JPH01147955A - Color picture reader - Google Patents

Abstract

PURPOSE:To suppress the generation of a color ghost by employing an achromatic lens for a lens forming the image of a reflected light from an original face so as to reduce the deviation of picture elements between solid-state image pickup elements. CONSTITUTION:The optical information obtained by radiating an original through a fluorescent light source is led to an optical information replacement unit 10 via a 1st mirror, a 2nd mirror and a 3rd mirror. An optical signal led to the unit 10 is collected by a lens 11. The achromatic lens is used for the lens 11. The collected light signal is separated into red optical information and cyan optical information by a dichroic mirror 13 provided on a prism 12. Each color separation image is formed on the light receiving face of each solid- state image pickup element and the picture signal converted into an electric signal is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a multicolor image in which a document light image obtained by an exposure optical system that scans the document surface while illuminating the document surface is formed in an imaging unit. The present invention relates to a color image reading device suitable for application to a forming apparatus, such as an electrophotographic color copying machine.

[Background of the invention]

Generally, in an image reading device, an optical image of the document surface obtained by exposure scanning is formed on a solid-state imaging device such as an image sensor installed around the optical axis via an imaging lens system. .

Furthermore, for example, in a color image reading device of a multicolor image forming apparatus, a light image of color image information on a document surface obtained by exposure scanning is passed through an imaging lens system, and is then placed on the optical axis of the document light image. After the light is separated by a light splitting means such as a prism, an image is formed on an image sensor that receives the light in each channel.

The optical images formed on each of the image sensors are photoelectrically converted and A/D converted, and then processed into three colors of red, blue, yellow (Y), and magenta by a color image forming device such as a laser printer. A color image is formed using four colors: (M), cyan (C), and black (K), or a composite color thereof.

Examples of conventional color image reading devices are shown in FIGS. 20 and 23.

FIG. 20 shows a configuration diagram of a color image reading device.

In the figure, reference numeral 1 denotes a transparent glass original platen, on which the original plate is placed. 2 is a light source, 3 is a first mirror, and these move together on a carriage 4 in the direction of arrow A shown in the figure. Reference numerals 5A and 5B denote a second mirror and a third mirror, which constitute a movable mirror unit 6 and move together in the same direction as the first mirror 3 at 1/2 the speed of the carriage 4.

Above 1st. Second. By the action of the third mirror, the reflected light from the irradiated portion moving at a constant speed on the document is sent to the lens 11 of the optical information conversion unit 10 with an equal distance optical path length. Lens 11
The light beam passing through is divided into R (red) by the three-color separation prism 12.
, G (green), and B (blue), and further three image sensors, i.e., linear solid-state imaging devices such as charge-coupled devices (hereinafter referred to as CCDs) 15B, 15G, 15
Images of each color are captured on R.

In the prism 12 shown in the figure, the reflected light from the original is sent to the CCDs 15B, 15G, 15R by the imaging lens 11.
A dichroic mirror 13 is placed in the imaging optical path to form an image on the
A and 13B are arranged. A dichroic mirror is an interference filter obtained by alternately vacuum-depositing low refractive index dielectric films and high refractive index dielectric films on a transparent substrate such as glass.

[Problem that the invention seeks to solve]

Although such conventional color image reading devices are capable of capturing images at high speed, (1) It is difficult to achieve accurate positioning of each CCD.

(2) In the prism 12 having a 45° transmission/reflection surface, the rise of the transmission/reflection curve of the dichroic film is too gradual, which is not favorable for color reproduction. Therefore, it is necessary to use the trimming filter 16 or the like together.

The above two points exist as major problems. Therefore, when capturing a halftone image with very smooth tones, it is good except for color reproduction, but when capturing images of thin lines such as characters, color ghosts appear and it is not suitable for practical use.

On the other hand, the solid-state image sensor (COD) is a line image sensor configured with minute pixel elements with a pixel width of about 7 μm. Therefore, these solid-state imaging devices are formed into an integrated unit after highly accurate positional adjustment is made to the imaging lens and light splitting prism in order to form the optical image of the original onto the solid-state imaging device. .

When the image pickup unit is shifted from the optical axis of the original optical image, the original optical image is also input shifted. When the front and rear portions of the imaging unit are shifted vertically from the horizontal plane of the optical axis, the position where the light image is formed on the image sensor is shifted vertically.

