JPH03202873A - Full-color copying machine - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a full-color copying machine.

[Conventional technology]

For example, in an electrostatic transfer copying machine as an electrophotographic device,
2. Description of the Related Art A full-color copying machine that reproduces the colors of an original image (hereinafter referred to as an original image) using color developers of yellow, magenta, and cyan has been put into practical use. With this full-color copying machine, most of the original images that are copied are
Alternatively, it is a halftone part, and it is required to be able to reproduce such rough parts and halftone parts with colors and density that are faithful to the original. For this reason, compared to black-and-white copying machines whose original images are line drawings such as characters drawn in black on a white background, full-color copying machines perform image processing that emphasizes fidelity to density changes, that is, gradation. In particular, the reproducibility of the halftone portion is improved, thereby making it possible to form a copy image that is more faithful to the color original image.

[Problem to be solved by the invention]

However, full-color copying machines such as those described above have a problem in that line drawings such as black characters drawn in a color original image tend to become unclear. That is, in the full-color copying machine as described above, the color black is reproduced by strictly balancing the concentrations of the three types of color developers, yellow, magenta, and cyan. However, in reality,
It is extremely difficult to reproduce black by controlling this density balance, and black is usually identified as black having some hue, such as red black or blue black. For this reason, black line drawings such as letters lack sharpness compared to the original drawing. In addition, in order to improve the gradation, for example, a process is performed in which the reflected light from the original image is transmitted through a special slit-shaped screen and incident on the photoreceptor, but in this case, line drawings such as characters are Since the image is reproduced as a series of dots, the sharpness also decreases.

The present invention has been made in view of the above, and an object of the present invention is to reproduce a full color image that can more clearly reproduce line drawings such as black characters in a color image, as well as suppress deterioration of image quality in the color image area as much as possible. The purpose is to provide copying machines.

[Means to solve the problem]

Therefore, the full color copying machine according to claim 1 of the present invention is as follows:
A full-color copying machine that is equipped with a color developer tank that stores color developers and a copy image formation control means that controls the color developer to form a full-color copy image of an original image, which stores black developer. The apparatus further includes a black developing tank and high-density image extracting means for extracting an image darker than a set density from the original image, and further includes converting the extracted image by the high-density image extracting means into a black copy image using the black developer. The black copy image is formed as a full-color copy image, and the copy image formation control means controls so as to superimpose this black copy image on the full-color copy image.

Further, the full-color copying machine according to claim 2 is the full-color copying machine according to claim 1, in which the above-mentioned image is generated according to an electrostatic latent image formed on the photoconductor by the reflected light of the light irradiated on the original image. While the copy image formation control means controls so that a full color copy image and a black copy image are sequentially formed,
Filter selection means is further provided for positioning a correction filter on the incident path of light from the original image to the photoreceptor when forming the black copy image, and the correction filter is configured to select the original image having the same density and different hues. It is characterized by having a light transmission characteristic that makes the potentials on the photoreceptor substantially the same in the incident state of each reflected light from the photoreceptor.

[For production]

According to the structure of the full-color copying machine according to claim 1 above,
By setting in advance a density level at which a dense black line drawing, such as black text, and a color image area consisting of a lighter hue can be almost distinguished, an image darker than this set density is formed from the extracted image. The black copy image is formed as a copy image that substantially corresponds to line drawings such as black characters in the original image. Then, this black copy image is superimposed on the full-color copy image, and therefore, the black developer is superimposed almost corresponding to line drawings such as black characters in the original image. As a result, a copy image with clearer line drawings such as characters can be obtained. Further, in this case, since the image area whose density is lower than the set density is almost maintained as a full-color copy image, a copy image is formed in which deterioration in image quality in the color image area is suppressed.

