JPH0451776A - Picture forming device - Google Patents

Abstract

PURPOSE:To prevent the density of a copied picture from being made thin even when copying is implemented again from a replica by setting a maximum density of a picture recording section and a density of an original almost identically. CONSTITUTION:A digital color copying machine of this embodiment is configurated such that a coefficient for gamma correction is selected by using a mode selection signal 13 of a mode selector switch 12. In the case of copying a usual original, a coefficient for gamma correction is selected so that a picture signal with respect to a density 2.0 of an original, e.g. takes a maximum value of 255 similarly to the case with a conventional device, and when a copy is made from a replica, the coefficient for gamma correction is selected so that a picture signal with respect to a density 1.5 of an original takes a maximum value of 255. As a result, the density of a copied picture is almost kept identical for the usual original and for the replica.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital image forming apparatus such as a digital copying machine.

[Toji and I Conventionally, the image of a document is read with a scanner (reading bag M), converted into an electrical signal (digital signal), and this electrical signal drives a recording head, laser printer, etc. to form an image. Digital image forming apparatuses are well known. Digital image forming apparatuses are characterized by the ability to freely perform image processing, editing, etc., and are rapidly becoming popular in recent years. In particular, digital color copiers are superior to analog color copiers in terms of image quality such as color reproduction, and they are rapidly gaining popularity because they can use various editing functions to produce a variety of color copies. Expanding the market.

The flow of image signals on the representative side of such a conventional digital color copying machine is shown in block diagram form in FIG. The reflected light image of the original image is read by a photoelectric conversion element 1 such as a CCD and converted into an electrical signal, and further converted into digital R, G, B signals 2a, 2b, 2c by an analog-digital converter (not shown). converted. These signals are sent to the black offset and shading correction circuit 3.
The black offset processing and shading correction processing are performed here. The document reading section is provided with a standard black board and a standard white board, and the black offset and shading correction circuit 3 uses these to perform the above processing. The standard black board is a black board with an optical density of 2.0, and the value A when it is read is stored for each pixel. Further, the standard white plate is a white plate with an optical density of 0.07, and the value B obtained when this is read is stored for each pixel. Letting X be the value when the image of the original is read, it is converted as follows by the black offset and shading correction circuit 3. However, the signal is an 8-bit signal, and the maximum value is 255.

R, G, B signals 4a, 4b, 4 subjected to such processing
C is sent to a logarithmic conversion circuit 5 and converted into a logarithm, and the cyan C, magenta M, and yellow Y density signals 6a, 6b, 6
Converted to C. These signals are sent to the color processing circuit 7, where color correction processing is performed. This color correction processing is black extraction and masking processing, and when the signals input to the color processing circuit 7 are C1M and Y, in black extraction, the black component is extracted by BK = min (C, M, Y). .

Next, C' = a ++ C+ a1wM+ a ICY +
814B MM =aa+C+aixM+a*iY+
ai4BxY' =aa+C+amaM+aisY+a
i413tBK = EL41C+ a4zM+ C
Color correction is performed by masking processing to obtain 4xY+C4,Bx. The masking parameters a++ to a44 are set so that the color reproducibility is the best.

C, M, Y, B, signals 8a, 8 color-corrected in this way
b, 8c, and 8d are γ-corrected by a γ (gamma) correction circuit 9. This γ correction circuit 9 corrects the gradation characteristics of the head so that the relationship between the signal and the print density becomes linear, and also corrects the gradation characteristics of the head so that the relationship between the signal and the print density becomes linear.

Adjust the balance between Y and B. Assuming that the gradation characteristics of the head are linear, the C%M% input to the γ correction circuit 9
Corrections such as C' = a, xC M = asXM Y' = ay XY Bll = aa XBI+ are added to the Y and B signals.

The C, M, Y, BK signals 10a corrected in this way,
Cyan, magenta, yellow, and black heads lla, llb, 1 by 10b, 10c, and 10d, respectively.
Drive the lcS lid and print on recording paper to obtain a color copy.

