JPH0453352A - Picture processing unit - Google Patents

Abstract

PURPOSE:To improve the color reproducibility by using a color component signal after elimination of background color and a color component signal before binarization so as to generate a recording color signal. CONSTITUTION:An error correction section 4 for processing each of Y, M, C colors, a requantization section 6 and memories 7, 5 form a so-called pseudo intermediate tone processing section. An RGB input picture data is separated into three recording colors C, M, Y and the color component signal of three colors is subject to pseudo intermediate tone processing for each color and binarization. Then a background color component is eliminated from the color component signal and a recording color signal is generated by using a color component signal after elimination of background color and a color component signal before binarization. Thus, the picture processing unit with excellent color reproducibility is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image processing apparatus such as a copier FAX that processes color images.

[Conventional technology]

Conventionally, in this type of device, color images are R9G, B
After color separation into three colors, the recorded colors C and M.

It is customary to generate Y and K (black) signals and perform pseudo-halftone processing for each of the four colors. The pseudo-halftone processing method used has long been known as the dither method, which can be constructed at low cost.
In recent years, data storage methods that perform requantization error correction, such as the error diffusion method, which can reproduce images with both resolution and gradation, have become commonplace.

[Problem that the invention is trying to solve]

However, in the above-mentioned data saving type (conditional dither method) pseudo-halftone processing method, since the requantization dot is not directly determined from one point of the input data, when input image data separated into four colors is processed independently, The requantized dots of the four colors may overlap. Therefore, for example, when recording using an electrostatic process based on requantized data, the four colors of toner locally overlap and form convex portions of several hundred micrometers on the transfer paper surface, reducing fixing performance. In addition, a problem arises in that the image quality deteriorates.

Furthermore, when recording using an inkjet method, for example, a large amount of ink is applied locally, causing similar problems such as bleeding on the back surface of the recording paper and a long drying time.

Furthermore, if the front positions of each color recording material for each pixel do not completely match due to mechanical accuracy, color misregistration occurs and color reproducibility becomes extremely poor.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above drawbacks and provide an image processing device with good color reproducibility.

[Means and operations for solving the problems] In order to solve the above problems, the image processing device of the present invention includes means for performing pseudo-halftone processing on a plurality of color component signals for each color and converting the signals into binarization; It is characterized by comprising means for removing an undercolor component from the component signal, and means for generating a recording color signal using the color component signal of the undercolor removal stage and the color component signal before binarization.

〔Example〕

FIG. 1 shows an overall block diagram of the present invention. In the figure, l is CC
r+ for each pixel in the image input section consisting of a D-line sensor
The analog image signals color-separated into g+b are quantized by the A/D converter 2 into digital image signals R, G, and B each having a width of 8 bits (0 to 255). The data is converted into Y, M, and C image signals of recording colors by logarithmic conversion in a data conversion section 3, which will not be described in detail.

The data conversion section generally performs known data conversion such as unevenness correction of the image reading section including the sensor (2), logarithmic conversion, so-called masking processing, enlargement, reduction, etc. according to the spectral characteristics of the sensor (1) and the recording material. .

The error correction unit 4, the requantization unit 6, and the memories 7 and 5, which process each color of Y, M, and C, constitute a so-called pseudo halftone processing unit, and each Y color has an 8-bit width.

M, C recording signals have fewer bits than y, m.

Requantize to C signal. and requantized y.

The m and C signals are input to the black signal generation section 9 to generate a new black recording signal K, and y, m', c' multiplied signal inputs y, m are actually used as recording data.

After correcting the C signal, a visible image is formed in the recording device 10.

<First Embodiment> Now, a first embodiment of the present invention in which pseudo halftone processing is performed on binary data will be described using FIG. The pseudo-halftone processing method used in this embodiment is a method already proposed by the applicant, and consists of a memory 7 that holds already binarized binary data with a delay of two lines; Binary data output for each pixel is held for 12 pixels each in the vicinity of the pixel of interest, a binarization threshold is determined from these 12 binary data, and the binary data is binarized and a binarization error is generated. Value conversion unit 60
It can be roughly divided into an error memory 5 that holds the error with a delay of one line, and an error correction section 4 that corrects the input image signal using the error.

[Binarization unit 60] The details of the binarization unit 60 will be explained in detail using FIGS. 3 and 4. In FIG. 3, F/Fs 605 and 601 input the binary data of one line and two lines before the line of interest delayed and held in the memory 7, respectively, and the F/Fs 602, 603 and 6
04 and F/F 606, 607, and 608, each pixel is delayed and held using a data clock (not shown).

On the other hand, the F/F into which the result of binarizing the pixel of interest is input
If the output of 610 is further delayed and held by F/F 609 and the input/output signals of the flip-flop are set to a as shown in the figure, 12 already binarized data are obtained.

