JPS63103568A - Color picture forming method and its device - Google Patents

Abstract

PURPOSE:To form a color picture including a black level signal with small circuit constitution by operating black picture data based on lightness information component and saturation information component in a color picture signal. CONSTITUTION:A luminance signal Y, color difference signals R-Y, B-Y are converted into digital color picture data by A/D converters 10a-10c, a masking ROM 11 applies masking processing and converts the system from (Y, R-Y, B-Y) into (Cy, M, Ye). On the other hand, the conversion table 12 extracts saturation C from the color difference signals R-Y, B-Y and the BkROM 13 inputs the saturation C and brightness Y to output Bk data. D/A converters 14a-14d convert the data into analog signals and a head driver 15 drives an ink head 16.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color image forming method and apparatus for forming a color image using subtractive color mixture color image data.

[Prior Art] In technology that handles subtractive color image signals, black is mixed with equal amounts of yellow (Y), magenta (M), and cyan (
For reasons such as the fact that color cannot be produced according to theory from color C) and the inks of the three primary colors mentioned above are expensive, in many cases a black (Bk) signal is generated and images based on color image data of four colors are often generated. is forming.

An example of a black (g) generation block in the prior art is shown in FIG. 2. In the conventional technique shown in FIG. For example, in the conventional example shown in Figure 2, to generate a black signal, luminance (Y) and
Color difference (R-Y.

A black generation table 1 is used which inputs B-Y). That is, the table 1 manually calculates Y, RY, and BY, and outputs Bk, which has been calculated and stored in advance by a predetermined calculation. The method for calculating Bk is as follows.

In addition, R, G, and B are the three primary colors that follow additive color mixture, and are respectively
They are red, green, and blue.

The value of Bk calculated in this way is
It is stored for the combination of R-Y and B-Y.

[Problems to be Solved by the Invention] However, in the above conventional example, Y,
The three signals R-Y and B-Y must be generated manually, and therefore, if the generation table is constructed from a ROM, for example, the disadvantage is that the capacity of the ROM and, by extension, the entire circuit will increase. there were. Bl(-Mln(Cy
1M, Ya) is the basis of undercolor removal, so the above problem can be solved by Y,RY,B
The same situation applies not only to the combination of -Y but also to the generation of Bk from other color systems.

The present invention was proposed in order to solve the problems of the prior art described above, and provides a method for forming a color image by generating black image data from color image data of at most two colors, and a method using a small-scale circuit configuration. The object of the present invention is to propose a color image forming method and apparatus that can form a color image including a black signal.

[Means for Solving the Problems] The structure of the color image forming method of the present invention for realizing the above-mentioned problems is to form a color image of three primary color image data and black image data according to the subtractive color mixing method from a color image signal. a color image forming method for forming a color image, the steps of: extracting a bright information component and a chroma information component from the color image signal; calculating black image data based on the bright information component and the chroma information component; The method includes a step of simultaneously outputting three primary color image data and black image data.

The configuration of the color image forming apparatus of the present invention is such that the color image forming apparatus converts a color image signal into three primary color image data according to the subtractive color mixing method and uses the bright information component and the chromatic information component in the color image signal. A color image forming apparatus that has a conversion table for manually converting black image data into black image data, and forms a four-color color image 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, a bright information component and a chromatic information component.

[Example] The present invention will be described in detail below according to an example with reference to the accompanying drawings.

<Principle of Examples> The meaning of the black (Bk) signal can be considered as follows.

It can be said that the image becomes darker when the brightness is lower, and therefore the black signal component increases. Therefore, you may think that the black signal is affected only by the brightness No. 13, but this only holds true for monochrome image forming devices; in the case of color images, it is actually affected by the saturation as well. . In other words, even if the luminance is the same, when the saturation decreases, the black signal component increases, and when the saturation increases, the black signal component decreases. In other words, in a color image, the black signal component can be considered to be determined mainly by brightness and saturation, and there is no need to consider the influence of hue. Furthermore, it can be said that the black signal component is mainly determined only by "brightness" meaning brightness and brightness, and "color" representing saturation.

From the above, the inputs to the table for generating the black signal can be, for example, only "brightness" such as luminance and lightness, and "color" such as saturation.