As the head, an inkjet head, a thermal head for thermal transfer, etc. are used, and in the case of electrophotography, a semiconductor laser, an LED array, a liquid crystal shutter array, etc. are used.

Although color copies can be obtained in this way, it may be necessary to use the output color copies as originals and make copies again. In such cases, there has conventionally been a problem in that the density of the copy is very low and the appearance is poor.The reason for this is as follows.

In general, most copies of manuscripts are printed matter, and the maximum density thereof is as high as 1.8 to 2.0. For this reason, for example, the image signal when reading the maximum density of 2.0 and performing image processing is
Image processing is performed so that the maximum value of the image signal is 255. If the density at which the image signal becomes 255 is lower than this,
This is because the gradations of densities higher than this density will be destroyed, and if the density is higher than this, the 8-bit signal will essentially be left over and wasted. Therefore, the relationship between the original density and the image signal is as shown by the solid line A in FIG.

However, the characteristics of the recording head do not necessarily have the ability to reproduce density equivalent to that of printing. For example, in the case of inkjet, the recording density depends on the amount of ink ejected and the dye concentration in the ink, but the amount of ink ejected is limited by the resolution and the absorption characteristics of the recording paper, and the dye concentration in the ink is stable. Due to limitations such as gender, it is not possible to set either of them to a very high optical density.In practical use, the optical density is at most around 1.5.Therefore, the relationship between the image signal and recording density is shown in Figure 6. as shown by solid line B.

As a result, the relationship between original density and output density is shown in Figure 6.
The result will be as shown in C. However, the maximum concentration is 1
, 4 or more, a sufficiently beautiful image can be obtained as a color copy, so there is usually no problem with this. However, when the copy output is copied again as an original, the maximum density of the original is 1.5, so the maximum density of the output is about , resulting in an ugly image. .

In general, when copying a printed original, it is known that unless the image signal for densities of 18 or higher is the maximum value, the gradation of high density areas will be insufficient. , when the image signal for a density of 1.8 is set to the maximum value, if the maximum value of the recording density is not 18 or more,
The density decreases each time copying is repeated.

Therefore, an object of the present invention is to provide an image that does not cause the problem that the density of the copied image becomes very thin and the visibility becomes poor even when copying is performed again based on the copied original. An object of the present invention is to provide a forming device.

The above-mentioned object to achieve this is achieved by an image forming apparatus according to the present invention. In summary, the present invention includes an image reading section that reads an original image and converts it into an electrical image signal, an image processing section that performs signal processing on the image signal to obtain an image recording signal, and an image processing section that performs signal processing on the image signal to obtain an image recording signal. In an image forming apparatus equipped with an image recording section that performs image recording using the image recording section, when the maximum recording density of the image recording section is Dl, and the document density when the image recording signal reaches the maximum is d, then D + This is an image forming apparatus characterized by having a first mode in which D's is set such that <D*, and a second mode in which D's is set such that D,→D2.

According to a preferred embodiment of the present invention, the maximum recording density D1 of the image recording section is 1.8 or less.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a first embodiment in which the present invention is applied to a digital color copying machine, showing the flow of an image signal.The digital color copying machine of this embodiment is provided with a mode selection switch 12, The configuration is similar to that of the conventional color copying machine shown in FIG. 5 described above, except that the mode selection signal 13 from the switch 12 is input to the γ correction circuit 9 to select the γ correction coefficient. Therefore, corresponding parts will be given the same reference numerals and their explanation will be omitted unless necessary.

When copying a normal original (an original that has not been copied at -degrees), the mode selection switch 12 is set so that, for example, the image signal for an original density of 2°0 becomes the maximum value of 255, as in the past. A mode selection signal 13 for selecting a coefficient for γ correction is output, and when copying a document that has been copied twice as an original, for example, γ correction is performed so that the image signal for an original density of 15 has a maximum value of 255. It outputs a mode selection signal 13 for selecting the coefficients. Therefore, in this embodiment, when copying a normal original, the relationship between the original density and the image signal is as shown by the solid line A in FIG. 2, and the relationship between the original density and the output density is as shown by the solid line C in FIG. become that way. On the other hand, when copying the outputted copy as an original, the γ correction coefficient is changed by the signal 13 from the mode selection switch 12 as described above, so the relationship between the original density and the image signal is as shown in Figure 2. As shown in the figure, the original density becomes saturated at 1.5 as a solid line, and the relationship between the original density and the output density is
As shown in the figure, the output density is saturated at approximately 15.
It will look like E.

