JPH10136159A - Light source for color image scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the reproducibility of a color of a read image by the color image scanner adopting the method of three-color light emitting diode switching. SOLUTION: An image of an original in full color is read by using light emitting diodes 2 that emit each of red, green, blue colors for the light Source, lighting sequentially the light emitting diodes 2 of each color sequentially to emit the original 5, leading its reflected light to light receiving elements 7 by an optical system 6 consisting of a lens or the like and forming the image on the elements. A plurality of kinds (G1, G2) of light emitting diodes of the same color group whose peak light emitting wavelength bands differ are used for at least one color light emitting diodes among the light emitting diodes 2 of each color. Thus, the wavelength band of the effective sensitivity distribution of the light emitting elements 7 is effectively widened to obtain the color image scanner with excellent color reproducibility of the read image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image scanner for reading an image of a document in full color as an input device for a computer, a facsimile, a copying machine or the like.
The present invention relates to a light source device for illuminating a document in a color image scanner.

[0002]

2. Description of the Related Art An image scanner has excellent operability and versatility as an image input device, and has recently been widely used in the fields of OA equipment, information equipment and the like. In particular, some color image scanners have excellent quality and quantity of data that can be input, and their development and spread are expected. A conventional color image scanner is disclosed in, for example, Japanese Patent Publication No. 55-15137.
As shown in FIG. 1 of the publication, a xenon tube or a cold-cathode tube that emits light of almost all visible wavelengths from red to green through blue is used as a light source. Then, red, green, and blue filters are arranged on a plurality of light receiving elements that read light formed by an optical system as reflected light of a color image recorded on a document, using the light of these light sources. The lower light receiving element is provided with the characteristic of the sensitivity distribution with respect to the wavelength as shown in FIG. 11 for each color, so that the color is determined and read.

FIG. 11 shows a sensitivity distribution of a light receiving element with respect to a wavelength of light when red, green and blue filters are attached to a light receiving element such as a photodiode (hereinafter simply referred to as "sensitivity distribution"). Where the horizontal axis represents wavelength and the vertical axis represents relative sensitivity. Where the curves Rf, Gf,
Bf indicates the sensitivity distribution of the light receiving element to which the filters of red, green, and blue are respectively attached. According to such a reading device, the brightness is read from the received light amount under the green filter close to the relative visibility distribution of the human eye, and the ratio of the received light amount under the green filter to the received light amount under the red filter, And chromaticity (hue) from the ratio of the amount of light received under the green filter to the amount of light received under the blue filter
You can read.

In this case, a light receiving element is required for each of the colors, and a light receiving element which is three or more times the number of light receiving elements of a black and white reading scanner is used and a color filter is used. Further, there are problems that the life of the xenon tube and the cold cathode tube is relatively short and that a special circuit for lighting is required.

[0005]

Therefore, light emitting diodes of three colors of red, green and blue are used as light sources instead of the light source 2 shown in FIG. 1 of the above publication, and the light emitting diodes are sequentially turned on for each color. Accordingly, a color image scanner capable of reducing costs can be used, in which a light receiving element for a black-and-white scanner can be used almost as it is. In this case, the effective sensitivity distribution of the light receiving element is a composite distribution of the sensitivity distribution of the light receiving element itself and the spectrum distribution of the light emission intensity of the light source, and has a discrete characteristic as shown in FIG. In FIG. 12, Rd, Gd, and Bd are curves showing the sensitivity distribution of the light receiving element when the red, green, and blue light emitting diodes are individually turned on. The reason that the effective sensitivity distribution becomes discrete as a whole is that the width of the spectrum distribution of the light emission intensity of the light emitting diode of each color in the light source is narrower than the distribution width of the spectrum distribution of the transmittance in the filter. by.

[0006] In such a time-division illumination type color image scanner, the sensitivity distribution in the light receiving element has discrete characteristics as described above, so that the color of the image recorded on the document cannot be read sufficiently. That is, in the case of the above-described filter system, the overall sensitivity distribution maintains a high level with a relatively wide width as shown by a dotted line Ff in FIG. 11, whereas the emission of the three colors shown in FIG. In the case of using the switching illumination method of the diode, the overall sensitivity distribution is as shown in FIG.
This has the disadvantage that the color of an image having a wavelength corresponding to this portion cannot be read out or discriminated, and the color reproducibility of the read image deteriorates.

