JPH0785269A - Image forming device - Google Patents

Abstract

PURPOSE:To make it possible to reproduce a faithful original without depending upon the reproducing capacity of a printer by converting a picture signal into a density signal based upon its size. CONSTITUTION:In a color scanner part, a luminance signal for an original picture is obtained by a CCD 51 and compensated by a shading compensating circuit 53. The compensated luminance signal is converted into a density signal by a LOG conversion circuit 54. When a reading signal is larger than a signal corresponding to maximum density to be reproduced by a printer part, the circuit 54 converts the reading signal into a density signal whose recording density difference can be judged by the printer part in accordance with the density area judgement of a density/color reproducing judging part 60 without converting the reading signal into a density signal proportional to the density of the original. When the reading signal is less than the signal corresponding to the maximum density to be reproduced by the printer part, the reading signal is converted into the density signal proportional to the density of the original.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus in which an original is read by a scanner unit, a predetermined image processing is performed, and then an image is formed on a recording material by a printer unit.

More specifically, according to the present invention, a scanner section for photoelectrically converting an original on a platen by a photoelectric conversion element or the like to convert it into a digital signal and performing image processing, and a digital image signal to be received and recorded. The present invention can be applied to an image forming apparatus provided with a printer unit for recording an image on a material, for example, an electrophotographic image forming apparatus, particularly an electrophotographic photosensitive member such as an image carrier having a plurality of different colors. It is suitable for a color electrophotographic copying apparatus that forms an image and sequentially transfers the image to the same recording material, or an image forming apparatus that includes a scanner section and an electrophotographic printer section.

[0003]

2. Description of the Related Art In recent copying machines, especially color copying machines, digitization is progressing because of the excellent color reproducibility of color originals. This digitization means CCD
The color-separated light image of the original is photoelectrically converted by a scanner using a solid-state image sensor represented by, and the obtained analog image signal is digitally converted, and this is input to a digital image data processing circuit for color processing, After that, it is output using a full-color printer.

Taking a CCD, which is a solid-state image sensor, as an example,
It is possible to read even a standard document with a maximum document density of 2.2.

On the other hand, what is read as a document by a scanner is a copy made by printing, a silver salt, an electrophotographic copying machine or the like. Among these, originals such as prints and silver salts have maximum image densities of 2.0 or more.

[0006]

However, from the point of view of the density color reproduction capability of a full-color printer, the reproducible density of the electrophotographic printer is 1.5 to 1.7 at present. Moreover, an electrophotographic printer sometimes uses static electricity as its basic principle, and the reproduced density fluctuates over time.

On the other hand, regarding the reproduction of a silver salt type color image, although satisfactory characteristics are seen in terms of the maximum reproduction density, the reproduction density also changes due to temperature changes.

In any case, the reading capability of the color scanner is satisfied with respect to the current full-color original, but the reproduction capability on the printer side is not satisfied.

For example, when a gray scale having a maximum density of 2.0 is read by a scanner having a maximum reading density of 2.0 and recorded by a printer having a maximum reproduction density of 1.5, the reproduced image has a ratio of 1.5 / 2.0. The whole becomes thin. Also, if this copy is reproduced as an original, the reproduction is made thinner, and if this operation is repeated, it becomes completely different from the original.

Therefore, if the maximum density that can be reproduced by the printer is to be reproduced with the same density as that of the original, the density will be all 1.5 at an image density of 1.5 or more. In this state, when the reproduced image is repeatedly reproduced as an original, the portion with an image density of 1.5 or less is reproduced, but the first reproduced image itself is not practical.

For this reason, when a printer having a maximum reproduction density of 1.5 is used, a specific process is performed on the image signal read by the scanner.

That is, the CCD output signal, which is a signal for reading the original image, is a signal proportional to the reflected light from the original, and this is converted into a signal proportional to the density (hereinafter, LO).
In this case, the LOG conversion table is operated so that the signal slightly thinner than the document density of 1.5 is output more thinly. Moreover, the contents of this table are fixed and used.

In this way, the original is faithfully reproduced in the highlight area that strongly affects the human visual sense, and is reproduced to the extent that the density change is visible in the high density portion that weakly affects the human visual sense. By doing so, I try not to pose a problem in practice.

