JP3020258B2 - Color image processing apparatus and color image processing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention performs different image processing depending on whether a document is a normal document or a document copied once, that is, image processing according to a generation copy. And a color image processing method.

2. Description of the Related Art Conventionally, an image of a document is read by a scanner (reading device), converted into an electric signal (digital signal), and a recording head or a laser printer is driven by the electric signal to form an image. Image forming apparatuses are well known. The digital image forming apparatus has a feature that image processing, editing, and the like can be freely performed, and has been rapidly spreading in recent years. In particular, digital color copiers are superior to analog color copiers in terms of image quality such as color reproducibility, and because various color copies can be obtained using various editing functions, The market is expanding.

FIG. 5 is a block diagram showing the flow of image signals of a typical example of such a conventional digital color copying machine. The reflected light image of the original image is read by a photoelectric conversion element 1 such as a CCD and converted into an electric signal, and further converted into digital R, G, and B signals 2a, 2b, and 2c by an analog-digital converter (not shown). Is converted. These signals are sent to a black offset and shading correction circuit 3, where black offset processing and shading correction processing are performed. The original reading unit is provided with a standard black plate and a standard white plate, and the black offset and shading correction circuit 3 performs the above processing using these. The standard black plate is a black plate having an optical density of 2.0, and stores a value A obtained by reading the value for each pixel. The standard white plate is a white plate having an optical density of 0.07, and stores a value B obtained by reading the white plate for each pixel. X is the value when reading the image of the original
Then, by the black offset and shading correction circuit 3, Is converted as follows. However, the signal is an 8-bit signal, and the maximum value is 255.

The R, G, and B signals 4a, 4b, and 4c that have undergone such processing are sent to a logarithmic conversion circuit 5 where they are converted into logarithms.
It is converted into density signals 6a, 6b, 6c for magenta M and yellow Y. These signals are sent to the color processing circuit 7 where color correction processing is performed. This color correction process is a black extraction and masking process, and signals input to the color processing circuit 7 are C, M,
Assuming that Y, in the black extraction, a black component is extracted by B _k = min (C, M, Y).

_{Next, C '= a 11 C +} a 12 M + a 13 Y + a 14 B k M' = a 21 C + a 22 M + a 23 Y + a 24 B k Y '= a 31 C + a 32 M + a 33 Y + a 34 B k B k' = a 41 C + a 42 Color correction is performed by a masking process of M + a ₄₃ Y + a ₄₄ B _k . The masking parameters a _{11 to} a ₄₄ are set so that the color reproducibility is the best.

The C, M, Y, _Bk signals 8a, 8b,
8c and 8d are γ-corrected by a γ (gamma) correction circuit 9. The γ correction circuit 9 corrects the gradation characteristic of the head so that the relationship between the signal and the print density becomes linear,
Adjust the balance of C, M, Y, _Bk . Assuming that the gradation characteristics of the head are linear, for the C, M, Y, and _Bk signals input to the γ correction circuit 9, C ′ = a ₅ × CM ′ = a ₆ × M Y ′ = Add _{a 7 × Y B k '=} a 8 × B k to become corrected.

The C, M, Y, and B _k signals 10a, 10
b, 10c, and 10d drive cyan, magenta, yellow, and black heads 11a, 11b, 11c, and 11d, respectively.
Print on recording paper to obtain a color copy.

As the head, an ink jet head, a thermal head for thermal transfer, or the like is used. In the case of an electrophotographic system, a semiconductor laser, an LED array, a liquid crystal shutter array, or the like is used.

Problems to be Solved by the Invention A color copy can be obtained in this way,
In some cases, it is necessary to make a copy again using the output color copy as a document. In such a case, conventionally, there was a problem that the density of the re-copied copy becomes extremely low, and the appearance becomes poor. This is for the following reason.

Generally, most of the copy original is a printed matter, and its maximum density is as high as 1.8 to 2.0. Therefore, for example, the maximum concentration
The image processing is performed such that the image signal obtained by performing the image processing by reading 2.0 has a maximum value of 255 of the image signal.
If the density at which the image signal becomes 255 is lower than this, the gradation of the density higher than the density will be destroyed, and if the density is higher than this, the 8-bit signal will be substantially surplus and wasted. It is. For this reason, the relationship between the document density and the image signal is as shown by the solid line A in FIG.