As a result, the leading edge starting position of the output image corresponding to the leading edge starting position of the original image is shifted back and forth in the image forming direction. If the left side and right side of the imaging unit with respect to the optical axis are shifted vertically from the optical axis horizontal plane, the portion of the original optical image on the optical axis horizontal plane will be imaged tilted to the left or right on the solid-state image sensor. , the document is output in a diamond-shaped state in which the left side and right side in the scanning direction are shifted back and forth.

FIG. 21 is a diagram showing the results obtained by analysis and experiment of how the screen vertical positional deviation of each G/R imaging device in the conventional example changes depending on the environmental temperature. According to the diagram, an optical axis position shift of about 40 μm occurs in the temperature range θ° to 40° C.

Similarly, FIG. 22 is a diagram showing the results obtained by the above analysis and experiment of how the vertical positional shift of the screen of each G/B image pickup device changes depending on the environmental temperature. In this case as well, a temperature change from 0° to 40° C. causes an optical axis position shift of about 40 μm, as described above.

In this way, it has been extremely difficult to improve positional accuracy in response to changes in environmental conditions.

FIG. 23 is a configuration diagram showing another example of a conventional color image reading device. In order to eliminate the factors that cause the positional accuracy to fluctuate due to temperature changes, as mentioned above, three light sources and filters with different emission colors are used to provide R (red), G and
This method captures color data of three colors: (green) and B (blue). In this example a single line image sensor (CCD)
Although there is no problem of alignment accuracy deviation between multiple CCDs due to the use of
This method has the disadvantage that the line imaging time is not shortened, and the number of exposures increases because exposure scanning is performed for every l line of each color, making high-speed imaging impossible.

[Means for solving problems]

The present invention has been made in order to solve the above-mentioned problems, and an object thereof is to provide a color image reading device that is capable of high-speed image pickup, good color reproduction, and good image pickup of line drawings. It is something to do.

A color image reading device of the present invention that achieves the above object includes color separation means in an imaging optical path that irradiates the document surface with a light source that moves relative to the document surface and forms an image of reflected light from the document surface with a lens. A color image reading device that forms a plurality of color images and photoelectrically converts each color image into a plurality of color signals using an individual line-shaped image sensor, characterized in that the lens is an achromatic lens.

Furthermore, the achromatic lens according to the present invention is characterized in that one of the reference lights is selected within the range of 620 to 700 nm.

〔Example〕

Hereinafter, an example of a color image processing apparatus including a color image reading apparatus according to the present invention will be described in detail with reference to FIG. 1 and subsequent figures.

FIG. 1 shows a schematic configuration of a color image processing apparatus according to the present invention.

The color image information (optical image) of the document is separated into two color separated images by the dichroic mirror 13 of the prism 12. In this example, the image is separated into a red R color separation image and a cyan cy color separation image. Therefore, the dichroic mirror 13 used has a cutoff of about 540 to 600 nm. As a result, the red component becomes transmitted light, and the cyan component becomes reflected light.

The color separated images of red R and cyan cy are supplied to image reading means, for example, CCDs 14R and 14C, and image signals of only the red component R and cyan component cy are output from each image reading means, for example.

The image signals R and Cy are supplied to A/D converters 30 and 31, where they are converted into digital signals having a predetermined number of bits, 6 bits in this example. Shading correction is performed simultaneously with A/D conversion. 32.33 is R for shading correction
Indicates AM/DA etc. Details of the shading correction will be described later.

The shading-corrected digital image signal is extracted by gate circuits 34 and 35 for a signal corresponding to the maximum original size width, and is supplied to a color separation circuit 36 at the next stage. When the maximum document width to be handled is 84 size, a size signal B4 generated by a timing signal generating means (not shown) of the system is used as a gate signal.

Here, if the digital image signals subjected to shedding correction are VR and VC, respectively, these image signals VR.

VC is supplied to a color separation circuit 36 and separated into a plurality of color signals.

In this example, a case is illustrated in which the signal is configured to be separated into three color signals: red, blue, and black.

Each separated color signal is composed of color code data (2-bit data) indicating its color information and its density data (6-bit data). Data for each of these color signals is stored, for example, in a color separation map configured in a ROM.

