JPS6237865B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for sequentially illuminating the surface of a document such as a facsimile with a plurality of light sources having different spectral radiation characteristics, and reading the document image on the document surface by separating it into a plurality of color signals. It concerns a reading device.

One of the methods for reading a calligraphy image on the surface of a document by separating it into a plurality of color signals is shown in FIG.
Figure 1 shows a two-color reader that can separate and read parts written in red and parts written in black on the surface of a document. 3 is a light source formed of a light body, that is, a red fluorescent lamp; 3 is a light source formed of a fast-response color phosphor, that is, a green fluorescent lamp; 4 is a lens; and 5 is a one-dimensional solid-state image sensor.

Next, this conventional operation will be explained. Second
The figure shows the spectral radiant energy characteristics of fluorescent lamps 2 and 3. The spectral distribution of red fluorescent lamp 2 has a band of 600 to 670 mm as shown in characteristic 6, and the spectral distribution of green fluorescent lamp 3 The distribution is 400~ as shown in characteristic 7.
It has a band of 600mm. On the other hand, the red part on the manuscript surface,
The spectral reflectance characteristics of the black portion and the white portion of the original background are shown at 8, 9, and 10 in FIG. 3, respectively.

The reading of the original is performed as follows. In FIG. 1, a document 1 is intermittently conveyed in the X direction by a conveying means such as a roll or a step motor (none of which are shown), and while the document 1 is stopped, a red fluorescent light is first illuminated. 2 to illuminate the original to obtain a red photoelectric conversion signal r, and then turn on the green fluorescent lamp 3 to obtain a green photoelectric conversion signal g. Fourth
Figure A shows a scanning line area having a red part 11, a black part 12, and a white part 13 of the original background, and Figures 4B and C show a red photoelectric conversion signal r obtained when scanning this scanning line area. and green photoelectric conversion signal g. By taking the difference between the red photoelectric conversion signal r and the green photoelectric conversion signal g, a difference signal as shown in FIG. 4D is obtained, but this difference signal has a positive signal level for the red part of the scanning area However, values close to zero are taken for black areas and white areas of the original background. This can be easily understood from the characteristics shown in FIGS. 2 and 3. Therefore, the difference signal is expressed as V in FIG.
If the signal is binarized using the threshold voltage indicated by _tr , the red signal can be separated and obtained. On the other hand, the black signal is obtained by binarizing the red photoelectric conversion signal r using a threshold voltage indicated by V _tb in FIG. 4B.

Next, the timing of signal processing in this color separation will be explained in relation to the scanning of the one-dimensional solid-state image sensor 5. In FIG. 5, A indicates the scanning timing of the one-dimensional solid-state image sensor 5, and in the figure, continuous scanning is performed. B shows the moving state of the document 1.
C indicates the timing of lighting of green fluorescent light 3,
D indicates the timing of lighting of the red fluorescent lamp 2.
E indicates an output signal of the one-dimensional solid-state image sensor 5, and a green photoelectric conversion signal g and a red photoelectric conversion signal r are obtained in time series.

Here, the structure of this one-dimensional solid-state image sensor 5 is as follows:
It consists of a large number of photoelectric conversion pixel columns and a shift register for sequentially sending out the photoelectric conversion signals of the pixel columns to the outside. For example, the photoelectric conversion signal accumulated in _the pixel column during _the scanning period n ₁ in FIG. Send a signal to the outside. On the other hand, the pixel column accumulates the next signal for a scanning period _n2 immediately after transferring the signal to the shift register section. By repeating this process, photoelectric conversion is performed sequentially.

In the case of FIG. 5, the green photoelectric conversion signal g is accumulated during the scanning period n ₁ and outputted to the outside during the scanning period n ₂ , and the red photoelectric conversion signal r is accumulated during the scanning period n 2 and is outputted to the outside during the scanning period n ₂ . ₃ to output externally. Therefore the scanning period n ₁
The document 1 must be completely stopped between n2 and _n2 , and if the document is moved during this period, color separation will deteriorate.

In addition, in this case, a scanning period _n3 is allocated to secure the moving time of the document, and the time to photoelectrically convert one scanning line of the document 1 requires three scanning periods of the one-dimensional solid-state image sensor 5. It is said that Conversely, the reading time for one scanning line needs to be at least three times the document moving time, which is a constraint when considering speeding up document reading.

