patents

Abstract

PURPOSE:To attain the distinction between two colors with simple circuit constitution by generating a density signal of an original image and a color signal representing whether or not the color is a specific color and applying logical operation to the signals by means of a logic circuit. CONSTITUTION:Red and blue/green signals S1, S2 outputted from photoelectric conversion elements 6, 8 are digitized, then the result is inputted to sum/ subtraction computing elements 13,14. The sum computing element 13 and a comaprator 15 generate a density signal S9 of an original image and the subtraction computing element 14 and a comaprator 16 output a color signal S10 representing whether or not the original image is red. A discrimination circuit comprising inverters 17,18 and AND circutis 19,20 outputs a red detection signal S11 when the density signal S9 represents ''deep'' and a color signal S10 represents a red signal and outputs a black detection signal S12 when the density S9 represents 'deep' and the color signal S10 is other than a red signal. Further, the circuit discriminates a signal as 'white' independently of the color signal S10 when the density signal S9 is 'light'.

Description

[Detailed description of the invention]

[Prior Art] The present invention relates to a two-color original reading device suitable for facsimile machines, copying machines, electronic blackboards, and the like.

[Prior art]

2. Description of the Related Art A two-color document reading device is known that, in addition to determining whether a document image is black and white, determines one specific color such as red, and outputs a black and white signal and a red signal. by the way. Actual documents may be colored on paper or written in blue or green ink, so these two
In a color document reading device, it is desirable to appropriately determine the density of colors other than red and read them as white or black. As a two-color original reading device as mentioned above, there is a
As seen in Publication No. 166377, an image signal of a red component and image signals of blue and green (hereinafter abbreviated as blue-green) color components, which are complementary colors thereof, are extracted from the original image, and the image signal of the red component is extracted from the image signal of the red component. 5111 L determines red based on the difference signal obtained by subtracting 1ilii (ti) of each green component and outputs a red signal, and also discriminates black and white based on the image signal of the red component and outputs a black and white signal. Other known methods for determining black and white include determining from an image signal of a blue-green component, and determining from an image signal containing a gold component rather than an image signal of a specific color component. However, in the above method of determining black and white from the red signal, the low level of the red signal is determined as black, so even in relatively pale (bright) blue or green parts of the original image, the level of the red signal is low. Therefore, for example, a document written in black on blue manuscript paper may become completely black and become unreadable.Also,
In the above method of determining black and white from the blue-green signal, it is determined to be white when the blue-green signal is at a high level, so for example, a document written in blue on white manuscript paper may become completely white and become unreadable. be. In this way, none of the above methods could properly determine the density of blue or green. There was a problem in that actual document reading was not carried out practically. As a solution to such problems, Japanese Patent Application Laid-Open No. 1987-
As seen in Publication No. 44825, a black and white signal is output based on the sum signal of a red component image signal and a blue-green component image signal, and the two image signals are logarithmically amplified and then the difference between the two is calculated. A system has been proposed in which a hue signal is created using the above-mentioned black and white signal and this hue signal to accurately discriminate between black and white and red, green and blue. However, since this proposal is constructed for the purpose of multicolor reading, it requires a special circuit called logarithmic amplification and many comparison circuits, resulting in a complicated circuit configuration. In addition, since two logarithmic amplifier circuits are required, if an analog circuit is used to handle high-speed image signal processing, there will be differences in characteristics between the two due to temperature changes, etc., making it impossible to perform accurate signal processing. There was a problem that it was difficult to extract the signal. [Objective] In view of the above points, it is an object of the present invention to provide a two-color original reading device that can perform two-color discrimination practically and appropriately with a simple circuit configuration. [Configuration] Therefore, the present invention distinguishes the darkness of an original image mainly based on an image signal having a specific color component and an image signal having a correction component thereof. A color signal for discriminating between black and black is generated, and only when the density signal indicates "dark", the specific one color or black detection signal is output based on the color signal, and when the density signal indicates "light" , the above two detection signals are turned off and a white detection signal is output. An embodiment of the present invention will be described below based on the drawings. FIG. 1 is a schematic configuration diagram showing an optical system of a two-color document reading device according to an embodiment of the present invention. This two-color document reading device uses two line sensors to simultaneously read image signals of two color components from one document. In the same figure, l