The color-separated image data is transferred to a color image processing step.

First, it is supplied to the next stage color ghost correction means 40, and color ghosts in the main scanning direction (horizontal scanning direction) and sub-scanning direction (drum rotation direction) are corrected. 41 is a color ghost correction circuit in the main scanning direction, and 42 is a color ghost correction circuit in the sub-scanning direction.

When separating colors, unnecessary color ghosts (especially around the black characters)
This is because color ghosts) occur. Depending on the configuration of the color separation map, red or blue color may appear around the edges of black characters. Image quality is improved by removing color ghosts.

Color ghost processing applies only to color code data.

In addition to color ghost correction, image processing includes resolution correction, partial color conversion processing, and threshold correction for multi-value conversion.

Other types of image processing include enlargement and reduction processing, but for convenience of explanation, specific examples of the three types of image processing described above will be shown.

45 is a resolution correction means. Since resolution correction is contour correction, the target image data for processing is density data.

An example of partial color conversion processing will be described next. The partial color conversion means 50 includes an area extraction circuit 51 that detects an original area marked with a color marker on a document or the like, and a color data selection circuit (color data selector) 52 that copies the extracted area in a specified color. It consists of Of course, it is also possible to record outside the designated area in a designated color.

The area extraction circuit 51 outputs a signal (area signal) indicating the area surrounded by color markers, and this and color code data are supplied to the color data selection circuit 52.

The color data selection circuit 52 receives a processing designation signal that instructs what kind of image processing is to be performed from the display/operation section;
A BBR signal indicating the color that must be currently captured and output is input, and selection is made as to whether or not to send density data whose resolution has been corrected from these and the above-mentioned input signals to the multi-value conversion means 60 at the next stage. will be done.

For example, when simply copying, only image data with the same color as the BBR signal is output, and when performing color conversion on the entire document, for example, when converting red to blue and blue to red, respectively. In this case, control is performed so that first, when recording blue, red image data is output, and when recording red, blue image data is output.

When partially performing color conversion, black information within an area surrounded by a color marker is recorded in the color of that marker. For example, if the black information of the area surrounded by the red marker is controlled to be output during the red recording phase, the area can be partially color-converted and recorded.

For such partial color conversion and color specification processing, when developing colors, a development system is used in which a drum is rotated to develop each color, and fixing is performed only after the development of the final color is completed. By doing so, it becomes possible.

In this case, the imaging operation is also performed multiple times. in this way,
By performing each of the imaging operation and the developing operation multiple times, image recording processing can be performed in real time.

Real-time processing can reduce memory for image storage.

The image data output from the color data selection circuit 52 (
(density data) is multi-valued by the multi-value coding means 60.

In this example, 6-bit density data is converted to 1-bit data (binary data) of 1.0. Threshold data (6 bits) serving as a reference for binarization is set manually or automatically.

Therefore, the threshold value selection means 61 includes a threshold value determination means 62 for manual setting (manual mode) and a threshold value determination means 63 for automatic setting (EE mode). The manual threshold value determining means 62 is configured to be able to independently determine a threshold value for each color, outputs an externally specified threshold value, and performs binarization using this threshold value.

The automatic threshold value determining means 63 is configured to use an RO in which a predetermined threshold value is stored.
Consists of M. Switching between manual and automatic is performed by an EE release signal. Normally, it is automatic setting mode (EE mode). Further, a BBR signal is supplied which indicates in which sequence the developing device is currently undergoing development processing.

The image data binarized by the binarization circuit 65 is supplied to the output device 70 via the interface circuit 66. The interface circuit 66 has first and second interfaces, one of which is for receiving batch image data and the like used for toner density control.

As the output device 70, a laser recording device or the like can be used. When a laser recording device is used, a binarized image is converted into a predetermined optical signal, and this is converted into a predetermined optical signal based on the binary data. It is modulated by

As the developing device, an electrophotographic color copying machine is used. In this example, two-component non-contact development and reversal development are employed. That is, the transfer drum used in conventional color image formation is not used. In this example, in order to reduce the size of the device, a three-color image of blue, red, and black was developed on an 0PC (organic photoconductive) photoreceptor drum for image formation in three rotations of the drum, and the image was transferred after development. This is done once and then transferred to recording paper such as plain paper.

