JPH07121074B2 - Color image forming method and apparatus thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a color image forming method and apparatus for forming a color image based on subtractive color system color image data.

[Prior Art] In the technique of processing a color image signal of a subtractive color mixture system, black cannot be theoretically developed from equal amounts of yellow (Y _e ), magenta (M) and cyan (C _y ), and the above three primary colors In many cases, the black ink is expensive, and therefore a black (B _k ) signal is generated to form an image based on the color image data of four colors.

An example of a black signal generation block in the prior art is shown in FIG. The signal generating block is applied to an ink jet printer in which the table 1 in the block is in the form of ROM, which is the conventional example shown in FIG. In the conventional example of FIG. 2, the black generation table 1 for inputting the luminance (Y) and the two color differences (RY, BY) is used to generate the black signal. That is, the table 1 inputs Y, R-Y, and B-Y, obtains and stores in advance by predetermined calculation, and outputs the _obtained Bk. The calculation method of B _k is as follows.

Furthermore, Here, R, G, B are the three primary colors according to the additive color mixture, respectively, red,
Green and blue.

The value of B _k calculated in this way is
It is stored for a combination of Y and BY.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional example, Y, R
-Y and BY signals must be input, and if the generation table is composed of, for example, a ROM, the R
There is a drawback that it increases the capacity of the OM and thus the entire circuit. Since the process of B _k = Min (C _y , M, Y _e ) is the basis of undercolor removal (undercolor removal), the above problem is not limited to the combination of Y, R−Y, and B−Y. The situation is the same for B _k generation from the color system.

The present invention has been proposed in order to solve the above-mentioned problems of the prior art, and includes a method of generating black image data from color image data of at most two colors to form a color image, and a small-scale circuit configuration. It is a point to propose a color image forming method device capable of forming a color image including a black signal.

[Means for Solving the Problems] The color image forming method of the present invention for achieving the above-mentioned object is configured such that a color image of three primary color image data and black image data according to a subtractive color mixture method is used for a color image signal. In the method for forming a color image, a step of extracting a bright information component and a chromatic information component from the color image signal, and a step of extracting the bright information component and the chromatic information component based on the bright information component and the chromatic information component before performing color correction for output. The method includes a step of calculating black image data and a step of simultaneously outputting the three primary color image data and the black image data.

The configuration of the color image forming apparatus of the present invention is a color image forming apparatus in which a color image signal is converted into three primary color image data according to a subtractive color mixture method and is used, in which the bright information component and the color information component in the color image signal are A color image forming apparatus which has a conversion table for inputting and converting into black image data and forms a color image of four colors together with the three primary color image data.

[Operation] According to the present invention having the above configuration, black image data can be obtained by inputting only two colors of the bright information component and the color information component.

[Examples] The present invention will be described in detail below with reference to the accompanying drawings.

<Principle of Example> The meaning of the black ( _Bk ) signal is considered as follows.

It can be said that the image generally becomes dark when the luminance is low, and accordingly the black signal component increases. Therefore, it may be considered that the black signal depends only on the luminance signal, but this is true only in the case of the monochrome image forming apparatus, and in the case of the color image, it is actually affected by the saturation. That is, even if the luminance is the same, the black signal component increases as the saturation decreases, and the black signal component decreases as the saturation increases. That is, it can be considered that the black signal component is mainly determined only by the luminance and the saturation in the color image, and the influence of the hue need not be considered. Furthermore, it can be said that the black signal component is mainly determined only by "brightness", which means brightness and lightness, and "color", which represents saturation and the like.

From the above, it is possible to input only “brightness” such as luminance and brightness and “color” such as saturation, for example, to the table for generating the black signal.

<Structure of Embodiment> FIG. 1 is an overall block diagram of an embodiment in which an image forming apparatus according to the present invention is applied to a printer (using an ink jet method). Incidentally, in the embodiment shown in FIG.
For convenience, the brightness (Y) is used as the "brightness" and the saturation (C) is used as the "color". As for the color system of the color image data input to the image forming apparatus, (Y, RY, BY) is used in comparison with the above-mentioned conventional example.

