JPH08116407A - Image scanner - Google Patents

Abstract

PURPOSE: To read a color of an image printed on a substantial original in a short time without being affected by an optical dot gain by lighting an area in a range of a read means reading an image on the original face with a light means. CONSTITUTION: A lighting means 10 lights up an area in a range in which a line sensor 8 being a read means reads an image of an original 5 on the face of the original 5. That is, the lighting width in the subscanning direction of the lighting means 10 lighting the original 5 and a picture element read width (detected picture element width) of the line sensor 8 reading the image on the original 5 are selected to be nearly the same and the length of the lighting region of the lighting means 10 in the main scanning direction is selected to light up the length equal to the read length of the line sensor 8 in the main scanning direction. Thus, the effect of an optical dot gain from the light other than that of the picture element read position is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus, and more particularly to reading an image (color image) of a document or the like illuminated by a light beam from an illuminating unit with a reading unit having discrete array pixels.
The present invention relates to an image reading device which outputs an image by using the read information and which is suitable for a color copying machine, a color scanner, or the like.

[0002]

2. Description of the Related Art When paper (copy), which is a recording medium generally used in a color copying machine or a color scanner, has a light-scattering property, a light beam incident on the surface of the paper propagates inside the paper, In the process, it collides with paper fibers several times and is absorbed or scattered. Then, the scattered light beam is bent in its traveling direction, and a part of the light beam is again emitted from the surface of the paper.

At this time, when a light beam having a certain light intensity passes through the paper fiber and is emitted again from the surface of the paper which is incident again, the light intensity of the light beam can be approximated by the following equation.

[0004]

[Equation 1] I: outgoing light intensity I ₀ : incident light intensity s: scattering coefficient
x: Distance FIG. 10 is an explanatory diagram showing the light intensity distribution of the light flux emitted from the paper, and usually the point spread function (hereinafter “ps
f ”. ) Called.

Here, the scattering coefficient s is one of the parameters showing the characteristics of the paper, and the material of the paper, the surface shape, the distribution density,
It is determined by the fiber orientation, the refractive index and the like. The larger the value of the scattering coefficient s in the above equation (1), the larger the spread of the light intensity distribution.

Since the scattering coefficient s of copy paper (copy) generally used in a copying machine is about 0.01 to 0.04, the width of psf is about 60 μm to 120 μm. The reading width of an image sensor (reading element) used in an image reading device such as a copying machine is 400 dpi (dot / dot / dot).
Inch), it is about 63 μm. On the other hand, the illumination width of the light source illuminating the document (for example, a halogen lamp or a fluorescent lamp) is about 1 cm, which is considerably large.

Therefore, although depending on the value of the scattering coefficient s of the copy paper, the influence on the pixel for which the image is to be read is considerably large. For example, considering a line sensor (CCD) with a reading width of 50 μm, the scattering coefficient s
When the value of 0.01 is 0.01, the luminous flux (illumination luminous flux) entering the reading width from a position other than the reading position in the reading width direction occupies about 10% of the amount of light entering the pixel of the line sensor. Further, when the value of the scattering coefficient s is 0.04, the luminous flux entering from the position other than the reading position within the reading width occupies about 30% of the amount of light entering the pixel of the line sensor.

In other words, in the case of an ink jet type printed matter, for example, as shown in FIG. 11, each light flux (illumination light flux) incident on the ink A is spectrally absorbed by the ink A and scattered inside the paper. . Then, a certain light beam 23 is spectrally absorbed by the ink B, a certain light beam 22 is again spectrally absorbed by the ink A, and a certain light beam 21 is emitted from a region other than the ink A and ink B portions.

Therefore, when a human (observer) observes an original (paper), it means that all the luminous fluxes emitted from the original are collectively observed.

On the premise of the above description, image reading in the line scanning system in an image reading apparatus such as a general color copying machine or a color scanner will be described with reference to FIG.

FIG. 12 is an explanatory diagram showing the occurrence of color fringing, and shows the relationship between the illumination width of a light source for illuminating an original (paper) and the pixel reading width of a line sensor as an image reading unit for reading an image of the original. Shows.

Here, consider a case where the reading area of the document surface which can be read practically by the image reading section is the portion indicated by W (pixel reading width) as shown in FIG.