Next, the configuration of each part of the color image processing apparatus according to the present invention configured as described above will be explained in detail.

First, a simplified color copying machine suitable for application to the present invention will be explained with reference to FIG. 2 and subsequent figures.

A simple color copying machine attempts to record a color image by separating color information into about three types of color information. In this example, black BK1 is used as the three types of color information to be separated.
Red R and blue B are illustrated.

By turning on the copy button of the apparatus, the original reading section A is driven.

First, an original placed on an original table L is optically scanned by an optical system.

This optical system includes fluorescent lamp light sources 2A, 2B and a first mirror 3.
The movable mirror unit 6 includes a carriage 4 provided with a mirror and a movable mirror unit 6 provided with a second mirror 5A and a third mirror 5B.

The carriage 4 and the movable unit 6 are caused to travel on a slide rail 8 at predetermined speeds and directions, respectively, by a stepping motor 7.

Optical information (image information) obtained by irradiating the original document with the fluorescent light sources 2A and 2B is transmitted to the first mirror 4. Second mirror 5A
, via the third mirror 5B, the optical information conversion unit) 10
guided by.

Note that when optically scanning a color document, the fluorescent lamp 2A is used to prevent optical attenuation of specific colors.

As 2B, a commercially available warm white fluorescent lamp is used, and in order to prevent flickering, these fluorescent lamps 2A and 2B are turned on and driven by a high frequency power source of approximately 40 kHz. In addition, in order to maintain a constant temperature of the tube wall or to promote warm-up, the tube wall is kept warm by a heater using a POSISTOR.

A standard white plate 9 is provided on the back side of the document stopper plate at the left end of the document table (platen glass) l.

This is to normalize the image usage to a white signal by optically scanning the standard white plate 9.

The optical information conversion unit IO includes a lens 11. prism 12
, a dichroic mirror 23, a C CD 14R from which a red color-separated image is projected, and a C CD 14C from which a cyan color-separated image is projected.

Optical signals obtained from the optical system are collected by a lens 11 and separated into red optical information and cyan optical information by a dichroic mirror 13 provided within the prism 12 described above.

Each color separation image is formed on the light receiving surface of each CCD, thereby obtaining an image signal converted into an electrical signal.

After the image signal is processed by the signal processing system, each color signal is output to the writing section B.

As shown in FIG. 1, the signal processing system includes signal processing circuits such as A/D conversion means, color separation means, and binarization means.

The writing section B has a deflector 71. As the deflector 71, in addition to a carbano mirror or a rotating polygon mirror, a deflector made of an optical deflector using crystal or the like may be used. A laser beam modulated by a color signal is deflected and scanned by this deflector 71.

When the deflection scan starts, the laser beam index,
The beam scan is detected by a sensor (not shown);
Beam modulation using a first color signal (for example, a blue signal) is started. The modulated beam is scanned by a charger 72 over an image forming member (photosensitive drum) 73 to which a negative charge is applied.

Here, an electrostatic image corresponding to the first color signal is formed on the image forming body 73 by the main scanning by the laser beam and the sub scanning by the rotation of the image forming body 73.

This electrostatic image is developed by a developer 74B containing blue toner. A predetermined bias voltage from a high voltage source is applied to the developing device 74B. A blue toner image is formed by development.

The blue toner image is rotated with the cleaning blade of the cleaning device 75 released, and then an electrostatic image is generated based on a second color signal (for example, a red signal) in the same manner as the first color signal. This is developed to form a red toner image by using developer 74R which is formed and contains red toner.

Needless to say, a predetermined bias voltage from a high voltage power source is applied to the developing device 74R.

Similarly, an electrostatic image is formed based on the third color signal (black signal), and a developing device 748K containing black toner forms an electrostatic image.
It is developed in the same way as before.

Therefore, a multicolor toner image is written on the image forming body 73.

Note that although the formation of a three-color multicolor toner image has been described here, it goes without saying that a two-color or single-color toner image can be formed.

As described above, the development process is a so-called two-component non-contact development process in which each toner is flown toward the image forming body 73 while AC and DC bias voltages from a high-voltage power source are applied. An example of development is shown.