According to the present invention, a light-emitting diode of three colors of red, green, and blue is used as a light source without using a filter, and the light-emitting diodes are sequentially turned on for each color, so that a light-receiving element is time-divisionally multiplexed. In the color image scanner that reads the brightness data of each color, the above problem is to be solved. SUMMARY OF THE INVENTION It is an object of the present invention to solve this problem and to provide a color image scanner which is excellent in color reproducibility of a read image, has a long service life, and has a low manufacturing cost.

[0008]

As a first means for solving the above-mentioned problems, the present invention uses a light emitting diode for emitting light of each color of red, green and blue as a light source and a light emitting diode for each color. The light source device of a color image scanner that reads a document image in full color by sequentially lighting the document and irradiating the document and guiding the reflected light to a light receiving element by an optical system including a lens and the like to form an image. As for at least one color light emitting diode among the diodes, a plurality of types of light emitting diodes of the same type having different peak emission wavelengths are used.

According to a second aspect of the present invention, there is provided a light source device for a color image scanner according to the first aspect, wherein at least one of the light-emitting diodes for each of the colors is provided. , Characterized in that a plurality of types of light-emitting diodes of similar colors having different peak emission wavelengths are simultaneously turned on and off.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a light source device for a color image scanner according to the present invention will be described below with reference to the drawings. FIG. 1 is a principle diagram showing a configuration of a color image scanner using a light source device according to an embodiment of the present invention, and FIG. 2 is a perspective view showing a configuration of the light source device. In FIG. 1, R, G1, G2, and B are light-emitting diodes of four wavelengths, which will be described later, arranged in a direction perpendicular to the operation direction of the color image scanner in the light source 1 shown in FIG. Reference numeral 3 denotes a light source driving circuit in the light source device 4, reference numeral 5 denotes a document surface disposed close to and opposite to the light emitting diode array 2, reference numeral 6 denotes an optical system including a condenser lens, and reference numeral 7 denotes a light receiving element including a photodiode or the like.
These elements are arranged such that the light source 1 irradiates the original surface 5 and the reflected light from the original surface 5 passes through the optical system 6 and forms an image on the light receiving element 7.

As shown in FIG. 2, the light source device 4 includes a light source 1 and a light source driving circuit 3. The light source 1 includes, on a light source substrate 1a, a light emitting diode R having a peak wavelength in a red region, light emitting diodes G1 and G2 having different peak wavelengths in a green region, and a light emitting diode B having a peak wavelength in a blue region. Has been implemented. FIG. 3 shows the spectral distribution of the light emission intensity of the light emitting diodes R, G1, G2, and B (hereinafter referred to as "intensity distribution").
FIG. In the figure, the horizontal axis represents the wavelength of the spectrum, and the vertical axis represents the relative radiation intensity. Curves R, G1, G2, and B indicated by solid lines indicate the intensity distributions of the light emitting diodes R and B, respectively, and a curve G indicated by a dotted line indicates the intensity distribution, G
5 shows an intensity distribution obtained by combining 1 and G2.

FIG. 4 is a diagram showing a circuit configuration of the light source drive circuit 3. As shown in FIG. The light source driving circuit 3 includes a first branch 10a having an adjustment resistor r and a plurality of light emitting diodes R connected in series;
A branch in which the adjusting resistor r and the plurality of light emitting diodes G1 are connected in series, the adjusting resistor r and the plurality of light emitting diodes G2
Are connected in parallel with each other, and a third branch 10b is connected in series with the adjustment resistor r and the plurality of light emitting diodes B.
c. One end of each of the branches 10a, 10b, and 10c is connected to one potential side of the power supply 11, and the other end is connected to the power supply
Is connected to the other potential side.