According to the structure of the full-color copying machine as set forth in claim 2, a black copy image is formed by positioning the correction filter on the incident path of light from the original image to the photoreceptor. In other words,
The spectral sensitivity of the photoreceptor and the energy distribution for each wavelength in the light source that irradiates the original image are usually not uniform, so the color image area extracted as an image area darker than the set density is not the same as the original image. For example, if the black developer is superimposed on the red side and the front side, it will cause a difference in the density level of the original image extracted on the red side and the front side. A different copy image is formed. Therefore, as mentioned above, by providing a correction filter for the spectral sensitivity of the photoreceptor, the energy distribution of the light source, etc., the black developer can be superimposed on the red side and the front side based on almost the same original image density level. As a result, a copy image whose balance with respect to the color image is more faithful to the original image is formed.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 to 8.

As shown in FIG. 1, the full-color copying machine according to this embodiment has a transparent original f2 holder 1 on the top surface, and an exposure optical system 2 is disposed below this original holder 1. has been done. The exposure optical system 2 includes two light source lamps 2a and 2a' that irradiate light onto the original 3 placed on the original placing table 1;
The reflected light from the original 3 is, for example, as shown by the - dotted chain line.
A plurality of reflecting mirrors 2b that guide the light onto the belt-shaped photoreceptor 4, an imaging lens 2c disposed on the optical path, and a color separation filter 2d having color filters of three primary colors (red, green, and blue). It is equipped with Further, a special screen 5 for improving gradation is disposed in a position close to the photoreceptor 4, and this special screen 5 is located between the insertion position in the optical path and the removal position shown by the broken line in the figure. Installations that can be switched are in a state.

Further, below the exposure optical system 2, there are provided four developing tanks 6 to 9, the above-mentioned belt-shaped photoreceptor 4, and two size-specific paper feed force rollers 11 and 12. . Furthermore, a belt-shaped intermediate transfer member 13 is provided on the paper output direction side of the photoreceptor 4;
A conveyor belt) 14 and a fixing device 15 are arranged in this order.

The photoreceptor 4 is rotationally driven by the first and twentieth rollers 16 and 17. A charger 18 for charging the photoreceptor 4 is disposed around the outer periphery of the photoreceptor 4 near the 10th line 16 on the side where the reflected light from the exposure optical system 2 is irradiated. A cleaning device 19 for removing toner remaining on the photoreceptor 4 is disposed below the photoreceptor 4 in the vicinity of the charger 18 .

Also, near the center above the photoreceptor 4, the photoreceptor 4
The developer tanks 6 to 9 described above are arranged in a non-contact state, and the three color developer tanks 6 to 8 contain yellow, magenta, and cyan color developers, and a black developer. The tanks 9 each contain a developer containing a black pigment such as carbon black.

On the other hand, the intermediate transfer body 13 includes three rollers 21 and 22.
- Rotationally driven by 23. The 20th-ra 17 side of the photoconductor 4 is pressed against one side of the intermediate transfer body 13, and a transfer charger 2 is attached to the back side of the intermediate transfer body 13 at the portion where the photoconductor 4 is pressed.
Further, a transfer charger 25 and a separation charger 26 are respectively arranged on the lower surface side of the intermediate transfer body 13.

Although not shown, the above-mentioned full-color copying machine is further provided with a control device having a built-in microcomputer or the like as a copy image formation control means, and the light source is controlled in accordance with a command from this control device. Lamp 2a/2a+
A lamp light amount control device (high-density image extraction means) that controls the voltage applied to the lamp, a filter setting actuator (filter selection device) that positions any of the color filters in the color separation filter 2d, and the correction filter described later on the optical path. means) are provided.

Next, the operation of the full color copying machine controlled by the above control device will be explained.

First, scanning is performed three times while the original 3 placed on the original placing table 1 is irradiated with light from the light source lamps 2a and 21. As a result, the reflected light from the original 3 via the reflecting mirrors 2b is separated into red, green, and
The blue color components are sequentially separated. Light for each color component for each scan is irradiated onto the photoreceptor 4, which is uniformly charged by the charger 18, and the photoreceptor 4 is exposed. As a result, electrostatic latent images for each color component corresponding to the image of the original document 3 are sequentially formed on the photoreceptor 4 . Note that during a scanning operation to obtain a latent image corresponding to blue light, the two light source lamps 2a and 2a+ are turned on at the same time because the sensitivity of the photoreceptor 4 to blue light is lower than that of other colors.