On the other hand, the feed belt 77 from the cassette 76 of the paper feeding device
and the recording paper P fed via the timing roll 78
is conveyed onto the surface of the image forming body 73 in a state in which the timing is synchronized with the rotation of the image forming body 73. Then, the multicolor toner image is transferred onto the recording paper P by the transfer pole 79 to which a high voltage is applied from the high voltage power supply, and separated by the separation pole 80 .

The separated recording paper P is conveyed to the fixing device 81, where it undergoes a fixing process and a color image is obtained.

The image forming body 73 after the transfer is cleaned by a cleaning device 75 and is prepared for the next image forming process.

The transmittance characteristic of the above-mentioned guichroic mirror 13 is
The emission spectrum of the light source is shown in Figure 4, and the CCD
The spectral sensitivity characteristics of each are shown in FIG.

As the light source, a daylight color (CD) or warm white (WW) type fluorescent lamp, a halogen lamp, or the like can be used. When using a halogen lamp, an appropriate filter is used to make the emission spectrum the same as that of a fluorescent lamp.

FIG. 6 is a mosaic diagram showing an example of an image in which color ghosts occur. As a color ghost, Figure 7 A-C
As shown in the enlarged view, red and blue appear at the edge of the black line, black appears at the edge of the blue line, and black appears at the edge of the red line.

It is clear that color ghosts appear differently in other color combinations.

The reason why such a phenomenon occurs will be explained using the above example.

As shown in Figure 8, if the alignment of the pixels of the two CODs is not performed strictly, during color separation, as shown in Figure 7, red and blue will appear at the black edge, black and blue at the red edge. A black ghost will appear at the edge.

Therefore, in order to prevent this, it is necessary to precisely align the two CCDs. Normally, it is necessary to perform alignment within one pixel, preferably within 1/4 pixel.

In this example, this is achieved by aligning the two CCDs on a jig and then fixing them with adhesive.

An example is shown in FIG. 9 and below. FIG. 9 is a sectional view of the optical information conversion unit. As shown in the figure, the lens barrel 16 that holds the lens 11 is housed in a 7-shaped receiver that opens upward at a right angle to the holding member 17, and is attached to the fastener 1.
8 and then attached to a predetermined position on the device board 19.

A mounting surface 17A into which the front part of the prism 12 can be dropped is provided on the rear side of the holding member 17.
The prism 1 held by the mounting member 20 against
2 can be fixed by pressing them together with screws.

Since the mounting surface 17A is formed by a simple machining process, the distance from the lens barrel 16 and the perpendicularity to the optical axis are extremely accurate.
A predetermined light image can be correctly formed on the light receiving surface of 4C.

FIG. 1O is a perspective view of essential parts of the optical conversion unit.

As shown in FIG. 1O, the amount of deviation (lens light The method of determining the perpendicularity of the dichroic surface to the axis (the amount of inclination R, , R,) is determined by the resolution (modulation transfer function) MTF MTF = (y − x / y+ x)X 100
It is given in %. Here, X indicates the minimum value of illuminance, and y indicates the maximum value of illuminance. The above MTF is normally a value of 30% or more, and the amount of inclination is around 30% (9%) in 10 minutes with respect to the angle.
It is important to maintain the surface accuracy during this period, as this will further reduce the angle by more than 50% (15%) in 30 minutes, which will hinder the extraction of black and white discrimination signals (in this case, the lens barrel (It is also possible to have a structure in which the prism surface is in contact with the end.)

The C CDs 14R and 14C to the prism 12 are fixed to the prism 12 with an adhesive via attachment members 24 and 25.

FIG. 11 is an embodiment showing a cross-sectional view of the main part of the prism 12 and the CCDs 14R and 14C in a joined state, in which mounting members 24a and 24b are attached to both sides of the prism 12 symmetrically with adhesive as light splitting members. CCDs 14R and 14C are fixed to the imaging section via (25a, 25b) with adhesive.

As for the material of the mounting members 24 and 25, a material with a small coefficient of linear expansion is desired for two reasons. One is to prevent pixel misalignment due to temperature fluctuations, and the other is to prevent internal distortion of the mounting members 24 and 25 bonded to the prism 12 due to the difference in linear expansion coefficient between the two.
This is to prevent the occurrence of cracks, etc. in 2.