However, the characteristics of the recording head do not always have the ability to reproduce the same density as that of printing. For example, in the case of inkjet, the recording density depends on the ink ejection amount and the dye concentration in the ink, but the ink ejection amount is limited by the resolution and the absorption characteristics of the recording paper, and the dye concentration in the ink is stable. Neither can be so high because of the limitations on gender. In practical use, the optical density is about 1.5 at most. Therefore, the relationship between the image signal and the recording density is as shown by the solid line B in FIG.

As a result, the relationship between the document density and the output density is as shown by the solid line C in FIG. However, when the maximum concentration is 1.4
With the above, a sufficiently beautiful image can be obtained as a color copy, so that there is usually no problem with this. However, when the copy output is copied again as a document, the maximum density of the document is 1.5, so the maximum density of the output is That is, it becomes an unsightly image.

Generally, when copying a print original, unless the image signal for a density of 1.8 or more is set to the maximum value,
It is well known that the gradation of a high density portion is insufficient. However, if the image signal for the density of 1.8 is set to the maximum value, if the maximum value of the recording density is not 1.8 or more,
The density decreases each time copying is repeated.

The present invention has been made in view of the above points, and even if a copy is performed again based on a copied original,
It is an object of the present invention to prevent the density of an output image from being reduced and the appearance from being deteriorated even in a generation copy.

Means for Solving the Problems The above object is achieved by a color image processing device and a color image processing method according to the present invention. In summary, according to a first aspect of the present invention, there is provided a color image processing apparatus having a copy mode and a generation copy mode, wherein a first gamma parameter corresponding to the copy mode and an output according to the copy mode are provided. Holding means for holding a second gamma parameter corresponding to the generation copy mode, which is a parameter for satisfactorily copying the copied original; mode setting means for setting a mode based on a manual instruction of a user; Parameter setting means for setting the holding means and the held first or second gamma parameter in accordance with the set mode, and gamma correction means for performing gamma correction processing using the set parameters. A color image processing apparatus is provided.

According to an embodiment of the present invention, the image processing apparatus further includes a masking processing unit that performs a masking process based on the image data, and the gamma correction unit performs the gamma correction process on the masked image data.

According to another embodiment of the present invention, the mode setting means sets a mode based on a manual instruction of a user.

According to still another embodiment of the present invention, the image processing apparatus further includes an image forming unit that forms an image based on the gamma-corrected image data.

According to a second aspect of the present invention, there is provided a color image processing method having a copy mode and a generation copy mode, comprising: a mode setting step of setting a mode based on a manual instruction of a user; , (I) a first gamma parameter corresponding to the copy mode, or (ii) a second gamma parameter corresponding to the generation copy mode, which is a parameter for satisfactorily copying a document output in the copy mode. And a gamma correction step of performing a gamma correction process using the set parameters. A color image processing method is provided.

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, and shows the flow of image signals. The digital color copying machine of the present embodiment is provided with a mode selection switch 12, and the mode selection signal 13 from the switch 12 is input to the gamma correction circuit 9 to select a gamma correction coefficient. Since it has the same configuration as the conventional color copying machine shown in FIG. 5, the corresponding parts are denoted by the same reference numerals and the description thereof will be omitted unless necessary.

The mode selection switch 12 is used to copy a normal document (a document that has not been copied once), that is, in the normal copy mode, as in the conventional case, for example, when the image signal for the document density 2.0 is the maximum value. Γ to be 255
When the mode selection signal 13 for selecting the correction coefficient is output, and a copy is made again using the original once copied as the original, that is, in the case of the generation copy mode, for example, the image signal corresponding to the original density of 1.5 has the maximum value of 255. The mode selection signal 13 for selecting the coefficient of the γ correction so that Accordingly, 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 the solid line C in FIG. become that way. On the other hand, if you want to copy the output once and then copy it again,
As described above, since the γ correction coefficient is changed by the signal 13 from the mode selection switch 12, the relationship between the document density and the image signal is as shown by the solid line D where the document density is saturated at 1.5 as shown in FIG. The relationship between the document density and the output density is as shown by a solid line E in which the output density is substantially 1.5 and saturated as shown in FIG.