Each of the above-mentioned electrostatic latent images is generated by each developer in a portion of the color separation filter 2d facing the color developer tanks 6 to 8 having developers of each color of yellow, magenta, and cyan, which are complementary colors of each color filter. It is developed and visualized to become a toner image.

These toner images for each color component are transferred to a transfer charger 24.
The images are transferred to the intermediate transfer body 13 in order.

In this way, a full-color toner image is formed by sequentially overlapping toner images for each color component.

In the embodiment described above, a process is further performed in which an image corresponding to the black image of the document 3 is superimposed on the full-color toner image. That is, the original 3 placed on the original placing table l is scanned again while being irradiated with the light source lamps 2a and 2a', and the image is transmitted through the imaging lens 2C and the color separation filter 2d by the reflecting mirror 2b... The emitted light forms an electrostatic latent image on the photoreceptor 4, which is uniformly charged again by the charger 18. At this time, within the color separation filter 2d, a correction filter, which will be described later, is set by the filter setting operation device so as to be located on the optical path. The function of this correction filter will be explained later, but it is designed to allow light of all wavelengths in the visible range to pass through. As a result, the electrostatic latent image is an image corresponding to the black and white density of the document 3, more specifically, an electrostatic latent image corresponding to an image or line having a predetermined document density or higher is formed. However, the details will be explained later.

The latent image in the above is a black developer tank 9 containing black developer.
After being developed and visualized with a developer in the image forming apparatus, the image is transferred by the transfer charger 24 to the intermediate transfer member I3 on which the above-mentioned full-color image is placed. As a result, yellow, magenta, cyan, and black component toner images are superimposed on the intermediate transfer body 13.

Next, the toner image on the intermediate transfer member 13 is transferred by the transfer charger 25 when the transfer paper 27 fed from one of the paper feed cassettes 11 and 12 is brought into close contact with the lower surface of the intermediate transfer member 13. , is transferred onto the transfer paper 27. Thereafter, the transfer paper 27 is separated from the intermediate transfer body 13 by the separation charger 26, and is sent to the fixing device 15 via the conveyor belt 14, where the image transferred to the transfer paper 27 is fixed, forming a full-color copy image. It is formed.

As described above, in the embodiment described above, a process of superimposing a black toner image on a full-color toner image is performed, which improves the sharpness of line drawings such as black characters in the full-color image. In other words, in a full-color toner image, by layering the black developer itself on top of the black area formed by the balance of yellow, magenta, and cyan color developers, line drawings such as black characters as shown above can be created. , will be reproduced more clearly.

In this case, if the black developer unnecessarily overlaps with the color areas of the original image, the overall image quality will deteriorate. In the above embodiment, when forming a black image, the lamp light amount control device performs control to increase the amount of light irradiated from the light source lamps 2a and 21 to the original image. As a result, the intensity of the reflected light from the color area outside the black coat in the original image increases, and as a result, the potential of the color area on the photoreceptor 4 decreases to a non-development potential. As a result, an electrostatic latent image is formed on the photoreceptor 4 corresponding to an extraction area that is almost limited to a line drawing area such as a black character. Note that if the amount of light is significantly increased, stray light in the optical system will cause a drop in potential even for thin black letters and the like. Therefore, in the above embodiment, when scanning to obtain the black image, for example, as shown in FIG. 2, in the density display where white is 0 and black is 2.0, the black and white density of the original is 0. The light source lamp 2a and
21 light amounts are set. As a result, black toner does not overlap unnecessarily in color image areas drawn with single-color inks of yellow, magenta, cyan, blue, green, and red, which are generally used in printing, and the black toner of characters, etc. The black toner adheres to the line drawings, resulting in a good graphic image.

Furthermore, as described above, even in the operation of increasing the light intensity of the light source lamps 2a, 2a, it is difficult to extract an image that is completely limited to only line drawings such as black characters from the color image area, and The black developer overlaps to some extent in the area as well. In this case, the balance between areas with different hues, for example, the balance state in the original image between the red side and the front side, is maintained as much as possible.
As mentioned above, when scanning to obtain a black image,
A correction filter is set in the color separation filter 2d.