2 is a light source that illuminates the document leaf passing on the image reading line RL, and 2 is a half mirror that branches the reflected light from the document DP received via the mirror 3 and lens 4 into two directions. One of the branched image lights passes through a red filter 5 that transmits only red component light, and forms an image on the light-receiving part of the photoelectric conversion element 6, and the other image light contains only blue and green component lights, which are complementary colors of red. The light passes through the blue-green filter 7 and forms an image on the light receiving portion of the photoelectric conversion element 8 . FIG. 2 is a block diagram of the signal processing system of the two-color original reading apparatus of this embodiment. In the figure, reference numerals 9 and 10 indicate an analog-to-digital conversion circuit (A/D) that converts the image signals extracted from the photoelectric conversion elements 6 and 8 into 4-bit digital signals.
), 11 and 12 are level adjustment circuits that match the maximum levels of the image signal taken out through the red filter 5 and the image signal taken out through the blue-green filter 7. 13 is a sum calculator that calculates the sum of the signals of the two color components; 14 is a difference calculator that calculates the difference between the signals of the two color components; 15.16
compares the output signal of the sum calculator 13 or difference calculator 14 with a certain threshold level, and converts the signal into 2
It is a comparator that converts into values. Further, 17.18 is an inverter circuit, and 19.20 is an AND circuit. FIG. 3 shows an example of the operation of this configuration when various documents DP of different colors and densities are set at the reading position of the optical system. FIG. 6(a) shows the reading color of the set document DP. The larger the number in the same color, the higher the density. When the document DP is set, the photoelectric conversion element 6,
The image signals SL and S2 outputted by the 8 are converted into a digitized image signal S s r 54 by an analog-to-digital conversion circuit (A/D) 9.10. Now, let us consider a situation in which the red filter 5 and the blue-green filter are not arranged in front of the photoelectric conversion elements 6 and 8. The image signals S3 and 54 have the maximum level when the document DP is white, as shown by the broken lines in FIG. Next, place the red filter 5 in front of the photoelectric conversion element 6. Further, a blue-green filter is arranged in front of the photoelectric conversion element 8. Then, since the red filter 5 suppresses light with blue and green components, the signal level of the single image signal decreases greatly when the document DP is blue or green, and even when the document DP is white, it contains blue and green components. Therefore, the image signal S3, which decreases by a certain amount, is transferred to the conversion circuit (A/
D) Output from 9. The level adjustment circuit 11 inputs this image signal S3, corrects it so that it reaches the maximum level when the original OP is white, as shown by the solid line in FIG. 3B, and outputs a red component signal S5. Similarly to the above, when the blue-green filter 7 is provided, the level adjustment circuit 12 inputs the image signal S4 and outputs a blue-green component signal S6 whose level is adjusted as shown by the solid line in FIG. Output. The sum calculation unit 13 inputs the red component signal Ss and the blue-green component signal S6, and outputs a sum signal S7 indicating the sum of the two, as shown in FIG. 4(d). Since this sum signal St is the sum of the red component and the blue-green component, it corresponds to the image signal obtained when the red filter 5 and the blue-green filter 7 are not provided. This sum signal S7 and a constant threshold level Dref
A comparator 15 compares the two values, and extracts a binarized density signal S9 as shown in FIG. This concentration signal S9
As shown in Table 1, the color density of the original DP can be determined. I On the other hand, the difference calculator 14 inputs the red component signal S5 and the blue-green component signal S6, and generates a difference signal indicating the value obtained by subtracting the signal S6 from the signal S5, as shown in FIG. Output Sa. This difference %Sa is a signal for detecting red color as has been conventionally done. Comparator 16 sets a constant threshold level Cref
The red signal S+o is extracted as a binarized red signal S+o as shown in FIG. 1st bladder Therefore, as shown in Table 3 (Q) and (b), color discrimination as shown in Table 3 (e) can be performed using the density signal S9 and red signal S1o. However, with this two-color document reading device, it is only necessary to distinguish between three colors: "red #l, #J black", and "white," so each color shown in table (e) is compared to table (f). As shown in this table, when the density signal S9 is "O", that is, dark
When it is determined, it is determined whether it is "red" or "black" based on the red signal 51G, and when the density signal S3 is "1", that is, "pale", it is determined that it is "white". In other words, the density signal S9 determines "white" rather than "red" or "black" based on the red signal Sho.
I try to prioritize judgment. The inverters 17.18 and the AND circuits 19.20 are circuits that output the red detection signal SL+ and the black detection signal 512 as shown in Table 3 (C) and (d) according to the above conditions. If color discrimination is performed in this way, Fig. 3(a)
When reading the colors of the various documents DP shown in Table 4, each signal is extracted as shown in Table 4 (b) and (c),