Originally, what is required is a pixel reading width W.
The light source has a pixel reading width W regardless of the color of the part
When illuminating a sufficiently large width, for example, as shown in the figure, the light flux (31, 34) incident on the paper from a position other than the pixel reading position of the line sensor is emitted as a light flux (35, 38). As a result, the light flux (32, 33) incident on the paper from the pixel reading position is incident on the read pixel of the line sensor in the same manner as the light flux (36, 37) is emitted.

Since the light flux passing through the path from the light flux 31 to the light flux 35 is spectrally absorbed by the ink A and the ink B, it is different from the actual color of the ink B to be read. Similarly, since the light flux that has passed through the path from the light flux 34 to the light flux 38 is spectrally absorbed by the ink C and the ink B, it is different from the actual color of the read ink B. As a result, these light fluxes enter the read pixels of the line sensor, making it difficult to detect (read) the original color of the pixel read width W portion.

Therefore, when the illumination width SL of the light source for illuminating the paper (original) is sufficiently larger than the pixel reading width W of the line sensor as described above, the image reading device is affected by the optical dot gain. There is a problem in that it is only possible to read an image, that is, an image in a state where color bleeding occurs.

Therefore, conventionally, an apparatus (method) capable of illuminating an area whose illumination area (illumination width) for illuminating a document is substantially the same as or smaller than the reading area (pixel reading width) of the sensor is used. To solve the above problems. A typical example of this device is a drum scanner.

In this drum scanner, an original is attached to a drum, the original is spot-illuminated, and the reflected light from the original is separated into three colors by a color filter and led to a photodiode as a photoelectric conversion element (reading element). , Each pixel is read by the photodiode.

However, this drum scanner has a problem that the reading time is considerably long.

[0019]

As described above, in the conventional image reading apparatus, the illumination area (illumination width) for illuminating the original document.
Is larger than the reading area (pixel reading width) of the line sensor, the area other than the reading area of the image in the original will be illuminated at the same time. It was difficult to get an accurate color because it was received. Therefore, when a drum scanner is used, this drum scanner has a problem that it takes a considerable time for reading as described above.

According to the present invention, when an image of a document or the like placed on a document table is read by a reading unit having discrete array pixels, an area within a range where the reading unit reads the image on the surface of the document. It is an object of the present invention to provide an image reading device capable of reading the color of an image (color image) printed on an original document in a short time without being affected by the light dot gain by illuminating the .

[0021]

An image reading apparatus according to the present invention comprises: (1-1) illuminating an image placed on a document table with a light beam from an illuminating means, and reading the image with discrete array pixels. An image reading apparatus for reading by means, wherein the illuminating means illuminates an area on the surface of the document which is read by the reading means.

In particular, the illuminating means has a light source arranged near the first focal point of the first elliptic mirror, and the luminous flux emitted from the light source is near the second focal point of the first elliptic mirror and at the second focal point. Illuminating the image on the platen placed near the second focal point of the second elliptic mirror through the slit disposed near the first focal point of the elliptic mirror. The illumination means is characterized in that the light flux emitted from the light source is condensed by the condensing means, and the image on the original table is spot-illuminated by the image forming means via the deflecting means.

(1-2) An image reading device for reading an image illuminated by a light beam from the illumination means in the main scanning direction by a reading means having discrete array pixels, wherein the illumination means illuminates the image. It is characterized in that the illumination width in the scanning direction is substantially equal to or less than the pixel reading width for reading the image by the reading means.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of the essential portions of a first embodiment of the present invention, and FIG.
1 is an enlarged explanatory view of the illuminating means shown in FIG. 1, and FIG. 3 is a relationship between the illuminating width of the illuminating means for illuminating the original and the pixel reading width of the image reading section for reading the image of the original according to the first embodiment of the present invention. It is the explanatory view shown.

In the figure, reference numeral 5 denotes a document, on which a color image is formed, which is placed on the surface of the document table 6. Reference numeral 2 denotes a light source, which is composed of, for example, a halogen lamp, a fluorescent lamp, or the like having a linear light emitting surface extending in the vertical direction (main scanning direction) with respect to the paper surface, and is a first reflecting means described later.
It is installed near the first focus of the elliptical mirror 1. The first elliptical mirror 1 efficiently collects the light flux emitted from the light source 2.