However, in the above-mentioned LOG conversion processing, even if the maximum density of the original is 1.5, there is a disadvantage that the density of 1.5 is not reproduced by the printer, and it is basically necessary to faithfully reproduce the original. This is not ideal for a copying machine.

Further, the human visual sensitivity is
As described above, in the case of a color image, the luminosity to the high density portion is much stronger than that in the case of black, and improvement of the above processing technique is desired.

Therefore, in view of the above points, an object of the present invention is to provide an image forming apparatus capable of faithful reproduction of an original by improving the image processing technique without depending on the reproduction capability of the printer. Especially.

[0017]

In order to achieve such an object, the present invention is an image forming method in which an original is read by a scanner unit, a predetermined image processing is performed, and then an image is formed on a recording material by a printer unit. In the apparatus, when the read signal proportional to the reflected light amount of the document is larger than the signal corresponding to the maximum density that can be reproduced by the printer unit, the read signal is not converted into a density signal proportional to the density of the document. First density converting means for converting a density signal capable of discriminating a difference in recording density in the printer unit, and a reading signal proportional to the reflected light amount of the original document is equal to or less than a signal corresponding to the maximum density reproducible in the printer unit. In some cases, a second density conversion means for converting the read signal into a density signal proportional to the density of the original is provided. In addition, it is also possible to provide a means for measuring the maximum recording density by the printer section and operate the first and second density converting means based on the maximum recording density.

In the scanner section, the original is read by a photoelectric conversion element as color separation information corresponding to blue, green, and red light, digitally converted and subjected to predetermined image processing, and the printer section records the recording material. In forming a full-color image on the above, it is preferable to provide the first and second density conversion means for the color separation information corresponding to each of the blue, green, and red. In this case, in addition, a control means for changing the coefficient of each color processing circuit for masking, undercolor removal, and inking based on the processing mode of the first and second density conversion means is provided. It is suitable. In addition, means for measuring the black single-color maximum density and reproduction color space information from each of yellow, magenta, and cyan recorded by the printer unit is provided, and the black single-color maximum density and yellow, magenta,
It is also possible to form a full-color image based on the reproduction color space information from each cyan.

[0019]

With the above arrangement of the present invention, when the image signal output in proportion to the reflected light amount of the original image is converted into the density signal in proportion to the original density, the signal proportional to the reflected light amount can be reproduced by the printer section. If it is larger than the signal corresponding to the maximum density, it is not converted into a signal proportional to the original density, but a density area of the image signal is provided for density conversion that allows the density difference to be discriminated when reproduced on the printer unit. If the proportional signal includes a signal corresponding to the maximum density reproducible by the printer unit and is smaller than this, the image signal is converted into a density signal proportional to the original density.

When the present invention is applied to a color image forming apparatus, a signal proportional to the amount of reflected light of each of blue, green and red light is more than a signal corresponding to the maximum density reproducible in the printer section. If it is large, a density area of the image signal that does not convert to a signal proportional to the original density and that allows density difference discrimination when reproducing in the printer section is provided, and a signal proportional to the amount of reflected light is reproduced in the printer section. If the signal contains a signal corresponding to the maximum possible density and is smaller than this, the image signal is converted into a density signal proportional to the document density. Further, by changing the coefficients of the respective color processing circuits for masking, undercolor removal, and inking based on the above conversion processing mode, practically sufficient image formation can be performed without particularly increasing the performance of the printer section.

[0021]

Embodiments of the present invention will now be described in detail with reference to the drawings.

Embodiment 1 FIG. 2 shows the overall construction of a color copying apparatus to which the present invention is applied. In this figure, an image signal is converted into laser light through a laser driver and a laser light source (neither is shown), and the laser light is converted into polygon mirror 1 and mirror 2.
Is reflected by and is irradiated onto the photosensitive drum 4.

The photosensitive drum 4 on which a latent image is formed by laser irradiation rotates in the direction of the arrow shown in the figure. Then,
The rotary developing device 3 develops each color. (Fig. 2
Indicates the case of development with yellow. )on the other hand,
The transfer sheet is wound around the transfer drum 5 and rotated once in the order of Y (yellow), M (magenta), C (cyan), and Bk (black), and the transfer is completed by rotating four times in total. When the transfer is completed, the transfer paper is separated from the transfer drum 5 and fixed by a pair of fixing rollers (not shown) to complete a color image print.