Another condition that limits the document reading speed is the response speed of the fluorescent lamp. When the fluorescent lamp is turned on intermittently as shown in FIG. Although the response speed of the discharge of the fluorescent lamp is sufficiently small compared to the scanning period of the one-dimensional solid-state image sensor 5, the afterglow time of the phosphor varies greatly depending on the phosphor. Generally, a blue or green phosphor with a fast response speed can be easily obtained, but a red phosphor often has a long afterglow time, which takes several ms to several tens of ms. The afterglow time _of the red fluorescent lamp 2 _shown in FIG. When the afterglow time of the fluorescent lamp 2 is longer than that, there is no problem. However, when increasing the reading speed by shortening the scanning period of the one-dimensional solid-state image sensor 5 or the document moving period, the afterglow time of the fluorescent lamp becomes a constraint, which prevents the speeding up.

As explained above, in the conventional two-color reading device, one scanning line is read by scanning the one-dimensional solid-state image sensor 5 three times, and during two of the scanning periods, the red fluorescent lamp 2 and the green fluorescent lamp are used. Since the scanning period was allocated to the lighting period of the lamp 3 and the remaining scanning period was allocated to the period of conveying the document 1, there was a drawback that the time required to read one scanning line was more than three times the period of document conveyance.

This invention has been made to eliminate the above-mentioned drawbacks of the conventional apparatus, and provides a document reading device that can increase the document reading speed by turning on the light source in flashes for a short period of time. It is something.

An embodiment of the present invention will be described below with reference to the drawings. The present invention is characterized in that a discharge lamp filled with a rare gas is used as the red fluorescent lamp 2 described above, and the reading of one scanning line of the original 1 by the one-dimensional solid-state image sensor 5 is Drive means that perform two scans of the one-dimensional solid-state image sensor 5, i.e., electronic circuit control equipment that outputs clock pulses to the shift register of the one-dimensional solid-state image sensor 5 mentioned above (for example, Basics and Applications (see page 32), the one-dimensional solid-state image sensor 5 flashes for a very short period of time at the end of the first scan and the start of the second scan of the two scans. In this way, a control means for controlling the drive of the red fluorescent lamp 2 and the green fluorescent lamp 3, for example, a blinking control circuit (see page 1541 of the Electrical Engineering Handbook published by the Institute of Electrical Engineers of Japan) is provided, and the rollers and steps described above are provided. - A microprocessor equipped with a timing generator (see page 178 of the Microcomputer Terminology Dictionary published by Nikkan Kogyo Shimbun Co., Ltd.) that can adjust the timing of the document 1 conveyance by the motor to continuous scanning that does not include a period during which the document is conveyed. The point is that electronic circuit control equipment such as a setsa was installed. FIG. 6 shows the scanning timing of the one-dimensional solid-state image sensor 5, the timing of transporting the document 1, the timing of turning on the green fluorescent lamp 2, the timing of turning on the red fluorescent lamp 3, and the timing of the primary timing. The signal output (E) of the original solid-state image sensor 5 is shown in relation to the signal output (E).

In this example, one scanning line of the original 1 is read by scanning the one-dimensional solid-state image sensor 5 twice by clock pulses output from the electronic circuit control equipment, that is, n ₁ and n ₂ in FIG. It is read by scanning n ₃ and n ₄ . . . twice each. Further, the green fluorescent lamp 3 is turned on for a short period of time at the end of the front scanning period of the two scans by the blinking control circuit, and the red fluorescent lamp 2 is similarly turned on by the blinking control circuit described above. The circuit turns on the light only for a short period at the beginning of the rear scan period. That is, in the reading period for one scanning line, the lighting period of the fluorescent lamps is concentrated in one place and is made as short as possible, and the remaining period is used for the period when the document 1 is transported. FIG. 6B shows the state in which the document 1 is conveyed by the rollers and step motors driven under the control of the microprocessor mentioned above. In this way, by shortening the lighting period of the fluorescent lamp, the period during which the document 1 is stopped can also be shortened, and the document reading speed can be increased. For example, if the lighting period of the fluorescent lamps 2 and 3 is sufficiently small with respect to the scanning period of the one-dimensional solid-state image sensor 5, the stopping period of the original 1 can be ignored, and the reading speed can be increased up to the limit of the original feeding speed. It is possible to increase the speed, and it is also possible to continuously feed documents without stopping periods.