Each CCD 14R has the problem of pixel misalignment due to temperature fluctuations.

By making the fixing conditions of 14C and the mounting members 24 and 25 exactly the same, pixel misalignment between CODs can be reduced, but the linear expansion coefficient needs to be smaller.

Normally, the linear expansion coefficient of a prism is as small as 7.4X 10-' (optical glass BK-7), so glass or ceramic materials (7.0 to 8.4X 10-') are used as mounting members.
) and low thermal expansion alloys, such as Invar alloy (1~3×l
Low"), Nijirest cast iron (4~IOX 10-'))
etc., and aluminum material (25 x 10-') is not so suitable.

In the above embodiment, the prism 12 and the mounting member 24 (25)
, mounting member 24 (25) and CCD 14R (14c'
), and after adjusting the relative positions of the CCDs 14R and 14c with respect to the divided optical images, the CCDs 14R and 14c are closely fixed with adhesive as in the example shown in FIG. In particular, in Fig. 11, even if iron (12 x 10-') with a large coefficient of linear expansion is used as the mounting member, the dimension in the C direction is short, so the elongation due to heat is not affected much, and the d direction is a line. This is the direction in which the sensors are arranged, and since the prism material and the line sensor package material are ceramic materials, their linear expansion coefficients are the same, and with this configuration, no pixel misalignment occurred.

The adhesive is a two-component type adhesive or a photocurable adhesive, and an ultraviolet curable adhesive is particularly preferred.

In particular, photo-curable adhesives can speed up the curing time of the adhesive simply by changing the intensity of light, improving workability, reducing costs, and stabilizing the product. Among photo-curable adhesives, ultraviolet-curable adhesives in particular exhibit almost no thermal change even when exposed to ultraviolet rays, and can be stably cured.

Three Pond T B 3060B as a light curing adhesive
(Product name), Denka 1045K (Product name), Norland 65 (Product name), etc., were used to irradiate ultraviolet light with a high-pressure mercury lamp, and good results were obtained in the environmental tests described later. .

Urethane-based Threepond 3062, which also has UV curing.
When B (trade name), L T 350 (trade name), etc. were used, it was possible to obtain an adhesive that was even more effective in moisture resistance and had strength compensation.

With the above method, the overall positional deviation of CCDs 14R and 14c is 774 μm = 1, assuming that one pixel is 7 μm.
．． It became possible to suppress the thickness to within 75 μm.

FIG. 13 is an explanatory diagram of Hosochromatic aberration showing each position where monochromatic light having different wavelengths passes through the lens 11 and forms an image on the optical axis.

The wavelengths of each monochromatic light are shown below.

G-line: 435.84nm F-line: 486.13nm D-line: 587.56nm C-line: 656.28nm For monochromatic light of each wavelength above, the axial chromatic aberration is as shown in Figure 13, and the chromatic aberration of the d-line is as follows. With respect to the imaging position (d), the imaging position (g) of the g-line is located at a position ΔXgd forward on the axis,
Further, this g-line light reaches a position ΔYgd downward on the d-line focus plane.

FIG. 14 is a chromatic aberration characteristic diagram of an achromatic lens and an apochromatic lens.

In the figure, the horizontal axis represents wavelength, and the vertical axis represents chromatic aberration (ΔY). Curve AC is an achromatic lens (f=300m
m, F: 4.0), curve AP
is an apochromatic lens using fluorite (f = 30
0mm, F: 5.6).

As shown in the figure, the chromatic aberration of an apochromatic lens is extremely small, which is ideal, but it requires the use of a special lens material such as fluorite, and lens polishing is difficult, so in reality it is difficult to use for astronomical objects. It is only used in a small number of special purpose devices such as telescopes. Therefore, for office equipment for general office use, there is a need for lenses that are inexpensive to manufacture and can be mass-produced, and from this point of view it is difficult to employ the above apochromatic lenses.

In contrast, it is desirable to use a general achromatic lens, which is superior in manufacturing cost and mass production. but,
A general achromatic lens has extremely large chromatic aberration as shown in FIG. In the figure, curve A
C has two wavelengths, namely point b near the d line and point a on the short wavelength side.
The point has the least chromatic aberration, and also almost coincides with the curve AP.