The near-infrared light emitting LED 8 and the light receiving element (hereinafter referred to as a sensor) 9 are for reading the toner image density on the photosensitive drum described later.

FIG. 3 shows a digital image signal processing circuit of a color reading scanner section for reading a color image and obtaining a color gradation image signal, and a digital signal processing circuit of a color printer section following the digital image signal processing circuit. In this figure, the luminance signal of the original image is obtained by the CCD 51, and the luminance signal is A / D.
The conversion circuit 52 converts the signal into a digital luminance signal.

The obtained luminance signal is corrected by the shading correction circuit 53 which corrects the sensitivity variations of the individual CCD elements. The corrected luminance signal is converted into a density signal by the LOG conversion circuit 54.

Y (yellow) thus obtained,
Masking circuit 5 for M (magenta) and C (cyan) signals
5, Bk (black) generation and UCR (undercolor removal) circuit 56, and become Y, M, C and Bk signals. Further, it is sent to the color printer section through the gradation characteristic (gamma characteristic) correction table 57 of the image output signal of the color scanner section.

The density / color reproduction judging section 60 judges the density area peculiar to this embodiment, which will be described later in detail.

In the color printer section, an LUT consisting of a correction table generated by the calculation result described later.
It is corrected by (lookup table) 58 and sent to the laser drive circuit 59.

In the laser drive circuit 59, the LUT 58
The signal passed through is modulated at the laser lighting time, for example, and the laser is driven. Then, a laser scan forms a latent image having gradation characteristics represented by dot area changes on the photosensitive drum (see FIG. 2), and a gradation image is obtained through the processes of development, transfer, and fixing. .

A test pattern generator 28 (see FIG. 2) for forming a test pattern image on the photosensitive drum 4 is provided in a part of the digital image processing circuit of the color scanner section or the color printer section.

Further, a specific pattern is formed on the image carrier,
The LED 8 is turned on at an appropriate timing to illuminate the toner image on the photosensitive drum 4, and the reflected light is measured by the sensor 9, and the measured value is compared with a preset reference value to determine the toner replenishment amount. By supplying the toner, the toner concentration in the developing machine can be kept constant.

Usually, when a specific pattern is formed for this purpose, it is preferably formed in the non-image area shown in FIG.

The toners used in this embodiment are yellow, magenta, cyan, and black color toners, and are formed by using styrene copolymer resin as a binder and dispersing color materials of respective colors. As for the spectral characteristics of yellow, magenta, and cyan, as shown in FIGS. 5 to 7, the reflectance of near infrared light (about 980 nm) is 80% or more. Further, in image formation using these color toners, a two-component developing method having a wide degree of freedom in terms of color purity and the like is adopted. The toner particle size used is 8 to 12 μm (by a known pulverization method). It was also confirmed that the same result was obtained for the polymerized color toner produced by the suspension polymerization method.

On the other hand, the black toner uses a one-component magnetic toner, and as shown in FIG.
The reflectance of m) is about 10%. Further, the average particle diameter and the shape were used in the same manner as the two-component toner.

The photosensitive drum 4 used in this embodiment is an OPC.
It is a photoreceptor and has a reflectance of about 40% at 960 nm.

As an exposure on the photosensitive drum at an appropriate latent image contrast with an appropriate developer density, a latent image created by gradually changing the laser lighting time for each color (pulse width modulation) is developed, and this is used as a density. It was read by the reading sensor 9 (see FIG. 2).

FIG. 9 shows that when the output range of the density reading sensor 9 is 0 to 5 (V), the density on the photosensitive drum is 0 to
The relationship in the case of 1.8 is shown. The density reading sensor 9 is of a voltage output type that is proportional to the amount of light received, and the output of the sensor 9 for the surface reflection of the photosensitive drum (when toner is not present on the photosensitive drum) is set to 2.5 (V).

As can be seen from FIG. 9, the yellow, magenta, and cyan color toners have a larger amount of reflected light as the area coverage on the photosensitive drum becomes larger than that at the time of surface reflection of the photosensitive drum 4, and the output of the sensor 9 increases. To do.

