JPS60150007A - Reader for color original - Google Patents

Abstract

PURPOSE:To obtain high color separability and to improve color reproducibility with a color copy by forming respective color filters of blue, green and red constituting a spectral filter is such a way that specific conditions are respectively satisfied with respect to transmittance. CONSTITUTION:The reflected light irradiated onto the original surface of a color original 2 from an illuminating light source 1 and is reflected by an original plane is condensed by a rod lens 3 and is then transmitted through a spectral filter 4 by which the light is separated to respective color components meeting transmission spectral characteristics. The filter is so constituted that the transmittance of the blue filter for light having 400nm wavelength is >=0.4, the transmittance at the wavelength transmitting about equally through the blue filter and the green filter is <=0.6 and the transmittance at the wavelength transmitting equally through the green filter and the red filter is <=0.6. The high color separability is obtd. and the color reproducibility of a color copy is improved by such constitution.

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 solinter technology, various research and development efforts have been made toward the practical application of color copying machines.

Color copying machines employ two types of methods: one that photoelectrically converts the original image information and forms color images through electrical processing, and the other that forms color images through chemical processing similar to conventional copying machines. ing. 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. A rod lens 3, a spectral filter 4, and an image sensor 5 are provided in this order on the optical path of reflected light that is irradiated from the illumination light source 1 onto the document surface of the color document 2 and reflected by the document surface. 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 includes, especially for the purpose of improving color resolution,
Three primary color filters are used: blue, green and red. The light of each color component is received on the light receiving surface of the image sensor 5 and extracted as each color signal.

Note that the image sensor 5 uses a silicon semiconductor device such as COD or amorphous silicon, for example.

Conventionally, this type of color image reading device has used a spectral filter for general color television cameras. However, such a device using a spectral cooler for a color television camera has the following problems.

Generally, in the case of a color television camera, the object to be imaged is not particularly specified, and the illumination light sources are extremely diverse, such as sunlight, fluorescent lights, and tungsten lamps. Therefore,
Spectral filters used in such color television cameras must be optimized in consideration of various spectral characteristics. Normally, such optimization is difficult, so this type of spectral filter has a transmission spectral characteristic that is
As shown in the figure, the sensitivity characteristics are close to those of the human eye.

However, as is clear from FIG. 2, in such a spectral filter, the peak value of the characteristic curve of the green filter (G filter) and the peak value of the characteristic curve of the red filter (R filter) are close to each other in the wavelength axis direction. The transmittance at the intersection of the double opening lines is high. For this reason, there is a problem in that light having a wavelength between the two peak values has poor distinguishability between green and red.

Therefore, the conventional color document reading device using a spectral filter for a color television camera has a problem of extremely poor color resolution.

Therefore, it has been considered to use a spectral filter, which is used for film exposure in color printing, etc., in such a color document reading device. This spectral filter for film exposure has transmission spectral characteristics as shown in FIG. 3, and has a low transmittance at the intersection of the G filter and the R filter, so it has superior color resolution compared to the above-mentioned filter. However, in such a spectral filter for film exposure, the transmittance of the B filter is extremely reduced on the short wavelength side of 450 nm or less, as shown in FIG.

However, in silicon semiconductor image sensors such as COD and amorphous silicon, their light-receiving sensitivity tends to decrease on the short wavelength side of 450 nm or less.

Therefore, the blue color signal output becomes smaller than the other color signal outputs, resulting in output imbalance. Therefore, if you set the blue color signal output sufficiently large, the green and red color signals will become saturated, and if you set the green and red color signal output so that they do not become saturated even at maximum output, the green and red color signals will become saturated. , the overall output level of the blue color signal output decreases, resulting in a decrease in the S/N ratio. As described above, color filters for film exposure suffer from a decrease in the number of distinguishable colors due to this. Therefore, in this case too,
However, it was not possible 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 provide a color copy that can obtain high color resolution and thereby contribute to the production of color copies with excellent color reproducibility. An object of the present invention is to provide a document reading device.

[Summary of the invention]

The present invention provides a spectral filter for a color document reading device, in which the blue filter has a transmittance of 0.4 or more for light with a wavelength of 400 nm, and the transmittance at a wavelength that passes through the blue filter and the green filter to the same extent is 0.4. 6 or less, and the transmittance at a wavelength that transmits the green filter and the red filter to the same extent is 0.6 or less.

〔Effect of the invention〕

According to the color document reading device according to the present invention, the transmittance at the intersection of the spectral characteristic curves of the blue filter and the green filter, and the green filter and the red filter, which constitute the spectral filter, is 0.6 or less. Compared to the conventional method, the distinguishability between blue and green and between green and red can be sufficiently improved. For this reason, the distances between blue and green, and between green and red in the Fengfu Sugio hue map can be increased, and in the end,
The number of distinguishable colors can be increased.

In addition, the spectral filter of the color original reading device according to the present invention has a transmittance of 0.4 or more for light of 400 nm, so its output balance is better than that of conventional film-sensing color filters. Become. As a result, the SN ratio of the color signal is improved, and the area of the noise region in the ≠ negative hue map is reduced, so that the number of distinguishable colors can also be increased.

When the above-mentioned effects are taken together, the color document reading device of the present invention can 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.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

The color document reading device according to this embodiment is equipped with a spectral filter to be described later, and an image sensor and an illumination light source each having spectral characteristics as shown in FIGS. 4 and 5.

As shown in Figure 6, the above spectral filter has transmission spectral characteristics of B near wavelengths of 440 nm and 530 nm, respectively.
The transmittance of the filter and the G filter has a peak point, and the transmittance of the R filter becomes maximum and flat at a wavelength of 650 nm or more. In addition, this spectral filter has a wavelength of 400
The transmittance of the B filter in nm is 0.7 or more, the transmittance curve of the 1B filter and the transmittance curve of the G filter intersect near a wavelength of 490 nm, and the transmittance is about 0.3, and Transmittance curve of G filter and R
The transmittance curve of the filter intersects near the wavelength of 580 nm, and the transmittance is about 0.3.

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 Oik 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. In other words, the color signal output 01 can be input as follows.

Now, the spectral characteristics of illumination light at one wavelength λ are expressed as L(λ)
, Ik(
λ), the same transmission spectral characteristic of the i-color filter constituting the spectral filter 4 is Fi (λ), and the same sensitivity spectral characteristic of the image sensor 5 is C (λ), then the color signal output of the image sensor 5 for five color inks is Oik is determined by the following formula.

01 = Door L (λ) 暉λ) Fl (λ) C (λ) dλ ・
(1) However, a-b is the sensitivity region of the image sensor 5.

Next, after normalizing this output 01k with the white reference signal OIW, the color difference signals Xk and Yk for the color ink are defined by the following equation. However, B, G, and R are subscripts indicating blue, green, and red, respectively.

Xk-Takumi Tamaichi! 2ik-□ ・・・・・・・・・(2)
OBW 0GW Yk=Arsenic-Orange (3) These color difference signals Xk, Yk are as follows: When the ink is achromatic, Xk=0, Yk=
It becomes 0.

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 (Ma) of any of the color signals is the saturation level of the CCD so that the CCD does not become saturated. If this standardized output [direct] is O1k', then this output value 01' will be as shown in the following equation.

Further, the output signal 01kVc from the CCD usually 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
The noise levels Xn and Yn included in k and Yk, respectively, are as follows. Therefore, the SN ratio of the color difference signals Xk and Yk of K color ink can be expressed as in the following equation.

By the way, now, let us take the color difference signals XkpYk of yellow (A), cyan (C), magenta (B), red (6), positive (B), and green (G) inks on the X and Y axes, respectively. , 7' in two-dimensional space, a hue map can be formed. Therefore, the value obtained by dividing the area of the region shown in this hue map by the product of the noise levels Xn and Yn included in each color difference signal, that is, 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, when the noise level N of the image sensor is set to 1.5% of the maximum output value Max of the element, and a hue map is created for the color document reading device according to this embodiment, the seventh
The map looks like the one shown in the figure. The number of colors that can be identified using this hue map is about 420.

On the other hand, when a hue map was created in the same manner as above for an apparatus using the conventional spectral filter for a color television camera shown in FIG. 2, the map was as shown in FIG. When we calculated the number of colors that could be identified using this hue mag, we found that the number of colors that could be identified was about 250 at most.

Further, when a hue map similar to that described above was created for the conventional spectral filter for film exposure shown in FIG. 3, the map obtained was as shown in FIG. 9. In this case, since the area of the noise region in the hue pine 7' increases, the number of distinguishable colors was about 320.

As described above, in this example, the transmittance of the B filter at a wavelength of 400 am has a sufficient value of 0.7 or more, so the blue color signal has a sufficient output power, and the other color signals The output ratio between the two will be good. Furthermore, in this example, the transmittance at the intersection of the B filter's transmittance curve and the G74 router's transmittance curve and the intersection of the G filter's transmittance curve and the R filter's transmittance curve is extremely high at 0.3. Since it is small, the discrimination between blue and green and between green and red is improved compared to the conventional method. As a result of these effects, the number of colors that can be identified can be greatly increased, and a color document reading device with extremely excellent color resolution can be provided.