In FIG. 3, the average value calculation ROM 614 connected to the input address terminal for the above-mentioned 12 binary data calculates the weighting coefficient applied to the binary data located at a - j with respect to the pixel of interest, as shown in FIG. 4. This is a ROM for multiplying the pixels at the positions a to j, respectively, to convert them into a weighted average value, and the output average value becomes a threshold value for binarizing the pixel of interest. The comparator 612 binarizes the input data whose error has been corrected by the error correction section described later using the above threshold, and sends the result to the memory 7 and the F/F/2 in order to binarize the next pixel.
Enter in F610. On the other hand, a subtracter 611 calculates the difference between the output of the average value calculation ROM 614 and the error-corrected input data. Unlike the known error diffusion method, the output of the subtracter 611 becomes a binarization error specific to this pseudo halftone processing method.

The same error is divided into two parts by a distributor 613, and one part e2 is input to the error memory 5 for next line pixel data correction, and the other part el is input to the error correction section 4 for next line pixel data correction.

"Error correction section 4" The error correction section 4 is shown in Fig. 5.The input 8-bit image data is divided into 01 and 01, which is the binarization error that occurred during the previous pixel binarization.
Output from error memory 5, that is, I line [) 11
The binarization error e2 generated during pixel binarization is added to the adder 42.
and add it. Input data after error correction is F/F 41
When the next clock is inputted manually, it is inputted to the subtracter 611 and the comparator 612, respectively, and the above-mentioned binarization process is similarly executed.

The following two binarization processes are similarly performed independently and in parallel on the C, M, and Y three color data to obtain binary data y', mC'.

[Black signal generation]

-AND gates 9Y and 9M which input the black signal and the y' and mC' signals, respectively, use the output of the AND gate 1-9 which inputs the signals y, m and c' as the black signal to be recorded.

The output of the 9C signal is recorded as y and m, respectively.

Let it be the C signal.

To explain the above processing using the MMC color space shown in Figure 6,
If the binarization threshold value (average value) obtained for each pixel in the YMC space is M, then the space is divided into 8 in each YMC axis direction, and now the input data after error correction is P. If the two colors are in the same position, the binarization results for each of the three colors will be 1". Therefore, the black recorded with the three colors will be replaced with the K1 color that can be expressed with the recording material A, and as a result, even in the most common case, 2 Recording is possible with color recording agents.In other words, the recording colors per pixel are Y, M, C, Y+M, M+C,
Seven colors of C+Y can be used.

Next, another embodiment of the black signal generating section 9 in the above embodiment will be described.

[Second Embodiment of Black Signal Generation Section] FIG. 7 shows another embodiment of the black signal generation section. 9 in Figure 7
1 inputs input Y, M, and C data, finds the minimum value, compares the obtained minimum value with a predetermined constant α set by a CPU (not shown) in a comparator 92, and if it is larger than α, AN
Outputs '1' to D games 1 to 90. In other words, Y, M,
The minimum value of the C signal is a value that indicates the brightness of the input pixel. Therefore, if it is bright to some extent, that is, the minimum value is smaller than α, it means that the recording dots are not densely packed near that pixel, and the signal - color changes. There is no need to replace the dots, and on the contrary, it is possible to prevent the sloppy texture caused by the replaced dots.

Moreover, the same effect can be obtained by using not only the minimum value but also the average value of Y, M, and C, for example.

[Third embodiment of black signal generation unit] In the two embodiments described above, most of the blackish parts of the input image are replaced with one color, but since it is one color, dots of other colors are also replaced with one color. By adding more depth to the recorded image. In the third embodiment shown in FIG. 8, when there is a minimum value exceeding a predetermined value β (greater than α) using a comparator 93, the color exhibiting the maximum value is detected at 94; Black can be expressed using two colors: color + maximum value color. In other words, c, m, and y' are all "1" in the AND gate 90.
If the minimum value exceeds β in the comparator 93 in the case of
The output of the D gate 96 is “]”, but the maximum value color detection unit 94
Since the output of only the maximum value color is "1", AND
One color of the N-gate cmy has an output of 1",
As a result, recording of 1+ colors is permitted.

[Other embodiments of the black signal generation section]

By combining the second embodiment and the third embodiment, recording with high image quality is possible. In other words, as shown in Figure 9, c
If ', m', and y' are all "l", use Table 1 below.
The relationship should be satisfied.

In this way, it becomes possible to record in two colors.

Note that the pseudo halftone processing used is not limited to this embodiment, and the same effects as in the embodiments of the present invention can be obtained even if an error diffusion method or the like is used.

Furthermore, in addition to maximum value color detection, edges may be extracted. That is, a known edge extraction circuit is provided as shown in Fig. 1O, and the above two-color recording is prohibited in the case of an edge in accordance with its 1-bit judgment signal (1 if it is an edge, 0 if it is not an edge). You may also do so. This can prevent color shift that may occur at the edges.

[Recording device 10] Next, the configuration of the recording apparatus 10 shown in FIG. 1 will be explained.

The present invention is applicable to various recording methods such as inkjet recording, thermal transfer recording, and electrostatic recording.

Here, an example of use in inkjet recording will be described.

