JPH01157857A - Color correcting device for full-color image output apparatus - Google Patents

Abstract

PURPOSE:To obtain a color image having good reproducibility by performing color corrections for the respective color areas fractionated on the basis of a plurality of conversion rules, thereby improving the degree of approximation of the color corrections. CONSTITUTION:A color signal converter comprises a color area detection device 12 for finding out a color area in which a color represented by a digital color signal is present when the digital color signal is fed thereinto, a color correcting device 13 for selecting a conversion rule corresponding to the color area so found from a ROM 10 for conversion rules and for converting the digital color signal so fed into an output digital color signal, a cyanogen binarizing device 14 for binarizing each digital color signal by utilizing a dither method, a magenta binarizing device 15 and a yellow binarizing device 16. This color correcting apparatus can select a conversion rule for each color area represented by an input color video signal and allows an output color image corresponding to the input color image to be obtained. The respective conversion rules may be low levelled ones, thus making it possible to obtain an output color image within a relatively short period of time.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a color correction device for a color image output device, and more specifically, the present invention relates to a color correction device for a color image output device, and more specifically, to correct an input digital color signal into a color that matches the color indicated by the signal. The present invention relates to a color correction device for a color image output device that converts a color signal into an output digital color signal that can be output in color.

[Prior Art] Conventionally, in a color printer, one linear path converts an input digital color signal into an output digital color signal using a nonlinear conversion law. The colors shown were printed in color.

[Problems to be solved by the invention] However, in general, the color reproduction characteristics of color printers are
Even in a single color, the pattern is as shown in Figure 4.

That is, if the horizontal axis shows the input density and the vertical axis shows the output density, the actual characteristic will not be a straight line but a so-called gamma curve. Therefore, if this color correction is expressed using one linear conversion rule, the approximation error will be large as shown in FIG. On the other hand, if a non-linear term is added to the conversion rule to avoid this problem, the processing time increases, making it difficult to print colors indicated by input digital color signals in a short period of time.

[Object of the Invention] The present invention has been made to solve the above-mentioned problems, and its purpose is to convert an input digital color signal into an output digital color signal in a color image output device such as a color printer. By using a means of color correction that uses multiple conversion rules to convert into signals,
It is an object of the present invention to provide a color correction device capable of printing colors indicated by the input digital color signal with good reproducibility in a short time.

[Means for solving the problem] In order to achieve this object, the color correction device according to the present invention has the following features:
In a color image output device that converts an input color image signal to a color image output signal and outputs a color image, means for storing a plurality of conversion rules for converting the input color image signal to the color image output signal, and the storage thereof. means for selecting a single conversion rule for each color region indicated by the input color image signal from a plurality of conversion rules, and processing the input color image signal based on the selected conversion rule; and means for obtaining a color image output signal.

[Operation] According to the color correction device of the present invention having the above-described configuration, a conversion rule is selected for each color region indicated by the input color image signal, thereby obtaining an output color image that matches the input color image. Moreover, since each conversion rule is a simple low-dimensional formula, an output color image can be obtained in a relatively short time.

[Example 1] Hereinafter, an example embodying the present invention will be described with reference to the drawings.

First, the overall configuration of an inkjet color printer will be explained with reference to FIG. A color signal separation device 2 that separates the three colors into separate digital color signals, a paper feed amount control device 4 that controls a paper feed device 3 that feeds the paper, and a nozzle moving device 5 that moves each nozzle of the inkjet. A nozzle control device 6 is connected thereto. Further, the color signal separation device 2 includes a cyan signal.

In order to control the cyan inkjet nozzle 7, magenta inkjet nozzle 8, and yellow inkjet nozzle 9 that eject magenta and yellow inks, color signal conversion involves a conversion rule ROM10 that stores a plurality of conversion rules. Device 11 is connected.

Also, with reference to FIG. 2, the configuration of the color signal conversion device 11 will be explained. The color signal converting device 11 includes a color region detecting device 12 which determines in which color region the color indicated by the digital color signal exists based on the input digital color signal, and a color region detecting device 12 that corresponds to the bundled color region. a color correction device 13 that selects a conversion rule from the conversion rule ROM10 and converts an input digital color signal into an output digital color signal; and a cyan 2 that binarizes each digital color signal using a dither method.
Value conversion device 14. It is composed of a magenta binarization device 15 and a yellow binarization device 16.

Next, the operation of the color printer of this embodiment will be explained with reference to FIGS. 1 to 3.