Next, the operation of this embodiment will be described. FIG.
In the light source driving circuit shown in FIG.
By sequentially switching the light emitting diodes 2, the light emitting diodes are switched and lighted in a time-division manner. FIG. 5 is a time chart showing the blinking operation of each light emitting diode in the above circuit. In FIG. 5, the horizontal axis represents time and the vertical axis represents blinking of each light emitting diode. f1 and f2 are frame periods, and sf1, sf2 and sf3 are periods of the first, second and third subframes, respectively. In FIG. 4, IR, I
G1, IG2, and IB are light-emitting diodes R, G1,
It shows the magnitude of the current flowing through G2 and B. 4 and 5
As shown in the figure, in the first sub-frame (period of sf1), current flows only in R and emits light, and in the second sub-frame sf2, current flows in only G1 and G2 and emits light, In the third sub-frame sf3, current flows only in B, and these emit light.

The light emitted in this manner causes the original surface 5
Is irradiated. The light reflected from the document surface passes through the optical system 6 and is incident on the light receiving element 7 to generate a detection signal e corresponding to the light amount. The magnitude of the detection signal generated in the light receiving element 7 in the first sub-frame sf1 is e1, and the magnitude e2 of the detection signal generated in the light receiving element 7 in the second sub-frame sf2 is represented by the third sub-frame sf3. Assuming that the magnitude of the detection signal generated in the light receiving element 7 is e3, e2 is the brightness of the color of the document surface, e1 / e2 is the ratio of (red component) / (green component) of the color of the document surface, and e3
/ E2 is the color of the document surface (blue component) / (green component)
And captures data for image reproduction.

In reproducing a color image, the color is discrete even if the original spectral distribution of the original surface is continuous, narrow or discrete. By appropriately selecting and combining the brightness ratios of the three primary colors of red, green and blue, it is possible to reproduce with good reproducibility.
In order to improve the reproducibility, the e1 / e2 is the ratio of the (red component) / (green component) of the color of the document surface and the e3 / e2 is the value of the document for any spectral distribution of the color of the document. It is desirable that the ratio of the color of the surface matches the ratio of (blue component) / (green component) as much as possible.

For this purpose, the effective sensitivity distribution of the light receiving element in each subframe is the sensitivity distribution Rf, Bf, G for each color of the filter in the case of the filter system shown in FIG.
the neighbors are deeply overlapping each other like f
That is, it is desirable that the common wavelength range covered by both is as wide as possible. This is because the spectrum of the color of the document having the wavelength in the common range is detected in both of the two sub-frames, and can be captured as the data of e1 / e2 or e3 / e2.

FIG. 6 is a diagram showing the inherent sensitivity distribution of the light receiving element 7 and the effective sensitivity distribution in each subframe. The horizontal axis indicates the wavelength of the spectrum, and the vertical axis indicates the relative sensitivity. In the figure, a dotted line F indicates a specific sensitivity distribution of the light receiving element 7, and solid lines F1, F2, and F3 indicate subframes sf1, s.
5 shows an effective sensitivity distribution at f2 and sf3. Here, the effective sensitivity distributions F1, F2 and F3 are obtained by combining the intensity distribution indicated by R, G and B in the intensity distribution of the light emitting diode shown in FIG. I have. As is clear from FIG. 6, in this embodiment, the effective sensitivity distribution of the light receiving element in each subframe is F
Since F1, F2 and F3 overlap considerably next to each other, the sensitivity distribution in all frames in the visible light wavelength range is compared with the sensitivity distribution in the conventional time-division illumination method shown in FIG. There are no missing parts or valleys that cannot be covered even with
It is possible to eliminate the state in which the color cannot be read, and to improve the color reproducibility as compared with the related art for the above-described reason.

This is because, in the present embodiment, in the second sub-frame sf2, the two types of light emitting diodes G1 and G2 having different peak wavelengths in the green range are turned on as light sources, so that the light emitting diodes G1 and G2 are turned on. This is because the combination G of the distribution characteristics of the respective emission wavelengths is reflected in the sensitivity characteristics, and the distribution width is significantly widened as compared with the sensitivity characteristics in the conventional green sub-frame. .