In other words, the color separation filter 2d does not allow any of the three primary colors (red, green, and blue) to pass through the color filter, so that a black and white image corresponding to the density of the document 3 can be formed.

However, the spectral sensitivity of the photoconductor 4 and the light source lamp 2a
- In the spectral energy distribution of 2a+, there are inherent variations for each wavelength in the visible range. For example, the photoreceptor 4 has a spectral sensitivity characteristic as shown in FIG. Depending on the voltage applied, it has energy radiation characteristics as shown in FIG. 6, for example. For these reasons, if correction is not performed between each wavelength, for example, black developer will be superimposed at different density levels for each dark color area on the red side and the front side, which will cause damage to the original image. On the other hand, a color copy image with a different balance is formed.

Therefore, in the above embodiment, when the original 3 is monotone (reflection in the visible range is uniform) as shown in FIG. 7, the potential on the photoreceptor 4 at each wavelength is approximately the same. A correction filter having such spectral transmission characteristics is set in the color separation filter 2d. In other words, correction is made such that [spectral sensitivity of photoreceptor 4] x [spectral energy distribution of light source lamps 2a and 2a'] x [spectral transmittance of correction filter] is approximately constant over the wavelength range in the visible region. A filter is set, and in the above case, for example, a correction filter having spectral transmittance characteristics as shown in FIG. 8 is used. This makes it possible to obtain a well-balanced full-color copy image even if there is a color image area with high density in the original image. Note that by using the correction filter as described above, the energy of short wavelengths is reduced, so when creating a black image, the light source lamps 2a and 21 are turned on simultaneously, similar to when creating the yellow image.

Figure 2 shows an example of test results regarding the reproducibility of copy density with respect to changes in original density, that is, gradation. The results of the gradation test by the conventional copying process, in which (B) is when the above-mentioned special screen for improving gradation 5 is used, and (C) is the result when the above-mentioned special screen for improving gradation is used. 5 is not used. This special screen 5 for improving gradation is shown in FIG.
), 100 to 133 slits with a width of 50 to 60 um are provided per inch.

Then, as shown in FIG. 3 (b), 1.0
By irradiating the photoreceptor 4 with the reflected light from the document 3 through the special screen 5 for improving gradation, which is set with a gap of ~1.8 mm, an ideal curve (Fig. A copy image with improved gradation similar to medium and D) is obtained. However, these (B) and (C)
In either case, if the original density is about 1.0 or higher,
This does not cause any change in copy density, and therefore it is not possible to produce gradation on the black side. Therefore, by superimposing black colors as in the above example, the characteristics of (A) are further overlapped with the above (B) and (C), so that black is clearly reproduced. . In this case, as described above, the carbon blank added as a pigment to the black developer has very strong hiding power and provides an ideal black color. Therefore, even if a small amount of black developer is attached to a line image that is reproduced in full color yellow, magenta, and cyan, a sufficiently sharp line image will be reproduced. The black developer is controlled not to adhere to areas where the document density is 0.6 or less, thereby suppressing deterioration in image quality in color image areas. In this way, by obtaining a color image with clear characters, etc.,
It can be configured as a copying machine suitable for office use where reproduction of characters and the like is important.

Further, as mentioned above, an image obtained by the screen method emphasizing gradation using the special screen 5 for improving gradation is shown in FIG.
The characters in the original picture shown in a) become dot-like as shown in FIG. 4(b), which also causes a decrease in sharpness. Therefore, by superimposing the black images together with such gradation improvement processing, it is possible to obtain a copied image in which both the color image and the black characters are clearer.

In addition, by providing a mode changeover switch for the user to select whether or not to superimpose black as described above, and also by allowing the user to select a combination with the mode selection of whether or not to use the screen method. , the copier configuration is suitable for a variety of uses. Further, in the above embodiment, the black and white density of the original is 0.6.
In order to form a black image at a level that does not reproduce the following, the amount of lamp light was changed. You can also.