Denoted at 3 is a slit, which is of a reflective type in which chromium is vapor-deposited on the surface of the glass material, and is located in the vicinity of the second focus of the first elliptical mirror 1 and as the second reflecting means 4 described later. It is installed near the first focus of the two elliptical mirrors and limits the amount of illumination light.

Reference numeral 4 is a second reflecting means, which is composed of two elliptic mirrors, a 2-1 elliptic mirror 4a and a 2-2 elliptic mirror 4b, and a slit 3 provided near both first focal points. The light flux that has passed through is condensed to illuminate the reading area of the document 5 on the surface of the document table 6 arranged in the vicinity of the second focus of the second reflecting means 4. In the present embodiment, the amounts of light emitted from the 2-1 elliptic mirror 4a and the 2-2 elliptic mirror 4b to the surface of the original 5 are set to be substantially uniform.

In this embodiment, the light source 2, the first reflecting means 1, the second reflecting means 4, and the slit 3 shown above are used.
The illuminating means 10 is composed of the respective elements.

The illuminating means 10 illuminates an area on the surface of the original 5 within a range where the line sensor 8 as a reading means, which will be described later, reads the image of the original 5.

That is, in the present embodiment, the illumination width SL of the illuminating means 10 for illuminating the original 5 in the sub-scanning direction and the pixel reading width (detection pixel width) of the line sensor 8 for reading the image of the original 5.
W is set to have substantially the same width, and the length of the illumination area of the illumination means 10 in the main scanning direction (direction perpendicular to the paper surface) is the same as the reading length of the line sensor 8 in the main scanning direction. It is possible to illuminate only one length at a time. As a result, in this embodiment, the influence of the optical dot gain from other than the pixel reading position is prevented.

The illumination area on the surface of the original 5 is controlled by the slit width in consideration of the image forming magnification of the illumination optical system.
Here, the illumination width SL of the illumination means 10 means the distance between the vertices of psf at both ends of the illumination range.

Reference numeral 7 denotes a monofocal lens array as an image forming means, which forms an image (color image) of the original 5 on the surface of the reading means 8 at an equal magnification.

The reading means 8 is composed of an image sensor (image reading section) having discretely arranged pixels, for example, as shown in FIG.
As shown in, a one-line sensor in which three light receiving elements (reading elements) 8a, 8b, and 8c for red (R) color, green (G) color, and blue (B) color are sequentially arranged in a one-dimensional direction Made of

In this embodiment, the light flux emitted from the light source 2 is reflected by the first elliptic mirror 1 in the above-described structure, and the luminous flux near the second focal point of the first elliptic mirror 1 and of the second reflecting means 4 is used. The light flux is limited through the slit 3 arranged near the first focal point, and the limited light flux is condensed via the 2-1 elliptic mirror 4a or the 2-2 elliptic mirror 4b, and the second reflecting means. The image of the document 5 placed on the document table 6 near the second focal point 4 is line-illuminated in the direction perpendicular to the paper surface (main scanning direction). Then, the reflected light from the original 5 is imaged on the surface of the line sensor 8 by the monofocal lens array 7 at an erecting equal magnification, and the light flux based on the image detected by the line sensor 8 is applied to each pixel by a color separation filter. , For example, red (R), green (G), blue (B) 3
It is converted into one color light. Then, the converted information is sent to a storage unit to create image data, and an accurate copy image is obtained based on the image data.

As described above, in the present embodiment, as described above, the illuminating means 10 illuminates the reading area (image area) of the original 5 with the same length as the main scanning direction (longitudinal direction) of the line sensor 8 and the same width. By doing so, the reflected light from the original 5 is incident only on the pixel portion detected by the line sensor 8. As a result, there is no luminous flux that enters the document from a position other than the pixel reading position, is scattered, and is emitted from the pixel reading position, and the color at the document reading position can be obtained more accurately and in a shorter time than the conventional document illumination method. Further, it is possible to obtain an accurate ink amount.

In this embodiment, the case where the present invention is applied to the image reading apparatus using the single focus lens array is shown.
For example, the present invention can be applied to the image reading apparatus having a structure using a scanning mirror and a normal imaging lens as shown in FIG.

That is, in FIG. 5, the light flux from the original 5 line-illuminated by the illumination means 10 is read by the imaging lens 11 via the scanning mirrors 9a, 9b and 9c as in the first embodiment. The image of the original 5 is read by forming an image on the surface of the line sensor 8 as described above. By configuring the image reading apparatus in this way, the present embodiment can obtain the same effects as those of the above-described first embodiment.

Next, a second embodiment of the present invention will be described with reference to FIGS.
Will be explained. FIG. 6 is an explanatory diagram showing the occurrence of color fringing, and shows the relationship between the illumination width of the illumination means for illuminating the original and the pixel reading width of the image reading unit for reading the image of the original. FIG. 7 is an explanatory diagram showing the difference in the illumination width with respect to the image reading width.

The present embodiment differs from the first embodiment described above in that the illumination width in the sub-scanning direction for illuminating the original by the illuminating means is made narrower than the pixel reading width for reading the image of the original by the line sensor. is there. Other configurations and optical actions are substantially the same as those of the first embodiment, and the same effect is obtained.

That is, the pixel reading width for reading the image of the original 5 by the line sensor 8 and the illuminating means 1 as in the first embodiment.
When the illumination width for illuminating the original at 0 is set to be approximately the same width, for example, as shown in FIG. 6, the process until the incident light 61, 64 incident from the ink B becomes the emitted light 65, 68 In some cases, the ink B of the original color may be spectrally absorbed by the other inks A and C and may pass therethrough. Therefore, it may be difficult to detect the original color (ink B) of the pixel reading width W portion.

Therefore, in the present embodiment, the above problem is solved by making the illumination width SL of the illumination means for illuminating the original document narrower than the pixel reading width W of the line sensor in order to reduce the appearance probability of such a luminous flux. are doing.

The outgoing light intensity distribution of the luminous flux is expressed by the above-mentioned equation (1).
It is shown that it is possible to approximate as shown in.
This equation (1) is a Gaussian function, and the scattering coefficient s defined in the first embodiment corresponds to the standard deviation σ. That is, 99.7% of the total amount of light is contained at a distance of 3 times the scattering coefficient s, and 95% of the total amount of light is included at a distance of 2 times the scattering coefficient s, with the vertex of the intensity distribution of emitted light as the center.

In the present embodiment, the illumination width SL for illuminating the original document is set to 73, as shown in FIG.
By making the length 74 shorter than the pixel reading width W of the line sensor 8 at both ends, the light flux that extends from the pixel reading width W of the line sensor 8 to the outside of the pixel reading width W of the line sensor 8 is effectively reduced.

As a result, in this embodiment, the influence of the optical dot gain is further reduced and the color of the image originally printed on the original is accurately read.

FIG. 8 is a schematic view of the essential portions of Embodiment 3 of the present invention, and FIG. 9 is an explanatory view of the line sensor shown in FIG.

The present embodiment differs from the above-described first embodiment in that the illuminating means is constituted so that the original illuminating method is not the line illuminating but the spot illuminating, and the image of the original illuminated by the spot illuminating is reading means. It was read by the line sensor.

That is, as the original illuminating method in the above-described first and second embodiments, the line illuminating method of illuminating the line sensor in the main scanning direction (longitudinal direction) with the same length and width is used. In this case, the influence of the optical dot gain caused by each pixel may appear on the pixels adjacent to each other in the main scanning direction of the line sensor or on the peripheral pixels in the main scanning direction.

Therefore, in this embodiment, in order to prevent the influence of the light dot gain, spot illumination is used which illuminates with a spot having a size equal to or smaller than the size of the minimum pixel area detectable by the line sensor.

That is, in this embodiment, the light beam emitted from the light source 80 is condensed by the condensing means (illumination optical system) 81, and is deflected and reflected by the optical deflector (polygon mirror) 82 as the deflecting means. It is incident on the cylindrical lens 83 having a predetermined refractive power only in a predetermined direction as an image forming means. Then, the light flux that has passed through the cylindrical lens 83 is spot-illuminated at a certain point under the line scanner of the document 5 via the folding mirror 84. This light flux is diffused by the original 5 and becomes psf, but when the center of the psf becomes the center of the read pixel, the reflected light of the pixel is detected.