From the above viewpoint, the inventors of the present invention have found, as a result of various studies, the optimal selection of two wavelengths with matching Hosochi chromatic aberrations and the optimal combination with a light source in the design of an achromatic lens.

FIG. 15 is a diagram explaining the relationship between magnification aberration and wavelength,
This is an enlarged view of the color blur (chromatic aberration) of the frame due to each color (g*d+0) of magnification. Note that the figure shows the lateral chromatic aberration of a convex lens having a rear aperture.

As shown in the figure, blue light with a short wavelength has a large magnification. When aligning the line image sensors 14R and 14C in the two-color separation optical unit IO shown in FIGS. Line image sensor (CCD etc.) 15R, 15
When aligning the B and 15G pixels, the most important point is to match the magnification of each image. That is, in such a color image reading device,
A serious issue is how to deal with image blurring (MTF deterioration) after matching the magnifications.

As shown in FIG. 13, in this example, CCD (blue) 14B and CCD (red) 1 are located at the best focus position g of the green light.
When 4R is combined, the MTF of green light is good, but the MTF of COD output with respect to blue light, rad light, and so on is significantly inferior, making it unsuitable for practical use. Normally, the margin for CCD alignment is approximately 20 to 60μ until the MTF drops to about 80% of the value at the best focus position. There is a range of degrees. Therefore, it is necessary to design the lens so that it falls within this width.

When separating into two colors of cyan and red instead of the three-color separation of red, green, and blue mentioned above, the imaging position changes rapidly depending on the wavelength as shown in Figure 14, and depending on the light source, the MTF may be significantly It gets worse.

As described above, it is generally necessary to take measures in lens design and to select a light source.

(Example 1) When separating two colors into cyan/red The light source is WW (warm white) and DL (daylight).

The test will be conducted using two types of lamps: fluorescent lamps such as BF, and halogen lamps with IR (infrared rays) cut filters.

FIG. 16 shows the wavelength and relative brightness of the light source, where the curve shown by the solid line is the characteristic of the WW fluorescent lamp, and the curves shown by the broken line are the characteristics of the WW fluorescent lamp. The characteristics of a halogen lamp with an R-cut filter are shown below. In the case of a fluorescent lamp, there is an Hg bright line spectrum, and the cyan side MTF value decreases due to the influence of the bright line spectrum particularly in the range of 400 to 450 nm. Therefore, the big problem is how to select the two points ◯ and ◯ in Fig. 14.

FIG. 17 is a diagram showing changes in the MTF value obtained from the CCD output when the dichroic wavelength (cutoff) is changed. As shown in the figure, the influence of the bright line spectrum is noticeable.

Table 1 shows the dichroic wavelength (cutoff) of 560n.
This is a table that outputs the chromatic aberration and MTF value due to the combination of the light source and the achromatic lens when set to m, and determines the pixel shift.

Table 1 According to Table 1, the pixel shift indicated by ◎ was at the maximum, which was as small as around one image, and good results were obtained. That is, in the case of a fluorescent light source, the dichroic light source has a cutoff wavelength of 560 nm.
, to remove the influence of the Hg bright line spectrum, and further set the vicinity of the g-line (436 nm) as the 0 point in FIG.
When selecting the vicinity of the C line (656 nm) as the 0 point, M
Good results were obtained with TF values of 32% for cyan and 33% for red.

Similarly, when using a halogen lamp with an infrared cut filter, when the 0 point was selected near the G-line and the 0 point was selected near the C-line, the MTF values were 32% for cyan and 33% for red, giving good results. .

(Example 2) When performing three-color separation into red/green/blue, two types of light sources are used as described above. FIG. 18 is a chromatic aberration characteristic diagram and a relative luminance characteristic diagram of light source light during three-color separation by an achromatic lens.

Table 2 shows the results obtained by setting the chromatic aberration due to the combination of the light source and the achromatic lens, measuring the MTF, and determining the pixel shift in the same manner as in the above-mentioned Table 1.