〔Effect of the invention〕

As described above, the full-color copying machine according to claim 1 of the present invention is provided with a color developer tank and a black developer tank respectively accommodating a color developer and a black developer. a high-density image extracting means for extracting an image; forming the extracted image as a black copy image using a black developer;
The apparatus is configured to include a copy image formation control means for controlling the black copy image to be superimposed on the full-color copy image formed using the color developer.

As a result, for dense black line drawings such as black letters,
By setting a density level in advance that allows color image areas that are composed of hues with lower density to be almost discernible, color image areas that are lighter than this set density are maintained as full-color copies, and black characters, etc. in the original image are maintained. A copy image is formed in which black developer is superimposed, approximately corresponding to the line drawing. As a result, it is possible to suppress deterioration in image quality in the color image area and improve the clarity of line drawings such as black characters.

Further, the full-color copying machine according to claim 2 is provided with a correction filter that makes the potentials on the photoreceptor substantially the same in the incident state of each reflected light from the original image having the same density and different hue, and When forming the above black copy image,
This configuration further includes filter selection means for positioning the correction filter on the incident path of light from the original image to the photoreceptor.

As a result, even if the spectral sensitivity of the photoconductor or the energy distribution for each wavelength in the light source that irradiates the original image is not uniform, when black developer is superimposed on a color image area darker than the set density, For example, the balance between the red side and the dorsal side is not impaired, and as a result, it is possible to form a copy image that is more faithful to the original image.

[Brief explanation of drawings]

1 to 8 show one embodiment of the present invention. FIG. 1 is a schematic diagram showing the configuration of a full-color copying machine, viewed from the side. FIG. 2 is a graph showing an example of each gradation test result when forming a black image, forming a full color image, and performing gradation improvement processing when forming a full color image. FIG. 3(a) is a perspective view of a special screen for improving gradation. FIGS. 3 to 3) are explanatory diagrams of an image forming method when using the above-mentioned special screen for improving gradation. FIGS. 4(a) and 4(b) are explanatory diagrams of a copy image obtained when the above-mentioned gradation improvement processing is performed, in which FIG. 4(a) shows the original text, and FIG. 4(5) shows the original This is a copy image of characters. FIG. 5 is a graph showing the spectral sensitivity of the photoreceptor, which is superior to ○PC (organic photoconductor). FIG. 6 is a graph showing the spectral energy distribution of a halogen lamp used as a light source lamp. FIG. 7 is a graph showing the spectral reflectance of a monotone original. FIG. 8 is a graph showing an example of the spectral transmittance of a correction filter used when forming a black image. 2a and 21 are light source lamps, 2d is a color separation filter, 4 is a photoreceptor, 6 to 8 are color developing tanks, and 9 is a black developing tank. Attachment quality □ Fig. 3 (a) Fig. S (b) Fig. Akane (a) (b) Fig. At (nm) Fig. Wavelength (nm)

Claims (1)

[Scope of Claims] 1. A full-color copying machine equipped with a color developer tank containing color developers and a copy image formation control means for controlling the color developers to form a full-color copy image of an original image. The apparatus further includes a black developer tank containing a black developer, and high-density image extracting means for extracting an image darker than a set density from the original image, and further includes an image extracted by the high-density image extracting means. A full-color copying machine characterized in that the copy image formation control means controls to form a black copy image using the black developer and superimpose the black copy image on the full-color copy image. 2. The copy image formation control means controls so that the full color copy image and the black copy image are sequentially formed in accordance with the electrostatic latent image formed on the photoreceptor by the reflected light of the light irradiated on the original image. , further provided with filter selection means for positioning a correction filter on the incident path of light from the original image to the photoreceptor when forming the black copy image, and the correction filters have the same density and different hues. 2. The full-color copying machine according to claim 1, wherein the full-color copying machine has a light transmission characteristic that makes the potentials on the photoreceptor substantially the same in each incident state of each reflected light from the original image.