As a result, the density of the copied image is maintained at approximately the same density both when using a normal original and when using an original that has been copied twice, and the problem of the image becoming lighter each time copying does not occur. .

The value of the γ correction coefficient after the change is determined according to the maximum output density of the copy image, but in the case of this example, C, M, Y, B
In cases such as when the maximum output concentration of each K is different,
It is sufficient to change the coefficients of each color independently.

Next, a second embodiment of the present invention will be described with reference to FIG. 3, in which the present invention is similarly applied to a digital color copying machine. In this embodiment, the mode selection signal 13 from the mode selection switch 12 is input to the color processing circuit 7 to change the masking coefficients a to a44.

That is, when copying a normal original, for example, a mode selection signal 13 is output that sets a masking coefficient so that the image signal for an original density of 20 has a maximum value of 255, while a - degree copied original is When a copy is to be made again, for example, a mode selection signal 13 is output for changing the masking coefficient so that the image signal for an original density of 1.5 has a maximum value of 255. In this embodiment, as in the first embodiment, when a normal original is copied, the relationship between the original density and the image signal is as shown by the solid line A in FIG. 2, and the relationship between the original density and the output density is becomes like the solid line C in FIG. On the other hand, when making another copy using the outputted copy as an original, the masking coefficient is changed by the signal 13 from the mode selection switch 12 as described above, so the relationship between the original density and the image signal is as shown in FIG. The relationship between the original density and the output density is as shown by the solid line E in FIG. Therefore,
It is clear that the same effects as in the first embodiment can be obtained. Note that the other configurations are the same as those of the first embodiment, so corresponding parts are given the same reference numerals and their explanation will be omitted.

In the second embodiment described above, not only the relationship between the original density and the final image signal is made as shown by the solid line in FIG. Generally, the color reproducibility of color copies is not perfect, and the colors change slightly, but when the copied original is copied again, the changes in color may be amplified and become noticeable. However, in this embodiment, when changing the masking coefficient, it is possible to set the masking coefficient so as to correct the change in color. It has the advantage of being able to solve problems.

Next, a third embodiment of the present invention will be described. In this embodiment, the γ coefficient and the masking coefficient are not changed, but instead the standard black board used when performing black offset correction is changed to obtain the same effect as the first and second embodiments. .

FIG. 4 shows a document table and a photoelectric conversion element (CC) when the present invention is applied to digital color copying as in the above embodiment.
FIG. 3 is a schematic diagram of D (charge coupled device) seen from the back side. C
GD 16 has R, G, B reading pixels 17a, 17b, 1
7c, each with a density of 16 pixels per imm, approximately 50
They are driven by a motor (not shown) in the direction of the arrow in the drawing to receive reflected light from the document and convert it into an electrical signal. This embodiment is configured to be able to read color originals up to A3 size. Reading pixel 17a
, 17b, and 17c are arranged on the back side of the CCD 16 in FIG. 4, and are not normally visible, but are shown so as to be visible for the purpose of explanation. A semi-white Keyaki plate 18, a first standard black plate 19, and a second standard black plate 2o are attached to one end of the document table glass 15, respectively.

Next, the operation of this embodiment will be explained.

In a normal usage state in which a color copy is made from a normal original (original that has not been copied), prior to reading the original, the CCD 16 reads the first standard black board 19 and outputs the COD output A for each pixel. Remember. The density of the first standard black board 19 is 2.0, then the density is 00
7 standard white plate 18 is read and its output B is stored for each pixel. Assuming that the value when an actual document is read is X, the black offset and shading correction circuit 3 converts it as follows, and then image processing is performed.