The size of the illumination spot at this time is such that, when the illumination spot is incident on a document, 80% or more of the amount of light output from the document surface is obtained from the minimum pixel area detectable by the line sensor. I am trying to become.

Then, the detected reflected light from each pixel is separated into three color lights of red (R), green (G) and blue (B) by a color separation filter, for example, and sent to a storage section. Creating data. When the detection of the reflected light from each pixel on the reading line is completed, the original 5
Scanning the next read line of.

As described above, in this embodiment, the reading area of the original is illuminated by the spot illumination as described above, so that the pixels adjacent to each other in the main scanning direction of the line sensor or the peripheral pixels in the main scanning direction are respectively illuminated. The effect of the optical dot gain caused by the pixel is effectively prevented.

In the present embodiment, the scanning method of the original table moving system is taken as an example, but it is also applicable to the image reading apparatus of the optical system moving system which scans the original by moving the optical system such as the line sensor and the mirror. Can be applied.

Further, although the line sensor is used as the reading means in each of the embodiments, it is not limited to the line sensor.
For example, the present invention can be applied in the same manner as the above-mentioned embodiment even if an area sensor or the like is used.

[0055]

According to the present invention, as described above, the illumination width in the sub-scanning direction for illuminating the document by the illumination means is set to be substantially the same as the pixel reading width of the reading means (image sensor) or less. The color of the image (color image) printed on the original document can be accurately read in a short time without being affected by the optical dot gain, and a more accurate copy image can be obtained based on the read information. It is possible to achieve an image reading device capable of

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

FIG. 2 is an enlarged explanatory view of the illumination means shown in FIG.

FIG. 3 is an explanatory diagram showing a relationship between an illumination width of an illumination unit that illuminates an original according to the first embodiment of the present invention and a pixel reading width.

FIG. 4 is an explanatory view of the line sensor shown in FIG.

FIG. 5 is a schematic view of another main part of the first embodiment of the present invention.

FIG. 6 is an explanatory diagram showing the occurrence of color bleeding.

FIG. 7 is an explanatory diagram showing a difference in illumination width according to the second embodiment of the present invention.

FIG. 8 is a schematic view of the essential portions of Embodiment 3 of the present invention.

9 is an explanatory diagram of the line sensor shown in FIG.

FIG. 10 is an explanatory diagram showing a light intensity distribution of a light beam emitted from paper.

FIG. 11 is an explanatory diagram showing the occurrence of color bleeding in a conventional image reading apparatus.

FIG. 12 is an explanatory diagram showing a relationship between an illumination width of an illumination unit that illuminates a document and a pixel reading width in a conventional image reading apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st reflection means 2 Light source 3 Slit 4 2nd reflection means 4a 2nd -1 elliptical mirror 4b 2nd 2-2 elliptical mirror 5 Original document 6 Original plate 7 Image forming means 8 Reading means 80 Light source 81 Condensing means 82 Deflection Means 83 Image Forming Means (Cylindrical Lens) 84 Reflecting Mirror 85 Reading Means

Claims (4)

[Claims] 1. An image reading apparatus which illuminates an image placed on a document table with a light beam from an illuminating unit and reads the image by a reading unit having discrete array pixels, the illuminating unit including the document surface. An image reading apparatus illuminating the reading range of the reading means. 2. The illuminating means has a light source arranged near a first focal point of the first elliptic mirror, and emits a light beam emitted from the light source near a second focal point of the first elliptic mirror, and The image on the platen placed near the second focal point of the second elliptic mirror is illuminated through the slit disposed near the first focal point of the second elliptic mirror through the second elliptic mirror. The image reading device according to claim 1. 3. The illumination means condenses a light beam emitted from a light source by a condensing means and spot-illuminates an image on the original table by an image forming means via a deflecting means. The image reading device according to item 1. 4. An image reading device for reading an image illuminated by a light beam from an illuminating unit in a main scanning direction by a reading unit having discrete array pixels, the illuminating unit illuminating the image in a sub-scanning direction. An image reading device characterized in that an illumination width is configured to be substantially equal to or less than a pixel reading width for reading the image by the reading means.