On the other hand, in the case of black toner, as the area coverage on the photosensitive drum increases, the amount of reflected light decreases and the output of the sensor 9 also decreases as compared with the surface reflection of the photosensitive drum 4.

By using these relationships, it is possible to know the actual output image state without transferring or fixing the toner on the copy paper from the sensor output even if the toner has different reflection characteristics.

The present inventor also monitored the output of the sensor 9 through a color separation filter (not shown) with a visible light source and examined the relationship with the image density. FIG. 10 shows the relationship between the density signal level and the output of the sensor 9 when the cyan toner is measured through a red color separation filter having a main wavelength of 600 nm. As can be seen from FIG. 10, when the output density is 1.0 or more, the change in the output of the sensor 9 is small, and the accuracy in this region is deteriorated. The reason is considered that visible light has a smaller amount of light penetrating into the toner layer than near-infrared light and is mainly reflected on the surface.

On the other hand, in the near infrared light, since the visible light transmittance is high and the wavelength is long, the amount of light penetrating into the toner layer is increased, so that the density at which the signal is saturated is increased to a high density. As a result, the width of the measurement range is widened and accuracy is improved.

The wavelength of the near-infrared light used is 980 nm in this embodiment, but it is 8 depending on the spectral characteristics of the toner and the photosensitive member and the characteristics of various light sources and light receiving elements.
It is preferably in the range of 00 nm to 1000 nm.

FIG. 11 shows the relationship between the density signal level and the sensor output when the developer density is changed for cyan. The density of the cyan developer is 6%, which is a proper toner-to-carrier mixing ratio with less fog and sufficient maximum image density.
Was used, and this characteristic was used as the setting for the printer of this embodiment.

On the other hand, it was found that when the developer concentration was changed to 4% and 8%, the change was as shown in FIG.
When the developer concentration is high, the gradation becomes hard, and when the developer concentration is low, the gradation becomes soft. Further, in the case of electrophotography, it is known that when the contrast potential for development is increased, a hard image is obtained, and when the contrast potential is lowered, a soft image is obtained.

Therefore, regarding cyan, a pattern image having a density signal level of 160 is formed as a specific pattern on the image carrier, and when the sensor output is higher than 4.0 V, an image having a higher contrast and a higher maximum density than the standard image is obtained. Therefore, the amount of decrease in the contrast potential was determined from the amount of deviation from 4.0 V for correction to the standard, and the image formation was performed after setting the contrast potential. On the contrary, when the sensor output is lower than 4.0V, the amount of increase in the contrast potential is determined from the deviation amount from 4.0V, and the image formation is performed after setting the contrast potential.

In this embodiment, cyan, magenta,
By storing the combination of the density signal level and the sensor output that can obtain an appropriate image in advance with one sensor 9 (see FIG. 2) for yellow and black, and performing the above control for all colors,
The maximum concentration could be stabilized.

The above control is preferably performed before the copy operation and the printout operation.

Here, the method of balancing the color of the full-color image will be described in detail.

In order to obtain color balance in a full-color image, for example, conditions are set so that the same density as the original image density is reproduced on the photosensitive drum in all density areas from the highlight area to the dark area for one color. In this case, the same setting may be made for the other colors, so only one color will be described.

In order to stably set the conditions for reproducing the same density as the original image density in all density areas from the highlight area to the dark area for a specific color, the control of this embodiment (hereinafter, gradation Control) is mainly composed of two controls. The first is control to set the maximum density set as the target value. The second is control for setting a look-up table (hereinafter referred to as LUT) so that the output image density has a linear correlation with the input image level.

In order to achieve the above two items, in the present embodiment, a predetermined image forming element is driven. At this time, in order to set the maximum density, image data PG1 is output from a fixed pattern output device (not shown) to form a latent image on the photosensitive drum 4. This image forming element is the same as the gradation control means described above, the primary charging current is I _P0 , the primary charging grid bias is V _G0 , and the developing bias is V _G0 .
_The drive is performed under each condition of _D0 (see above, FIG. 13A). As a result, the sensor 9 reads the image density of D ₁₀ (see FIG. 13B).