As a result, the density of the copied image is maintained at substantially the same density both when using a normal document and when using a once copied document, and there is no problem that the image becomes lighter each time copying is repeated.

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 embodiment, Should be changed to When the maximum output densities of C, M, Y, and B _k are different, the coefficients of the respective colors may be changed independently.

Next, a second embodiment of the present invention in which the present invention is applied to a digital color copying machine will be described with reference to FIG. In this embodiment, the mode selection signal 13 from the mode selection switch 12 is input to the color processing circuit 7 and the masking coefficient
It is obtained by configured to change a ₁₁ ~a _44. That is,
In the case of a normal original copy, for example, a mode selection signal 13 for setting a masking coefficient so that the image signal corresponding to the original density of 2.0 becomes the maximum value of 255 is output, while the original once copied is used as an original to copy again. For example, the mode selection signal 13 for changing the masking coefficient so that the image signal for the original density 1.5 becomes the maximum value 255
Is output. In this embodiment, as in the first 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. On the other hand, when a copy is output once and the original is to be copied again, the masking coefficient is changed by the signal 13 from the mode selection switch 12 as described above. Therefore, the relationship between the original density and the image signal is shown by the solid line in FIG. D, and the relationship between the document density and the output density is as shown by the solid line E in FIG. Therefore, it is clear that the same effect as in the first embodiment can be obtained. Since other configurations are the same as those of the first embodiment, the corresponding portions are denoted by the same reference numerals and description thereof will be omitted.

In the second embodiment, not only the relationship between the original density and the final image signal as shown by the solid line D in FIG. 2 but also it is easy to set the masking coefficient so that the color reproducibility is slightly changed. Can be. Generally, the color reproducibility of a color copy is not perfect, and the color slightly changes.
When the copy original is copied again, the color change may be amplified and noticeable. However, in this embodiment, when the masking coefficient is changed, it is possible to set the masking coefficient so as to correct the change in the color, so that not only the change in density but also the change in color occurs. There is an advantage that can also be solved.

Next, a third embodiment of the present invention will be described. In the present embodiment, the same effect as that of the first and second embodiments is obtained by changing the standard black plate when performing black offset correction instead of changing the γ coefficient and the masking coefficient. .

FIG. 4 shows a document table and a photoelectric conversion element CC when the present invention is applied to a digital color copying machine as in the above embodiment.
It is the schematic which looked at D (charge-coupled device) from the back side. CCD16
Has approximately 5,000 R, G, and B read pixels 17a, 17b, and 17c at a density of 16 pixels per mm, each of which is driven by a motor (not shown) in the direction of the arrow shown in FIG. And converts it into an electric signal. In this embodiment,
It is configured to read color documents up to A3 size. In FIG. 4, the read pixels 17a, 17b, and 17c are disposed on the back side of the CCD 16 and are originally invisible, but are shown for explanation. One end of the platen glass 15 has a standard white plate 18, a first standard black plate 19, and a second standard black plate
20 are stuck on each.

 Next, the operation of this embodiment will be described.

In a normal use condition in which a color copy is made from a normal original (an original that has not been copied), before reading the original, the CCD 16 reads the first standard black plate 19, and outputs the CCD output A of each pixel. Remember. The density of the first standard black plate 19 is 2.0. Next, the standard white plate 18 having a density of 0.07 is read, and the 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 After such a change, image processing is performed. Therefore, if the document density is 2.0, the read value is X = A, so that X '= 0, which is the darkest output on the signal.