As shown in Table 2 and above and Examples 1 and 2, in this example,
The 0 point was fixed at the C line, but when cyan (or blue) is used as one of the colors during color separation, (1) When using a fluorescent lamp, the 0 point is set to 400 to 480 nm, and the ■ point is set to 620 nm.
~700 nm and the peak of the bright line spectrum is below the set wavelength of the 0 point to obtain good results.

(I[) When using a halogen lamp, set 0 to 400.
It is possible to use a material with a wavelength of 620 to 700 nm and a point ① of 620 to 700 nm.

The above (I) and (n) can be summarized as shown in FIG. 19. In this way, along with the light source settings, by setting the 0 points and 0 points within the ■ point ■ point setting area in Figure 19 and at locations where there is no peak in the bright line spectrum, images with less chromatic aberration and excellent resolution can be obtained. Obtainable.

〔Effect of the invention〕

As explained above, the present invention relates to an image processing device that uses a plurality of one-dimensional image sensors and has an imaging system that photoelectrically converts color-separated light including cyan or blue light.
This study clarified the optimal settings for the lens/light source for an imaging system that suppresses the occurrence of color ghosts and provides a high MTF value.

As a result of using the present invention, high-speed imaging (l ms/1ine
(below), pixel shift amount reduction between each CCD (1/4 pel)
, it has become possible to create a system that achieves high MTF (about 30% each).

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a color image processing device including a color image reading device according to the present invention, FIG. 2 is a block diagram of a color copying machine to which the present invention is applied, and FIG. 3 is a transmittance characteristic diagram of a dichroic mirror. Figure 4 is an emission spectrum characteristic diagram of the light source, Figure 5 is a spectral characteristic diagram of CCD, Figure 6 is a mosaic diagram showing an example of an image with color ghosts, Figure 7 is an enlarged explanatory diagram of color ghosts, Figure 8 is COD
FIG. 9 is a cross-sectional view of the optical information conversion unit, FIG. 12 is an optical path diagram of the optical information conversion unit of the three-color decoding device. FIG. 13 is an optical path diagram explaining chromatic aberration. FIG. 14 is a chromatic aberration diagram of an achromatic lens and an apochromatic lens. is an optical path diagram explaining magnification aberration, Fig. 16 is a luminance characteristic diagram of the light source, Fig. 17 is an MTF characteristic diagram of CCD output, Fig. 18 is a chromatic aberration characteristic diagram of three-color separation by an achromatic lens, and Fig. 19 is a diagram A diagram explaining the wavelength setting of a light source, FIG. 20 is a configuration diagram of a conventional color image reading device, FIG. 21, and FIG.
FIG. 2 is a diagram showing displacement of the CCD mounting position due to temperature change, and FIG. 23 is a configuration diagram showing another example of a conventional color image reading device. lO... Optical information conversion unit 11... Lens 12, 120... Color separation prism 13... Dichroic mirror 14R, 14C, 15R, 15B, 15G... CC
D (line image sensor)

Claims (1)

[Scope of Claims] (1) A color separation means is provided in the imaging optical path in which the document surface is irradiated with a light source that moves relative to the document surface and the light reflected from the document surface is imaged by a lens, and a plurality of color images are formed. 1. A color image reading device that forms an image and photoelectrically converts each color image into a plurality of color signals using an individual line-shaped image sensor, wherein the lens is an achromatic lens. (2) The color image reading device according to claim 1, wherein the achromatic lens has one of its reference lights selected within a range of 620 to 700 nm. (3) The color image reading device according to claim 1 or 2, characterized in that the color separation means is used so that the mounting positioning accuracy of each of the plurality of image sensors is within one pixel. (4) When imaging using cyan light as one of the color separation lights by the color separation means, providing another reference light of the achromatic lens within the range of 440 to 540 nm;
The color image reading device according to any one of claims 1 to 3, characterized in that a light source having no spectral peak at a wavelength of 500 nm or less is used. (5) When imaging using cyan light as one of the color separation lights by the color separation means, providing another reference light of the achromatic lens within the range of 440 to 480 nm;
5. The color image reading device according to claim 4, wherein the light source has a sharp spectral peak of 500 nm or less that is below the reference wavelength. (6) In the case of imaging using cyan light as one of the color-separated lights by the color separation means, the other reference wavelength of the achromatic lens is set within the range of 400 to 480 nm. The color image reading device according to any one of the ranges 1 to 3.