This is compared with the image density target value D _1R, and the primary charging current, the primary charging grid bias and the developing bias capable of controlling the developing density are respectively calculated based on the difference.

[0055]

[Equation 1] I _P1 = (D _1R −D ₁₀ ) k ₁ × I _P0 (1)

[0056]

[Formula 2] V _G1 = (D _1R −D ₁₀ ) k ₂ × V _G0 (2)

[0057]

## EQU3 ## V _D1 = (D _1R −D ₁₀ ) k ₃ × V _D0 + V ₀ (3) Here, k ₁ , k ₂ and k ₃ are constants determined in advance.

Further, V ₀ in the developing bias is a development fog correction amount.

The new I _P1 thus obtained,
According to V _G1 and V _D1 , the primary charging power source 2 shown in FIG.
9. The primary charging grid bias source 30 and the developing bias source 28 are driven. In addition, the CPU 33 that performed this calculation
Stores the calculation result (see FIG. 13D) in the rewritable nonvolatile memory 34.

Next, gradation reproduction is performed under the driving conditions I _P1 , V _G1 , and V _D1 of the image forming element whose maximum density is the target value (in this embodiment, the reproduction density is proportional to the image signal proportional to the density). Density pattern PG for LUT creation
Image formation of 1, PG2, PG3, PG4 is performed. Here, the number of patches of PG1, PG2, PG3, PG4 is L
The level required for UT creation may be used, and may be added if necessary. The patch density is read by the sensor 9 and converted into density data.

Next, the LUT creating method will be described.

Patches PG1 and P corresponding to the specific image density
For G2, PG3, and PG4, the concentration levels are set to a _1h , a _2h , a _3h , and a _4h , respectively, and the data read by the sensor 9 and converted into the concentrations are b _1h and b in the corresponding order.
_{If 2h} , b _3h , and b _4h are set, the density reproduction characteristics for the input data can be obtained. In the LUT, the data of (a _nh , b _nh ) n = 1 to 4 is replaced with (b _nh , a _nh ) n = 1 to 4 and expressed on the same coordinate.

At the time of actual image formation, the image density data is converted into the level of a _nh via the LUT in the case of b _nh , for example, and sent to the next step. The LUT is (b _nh , a _nh ) n
= 1 to 4 points may be linearly connected, but smoothing processing may be performed as necessary. The table created through these steps is set in the LUT 25 in FIG.

In the color image forming apparatus described above, the color printer section performs the maximum density adjustment and the gradation reproducibility adjustment for each color, and the color balance adjustment that is an adjustment between the colors. .

As described above, the adjustment of the image forming conditions of the printer unit is performed prior to the image formation, and the information at that time is transmitted to the color scanner unit which reads the original image image as the image processing method switching determination information.

Of the information transmitted to the color scanner section as the image processing method switching determination information, the important information is the information that conveys the density and color reproduction range of the printer section. Here, magenta, yellow, cyan, and black are respectively represented by Mmax, Cmax, and Y as reproduction maximum density information signals of respective colors.
Let max and Bkmax.

Next, these signals are converted into green, red,
The conversion is performed as follows so that it can be compared with blue and ND (neutral density: black and white).

[0068]

## EQU00004 ## Gmax = log (M) Rmax = log (C) Bmax = log (Y) Nmax = log (Bk) (4) In the color scanner section, the original image signals G, R, which have passed through the shading correction circuit. When at least one of the following conditions is satisfied for B and ND, A in FIG.
The signal proportional to the light amount of the original is converted into a signal proportional to the density by using the LOG conversion table (see FIG. 2).

[0069]

(5) G> Gmax R> Rmax B> Bmax ND> NDmax (5) Here, (G + R + B) / 3 is used as the ND signal, or the maximum signals of G, R, and B are substituted. However, it has been confirmed that there is no problem in practical use. Especially in the latter case, the determination of ND> Nmax can be omitted, and it is effective when a color scanner that reads an original with only G, R, and B outputs is used for color separation.