<Configuration 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 (based on an inkjet system). In the embodiment shown in FIG.
Luminance (Y) is used as "brightness", and saturation (C) is used as "color".
) is adopted for convenience. Further, as for the color system of color image data input to the image forming apparatus, (Y, RY, B-\) is used for comparison with the conventional example described above.

The operation outline of the embodiment shown in FIG. 1 is as follows:
When a luminance signal (Y) and two color difference signals (RY, B-Y) are input, the A/D converters 10a to 10C convert them into digital color image data. This digital image data
While the masking ROM 11 performs masking processing (Y
, R-Y, B-Y) system to (C,, M, Y,). On the other hand, the conversion table 12 extracts saturation (C) from (RY, BY). Next, the BkROM 13 receives the saturation (C) and brightness (Y) and outputs Bk data.

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

The calculation method for the saturation (C) data value stored in the conversion table 12 is: c=J (RY) 2+ (B-y) 2.

The calculation method for the B data stored in the ROM 13 is as follows. First, the saturation (C
), find (RY, B-Y). In other words, if the hue is H, then R-Y=CXSIN(H) B-Y=CXCO5(H) Since black does not depend on hue (H), set H to an arbitrary value (R-Y, B -Y), for example, if H=90°, then R-Y=C B-Y=0.

Next, from (Y, R-Y, B-Y), R,
Find G and B.

From this RGB, calculate B, = MIN(c, , M, Y-).

Since Y and C are manually stored in the BkROM 13, and any value can be set for H as described above, Bk calculated based only on these Y and C can be stored in advance.

For other C, M, Y, and signal creation methods, masking ROM II inputs Y, R-Y, and B-Y, respectively.
The asymmetric color components of the ink used are corrected by C,
MY, output as a signal. This masking ROMI
The method of calculating the stored data of I is as follows. First of all,
(Y.

RGB is calculated from R-Y, B-Y).

Margin below Next, calculate from this RGB. Correction of asymmetric color components is generally calculated by matrix approximation. Here, all to a33 are predetermined constants.

Bk obtained as above and (C,,M.

Y, ) are input to the head driver 15.

<Modifications> In the above embodiments, a printer in which luminance and two color differences are manually controlled has been described as an example, but a blink printer in which R, B, and 2 color differences are manually controlled may also be used. In that case, matrix conversion to color difference may be performed before A/D conversion.

Similarly, the YIQ system of the NTSC system may be used.

In this case, "color" becomes J■ +Q.

Further, in the above embodiments, the printer was mainly described with reference to the black component, but of course the present invention may be applied to color separation in other fields such as printing.

[Effects of the Invention] As explained above, according to the present invention, black component determination can be changed from the conventional method requiring at least three color image data to two color image data, and as a result, the above method can be performed. If a ROM is used, for example, in a color image forming apparatus in which the above is applied to a conversion table for determining the black component, not only the ROM capacity can be reduced, but also the peripheral devices can be simplified.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a color image forming apparatus M according to an embodiment of the present invention, and FIGS. 2 and 3 are illustrations of a conventional image forming apparatus. In the figure, 10a to 10c... A/D converter, 11... Masking ROM, 12... Conversion table, 13... Bk
ROM, 14a-14d-D/A converter,
15-...Head driver, 16...Head, 20-...
...is a CPU.

Claims (6)

[Claims] (1) In a color image forming method for forming a color image of three primary color image data and black image data according to a subtractive color mixing method from a color image signal, a bright information component and a chromatic information component are extracted from the color image signal. A method for forming a color image, comprising the steps of: calculating black image data based on the brightness information component and the chrominance information component; and outputting the three primary color image data and the black image data simultaneously. (2) The color image forming method according to claim 1, wherein the brightness information is brightness or brightness. (3) The color image forming method according to claim 1, wherein the color information is saturation. (4) In a color image forming apparatus that converts a color image signal into three primary color image data according to a subtractive color mixture method, the bright information component and the chromatic information component in the color image signal are inputted and converted into black image data. A color image forming apparatus that has a conversion table for conversion and forms a four-color color image together with the three primary color image data. (5) The color image forming apparatus according to claim 4, wherein the brightness information is brightness or lightness. (6) The color image forming apparatus according to claim 4, wherein the color information is saturation.