Next, a light source device of a color image scanner according to another embodiment of the present invention will be described with reference to the drawings. FIG. 7 is a perspective view illustrating a configuration of the light source device 4 of the present embodiment, and FIG. 8 is a diagram illustrating a circuit configuration of the light source driving circuit 3. The light source device 4 includes the light source 1 and the light source driving circuit 3. The light source 1 has light emitting diodes R1, R having different peak wavelengths in a red region on a light source substrate 1a.
2. Light emitting diodes G1 and G2 having different peak wavelengths in a green region and light emitting diodes B1 and B2 having different peak wavelengths in a blue region are arranged and mounted.

As shown in FIG. 8, the light source drive circuit 3 has a branch formed by connecting an adjusting resistor r and a plurality of light emitting diodes R1 in series and a branch formed by connecting an adjusting resistor r and a plurality of light emitting diodes R2 in series. Are connected in parallel to each other, a first branch 10a in which the adjustment resistor r and the plurality of light emitting diodes G1 are connected in series, and a branch in which the adjustment resistor r and the plurality of light emitting diodes G2 are connected in series. Are connected in parallel with each other, and a branch where the adjustment resistor r and the plurality of light emitting diodes B1 are connected in series, the adjustment resistor r and the plurality of light emitting diodes B2 are connected.
Have a third branch 10c, which is connected in series with a branch that is connected in series. Each branch 10a,
One end of each of 10b and 10c is connected to one potential side of the power supply 11, and the other end is connected to the other potential side of the power supply 11 in a time-division manner via the switch unit 12.

The components of the color image scanner using the light source device according to the present embodiment except for the light source device and the entire configuration are the same as those of the color image scanner shown in FIG.

FIG. 9 shows a spectrum distribution of light emission intensity of the light emitting diodes R1 and B2 (hereinafter referred to as "intensity distribution").
FIG. In the figure, the horizontal axis represents the wavelength of the spectrum, and the vertical axis represents the relative radiation intensity. Curves R1 to B1 indicated by solid lines indicate the intensity distributions of the light emitting diodes R1 and B2, respectively, and curves R, G and B indicated by dotted lines indicate the intensity distributions R1 and R2, G1 and G2, and B1 and B2, respectively. 3 shows a synthesized intensity distribution.

Next, the operation of this embodiment will be described. In the light source driving circuit shown in FIG.
Are sequentially switched, the light emitting diodes are switched on in a time-division manner and turned on. As can be seen from FIG.
In the first sub-frame sf1 which is the same as the frame shown in, current flows only in R1 and R2, and they emit light.
In the second sub-frame sf2, current flows only in G1 and G2, and they emit light, and the third sub-frame sf2 emits light.
In No. 3, current flows only in B1 and B2, and these emit light.

The original surface is illuminated with the light thus emitted. The light reflected from the document surface passes through the optical system 6 and is incident on the light receiving element 7 to generate a detection signal e corresponding to the light amount. The magnitude of the detection signal generated in the light receiving element 7 in the first sub-frame sf1 is e1, and the magnitude e2 of the detection signal generated in the light receiving element 7 in the second sub-frame sf2 is represented by the third sub-frame sf3. When the magnitude of the detection signal generated at the light receiving element 7 is e3,
e2 is the brightness of the color of the document surface, e1 / e2 is the ratio of (red component) / (green component) of the color of the document surface, and e3 / e.
2 recognizes the ratio of (blue component) / (green component) of the color of the document surface, and takes in data for image reproduction. At this time, in order to capture data having excellent color reproducibility, the effective sensitivity distribution of the light receiving element in each subframe becomes a problem as described above.

FIG. 10 is a diagram showing an effective sensitivity distribution of the light receiving element in each subframe in this embodiment.
Curves F21, F22, and F23 show the effective sensitivity distribution of the light receiving element 7 in the first, second, and third subframes sf1, sf2, and sf3, respectively. Here, the effective sensitivity distribution of the light receiving element in each subframe is obtained by combining the sensitivity distribution F unique to the light receiving element shown in FIG. 6 and the intensity distribution of the light emitting diode emitting light in the subframe. That is, the sensitivity distribution F21 inherent to the light receiving element shown in FIG. 6 and the combined intensity distribution R of the light emitting diodes R1 and R2 shown in FIG.
In the second sub-frame, a sensitivity distribution F22 obtained by combining the inherent sensitivity distribution F of the light receiving element and the intensity distribution G obtained by combining the light emitting diodes G1 and G2 shown in FIG.
In the sub-frames of FIG.
And a sensitivity distribution F23 obtained by combining the intensity distributions B of the light emitting diodes B1 and B2 shown in FIG.

As shown in FIG. 10, the effective sensitivity distributions F21, F22 and F22 of the light receiving element in each subframe are shown.
22 and F23 overlap with each other sufficiently deeply, and the wavelength intervals of the peak wavelengths λp1 and λp2 and λp1 and λp3 of the respective sensitivity distributions F1, F2 and F3 are sufficiently far from each other. Therefore, for the reasons already explained, the scanner using the light source of the present embodiment can faithfully reproduce the color of the document in a wider wavelength range than the embodiment shown in FIG. Here, such ideal sensitivity distribution characteristics F21, F22, and F23 can be obtained because a plurality of types of light-emitting diodes of similar colors having different peak emission wavelengths are simultaneously turned on in each subframe. It is clear from the description so far that this is the case.

[0027]

As described above, according to the present invention,
Without using a filter, light-emitting diodes of three colors, red, green, and blue, are used as light sources, and the light-emitting diodes are sequentially turned on for each color. In a color image scanner for reading data, by illuminating a plurality of types of light-emitting diodes of similar colors, each having a different peak emission wavelength at the same time for each color, the wavelength width of the effective sensitivity distribution of the light-receiving element is increased. Further, it is possible to provide a color image scanner which is excellent in color reproducibility of a read image, has a long service life, and is low in manufacturing cost as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a principle diagram showing a configuration of a color image scanner using a light source device according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a light source device according to one embodiment of the present invention.

FIG. 3 is a diagram showing a spectrum distribution of light emission intensity of a light emitting diode of the light source device according to one embodiment of the present invention.

FIG. 4 is a circuit diagram of a light source driving circuit in the light source device according to one embodiment of the present invention.

FIG. 5 is a time chart showing a blinking operation of a light emitting diode in the light source device according to one embodiment of the present invention.

FIG. 6 is a diagram illustrating sensitivity characteristics of a color image scanner using a light source device according to an embodiment of the present invention.

FIG. 7 is a perspective view showing a light source device according to another embodiment of the present invention.

FIG. 8 is a circuit diagram of a light source driving circuit in a light source device according to another embodiment of the present invention.

FIG. 9 is a diagram showing a spectrum distribution of light emission intensity of a light emitting diode of a light source device according to another embodiment of the present invention.

FIG. 10 is a diagram illustrating sensitivity characteristics of a color image scanner using a light source device according to another embodiment of the present invention.

FIG. 11 is a diagram showing sensitivity characteristics of a conventional filter-type color image scanner.

FIG. 12 is a diagram showing sensitivity characteristics of a conventional time-division illumination type color image scanner.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source 2 Light emitting diode array 3 Light source drive circuit 4 Light source device 5 Original surface 6 Optical system 7 Light receiving element 10 Branch 11 Power supply 12 Switch means

Claims (2)

[Claims] 1. A light emitting diode for emitting light of each color of red, green, and blue is used as a light source, and the light emitting diodes of each color are sequentially turned on to irradiate an original, and the reflected light is received by an optical system including a lens or the like. In a light source of a color image scanner that reads an image of a document in full color by guiding and forming an image on an element, at least one of the light-emitting diodes of each color has a peak emission wavelength different from a similar color. A light source device for a color image scanner, wherein a plurality of types of light emitting diodes are used. 2. A light-emitting diode of at least one color among the light-emitting diodes for each color, wherein a plurality of types of light-emitting diodes of the same color having different peak emission wavelengths are simultaneously turned on and off. The light source device for a color image scanner according to item 1.