JPH0418745B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention removes the reflected light component of the color that is desired to be removed from the image information on the document, and uses a color that is different from the color that exists in the same area and has a low reflectance to be removed. The present invention relates to a document reading device that can separate and read only drawn information.

BACKGROUND TECHNOLOGY Conventionally, this type of document reading device is disclosed, for example, in Japanese Patent Application Laid-Open No. 105669/1982, which includes a two-color separation mirror that separates reflected light from a document into two colors, and a two-color separation mirror that allows each of the separated reflected lights to pass through. Discloses a technology that uses an optical filter, lens, and image sensor to separate the colors drawn on a document and accurately separate and read characters and figures drawn in different colors without distinguishing between their areas. has been done.

Problems to be Solved by the Invention However, in the conventional configuration described above, reflected light is separated into two colors in the visible light range and guided to a filter and an image sensor, respectively, so the configuration is complicated and the device becomes large. Others, decreased productivity,
This had the problem of high cost.

The present invention solves the above-mentioned conventional problems, and has a simple configuration without using a dichroic separation mirror that separates the reflected light from the original into two colors, and has a low reflectance that exists in the same area. An object of the present invention is to provide a document reading device that can separate and read only information drawn in color.

Means for Solving the Problems In order to achieve this object, the document reading device of the present invention includes a light source whose main component of the emitted wavelength is in a range where the wavelength changes from visible light to infrared light, and an electric light source that changes the intensity of the light. An image sensor that converts the image into a signal, a lens that forms an image of the original on the light-receiving surface of the image sensor, and a lens that has a different cutoff wavelength for each color to be removed and is selectively inserted into and removed from the optical path from the light source to the image sensor. and an infrared cut filter arranged so that the peak of the overall spectral characteristic of the reading system composed of the image sensor, lens, and infrared cut filter can be detected by the infrared cut filter.
The configuration is such that infrared light of a predetermined wavelength or more is blocked in order to be optimized in accordance with the color to be removed.

Function: With this configuration, infrared light of a predetermined wavelength or more is blocked in order to optimize the peak of the overall spectral characteristics of the reading system consisting of the light source, lens, image sensor, and infrared light cut filter in accordance with the color to be removed. Set it as follows. As a result, the image sensor hardly reads the reflected light from the document in the visible light range, and removes the reflected light component of the desired color from the reflected light from the near-infrared light to the infrared light range, and removes the reflected light component of the color that exists in the same area. It is possible to separate and read only the information drawn in colors with low reflectance.

Embodiment FIG. 1 shows an embodiment of the invention. The original 1 is sent in the direction of the arrow by a transport roller (not shown). The image plane of the document 1 is illuminated by a light source 2, such as a tungsten lamp, whose main component of the wavelength of light emitted is in a range from visible light to infrared light. Reflected light from the original 1 passes through an infrared light cut filter 3 and a lens 4 and is focused on a light receiving surface of an image sensor 5. The image sensor 5 converts the partial intensity of the reflected light from the original 1 into time-series electrical signals to read the original image.

The infrared light cut filter 3 includes two filters 3a and 3b having different spectral characteristics, and a lens 4.
It is arranged so that it can be selectively inserted into and removed from the optical path in front of the. The infrared cut filter 3 may be placed in the optical path between the light source 2 and the document 1 as shown in FIG. 2, or in the optical path between the lens 4 and the image sensor 5 as shown in FIG. It may be placed inside.

The infrared light cut filter 3 is for cutting out unnecessary component light, and its dropout characteristics are influenced by its spectral characteristics. Figure 4 shows the spectral reflection characteristics of an image written in pencil, which is generally recognized as black, Figure 5 shows the spectral reflection characteristics of an image written in blue ink, and Figure 6 shows the spectral reflection characteristics of an image written in blue ink. The spectral reflection characteristics of the ink image are shown. As is clear from Figures 5 and 6, in order to drop out blue and reddish-violet colors, the peak of the overall spectral characteristics of the device must be set at 700 nm.
It would be good if it could be more than m. The overall spectral characteristics of the device are light source 2, filter 3, lens 4,
It is determined by the product of the respective spectral characteristics of the image sensor 5. FIG. 7 shows an example of the overall spectral characteristics of the device when the 50% cutoff wavelength of the infrared light cutoff filter 3 is set to 830nm.

Whether or not it is dropped out, or whether it is identified as black information or white information, depends on the contrast of the image. Contrast is determined by the following formula.

∫ (spectral characteristics of the image area of the original) x (overall spectral characteristics of the device) dλ/∫ (spectral characteristics of the background area of the original) x (overall spectral characteristics of the device) dλ x 100 Generally, it is calculated from the above formula. If the contrast is between 0 and 60%, it is identified as black information, and when it is between 60 and 100%, it is identified as white information and dropped out.

FIG. 8 shows a specific example of contrast in this invention. The horizontal axis shows the 50% cut-off wavelength of the infrared cut filter 3 when cutting the net wavelength side, that is, the overall spectral characteristics of the device.
Contrast is plotted on the vertical axis. It can be seen that the contrast of both the reddish-purple ink image shown by curve a and the blue ink image shown by curve b decreases as the overall spectral characteristics of the device move toward the shorter wavelength side. On the other hand, the contrast of the black pencil image indicated by the straight line c is almost constant regardless of the overall spectral characteristics of the device. However, in the case of red-purple ink, more than 60% contrast can be obtained even at 700 nm, and in the case of blue ink, it is possible to obtain contrast of 60% or more even at 700 nm.
With this, a contrast of 60% or more can be obtained. Therefore, if you want to drop out the magenta color,
If you want to drop out blue light by using an infrared cut-off filter with a 50% cut-off wavelength of 700 nm or more, you can use an infrared cut-off filter with a 50% cut-off wavelength of 820 nm or more.

On the other hand, as a characteristic of image sensors, the longer the wavelength of light, the lower the resolution performance (MTF) tends to be.
FIG. 9 shows an example of MTF characteristics in this invention. As is clear from this figure, the fewer the long wavelength components of the light incident on the image sensor, the better the MTF characteristics. In particular, it can be seen that the MTF characteristics are considerably improved by inserting an infrared cut filter compared to the case where no infrared cut filter is inserted.

From these points of view, the spectral characteristics on the long wavelength side of document reading devices can be improved without reducing contrast.
The optimum value of the 50% cutoff wavelength for increasing the MTF is inevitably determined. Its optimal value is
For blue ink, it is 820 nm, and for red-purple ink, it is around 700 nm. Similarly, a 50% cutoff wavelength on the long wavelength side can be set for ballpoint pen ink and red colors that reflect high infrared light.

In this way, the spectral characteristics of the infrared cut filters 3a and 3b in the document reading apparatus of the present invention shown in FIGS. 1 to 3 are determined.

Effects of the Invention As explained above, the present invention provides a light source whose main component of emitted wavelength is in a range where the wavelength changes from visible light to infrared light, an image sensor that converts the intensity of light into electrical signals, and this image sensor. a lens that forms an image of the original on the light receiving surface of the image sensor; and an infrared cut filter that has a different cutoff wavelength for each color to be removed and is selectively placed in and out of the optical path from the light source to the image sensor. The infrared cut filter cuts infrared light of a predetermined wavelength or more to optimize the peak of the overall spectral characteristics of the reading system consisting of the image sensor, lens, and infrared cut filter in accordance with the color to be removed. By using a blocking configuration, the image sensor reads almost no reflected light in the visible light range from documents drawn in multiple colors, and only specifies reflected light in the near-infrared to infrared light range. Remove colored line segments. At this time, the cutoff wavelength of the infrared light cut filter is determined so that the reflected light of the color to be removed is dropped out, and the reflected light with a wavelength longer than this cutoff wavelength is removed. As a result, it has the excellent effect of being able to separate and read only the information drawn in colors with low reflectance existing in the same area with a simple configuration as described above.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention;
Fig. 2 is a schematic diagram showing another embodiment of the present invention; Fig. 3 is a schematic diagram showing another embodiment of the invention; Fig. 4 is a diagram showing spectral reflection characteristics of a black image;
Figure 5 is a diagram showing the spectral reflection characteristics of a blue image, Figure 6
The figure shows the spectral reflection characteristics of a reddish-purple image. Figure 7 shows an example of the overall spectral characteristics of the document reading device according to the present invention. Figure 8 shows the 50% infrared cut filter for a specific color in the present invention. FIG. 9 is a diagram showing the relationship between cut-off wavelength and contrast, FIG. 9 is a diagram showing an example of the MTF characteristic in the present invention, and FIG. 10 is a schematic configuration diagram showing an example of a conventional device. 1... Document, 2... Light source, 3... Infrared light cut filter, 4... Lens, 5... Image sensor, 6... Blue light source, 7... Red light source, 8... Infrared light source.

Claims (1)

[Claims] 1. A light source whose main component of emitted wavelength changes from visible light to infrared light, an image sensor that converts the intensity of light into an electrical signal, and an image of the document that is formed on the light-receiving surface of this image sensor. and an infrared light cut filter having a different cutoff wavelength for each color to be removed and disposed selectively in and out of the optical path from the light source to the image sensor, and the infrared light cut filter allows the image to be removed from the image. A document reading device that blocks infrared light of a predetermined wavelength or more in order to optimize the peak of the overall spectral characteristics of a reading system composed of a sensor, a lens, and an infrared light cut filter in accordance with the color to be removed.