JPH0546742B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a color document reading device applicable to facsimile machines, digital copying machines, and the like.

[Conventional example]

Conventionally, devices for reading color originals have been used in various devices, and one example thereof is shown in FIG. In FIG. 1, 1 is a light source, 2 is a reflector for directing the luminous flux from the light source 1 to a predetermined position on the document to improve illumination efficiency, 3 is a document table on which the document is placed;
4 is an imaging lens; 5 is a color filter that selects the light flux from the original according to color; 6 is a solid-state image sensor such as a CCD that receives the light flux from each color filter; It is arranged at a position optically conjugate with the original on the original platen 3. A halogen lamp is generally used as the light source 1 because it is easy to obtain a large amount of light, and this halogen lamp is usually used at a color temperature of 2800° to 3000°. FIG. 2 shows the wavelength energy distribution characteristics of a halogen lamp used at this color temperature. FIG. 3 shows the light amount distribution in the length direction (in-plane direction of the paper) on a document when illuminated by the illumination system shown in FIG. Curve 3a shown in Fig. 3 is the light intensity distribution on the document illuminated by the right illumination system (facing the page) shown in Fig. 1, and curve 3b is the light intensity distribution on the document illuminated by the left illumination system. Light amount distribution, curve 3c is the same as curve 3a and curve 3
b, that is, the document table 3 illuminated by the left and right illumination systems;
This is the overall light intensity distribution above. In this way, the area of the document to be read by the solid-state image sensor is illuminated so that the amount of illumination light flux is uniform. FIG. 4 is a diagram showing an example of the spectral transmittance of the imaging lens. FIG. 5 is a diagram showing an example of the spectral transmittance characteristics of each of the filters 5, and the characteristics of the filter in this case are as follows:
It shows the characteristics of each filter that transmits light beams in the blue (B), green (G), and red (R) regions. FIG. 6 shows the relative spectral sensitivity characteristics of the CCD used in the image sensor 6, and the vertical axis represents the output voltage ratio of the CCD according to the wavelength of light.

In a conventional reading device configured in this way,
When reading a white original, there are three types: B, G, and R.
Figure 7 shows the output ratio of the CCD. When reading an originally white document, ideally the output ratios of the B, G, and R CCDs should be the same. However, in conventional devices of this type, the output increases in the order of R>G>B. This is largely influenced by the fact that the spectral energy distribution of the light source is high, R>G>B (Fig. 2), and the CCD spectral sensitivity is high, R>G>B (Fig. 6). In order to correct these effects, in the conventional example, each output from the image sensor 6 for each of the B, G, and R light fluxes is corrected using an electric circuit.

() Correct by changing the filter characteristics of the wavelength selection filter 5. For example, the reading wavelength width for R is narrowed, and the reading wavelength width for B is widened.

() An ND filter is provided in front of the element 6 that detects the R and G light fluxes to reduce the amount of light that enters the image sensor that detects the R and G light fluxes.

A method is being taken. However, regarding (), the equipment becomes larger and the cost increases due to the electric circuit for correction;
The G and B color separation purity deteriorates, and the color characteristics as a color original reading device deteriorates.As for (), the light intensity from the light source is reduced by a filter, resulting in a significant deterioration in illumination efficiency. .

Furthermore, if the light source 1 is replaced due to the light source's lifespan or other reasons, the light intensity distribution on the document table will normally change, so in order to return to the light intensity distribution as shown in Figure 3,
Although it is necessary to change the installation state of the light source and finely adjust the voltage applied to the light source, these operations are complicated and require skill. Therefore, in this case, instead of correcting the illumination light intensity distribution on the document table, ()
In this case, the output correction amount of the image sensor 6 is ()
In the case of , the spectral characteristics of filter 5 are ()
In this case, the transmittance of the ND filter must be changed. However, in practice it is difficult to take such measures.

[Summary of the invention]

SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks of the conventional reading apparatus, an object of the present invention is to provide a reading apparatus that can obtain information on the luminous flux in each wavelength range with approximately equal output using simple means.

A further object of the present invention is to provide a reading device that does not cause loss in the amount of reading light beam.

A further object of the present invention is to provide a reading device in which the information output obtained can be easily reproduced even if the light source such as a halogen lamp is replaced.

A further object of the invention is to provide an inexpensive reading device.

In the reading device according to the present invention, the above object is achieved by giving a distribution of the magnitude of the illumination light amount on the document surface to compensate for the difference in the magnitude of the unique output signal of the reading system for each wavelength. It is. In other words, in the past, the light intensity distribution on the document was made uniform, but in this application, a light intensity distribution that actively causes light intensity unevenness on the document surface is provided, and the light receiving element that reads the wavelength region where the detection signal is large is The device is provided so that the light-receiving element reads the portion of the document table where the amount of light is small, while the light-receiving element reads the portion of the document table where the amount of light is large. in particular,
In the reading device according to the present invention, a document table on which a document is placed is illuminated with an illumination system consisting of a light source and a reflecting mirror, and R, G, and B light fluxes from different positions in the length direction of the document table are detected. Three CCDs to
, and the spectral energy distribution of the light source is R>G
>B is the highest, and the spectral sensitivity of the CCD is R
In the document reading device in the order of height >G>B, an illumination system for illuminating the document table is disposed only on one side in the length direction of the document table, and the light source is illuminated at each position in the length direction of the document table. The light amount is large on the side of the document table near the document table, and the amount of light is small on the side of the document table far from the light source, and the light beam is received from the part of the document table near the light source where the amount of light is large.
The CCD receives the B light flux, the second CCD receives the light flux from the central part of the document table where the light intensity is the highest, the CCD receives the G light flux, and the CCD receives the light flux from the part of the document table far from the light source where the light intensity is the smallest.
The CCDs are arranged in the following order: CCD receiving the R light beam; The present invention will be explained in detail below.