By the way, in order to achieve this speed increase, a light source with a fast response speed is required. First, green fluorescent light 3
Considering this, it is easy to obtain a light output with a fast response time as described above. Furthermore, unless the light output during lighting is increased in inverse proportion to the shortening of the lighting period, a photoelectric conversion output level equivalent to that of the conventional case shown in FIG. 5 cannot be obtained. In general, the light output of a fluorescent lamp increases as the tube current increases, but in the case of continuous lighting, increasing the tube current causes the temperature of the tube to rise and the luminous efficiency of the fluorescent lamp to decrease. However, in the case of the embodiment shown in Figure 6, even if the tube current during the lighting period is increased, the effective tube current will not increase much because the lighting period is short. Therefore, the temperature rise is small, and the optical output can be increased.

On the other hand, regarding the red fluorescent lamp 2, the response speed of the light output becomes a problem. In an embodiment of the invention, a discharge lamp filled with rare gas is used instead of a fluorescent lamp. For example, instead of the red fluorescent lamp 3, a neon discharge lamp can be used. The lighting conditions for Ne discharge lamps are not much different from those for fluorescent lamps, and the same lighting power source can be used. Furthermore, the response speed of light output is extremely fast, unlike light emission from a phosphor.

As explained above, by selecting a phosphor or using a rare gas discharge lamp, it is possible to light up the light source for document illumination in a flash manner, and the embodiment shown in FIG. 6 can be fully realized. It is.

In the above embodiment, two-color scanning was explained in which the red and green illumination light sources are turned on in flashes to separate and read the red and black parts of the document surface. The present invention can be similarly applied to a multicolor reading device that lights up and reads multiple types of colors separately.

As described above, according to the present invention, since the surface of the document can be conveyed substantially continuously during the document conveyance period, the document conveyance period can be significantly longer than that of the conventional method. As a result, it has become possible to read the surface of a document at an extremely high speed compared to conventional document reading devices. Furthermore, it has become possible to set the lighting period of the light source to an extremely short period between the end of the first scan and the start of the second scan in the two scans performed by the one-dimensional solid-state image sensor.
It is possible to provide a document reading device that can substantially eliminate deterioration in image quality that occurs during reading even when reading a document at high speed, and can obtain high-quality image data.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing the principle of the document reading device;
Figure 2 is a characteristic diagram showing the spectral radiant energy distribution of a fluorescent lamp, Figure 3 is a characteristic diagram showing the spectral reflectance of the red, black, and white parts of the document surface, and Figure 4 is a characteristic diagram showing the spectral reflectance of the red, black, and white parts of the document surface.
FIG. 5 is a timing diagram showing the photoelectric conversion and color separation operations in the document reading device shown in FIG. 5. FIG. 5 is a timing diagram for explaining the reading operation in the conventional reading device. FIG. FIG. 2 is a timing chart for explanation. 1... Manuscript, 2... Red fluorescent light, 3... Green fluorescent light, 4... Lens, 5... One-dimensional solid-state image sensor, and the same reference numerals in the drawings indicate the same or equivalent parts. .

Claims (1)

[Claims] 1. A light source formed by a phosphor of a color system with different spectral radiation characteristics and a fast response speed and a light source formed of a phosphor of a color system with a slow response speed are synchronized with the main scanning by a one-dimensional solid-state image sensor, respectively. The light is sequentially turned on to illuminate the document surface, and the written image on the document surface is imaged on the light receiving surface of the one-dimensional solid-state image sensor and photoelectrically converted, and the one-dimensional solid-state image sensor performs main scanning and the original document. In the document reading device configured to read image signals from the entire surface of the document by sub-scanning that drives a conveyance means for moving the surface, the phosphor of a color system with a slow response speed is provided. A discharge lamp filled with a rare gas is used as the light source, and a drive means is provided to cause the one-dimensional solid-state image sensor to read one scanning line of the original by scanning the image sensor twice, A control means for controlling the driving of the two types of light sources so that the two types of light sources are illuminated for a certain period at the end of the first scan and the start of the second scan in the two scans of the one-dimensional solid-state image sensor. A document reading device further comprising a conveyance timing adjustment means that can adjust the timing of document conveyance by the conveyance means to continuous sub-scanning that does not include a conveyance stop period.