Can distinguish colors. (Margin below) As a result, for red-based colors, only when the concentration is high (components other than red are small) are they judged as "red". When the density is low (components other than red are large), it is determined as "white" and it becomes possible to distinguish between the two. Also, for colors other than red, when the density is high, it is judged as "black". When the density is low, it becomes possible to distinguish it as "white."This means that only characters written in dark red on the manuscript OP can be read as red, and characters written in dark color on manuscript paper with a light background can be read as red. For reference, Table 4 (d) shows an example of color discrimination when the discrimination of "red" is given priority over the discrimination of "white" in the above. According to this, A red color with a low density is also discriminated as "red". To prevent this, it is possible to increase the value of the threshold level Cref when binarizing the difference signal S8. FIG. 4(b) shows , shows an example of the actual measured value of the change in the difference signal S8 when the red density of the document DP is gradually increased and read as shown in (a) of the figure.The difference signal Sa is proportional to the red density. Now, when the threshold level is Cref, color discrimination is performed as shown in the same figure (c).Here, in order to prevent the above-mentioned interlayer, only the high concentration is red. The threshold level C e f
If it were to be increased to C' ref, there would be an inconvenience that the highest density red would be determined as "white", as shown in FIG. 2(d). If color discrimination is performed by giving priority to discrimination of "red" over discrimination of "white" in this way, correct color discrimination cannot be performed. As described above, in this embodiment, the density signal S9 is created from the sum signal Sy of the red component signal S5 and the blue-green component signal S6, and is used to discriminate between "dark" and "light". on the other hand,
From the difference signal S8 between the above two signals S5 and 56, the red signal S
ho is created, and this is used to determine whether it is "red" or "black", and only when it is determined to be "dark" above, the door detection signal S++ or black detection signal S1= is generated based on the red signal Sho. I am trying to output it. As a result, it is possible to read each color separately, such as only a dark red is read as "pa-red", a light color as "pa-white", and a dark color as "black". Additionally, the logarithmic amplification circuit required for conventional multicolor reading is no longer required. The number of comparison circuits is reduced and the circuit configuration is simplified. In this embodiment, two sets of photoelectric conversion elements and image signal circuits are arranged, but these are set as one set, and the red filter 5 and the blue-green filter 7 are switched in a time-division manner, and the time It may also be implemented by correcting the delay and calculating the sum and difference. Further, it is also possible to perform color discrimination based on the difference from the red component signal without using the blue-green filter 7, or to perform the density using the unfiltered signal as it is rather than the sum. Furthermore, a three-color reading device of red, black, and blue (green) is also possible by utilizing the fact that the difference signal of the green-blue color system has a negative value. Furthermore, since the effect of the filters 5 and 7 is to emphasize the difference value, it is not necessary to have a completely complementary color relationship.
L3. Difference calculator 14, comparators 15, 16, inverter 1
7.18. Instead of the AND circuits 19 and 19, 20, a ROM may be used for encoding, or a cPu may be used for software. [Effects] As described above, according to the present invention, a density signal for determining the density of an original image and a color signal for determining whether a specific color or "black" are created, and the density signal indicates "dark". Since only a specific color detection signal or a black detection signal is output based on the above color signal, it can be configured with a simple circuit with a few comparison circuits and condition judgment circuits, and it is possible to Since it can be distinguished, it becomes possible to read documents written in dark colors on manuscript paper with a pale background, and it becomes possible to practically and appropriately discriminate between two colors.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram of the optical system of a two-color original reading device according to an embodiment of the present invention, FIG. 2 is a block diagram of the signal processing system of the two-color original reading device, and FIG. 3 is a color FIG. 4 is an explanatory diagram of red color discrimination. l...Light source, 2...Half mirror-13...Mirror, 4
... Lens, 5... Red filter, 6, 8... Photoelectric conversion element, 7... Blue-green filter, 9... Analog-to-digital conversion circuit (A/D), 11.12... Level adjustment circuit, 13... Sum calculator, 14... Difference calculator, 15.16... Comparator, 17.18... Inverter, 19.20... AND circuit. Agent Patent attorney Crest 1) Makoto) --,7 Hanging 1 Figure L Figure 3 Figure 4 Ihe, I-Fu-Jn・1 ij I l l i 1 . 1
1(c)Cref IcJ donation 11iNll
lil亦e(!'S S+o OO11111
111 colors by °j white and white and red and white/frX/
frX(f)C'ref IcJ bjTocombined with color Ig! S++o OOO○111110kiP
Part I White Confession 亦亦亦亦亦度度Proceedings Ne 113 Official Book (
(Voluntary) June 25, 1986

Claims (1)

[Claims] The image on the same reading line of the original is detected by light detection means with different spectral sensitivity characteristics, and two types of image signals are extracted.
In a two-color document reading device that discriminates and outputs a black detection signal and a specific color detection signal of a document image based on the image signal, the shading of the image is determined and binarized based on the two types of image signals. a color detection means for discriminating between a "specific color" and "black" in the image and extracting a binarized color signal; White priority output means is provided which outputs the specific color detection signal and the black detection signal separately based on the signal, and turns off the specific color detection signal and the black detection signal when the density signal indicates "light". A two-color document reading device characterized by: