JPS60150008A - Reader for color original - Google Patents

Abstract

PURPOSE:To improve color separability and the color reproducibility of a color copy by constituting a light source for illumination in such a way that the radiation energy of the light source for irradiating a color original satisfies specific conditions with respect to the wavelength region. CONSTITUTION:A light source 1 for illumination has no radiation energy of >=650nm wavelength and therefore the decrease in the color discriminating performance generated when the light in said wavelength region transmits blue and green filters 4 is prevented. Since the radiation energy on the short wavelength side near 450nm wavelength of the light source 1 is set larger than the radiation energy on the long wavelength side near 600nm wavelength, the color signal of blue from an image sensing element 5 increases and the output balance with the other color signal is improved. The radiation energy in the region near 520nm wavelength, i.e., green of the light source 1 is smaller than the radiation energy near 450 wavelength and 600nm wavelength and therefore the color signal of green is suppressed and the output balance is improved. The color reproducibility of the copy is thus improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a color document reading device with excellent color resolution used in color copying machines and the like.

[Technical background of the invention and its problems]

In recent years, with the progress of color printer technology, various research and development efforts have been made toward the practical application of color photocopiers.

Color copying machines employ two types of methods: one that photoelectrically converts the original image information and forms a color image through electrical processing, and the other that forms color images through chemical processing similar to conventional copying machines. has been done. The former method is attracting a lot of attention because it allows more extensive processing in image formation than the latter method.

2. Description of the Related Art A color copying machine using electrical processing usually uses a color document reading device for obtaining image information from a color document. FIG. 1 is a schematic diagram showing a part of a color document reading device.

That is, in FIG. 1, reference numeral 1 denotes an illumination light source that illuminates the surface of a color document 2. As shown in FIG. There is a rod lens in the optical path of the reflected light that is irradiated from this illumination light source 1 onto the document surface of the color document 2 and reflected by the document surface. , a spectral filter 4, and an image sensor 5 are provided in this order. Therefore, the light reflected from the document surface is collected by the rod lens, and then transmitted through the spectral filter 4 and decomposed into light of each color component according to the transmission spectral characteristics of the spectral filter 4. This spectral filter 4 uses three primary color filters of blue (or cyan), green, and red, especially for the purpose of improving color resolution. The light of each color component is received on the light receiving surface of the image sensor 5 and extracted as each color signal. Incidentally, for example, a silicon semiconductor element such as a CCD or amorphous silicon is used for the image sensor 5. However, conventionally, in this type of color document reading device, the image sensor 5 has a radiation energy spectral characteristic as shown in Fig. 2. A lighting source was used. However, an apparatus having an illumination light source having such radiant energy spectral characteristics has the following problems.

That is, in color document reading apparatuses, as mentioned above, it is necessary to particularly improve color resolution, so a spectral filter consisting of three primary color filters of blue (or cyan), green, and red is usually used. However, in such three primary color spectral filters, as shown in FIG. 3, for example, the transmission spectral characteristic curves of the B filter and G filter are
It has the property that it increases rapidly when it exceeds 0 nm. For this reason, there is a problem that the change in the color difference signal with respect to the wavelength is small, resulting in poor color discrimination. Therefore,
Conventionally, it has been done to cut off the source in the above wavelength range by using, for example, an infrared cut filter or a filter of a specific color, but this has resulted in a problem of increased costs.

An image sensor made of a silicon semiconductor element such as COD or amorphous silicon is
The distance between the light receiving paths tends to decrease on the short wavelength side. For this reason, with the above-mentioned illumination light source, which has radiant energy characteristics similar to the light-receiving sensitivity of such an image sensor, the color signal output from the back becomes smaller than the other color signal outputs, resulting in an output imbalance. . Therefore, if the blue color signal output is set to be sufficiently large, the green and red color signals will become saturated, and if the green and red color signal outputs are set so as not to be saturated even at maximum output, The overall output level of the blue color signal output is reduced, resulting in a reduction in the signal-to-noise ratio. For this reason, color document reading devices using such illumination light sources have a problem of extremely poor color resolution.

Therefore, as shown in FIG. 5, it has been considered to use an illumination light source whose radiant energy spectral characteristics deteriorate at 6QOnm or more in a color original reading device. According to a color document reading device using such an illumination light source,
It has superior color resolution compared to the above-mentioned ones.

However, in general, three primary color filters have the property that the amount of light that passes through the G74 filter is the largest. Therefore, as shown in FIG.
In a color document reading device that uses an illumination light source that has uniform radiant energy in the 0 nm wavelength range, the green color signal output increases compared to other color signal outputs, and the output balance decreases. I had something to do.

As described above, conventional color document reading devices have been unable to obtain satisfactory color resolution.

[Purpose of the invention]

The present invention has been made in consideration of these circumstances, and its purpose is to be able to obtain high color resolution, thereby contributing to the production of color copies with excellent color reproducibility. An object of the present invention is to provide a color document reading device.

[Summary of the invention]

The present invention provides an illumination light source of a color document reading device with a 450 nm
The radiant energy at wavelengths near m is greater than the radiant energy at wavelengths near 600 nm, the radiant energy at wavelengths near 600 nm is greater than the radiant energy at wavelengths near 520 nm, and the radiant energy at wavelengths above 650 nm is greater than the radiant energy at wavelengths near 650 nm. It is characterized by having almost no .

〔Effect of the invention〕

According to the color document reading device according to the present invention, since the illumination light source does not have radiant energy with a wavelength of 550 nm or more, conventionally, light in this wavelength range is generated by passing through a blue (or cyan) green filter. This makes it possible to prevent the color discrimination performance from deteriorating.

In addition, the illumination light source is set so that the radiant energy on the short wavelength side near 450 nm is greater than the radiant energy on the long wavelength side near 600 nm, so the blue color signal from the image sensor increases. , the output balance with other color signals is good. Further, the illumination light source has a wavelength of 5
Since the radiant energy in the vicinity of 20 nm, that is, the green band, is smaller than the radiant energy in the vicinity of wavelengths of 450 nm and 600 nm, the output of the green color signal is suppressed, and this also makes it possible to improve the output balance. . By improving the output balance, the color signal S/N
The ratio can be improved, the area of the noise region in the hue map can be reduced, and the number of distinguishable colors can be increased as a result.

When the above-mentioned effects are taken together, the power error reading device M of the present invention can be made to have extremely excellent resolution. Therefore, according to the present invention, it is possible to provide a color original input device that can contribute to the generation of color copies with excellent color reproducibility.

[Practice of invention? 1] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

The color document reading device according to this embodiment includes an illumination light source, which will be described later, and a spectral filter and an image sensor having transmission spectral characteristics and sensitivity spectral characteristics as shown in FIGS. 3 and 4, respectively. It becomes.

The illumination light source has radiant energy spectral characteristics as shown in FIG. That is, this illumination light source has extremely thick values at wavelengths of 460 nm and 590 nm,
It has spectral characteristics such that the minimum value is reached at 530 nm, and the radiant energy decreases relatively rapidly at 590 nm or more. The relative values of radiant energy at wavelengths of 460 nm, 530 nm, and 590 nm are 0.8, 0.55, and 0.7, respectively, and the relative value of radiant energy at wavelengths of 650 nm and above is 0.
．． It is 2 or less. As will be described later, the radiant energy spectral characteristics of this illumination light source can be obtained by mixing the radiant energy characteristics of a plurality of phosphors.
The term "relative value of radiant energy" refers to a relative value when the sum of the maximum radiant energies of each phosphor is set to 1.

The color resolution of the color document reading device configured as described above will be described in detail below.

That is, in this type of color document reading device, the color signal output 01k is usually determined by the spectral characteristics of the illumination light source, the ink of the color document, the spectral filter, and the image sensor.

The color signal output 01 can be set as follows. Now, the spectral characteristics of the illumination light source 1 at wavelength λ are L(λ), the reflection spectral characteristics of the color ink on the color original 2 are k(λ), and the transmission spectral characteristics of the i color filter constituting the spectral filter 4. If FJ (λ) is FJ (λ) and the same sensitivity spectral characteristic of the image sensor 5 is C (λ), then the color signal output 01k of the image sensor 5 for one color ink is 9°, which is charged by the following formula. is the sensitivity region of the image sensor 5.Next, after this output 01k is normalized by the white reference signal Oiw, the color difference signals Xk and Yk for color ink are defined by the following equation. However, B, G, and Rri are blue, green, and
This is a subscript indicating each color of red.

This color difference signal Xk%Yk[, when the ink is achromatic, Xk
= o, Yk = o.

Furthermore, when a CCD is used as the image sensor 5, the output value of each color signal of the CCD is normally set such that the maximum output value (Max) of any of the color signals is the saturation level of the COD, so that the COD does not become saturated. Standardized. If this standardized output value is O1k', this output value 01' is
It becomes like the following formula.

The output signal 01kKri from the CCD and other sources normally contains stationary noise such as reset noise and dark current. If the level of this noise is N, then the normalized noise level N' is expressed by the following equation.

Therefore, the color difference signal X when the noise level is N
If the noise levels Xn1Yn are respectively expressed by k and Yk, then the following equations are obtained. Therefore, the color difference signal Xk of k color ink.

The SN ratio at Yk can be expressed as follows.

In N υRw' 10 (JGW' By the way, now, each color difference signal of the ink of each color of yellow (Y), cyan (C), magenta, red @), and green (G) is Xk%Yk, respectively. For X@, Y@, when plotted in two-dimensional space, a hue map can be formed. Therefore, the area of the region shown in this hue map is determined by the noise level xns included in each color difference signal.
The product of Yn, that is, the value when divided by the area of the noise region, is defined as the "number of distinguishable colors." This "number of distinguishable colors" is a value representing the color resolution of the color document reading device.

Therefore, we now set the noise level N of the image sensor to 1.0% of the maximum output value Max of the element.・What is the hue map for the color document reading device according to this embodiment with 5 pixels? When created, the map was as shown in Figure 7. The number of distinguishable colors (-9) in this hue mag is about 350.In contrast, a conventional illumination light source with radiant energy spectral characteristics as shown in Figure 2 was used. When a full hue map similar to that described above was created using the apparatus used, the map shown in FIG. 8 was obtained.

Using this hue map, we found the number of distinguishable colors.
The number was extremely low at 99.

In addition, when a hue map was similarly created for a device using a conventional illumination light source having the radiant energy spectral characteristics as shown in FIG. 5, the area was as shown in FIG. increased more than However, in this case, the output ratio is 3.0: 4.6: 3.
2, the area of the noise region increases, and in the end, the number of distinguishable colors is as small as 2.0.

As described above, according to this embodiment, the relative value of the radiation energy of the illumination light source is extremely small at 0.2 or less in the wavelength region of 650 nm or more. Therefore, the blue and green color filters are 650
Since there is almost no radiant energy of light in the long wavelength region of nm or more, color discrimination performance can be improved as described above.

In addition, the radiant energy near the wavelength 450 nm is
It is larger than the radiation energy near nm, and the wavelength is 520 nm.
The radiant energy near the wavelength of 600 nm is smaller than the radiant energy near the wavelength of 600 nm. Is this why the output of the image sensor is unbalanced? Since this can be prevented and the green color signal level can be suppressed, the output balance of each color signal is extremely good. Therefore, the area of the noise region in the hue map can be reduced, thereby increasing the number of distinguishable colors.

Such an illumination light source can be composed of, for example, three fluorescent lamps shown below. That is, Fig. 10, 1st
1 and 12 are 600 nm and 490 nm, respectively.
m, the first with a peak value of radiant energy at 420 nm
~ FIG. 7 is a diagram showing the radiant energy component characteristics of the third phosphor.

These first to third phosphors include, for example, SPD.
-1457, SPD-2, and SPD-I B (manufactured by Toshiba) can be used. If the radiant energy of these first to Wc3 phosphors is emitted at a ratio of 57:65 near 4, an illumination light source having spectral characteristics as shown in the eighth example can be obtained.

Note that the present invention is not limited to the above embodiments,
For example, if the first to third phosphors described above are made to emit radiant energy at a ratio of 1:1:1, an illumination light source with spectral characteristics as shown in FIG. 13 can be obtained. A color original reading device using this illumination light source can also sufficiently exhibit the effects of the present invention.0 In addition, the SPD-1 having the spectral characteristics as shown in FIG.
When tJ (manufactured by Toshiba) is used as the third phosphor, an illumination light source with spectral characteristics as shown in FIG. 15 can be obtained. The effects of the present invention can also be achieved when loading a color original using this illumination light #.

As long as it is a photocritical material that satisfies all of the radiant energy spectral characteristics described above, the number, type, etc. of the particles can be modified in various ways.

[Brief explanation of drawings]

Fig. 1 is a diagram schematically showing a partial configuration of a color original reading device, Fig. 2 is a characteristic diagram showing the radiant energy spectral characteristics of an illumination light source used in a conventional color original reading device, and Fig. 3 is a diagram showing a color original reading device. A characteristic diagram showing the transmission spectral characteristics of the spectral filter used in the reading device, FIG. 4 is a characteristic diagram showing the sensitivity spectral characteristics of the image sensor used in the same device, and FIG. 5 is a characteristic diagram showing the sensitivity spectral characteristics of the image sensor used in the same device. FIG. 6 is a characteristic diagram showing the radiant energy characteristics of the illumination light source used in the color original reading device according to an embodiment of the present invention, and FIG. Pine 1 diagram,
Fig. 8 shows the hue of a conventional color document a taking device using an illumination light source with the characteristics shown in Fig. 2; A hue map diagram of the document reading device, FIGS. 10 to 12 are characteristic diagrams showing the radiant energy characteristic sound of the first to third phosphors constituting the illumination light source of the device, and FIG. A characteristic diagram showing the radiant energy spectral characteristics of an illumination light source used in a color original reading device according to another embodiment, FIG. 14 shows an illumination light source used in a color original reading device according to still another embodiment of the present invention. FIG. 15 is a characteristic diagram showing the radiant energy characteristics of the phosphor used for illumination, and FIG. 15 is a characteristic diagram showing the radiant energy characteristics of the same illumination light source. Lens: 4...Spectral filter, 5...Image sensor, Y...Yellow, C...Cyan, M...Mazen f, R...Red, B...Blue, G... ·green. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 Figure 4 fsS Figure 6 Force Moxibustion (nrrB Figure 7 Color Figure 8 Figure 9 Figure 10 Figure 11 Figure 13 Figure 14 Wavelength (nm)

Claims (2)

[Claims] (1) A spectral filter consisting of an illumination light source that irradiates a color document, and color filters of green, green, and red that transmit the light emitted from the illumination light source and reflected by the color document based on their respective spectral characteristics. and an image sensor made of a silicon semiconductor that receives the light transmitted through the spectral filter and outputs the front, green, and red color signals, wherein the illumination light source includes:
The radiant energy at wavelengths near 450 nm is greater than the radiant energy at wavelengths near 600 nm, the radiant energy at wavelengths near 600 nm is also greater than the radiant energy at wavelengths near 520 nm, and furthermore, the radiant energy at wavelengths above 650 nm is larger than the radiant energy at wavelengths near 600 nm. A color document reading device that is characterized in that it does not have to be carried around often. (2) The illumination light source includes a first light source having a peak value of radiant energy near a wavelength of 450 nm, and a first light source having a peak value of radiant energy near a wavelength of 520 nm.
The light source according to claim 1, which is composed of a second light source body having a peak value of radiant energy near m and a third light source body having a peak value of radiant energy near a wavelength of 600 nm. Color document reading device.