The outline of the operation of the embodiment shown in FIG. 1 is that, when a luminance signal (Y) and color difference signals (RY, BY) are input with the support of the CPU 20, A
The / D converters 10a to 10c convert the digital color image data. Masking ROM 11
Performs a masking process and converts the (Y, RY, BY) system to ( _Cy , M, _Ye ). On the other hand, the conversion table 12 is (R
-Y, BY) to extract the saturation (C). Next, the B _k ROM 13 inputs the saturation (C) and the luminance (Y) and outputs B _k data.

In this way, digital (C _y , M, Y _e ) color image data was obtained. The D / A converters 14a to 14d convert these generated data into analog signals and output them to the head driver 15, and the head driver 15 drives the ink head 16.

The calculation method of the saturation (C) data value stored in the conversion table 12 is: Is.

The calculation method of B _k data stored in B _k ROM 13 is as follows. First, from the saturation (C) from the conversion table 12,
Calculate (RY, BY). That is, when the hue is H, RY = C × SIN (H) BY−C = COS (H) Since black does not depend on the hue (H), H is set to an arbitrary value (R -Y, B-Y) can be calculated, for example H
= 90 °, R−Y = C B−Y═O.

Next, from (Y, RY, BY), R, G, B are calculated according to the following equation.

From this RGB, Finally, B _k = MIN (C _y , M, Y _e ) is calculated.

Since Y and C are input to the B _k ROM 13, and an arbitrary value can be set for H as described above, B _k calculated based only on these Y and C must be stored in advance. You can

For other C _y , M, Y _e signals, see Y, R-
The asymmetrical color components of the ink used are corrected by the masking ROM 11 for inputting Y and BY, and output as a C _y MY _e signal. The method of calculating the data stored in the masking ROM 11 is as follows. First, RGB is calculated from (Y, RY, BY).

Next, from this RGB, To calculate. Correction of asymmetric color components is generally performed by matrix approximation, Is calculated. Here, a _{11 to} a ₃₃ are predetermined constants.

B _k and (C _y , M, Y _e ) thus obtained are input to the head driver 15.

<Modification> In the above embodiments, the printer that inputs the luminance / two-color difference has been described as an example, but a printer that inputs R, B, and G may be used. In that case, matrix conversion to color difference may be performed before A / D conversion.

Similarly, the NTSC type YIQ system may be used. In this case, "color" is Becomes

Further, in the above-mentioned embodiment, the printer is described focusing on the black component, but of course, it may be applied to color separation in other fields such as printing.

[Effects of the Invention] As described above, according to the present invention, two color image data are sufficient for determining the black component from the conventional one that requires at least three color image data. As a result, the above method is used. For example, if a ROM is used for the color image forming apparatus applying the conversion table for determining the black component, the ROM capacity can be reduced, and peripheral devices can be simplified.

[Brief description of drawings]

FIG. 1 is a block diagram of a color image forming apparatus according to an embodiment of the present invention, and FIGS. 2 and 3 are pictorial charts of an image forming apparatus according to a conventional example. In the figure, 10a to 10c ... A / D converter, 11 ... masking ROM, 12 ... conversion _{table, 13 ... B k ROM, 14a~14d} ... D / A converter, 15 ... head driver, 16 ... head, 20 ... CPU.

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Claims (6)

[Claims] 1. A color image signal is subjected to a subtractive color mixture method.
In a color image forming method for forming a color image of primary color image data and black image data, a step of extracting a bright information component and a color information component from the color image signal, and before performing color correction for output A color image forming method comprising: a step of calculating black image data based on the bright information component and the color information component; and a step of simultaneously outputting the three primary color image data and the black image data. 2. The color image forming method according to claim 1, wherein the light information is luminance or lightness. 3. The color image forming method according to claim 1, wherein the color information is saturation. 4. A color image forming apparatus for converting a color image signal into three primary color image data according to a subtractive color mixture method for use, and inputs a bright information component and a color information component in the color image signal to obtain a black image. A color image forming apparatus having a conversion table for converting into data and forming a color image of four colors together with the color image data of the three primary colors. 5. The color image forming apparatus according to claim 4, wherein the light information is luminance or lightness. 6. The color image forming apparatus according to claim 4, wherein the color information is saturation.