JPH0746379B2 - Image processing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention inputs a plurality of color component signals generated by reading a color original image by a reading unit, and inputs the plurality of color component signals. The present invention relates to an image processing method in which image processing is performed with a predetermined color correction characteristic, a plurality of recording color component signals are output, and a color image is formed by an image forming unit based on the plurality of recording color component signals.

[Prior Art] Conventionally, as a color image processing device for printing a color image with good color reproducibility, a device using a masking method is well known. This masking method uses many high-order masking equations (for example, Clapper's equation) in order to perform advanced color correction.

However, such an equation is at most a quadratic equation or 3
With the following equation, it is not always possible to obtain sufficient color reproducibility. Moreover, it is extremely difficult to determine the coefficient of this equation, and it is obtained by empirical accumulation. Further, there is a disadvantage that the coefficient must be corrected even when the color temperature of the input optical system (lens system) and the illumination system for reading the original image or the color of the background of the transfer paper changes. .

Therefore, such a color image processing apparatus is provided with a predetermined image data, for example, a pattern generator (hereinafter referred to as PG) for outputting color patches of several hundreds of colors, and the image data based on these color patches is recorded by the recording apparatus ( A method of printing on paper with a printer (hereinafter referred to as a printer), reading this with a reading device (hereinafter referred to as a reader), and converting the relationship between the read data and PG data into a lookup table (hereinafter referred to as LUT) is available. Proposed. As a result, the color correction error becomes small, and it becomes possible to compensate for differences in paper, aging of the reader unit, aging of the printer unit, and the like.

However, making LUTs for all readable or recordable colors causes the LUT to become huge. In order to avoid this, it is possible to thin out the LUT and obtain a value thinned out by interpolation or an intermediate value, but there is a problem that the error due to interpolation becomes larger as the LUT becomes smaller.

That is, the error cannot be eliminated by a small number of parameters regardless of the masking equation or the LUT method.

[Problems to be Solved by the Invention] The present invention has been made in view of the above-described conventional example, and not only makes it possible to compensate for changes over time and differences in paper, but also to improve color reproducibility better than before. With the goal.

In order to solve this problem, the color image processing method of the present invention includes the following steps. That is, a plurality of color component signals generated by reading a color original image by a reading unit are input, and image processing is performed on the input plurality of color component signals with a predetermined color correction characteristic to obtain a plurality of recording colors. An image processing method of outputting a component signal and forming a color image by an image forming means based on the plurality of recording color component signals, wherein a reference color signal representing a color patch composed of a plurality of colors is generated by the reference signal generating means. The medium having the color patches formed by the image forming unit according to the reference color signal is read by the reading unit, and a plurality of color component signals from the reading unit are stored in the first storage unit, The original document to be processed is read by the reading means, and a plurality of color component signals from the reading means are stored in the second storage means. Calculating the color correction characteristics based on the plurality of color component signals stored in the first and second storage means, and determining.

[Embodiment] In order to solve the above problem, for example, the color copying machine of the embodiment shown in FIG. 1 has a pattern generator (PG) 4 as a color pattern holding unit, a printer 3 as a printing unit, and image data. The reader 1 as an input unit, the memory B7 as a unit for storing the color appearance frequency, the memory A6 as a unit for storing the input information of the color pattern, the parameter calculation unit 5 as the correction unit, and the color correction circuit 2. Equipped with.

In the configuration of FIG. 1, the reader 1 reads the paper 8 printed by the printer 3 based on the color pattern of PG4. The data read by the reader 1 is stored in the memory A6 in association with the color pattern. Next, the document 9 to be copied is read by the reader 1 and the color appearance frequency of the document 9 is stored in the memory B7. Memory A6, memory
Parameters are calculated by the parameter calculation unit 5 according to the information of B7 and set in the register group 2-1 of the color correction circuit 2. After that, when the original 9 is set on the reader 1 again and read, the color information input by the reader 1 is corrected by the color correction circuit 2 according to the appearance frequency of the color, and is output to the printer 3.

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

[Description of Color Copier (FIG. 1)] FIG. 1 is a block diagram of a color copying apparatus according to an embodiment of the present invention, in which arrows indicate the signal flow direction.

Reference numeral 1 is a reading unit (reader), 2 is a color correction circuit for performing color correction, and a group of registers 2 that internally holds color correction parameters
-1. 3 is a recording unit (printer), 4 is YMC
This is a pattern generator (PG) having a total of 125 (= 5 ³ ) color patches, each of which has 5 gradations, and printing color patches can be printed on paper through the printer 3. Reference numeral 5 is a parameter calculation unit for calculating a color correction parameter based on information in a memory B7, which will be described later, and sending it to the register group 2-1 of the color correction circuit 2. Reference numeral 6 is a printer 3 based on PG4.
Each of the 125 color patches printed by
A memory for storing the data read by the reader 1,
It consists of 125 sets of data. Reference numeral 7 denotes a memory which stores a value obtained by reading the original and counting the frequency of appearance of the colors contained in the original in the area around the 125 colors, and is composed of 125 sets of data.

[Explanation of Memory A and Memory B (FIGS. 2 to 4)] FIG. 2 is a diagram showing a relationship between the memory A6 and the memory B7, which corresponds to the output number 6-1 of the color patch and the memory A6. Both memories B7 have 125 memories.