Therefore, if the original density is 2.0, the reading value is X=A
Therefore, X'=0, which results in a dark signal output.

Since each parameter is set so that the final image output after logarithmic conversion, color correction, and γ correction is the maximum value of 255 when X' = 0, the image signal when the original density is 2.0 has a maximum value of 255, and the relationship between the original density and the image signal becomes as shown by the solid line A in FIG.

On the other hand, when making a color copy again using a copy as an original (making a copy of a copy), the motor that drives CCD 1.6 is controlled by a signal from a mode selection switch (not shown), and when performing black offset correction. The standard blackboard to be read is configured to be the second standard blackboard 20. This second standard black plate 20 is set so that its density is approximately equal to the maximum recording density of the head, and in this embodiment, the maximum recording density of the head is 1.
．． 5, the density of the second standard black board 20 is also l 5
It has become. Therefore, when the original density is 15, x'
=o, and the final image signal becomes 255, which is the maximum value.

Therefore, the relationship between the original density and the image signal is as shown by the solid line in FIG. 2, and the same effects as in the first and second embodiments can be obtained.

With such a configuration, there is no need to store the γ coefficient, masking coefficient, etc. to be changed, so there is also the advantage that circuitry and memory can be saved. Furthermore, if it is desired to change C, M, and Y independently, separate standard black plates for each color may be prepared.

In the above embodiment, the original density at which the image signal reaches the maximum value when making a copy from a full original is set to 2.0, and the maximum density of one image recording section is set to 1.5. It is not limited to the value. In short, as long as the original density at which the image signal reaches its maximum value when making a copy from a normal original is higher than the maximum density of the image recording section, the present invention can be implemented in the same manner and similar effects can be expected. However, when the maximum density of the printed document is approximately 1.8 or higher and the maximum density of the image recording section is lower than this, the problems of the conventional method become noticeable. When the present invention is applied to an image forming apparatus such as a copying machine of .8 or less, the obtained effects will be even more remarkable.

It goes without saying that the present invention is applicable not only to digital color copying machines but also to various digital electrophotographic and electrostatic recording image forming apparatuses having the same configuration.

1. As explained above, according to the present invention, when making another copy from a copied original, the original density at which the image signal reaches its maximum value is approximately equal to the maximum density of the image recording section. Because the copy is created using the copy mode set to the value, even if you re-copy the copy or repeat the copy repeatedly, the density will be very light and the appearance will be poor. It has the remarkable effect of not causing any defects.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of an image forming apparatus according to the present invention. FIG. 2 is a line section illustrating the relationship between original density and output density of the image forming apparatus according to the present invention. FIG. 3 is a block diagram showing a second embodiment of the image forming apparatus according to the present invention. FIG. 4 is a schematic diagram of a document table and a CCD, which is a photoelectric conversion element, of a third embodiment of an image forming apparatus according to the present invention, viewed from the back side. Section 5 is a block diagram showing a typical example of a conventional digital color copying machine. FIG. 6 is a diagram illustrating the relationship between original density and output density in conventional digital color copying. Photoelectric conversion element (CCD): Black offset and Shady logarithmic conversion circuit Color processing circuit: γ (gamma) correction circuit a~lid Record mode selection switch: CCD Standard white board 1st standard black board 2nd Keyaki semi-black board correction circuit

Claims (1)

[Scope of Claims] 1) An image reading unit that reads an original image and converts it into an electrical image signal, an image processing unit that performs signal processing on the image signal to obtain an image recording signal, and an image processing unit that performs signal processing on the image signal to obtain an image recording signal; In an image forming apparatus equipped with an image recording section that performs image recording using the image recording section, when the maximum recording density of the image recording section is D_1 and the document density when the image recording signal becomes maximum is D_2, D_1<D_2. An image forming apparatus comprising: a first mode in which D_2 is set so that D_2 is set; and a second mode in which D_2 is set so that D_1≈D_2. 2) The image forming apparatus according to claim 1, wherein the D_1 is 1.8 or less.