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

On the other hand, when a color copy is to be made again using a copy as an original (to make a copy of a copy), the motor for driving the CCD 16 is controlled by a signal from a mode selection switch (not shown), and the standard read when performing black offset correction is performed. The black plate is configured to be the second standard black plate 20. The density of the second standard black plate 20 is set to be substantially equal to the maximum recording density of the head. In this embodiment, the maximum recording density of the head is 1.5. Is also 1.5.
Therefore, when the document density is 1.5, X ′ = 0, and the final image signal has the maximum value of 255. Therefore, the relationship between the document density and the image signal is as shown by the solid line D in FIG. 2, and the same effects as in the first and second embodiments can be obtained.

In such a configuration, there is no need to store a γ coefficient, a masking coefficient, and the like to be changed, so that there is an advantage that circuits and memories can be saved. If it is desired to change C, M, and Y independently, a standard black plate for each color may be prepared separately.

In the above embodiment, when a copy is made from a normal document, the document density at which the image signal has the maximum value is set to 2.0, and the maximum density is set to 1.5 in the image recording unit, but the present invention is limited to this value. Not something. In short, the present invention can be implemented similarly and the same effect can be expected if the original density at which the image signal has the maximum value when making a copy from a normal original is higher than the maximum density of the image recording unit. However, the maximum density of the printed manuscript is about 1.8 or more,
When the maximum density of the image recording unit is less than this, since the problem of the conventional example is remarkable, when the present invention is applied to an image forming apparatus such as a copying machine having a maximum density of 1.8 or less of the image recording unit, The effect obtained is more pronounced.

It is needless to say that the present invention is not limited to a digital color copying machine, but can be applied to various color image forming apparatuses of a digital electrophotographic system or an electrostatic recording system having the same configuration.

According to the present invention, it is possible to prevent the quality of an output image obtained by performing copying again based on a copied original, that is, an output image obtained in the jeheration copy mode. In other words, even if copying is performed again based on the copied document, it is possible to prevent the density in the output image from decreasing and the appearance from becoming worse.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a color image processing apparatus according to the present invention. FIG. 2 is a diagram illustrating the relationship between the original density and the output density of the color image processing apparatus according to the present invention. FIG. 3 is a block diagram showing a second embodiment of the color image processing apparatus according to the present invention. FIG. 4 is a schematic diagram of a third embodiment of a color image processing apparatus according to the present invention, as viewed from the back side of a platen and a CCD which is a photoelectric conversion element. FIG. 5 is a block diagram showing a typical example of a conventional digital color copying machine. FIG. 6 is a diagram for explaining the relationship between the original density and the output density of a conventional digital color copying machine. 1: photoelectric conversion element (CCD) 3: black offset and shading correction circuit 5: logarithmic conversion circuit 7: color processing circuit 9: γ (gamma) correction circuit 11a to 11d: recording head 12: mode selection switch 16: CCD 18 : Standard white plate 19: First standard black plate 20: Second standard black plate

Claims (5)

(57) [Claims] 1. A color image processing apparatus having a copy mode and a generation copy mode, wherein a first gamma parameter corresponding to the copy mode and a parameter for satisfactorily copying an original output in the copy mode are provided. And holding means for holding a second gamma parameter corresponding to the generation copy mode; mode setting means for setting a mode based on a user's manual instruction; and the holding means according to the set mode. A color image processing apparatus comprising: parameter setting means for setting the held first or second gamma parameter; and gamma correction means for performing gamma correction processing using the set parameters. 2. The image processing apparatus according to claim 1, further comprising a masking processing unit that performs a masking process based on the image data, wherein the gamma correction unit performs the gamma correction process on the masked image data. 1. A color image processing apparatus. 3. The color image processing apparatus according to claim 1, wherein said mode setting means sets a mode based on a manual instruction of a user. 4. The color image processing apparatus according to claim 1, further comprising image forming means for forming an image based on the gamma-corrected image data. 5. A color image processing method having a copy mode and a generation copy mode, wherein: a mode setting step of setting a mode based on a user's manual instruction; A parameter for setting a first gamma parameter corresponding to the copy mode or (ii) a second gamma parameter corresponding to the generation copy mode, which is a parameter for satisfactorily copying the document output in the copy mode. A color image processing method, comprising: a setting step; and a gamma correction step of performing a gamma correction process using the set parameters.