When the color processing thereafter including the color that cannot be reproduced by the printer unit is reproduced, the adverse effect such that the color that does not match the original is particularly emphasized and reproduced may be emphasized. Therefore, in this embodiment, the reproduced colors are determined in advance, all the colors are converted into signals in the reproducible range, and the LOG
By performing the color processing after the conversion in the optimum form, the optimum image formation is performed without the above-mentioned adverse effects.

If none of the above conditions is satisfied for the original image signals G, R, B, and ND that have passed through the shading correction circuit, the light amount of the original is calculated using the LOG conversion table of B in FIG. A signal proportional to is converted into a signal proportional to concentration.

In this case, since the color range of the read document is within the reproduction color range, the process after the LOG conversion may be performed as it is.

Embodiment 2 As the switching judgment information of the image processing method of the color scanner section, when it is possible to stably design the printer characteristics in advance, the information of the density and color reproduction range of the printer section is predetermined by the scanner section. The method of storing and using in the place of is also practical.

Here, as the previously obtained information, the reproduction maximum density information signals of magenta, yellow, cyan and black are Mmax, Cmax, Ymax and Bkmax. These signals are converted as follows so that they can be compared with green, red, blue and ND (neutral density: black and white).

[0075]

## EQU6 ## Gmax = log (M) Rmax = log (C) Bmax = log (Y) Nmax = log (Bk) (6) In the color scanner section, the original image signals G, R, which have passed through the shading correction circuit. If at least one of the following conditions is satisfied for B and ND, the LOG conversion table of A in FIG. 14 is used to convert the signal proportional to the light amount of the document into a signal proportional to the density.

[0076]

## EQU7 ## G> Gmax R> Rmax B> Bmax ND> NDmax (7) Here, (G + R + B) / 3 is used as the ND signal, or the maximum signal of G, R, B is substituted. However, it has been confirmed that there is no problem in practical use. Especially in the latter case, the determination of ND> NDmax can be omitted, and it is effective when a color scanner that reads an original with only G, R, and B outputs is used for color separation.

When the color processing thereafter is performed including the color that cannot be reproduced by the printer unit and the color is reproduced, the adverse effect such that the color that does not match the original is particularly emphasized and reproduced may be emphasized. Therefore, in this embodiment, the reproduced colors are determined in advance, all the colors are converted into signals in a reproducible range, and the LO
By performing the color processing after the G conversion in an optimum form, optimum image formation is performed without causing the above-mentioned adverse effects.

If none of the above conditions is satisfied for the original image signals G, R, B, and ND that have passed through the shading correction circuit, the light amount of the original is calculated using the LOG conversion table of B in FIG. A signal proportional to is converted into a signal proportional to concentration.

In this case, since the color range of the read document is within the reproduction color range, the process after LOG conversion may be performed as it is.

Embodiment 3 Of the information transmitted to the color scanner section as the image processing method switching determination information, the important information is the information that conveys the density and color reproduction range of the printer section. Here, magenta, yellow, cyan, and black are respectively represented by Mmax, Cmax, Ymax, and B as reproduction maximum density information signals of respective colors.
Let kmax. These signals are converted as follows so that they can be compared with green, red, blue and ND (neutral density: black and white).

[0081]

## EQU00008 ## Gmax = log (M) Rmax = log (C) Bmax = log (Y) Nmax = log (Bk) (8) In the color scanner section, the original image signals G, R, which have passed through the shading correction circuit. For B and ND, the consistency with the color reproduction range in the printer section is checked. in this case,
In order to make the color reproduction judgment more accurate, not only the maximum values of the G, R, and B signals are compared, but the comparison described below is performed.

Letting P be a read image signal composed of G, R, B, ND, etc., P is represented by a coordinate point of a color space composed of G, R, B, ND. Therefore, in this embodiment, Bmax
, Rmax, Gmax, Nmax, it is judged whether or not the read image signal P exists in the reproduction color space of the printer. If there is no original reading signal in this reproduction color space, A in FIG. The image signal is converted into a signal proportional to the density by using the LOG conversion table of.

On the other hand, when it is found that the image reading signal exists in the reproduction color space, the image signal is converted into a signal proportional to the density by using the LOG conversion table of B in FIG.