FIG. 11 is a perspective view of the periphery of a head of an inkjet recording apparatus using heating elements.

In the figure, a head unit 51 serves as a total of four nozzles 52. That is, the head unit 51 has a black ink discharge nozzle 52, a yellow ink discharge nozzle 52Y, a magenta ink discharge nozzle 52M, and a cyan ink discharge nozzle 5.
It has 2C. 53 is an ink supply tube, 54 is a main tank, and four main tanks are provided for each nozzle.

The configuration of the nozzle 52 will be explained using the cross-sectional view of FIG. 12. 55 is a top plate, 56 is a bottom plate, 57 is a heating element, 58 is an orifice portion, and 59 is ink.

When voltage is applied to the heating element 57, heat is generated, bubbles are formed around the element 57, and when the voltage application ends, the bubbles contract. Ink near the orifice portion 58 is ejected from the orifice portion 58 as the bubbles form and contract.

This recording head uses thermal energy to cause state changes in the ink, such as film boiling, to generate air bubbles, and these bubbles are used to direct the ink to the ejection ports (nozzles).
The liquid is ejected toward the recording material to record characters, images, etc. This is a so-called bubble jet recording head. In this recording head, the size of the heating resistor (heater) installed in each nozzle is much smaller than the piezoelectric element used in conventional inkjet recording, making it possible to have multiple nozzles at a high density. This allows high-quality recorded images to be obtained, and has features such as high speed and low noise.

A recording device having multiple heads for one type of coloring material may be used.

In FIG. 13, numeral 101 is a head unit in which a large number of inkjet heads for one type of coloring material are arranged in the sub-scanning direction, and includes units for black, yellow cyan, and magenta. 107 is an ink tank for each head unit, 109 is a signal line, and 104 is a carriage drive motor that moves the carriage 105 to which the head unit is attached along the rail 103 in cooperation with the conveyor belt 105. 106 is a recording paper, 120 is a platen, 111. Reference numeral 112 indicates a recording paper transport roller, 113 indicates a recording paper roll, and 114 indicates a guide roller. The head unit 101 is composed of a plurality of inkjet heads using the heating elements shown in FIG. 12, but it is also possible to use inkjet heads using electromechanical conversion means such as piezo elements.

According to an embodiment of the present invention, RGB input image data is
The image data of the three colors is separated into three recording colors of M and Y, and the image data of these three colors is independently subjected to pseudo halftone processing and requantized, and based on this requantized data, the four colors are recorded in C, M, and Y. By generating data, it becomes possible to manage the amount of all recording materials recorded at one point on the recording paper surface.

That is, (1) the number of color dots recorded at one point on the recording paper surface is C2M, Y
, high-quality recording is possible by limiting the number of colors to approximately two of the four colors.

(2) Furthermore, compared to the case where signals are generated independently and binarized using masking UCR, a binarization circuit for one color is not required, making it possible to realize the method at a lower cost.

In addition, multiple color component signals are subjected to pseudo-halftone processing for each color.
means for converting into a value, means for removing an undercolor component from the color component signal, and means for generating a recording color signal using the undercolor removing color component signal and the color component signal before binarization. By having this, the color reproducibility especially of the black thin line portion becomes good.

Note that as a printer for outputting the recording signal generated as described above, a printer capable of color recording such as a color inkjet printer, a color thermal transfer printer, a color dot printer, a color laser beam printer, etc. can be used.

In particular, VSP4723129, VSP47407
This method is effective for printers using a type of head that ejects droplets by utilizing film boiling caused by thermal energy as shown in No. 93 D.

Further, the two arithmetic circuits may be configured using ROM, RAM, etc., or may be realized by computer software that can perform the above-mentioned arithmetic operations.

In addition to inputting image data using a CCD sensor,
It may be input from the host computer via an interface or from memory.

Further, the binarization process is not limited to the above-described embodiment, and may be an error diffusion method, a pseudo halftone process similar thereto, or another binarization process.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide an image processing device with good color reproducibility.

[Brief explanation of the drawing]

1 and 2 are diagrams showing the overall configuration of an embodiment of the present invention; FIG. 3 is a diagram showing the configuration of the binarization section 60; FIG. 4 is a diagram explaining the binarization method; The figure shows the configuration of the error correction section 4, and FIG. 6 shows the YMC
Figures 7, 8, 9, and 10 showing color spaces are diagrams for explaining other embodiments of the present invention. FIG. 11, FIG. 12, and FIG. 13 are diagrams showing the recording apparatus. 60 Y, 60 M, 60. C...Binarization section 9...Black signal generation section

Claims (2)

[Claims] (1) Pseudo-halftone processing of multiple color component signals for each color
means for converting into a value, means for removing an undercolor component from the color component signal, and means for generating a recording color signal using the undercolor removing color component signal and the color component signal before binarization. An image processing device comprising: (2) The image processing apparatus according to claim 1, wherein the binarization means performs pseudo-halftone processing accompanied by correction of binarization errors.