〔Example〕

FIG. 8 is a diagram showing an embodiment of the document reading device according to the present invention, in which the same reference numerals as in the conventional device represent the same members. The major differences between the device shown in FIG. 8 and the device shown in FIG. 1 are as follows:
The light source that illuminates the original is on one side, and the illuminance of the illumination light beam is intentionally made different at each position on the original table, which is an optically conjugate position with respect to the solid-state image sensor 6 and the imaging lens 4. . For example, as shown in FIG. 7, the solid-state imaging device that receives the light beam in the region R where the detection signal is large is optically conjugate with the region of low illuminance on the document table with respect to the imaging lens 4. On the other hand, the solid-state imaging device that receives the light beam in the region B where the detection signal is small is arranged so as to be optically conjugate with the region of high illuminance on the document table with respect to the imaging lens 4. The solid-state image pickup device that detects the light beam in the region G, which receives a detection signal of intermediate magnitude, is arranged so that its illuminance is conjugate with the region of the document table whose illuminance is intermediate.

In the embodiment shown in FIG. 8, the distribution of the amount of illumination light on the document table 3 has a shape as shown in FIG. That is, the amount of light is large on the _S1 side of the document table near the light source, and the amount of light is small on the _S2 side, which is far from the light source. Therefore, the image sensor that receives the light beam from the part of the document table on the _S1 side where the amount of light is large is the image sensor that receives the light beam B, and the image sensor that receives the light beam from the center part of the document table where the amount of light is next largest is the image sensor that receives the light beam G. S ₂ image sensor with low light intensity
The image sensor that receives the light beam from the side document table is an image sensor that receives the R light beam. As shown in FIG. 9, the outputs from the B, G, and R image pickup elements can be easily corrected by making the light intensity distribution on the document table 3 sloped instead of being flat as in the conventional case. In addition, the method of correction is simple and only one illumination system is required, so the cost is low and the device can be downsized.

Furthermore, in the apparatus of the present invention, even if the lamp is replaced, only one lamp is used, so it is easy to obtain reproducibility of the relative distribution of the illumination light amount on the document table, and the absolute light amount can be easily obtained. Even if a change occurs, it can be corrected simply by changing the voltage applied to the light source. As shown in FIG. 10, even if the voltage input to the light source is changed to change its color temperature, R, G, B
This is because the relative light amount of the light also hardly changes. Even when the lamp is replaced in this way, the desired light intensity distribution on the document surface 3 can be easily reproduced. Incidentally, the distribution of light amount on the document table as shown in FIG. 9 can be achieved at the time of designing the shape of the reflecting mirror.

In the explanation so far, we have not specifically mentioned the variations in the spectral characteristics of each optical system due to parts lot, etc., but in reality, the spectral characteristics of spectral filters and the relative spectral energy distribution of light sources vary considerably. Conventionally, sensitivity adjustment functions were provided for each color channel using an electric circuit or the like to deal with these variations, but in this application, as shown in FIG. , B output can be easily adjusted.

As described above, in the reading device according to the present invention, it is possible to correct the imbalance in the amount of each detection signal inherent in the color light flux detection system by a simple and low-cost means, and further improve the reproducibility of the reading characteristics. It has various effects, such as being excellent in terms of performance and being able to be formed as a compact device.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a conventional document reading device, FIG. 2 is a diagram showing wavelength energy distribution characteristics of a halogen lamp, and FIG. 3 is a diagram showing the distribution of illumination light flux of the device shown in FIG. 1. , FIG. 4 is a diagram showing an example of the spectral transmittance of the imaging lens, FIG. 5 is a diagram showing an example of the spectral transmittance characteristic of the filter, and FIG.
Figure 7 showing an example of relative spectral sensitivity characteristics of CCD.
The figure shows an example of the B, G, and R output signals read by a conventional device, FIG. 8 shows an embodiment of the document reading device according to the present invention, and FIG. FIG. 10 is a diagram showing an example of the wavelength light amount distribution characteristic of a light source when the color temperature changes, and FIG. 11 is a diagram showing an example of the light amount distribution of the apparatus according to the present invention. The figure which shows an example of an adjustment means. 1...Light source, 2...Reflector, 3...Original table, 4
...imaging lens, 5...filter, 6...imaging element.

Claims (1)

[Claims] 1 A document table on which a document is placed is illuminated with an illumination system consisting of a light source and a reflecting mirror, and three CCDs are provided to detect R, G, and B light beams from different positions in the length direction of the document table. , in a document reading device in which the spectral energy distribution of the light source is high in the order of R>G>B, and the spectral sensitivity of the CCD is high in the order of R>G>B, an illumination system for illuminating the document table is set to a length of the document table. The light source is arranged only on one side of the document table in the longitudinal direction, and is configured such that at each position in the length direction of the document table, the amount of light is large on the side of the document table near the light source, and the amount of light is small on the side of the document table far from the light source. The CCD that receives the light beam from the part of the document table near the light source where the amount of light is large is the CCD that receives the light beam B, and then the CCD that receives the light beam from the central part of the document table where the amount of light is large.
The CCD receives the G light flux, and the CCD receives the light flux from the part of the document table far from the light source where the light intensity is small.
A document reading device characterized in that CCDs are arranged in the following order: CCD receives R light beam;