FIG. 1 shows an example of performing the above-mentioned color space discrimination method. That is, the image point P _BR determined by the Bmax-Rmax space and the B and R signals of the read image P.
And to determine if it is inside or outside the space. Hereinafter Similarly, Rmax -Gmax and P _RG, Gmax -Bmax and P _GB,
And performs the same judgment Bmax -Nmax and P _BN, Rmax -Nmax and P _RN, for Gmax -Nmax and P _GN like.

Although the switching of the LOG table has been described based on the judgments described above, particularly in the color image forming apparatus, the processing peculiar to the color image forming apparatus such as masking, UCR, and inking can also be selectively linked. Is possible.

[0086]

As described above, according to the present invention, when the signal proportional to the amount of reflected light is larger than the signal corresponding to the maximum density reproducible in the printer unit, the signal is not converted into the signal proportional to the document density, and the printer unit is not converted. In addition to providing a density area of the image signal that performs density conversion that enables density difference determination at the time of reproduction, the signal proportional to the reflected light amount includes a signal corresponding to the maximum density that can be reproduced by the printer unit and is smaller than this. Since the image signal is converted into a density signal proportional to the density of the original, it is possible to form a practically sufficient image without particularly increasing the capability of the printer unit.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an area discrimination method according to an embodiment of the present invention.

FIG. 2 is a diagram showing an overall configuration of a color copying apparatus to which the present invention is applied.

FIG. 3 is a block configuration diagram of a color scanner unit and a color printer to which the present invention is applied.

FIG. 4 is an explanatory diagram of a photosensitive drum.

FIG. 5 is a diagram showing a spectral characteristic of toner.

FIG. 6 is a diagram showing a spectral characteristic of toner.

FIG. 7 is a diagram showing a spectral characteristic of toner.

FIG. 8 is a diagram showing a spectral characteristic of toner.

FIG. 9 is a diagram showing an output characteristic of a reading sensor.

FIG. 10 is a diagram showing an output characteristic of a reading sensor.

FIG. 11 is a diagram showing an output characteristic of a reading sensor.

FIG. 12 is a diagram showing the relationship between image density and density signal level when the developer density is used as a parameter.

FIG. 13 is an explanatory diagram of gradation control according to an embodiment of the present invention.

FIG. 14 is a diagram showing input / output characteristics of a LOG conversion table.

[Explanation of symbols]

 3 Rotational Developing Device 4 Photosensitive Drum 5 Transfer Drum 33 CPU 51 CCD 53 Shading Correction Circuit 54 LOG Conversion Circuit 60 Density / Color Reproduction Judgment Section

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location G03G 15/01 S H04N 1/19 7251-5C H04N 1/04 102

Claims (5)

[Claims] 1. An image forming apparatus in which an original is read by a scanner unit, a predetermined image processing is performed, and then an image is formed on a recording material by a printer unit. In the image forming apparatus, a read signal proportional to the reflected light amount of the original is used. If the read signal is larger than the signal corresponding to the maximum density that can be reproduced by the printer unit, the read signal is converted into a density signal in which the difference in recording density in the printer unit can be discriminated without converting into a density signal proportional to the density of the original. When the read signal proportional to the reflected light amount of the original is less than or equal to the maximum density that can be reproduced by the printer unit, the read signal is converted into a density proportional to the density of the original. An image forming apparatus comprising: a second density conversion unit that converts the signal into a signal. 2. The apparatus according to claim 1, further comprising means for measuring the maximum recording density by the printer unit, and operating the first and second density converting means based on the maximum recording density. A characteristic image forming apparatus. 3. The scanner unit according to claim 1, wherein the original document is read by a photoelectric conversion element as color separation information corresponding to blue, green, and red light, digitally converted, and subjected to predetermined image processing. When forming a full-color image on the recording material, the blue,
An image forming apparatus comprising the first and second density converting means for color separation information corresponding to each of green and red. 4. The control means for changing the coefficient of each color processing circuit for masking, undercolor removal, and inking according to the processing mode of the first and second density converting means. An image forming apparatus comprising: 5. The method according to claim 3 or 4, further comprising means for measuring maximum density of a single black color recorded by the printer unit and reproduction color space information from each of yellow, magenta and cyan. An image forming apparatus, which forms a full-color image based on the maximum density of black single color and reproduction color space information from each of yellow, magenta, and cyan.