Reference numeral 8 in FIG. 3 is a paper on which 125 color patches are printed based on PG4. As shown in FIG. 3, first, 125 color patches are created on the paper 8 from the PG4 through the printer 3, and The paper 8 is read by the reader 1. Read 125
The set of data is stored in the memory A6, for example, as density data.

Next, as shown in FIG. 4, the original 9 to be copied is set on the reader 1, and the original 9 is first prescanned to measure which color appears in the original and to what extent. The above 125
The value counted in the vicinity of the color is stored in the memory address corresponding to 125 sets of color patches in the memory B7.

[Calculation of Color Correction Parameters (FIGS. 5 and 6)] In FIG. 5, the color correction parameters are calculated by a method described later based on the data of 125 sets of each of the memory A6, the memory B7, and the PG4. This color correction parameter is held in the register 2-1 in the color correction circuit 2.

FIG. 6 shows an operation of reading the original 9 and performing color correction using the value of the register 2-1 to make a copy 10 of the original 9.

Next, when copying another document, the processes shown in FIGS. 4 to 6 are performed. Further, the process of FIG. 3 is performed, for example, when the power is turned on and by the user.

Next, a method of calculating the color correction parameter will be described.

For example, if a quadratic masking equation is used as the color correction method, the number of parameters is 3 colors × 10 = 30. These 30 parameters are the contents of the memory A6, that is, the set of values obtained by reading the pattern created by PG4 with the reader 1, and PG
It can be obtained from the pattern data of 4 using the least squares method. Furthermore, for each set of 125 sets of data,
By changing the weight of the appearance frequency of the original 9 and calculating the color, the color having a higher appearance frequency can be made more accurate.

Now, the data of PG4 is Y _i , the data of memory A6 is X _i , the masking equation is F (x), the data of memory B7, that is, the appearance frequency data is a _i. The parameter of F (x) may be determined so that

As described above, it is possible to perform color correction according to the original.

Although the color copying machine has been described in this embodiment,
However, the present invention is not limited to this, and of course, a color printer, a color facsimile, or the like can be realized if the appearance frequency of the color and the printed color information are given.

In this embodiment, the color appearance frequency in the original document is described as being based only on the data of the original document, but the present invention is not limited to this. By storing the total color appearance frequency and using this data as a weight for correction, it is advantageous when a large number of originals of a particular type are handled.

Further, by allowing the operator to arbitrarily change the contents of the memory B7 before the step of FIG. 5, the appearance frequency of a specific color can be changed, so that at least the reproduction accuracy of the specific color can be adjusted. It will be possible.

Further, in the present embodiment, the correction method of the color correction circuit 2 is
It is also possible to use the LUT instead of the masking calculation. In this case, the LUT data is interpolated at the time of color correction. At this time, the interpolation weight may be changed according to the appearance frequency of the memory B7.

As described above, according to this embodiment, by changing the color correction parameter according to the appearance frequency of the color in the original,
Color reproduction accuracy can be improved for the entire image. At the same time, it is possible to compensate for changes over time in the reader, printer, etc., and also to cope with different types of paper.

EFFECTS OF THE INVENTION As described above, according to the present invention, in determining the color correction characteristic used for processing the color original image to be processed, based on the reference color signal representing the reference color patch. The color correction characteristic is obtained in consideration of both the color component signal obtained by reading the medium on which the color patch is formed by the image forming means and the color component signal obtained by reading the color original image to be processed. Therefore, there is an effect that the optimum color correction characteristic can be determined based on both the image forming characteristic of the image forming unit and the characteristic of the color information of the color original image.

[Brief description of drawings]

FIG. 1 is a block diagram of a copying apparatus according to an embodiment of the present invention, FIG. 2 is a diagram showing the configurations of a memory A and a memory B, and FIG. 3 is a reader for a color patch printed based on PG data. FIG. 4 is a diagram showing a process of reading and storing, FIG. 4 is a diagram showing a process of reading a document, measuring the frequency of appearance of colors, and storing it. FIG. 5 is a diagram showing a process of calculating color correction parameters, FIG. FIG. 8 is a diagram showing a copying process. In the figure, 1 ... reading unit (reader), 2 ... color correction circuit, 2-1 ... register, 3 ... printer, 4 ... pattern generator (PG), 5 ... parameter calculation unit, 6,
7 …… Memory, 8 …… Paper with color patches printed, 9 ……
Manuscript, 10 ... Copies.

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Claims (1)

[Claims] 1. A plurality of color component signals generated by reading a color original image by a reading unit are input, and a plurality of image processing is performed on the input plurality of color component signals by a predetermined color correction characteristic. An image processing method for outputting a recording color component signal of No. 1, and forming a color image by an image forming unit based on the plurality of recording color component signals, wherein a reference color signal representing a color patch consisting of a plurality of colors is generated. Means for causing the reading means to read the medium on which the color patches have been formed by the image forming means according to the reference color signal, and the plurality of color component signals from the reading means are stored in the first storage means. The color document to be stored and processed is read by the reading means, and a plurality of color component signals from the reading means are read by the second means.
Image processing, characterized in that the color correction characteristics are calculated and determined based on the reference color signal and the plurality of color component signals stored in the first and second storage means. Method.