Furthermore, in such a color document reading device, the object to be read is almost always a color printed matter. Most of the current color printed materials are printed using so-called process inks, and the basic colors thereof are four colors. The spectral characteristics of this process ink have very little difference between manufacturers, and have been determined based on color rendering properties and economic efficiency over a long history, so it is not expected that there will be any major changes in the future. . In this example, the peak values of the spectral characteristic curves of the 81G and 81R spectral filters are set to match the spectral characteristics of the process ink, so this also improves the color resolution. can.

Note that the present invention is not limited to the above embodiments.

For example, it is preferable that the transmittance at the intersection of the transmittance curve of the B filter and the transmittance curve of the G filter, and the transmittance curve of the G filter and the transmittance curve of the R filter is lower, and as shown in FIG. The rate is 0115.0 respectively.
．． When a spectral filter of 2 is used, the hue map becomes as shown in FIG. 11, and the number of distinguishable colors can be increased to about 480. In this case, the transmittance at each of the intersection points is extremely reduced, so the sensitivity characteristics of light whose spectral characteristics have peak values at these intersection points are reduced. However, when gross ink is used, the peak value usually occurs at these points. There is no value and there is no particular problem.

In the above example, the illumination light source used had spectral characteristics as shown in Figure 4, or the transmittance at a wavelength of 480 to 600 nm was different from that at other wavelengths, as shown in Figure 12, for example. When using a spectral filter with a high transmittance compared to the G filter, as shown in FIG. 13, output imbalance can be prevented by using a spectral filter with a particularly low transmittance. In this case, the number of distinguishable colors is approximately 350.

In this manner, the present invention can increase the number of distinguishable colors to 350 or more by satisfying the above-mentioned spectral filter conditions.

[Brief explanation of drawings]

Figure 1 is a diagram schematically showing a partial configuration of a color document reading device, Figure 2 is a characteristic diagram showing the transmission spectral characteristic curve of a spectral filter used in a color television camera, and Figure 3 is a diagram showing the transmission spectral characteristic curve of a spectral filter used in a color television camera. FIG. 4 is a characteristic diagram showing the sensitivity spectral characteristic curve of COD, and FIG. A characteristic diagram showing an example,
FIG. 6 is a characteristic diagram showing a transmission spectral characteristic curve of a spectral filter used in a color document reading device according to an embodiment of the present invention, FIG. 7 is a hue map diagram of the same color document reading device, and FIG. FIG. 9 is a hue map diagram of a color document reading device using a spectral filter for color television cameras, FIG. 9 is a hue map diagram of a color document reading device using a spectral filter for film exposure, and FIG. 10 is a diagram of another color document reading device according to the present invention. A characteristic diagram showing a transmission spectral characteristic curve of a spectral filter used in a color document reading device according to an embodiment, FIG. 11 is a hue Matsuda diagram of the same color document reading device, and FIG. 12 is a further embodiment of the present invention. FIG. 13 is a characteristic diagram showing the radiant energy spectral characteristic curve of the illumination light source used in the color document reading device according to the invention, and FIG. 13 is a characteristic diagram showing the transmission spectral characteristic curve of the spectral filter used in the same color document reading device. DESCRIPTION OF SYMBOLS 1... Illumination light source, 2... Color original, 3... Rod lens, 4... Spectral filter, 5... Image sensor,
Y...yellow, C...cyan, M...mazen/
, R...red, B...blue, G...green. Applicant's representative Patent attorney Hikosuke Suzue 1 Figure 2 Liquid length (nm) Figure 3 Liquid length (nm) Figure 4 Liquid length (nm) Figure 5 Wavelength (nm) Figure 6 Figure 7 k Fig. 9 V and Fig. 10 Liquid length (nm) Fig. 11 and Fig. 12 Efficiency liquid length (nm) Fig. 13 Sawa length (nm)

Claims (1)

[Claims] A spectral filter consisting of blue, green, and red filters, and an image sensor made of a silicon semiconductor that receives the light transmitted through the spectral filter and outputs the above-mentioned color signals, green and red. In the color document reading device, the spectral filter has a blue filter having a transmittance of 0.4 or more for light with a wavelength of 400 nm, and a transmittance of 0.4 at a wavelength that passes through the blue filter and the green filter to the same extent. 6 or less, and the transmittance at a wavelength that transmits the green filter and the red filter to the same degree is 0.6
A color document reading device characterized by the following.