Red, green, and blue digital signals are input to the digital signal input device 1 pixel by pixel.

When a digital color signal is input to the digital signal input device 1, the nozzle control device 6 operates the nozzle moving device 5 to align the dot positions. Further, at the time of line feed, the paper feed amount control device 4 controls the paper feed amount control device 3.
Activate. The input digital color signal is sent to the color signal separation device 2, where it is separated into separate digital color signals of red, green, and blue.
Sent to 1. This color signal conversion device 11 first converts the three digital color signals and the color area detection device 12 into
detects in which color region the input digital color signal exists as shown in FIG. A corresponding conversion rule is selected, and the color correction device 13 uses the selected conversion rule to produce red color as shown in the following equation.

Green and blue digital color signals are cyan and magenta.

It is converted into a yellow digital color signal.

Here, D R, D e, and D are the input digital density values of red, green, and blue, and D c, D H, and D Y are the output digital density values of cyan, magenta, and yellow, and a II to a 3. indicates the selected transformation rule parameters.

FIG. 3 shows how the color area is divided for selecting a conversion rule. According to this, the axes in three directions orthogonal to each other are the R axis, G axis, and B axis, and an arbitrary intermediate density point within 100% density of each axis is the point r.

Assuming that there are 81 points, 8 blocks of color area are formed by dividing the area by planes passing through each point r, g, and b and parallel to each axial plane. Therefore, a desired conversion rule is assigned to each color area as shown in the following table.

Next, each digital color signal is converted into an on/off signal for each ink in the ink binarization devices 14 to 16 using a dither method or the like. When the ink on/off signal is on, ink is ejected from each of the inkjet nozzles 7 to 9, and color printing is performed on the paper 17. Figure 6 shows an example of color correction using the conversion rule based on the present invention, and it is clear that the degree of approximation is improved compared to the conventional example shown in Figure 5. Probably.

The present invention is not limited to the embodiments described above,
Various changes can be made without departing from the spirit of the invention.

For example, in this embodiment, the color signal conversion device is separated into each function and each color component, but it is also possible to perform the conversion all at once, or to use a central control device, RAM, ROM, and software instead. Another way to select a conversion rule is to divide the color space representing the input color image signal by a plane parallel to or intersecting the digital density axis, or by a curved surface, and apply a different conversion rule to each subspace. The approximation of color correction may be further improved.

It goes without saying that the plurality of conversion rules of the present invention may each use polynomials with different coefficients and orders as in the prior art.

[Effects of the Invention] As is clear from the detailed description above, according to the present invention, color correction is performed for each subdivided color area using a plurality of conversion rules, so compared to the conventional method, The approximation of color correction is improved, and color images with good reproducibility can be obtained. Furthermore, since color correction is performed using a plurality of conversion rules, each conversion rule may be a simple low-dimensional formula, and quick response of color output can be achieved.

[Brief explanation of the drawing]

1 to 5 show embodiments embodying the present invention. FIG. 1 is a block diagram showing the electrical configuration of a color printer to which this embodiment is applied, and FIG. A block diagram showing the contents of the color signal conversion device in the printer,
Figure 3 is a diagram showing how the color region space is divided, Figure 4 is a diagram showing the relationship between input density and output density when color correction processing is not performed, and Figure 5 is a diagram showing the relationship between input density and output density when color correction processing is not performed. FIG. 6 is a diagram showing the relationship between input density and output density when color correction is performed in this embodiment. In the figure, 1 is a digital signal input device, 2 is a color signal separation device, 6 is a nozzle control device, 10 is a ROM for conversion rules, 11
1 is a color signal conversion device, 12 is a color area detection device, and 13 is a color correction device.

Claims (1)

[Scope of Claims] 1. A color image output device that converts an input color image signal to a color image output signal and outputs a color image, which stores a plurality of conversion rules for converting the input color image signal to the color image output signal. means for selecting a single conversion rule for each color region indicated by the input color image signal from a plurality of stored conversion rules; and means for converting the input color image signal based on the selected conversion rule. A color correction device in a color image output device, comprising: means for processing the color image output signal to obtain the color image output signal. 2. In the color correction device described in item 1, the conversion rule selection means divides the color space representing the input color image signal by a plane or curved surface parallel to or intersecting the digital density axis, and selects each subspace. A color correction device for a color image output device, characterized in that a different conversion rule is assigned to a color image output device.