JPH04346571A - Black replacing method and black replacement processing circuit - Google Patents

Abstract

PURPOSE:To reduce a memory capacity by providing a table previously deciding the combination of amounts for transferring respective three primary colors in subtraction and a subtraction circuit to subtract the transfer amount of black from the respective color transfer amounts of picture elements. CONSTITUTION:A color information storage circuit 13 receives color information 12 showing the colors of picture elements from an information source, and the address of a memory 6 for black replacement processing is added synchronously with the reception of pixel information 1. Values outputted from black density change tables 24-26 are multiplied with a value 9, which is set from '0' to '1' in advance, by a coefficient multiplication circuit 3 and afterwards compared with the contents of the memory 6 at the position of the correspondent picture element by a comparator circuit 4, and a smaller value is selected and stored in the memory 6 at the corresponding picture element position. The value is inputted to one of primary color separation and change tables 31-33 selected by a table selection circuit according to the value of the color information storage circuit 13 for which black density information 15 to be replaced is outputted from the memory 6. For the value outputted from one of the tables 31-33, the information 1 is subtracted by a subtraction circuit 8, and a real transfer amount 17 in the color is calculated.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing technique for improving the image quality of multicolor printing.

0002

BACKGROUND OF THE INVENTION Improvements in color reproducibility, sharpening of image contours, etc. by black replacement are reported in Part 1 of the book edited by the Imaging Electrophotography Society, and are particularly effective in the printing field.

FIG. 3 shows a block diagram of a conventional black replacement processing circuit.

The input pixel information is density information based on red information 41, blue information 42, and green information 43, which are called additive three primary colors. The selection circuit 44 selects the smallest value among these pieces of color density information and sets it as achromatic color information 45.

[0005] The replacement process can be expressed by the equation shown in equation 1.

[0006]

[Math 1]

After each of the achromatic color information 45 is subtracted from the additive three primary color density information 41 to 43, a conversion processing circuit 46 processes the conversion into subtractive three primary colors suitable for printing, and sends the information to a driving section of the printer.

[0008]

[Problems to be Solved by the Invention] In the conventional method, the black density is determined by simultaneously calculating the three additive primary color components.
In order to subtract black from the three additive primary color components and convert them into the three subtractive primary colors suitable for printing, when performing black replacement processing on the printer side based on the three subtractive primary colors, the printer side needs to subtract black from the three additive primary color components. It becomes necessary to receive pixel information and perform black replacement processing and subtractive three primary color conversion processing.

In particular, in the case of a printer that needs to print in plane sequential order, a memory is required to store the image information of the three additive primary colors, and at least one page for each color, three pages in total, and at least one page for storing the black image. A total of four pages of memory are required, and a conversion process from the three additive primary colors to the three subtractive primary colors is also required, which increases the overall cost of the printer.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to reduce the memory capacity required for processing on the printer side and perform black replacement processing at low cost.

[0011]

[Means for Solving the Problems] Therefore, the black replacement processing circuit of the present invention uses four colors, which are three subtractive primary colors plus black, to obtain black from 0 to maximum density in a printer that prints in field sequential order. A table predetermining the combinations of the transfer amounts of each of the three subtractive primary colors, and at least one table containing the maximum black density for each pixel obtained by referring to the table with the transfer amount of each color of the pixel composed of the three subtractive primary colors. Comparison replacement in which the black replacement processing memory for the screen and the maximum black density obtained by referring to the table are compared with the contents of the black replacement processing memory at the position of the target pixel, and the smaller value is stored in the black replacement processing memory. The present invention is characterized by being equipped with a circuit, a predetermined table for converting black density into a black transfer amount, and a subtraction circuit for subtracting the black transfer amount from each color transfer amount of a pixel.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a conceptual diagram showing the black replacement method of the present invention.

Pixel information 21 to 23 consisting of subtractive three primary color transfer amounts (yellow, violet, and blue) is input to optimum black density conversion units 24 to 26 corresponding to the respective colors.

The optimum black density converters 24 to 26 are composed of combinations of the transfer amounts of each of the three subtractive primary colors to obtain black from 0 to the maximum density, and when the combinations have a nonlinear relationship, the table defined by the shape.

The maximum black components 27 to 29 that can be generated independently for each color are determined for each color transfer amount input. In this determination process, the transfer amount of colors other than the input color is assumed to be an amount that will generate the highest black density for the input color.

The smallest value min (Ky, Km, Kc) among the maximum black densities 27 to 29 is the equivalent black component of the target pixel.

Further, the value multiplied by the black replacement ratio p is output as the actual black density 15. Further, the actual density 15 is passed through a density transfer amount converter 14 to determine a transfer amount 16.

The density transfer amount converter 14 converts the actual black density to 15.
A conversion operation is performed in which the input is the black transfer amount 16, and if the input/output relationship has a nonlinear relationship, it is defined in the form of a table.

The determined actual density 15 is sent to the primary color separation units 31 to 3.
3 and subtractively decomposes it into three primary color components to determine the transfer amounts 34 to 36 to be replaced in each color.

The primary color separation units 31 to 33 are defined to have an inverse input-output relationship to the optimum black density conversion units 24 to 26.

Transfer amounts 37 to 39 of the subtractive three primary colors are determined by subtracting the transfer amounts 34 to 36 to be replaced from the primary color information 21 to 23 of the pixels to be replaced with black.

In this black replacement method, the black component is extracted using the conventional three additive primary colors, and only the hue components excluding the black component are converted into the three subtractive primary colors, thereby nullifying the color mixing characteristics of each color ink as much as possible. This has suppressed the occurrence of color differences due to black replacement processing, but conversely, the maximum amount of black component contained in each color of the corresponding pixel is estimated from the subtractive three primary colors, taking into account the color mixing characteristics of each color ink, and all inks are From the amount of black component common to , this is regarded as the black component density of the corresponding pixel, and the transfer amount of each of the subtractive three primary colors that achieves the black component density is calculated and subtracted from the pixel information to reduce the color difference due to black replacement. The occurrence is kept to a minimum.

[0023] Therefore, a feature of this method is that all processing is completed using the three subtractive primary colors, and especially when applied to a printer that prints in plane sequential order, the memory required to handle the three additive primary colors can be significantly reduced. becomes possible.

FIG. 2 is a block diagram showing the black replacement processing circuit of the present invention.

This circuit has two operating modes: a black component extraction mode and a black replacement execution mode. In black component extraction mode, pixel information 1 of each color is sequentially obtained from an information source (not shown).
and stores the black component in the black replacement processing memory 6;
In the black replacement execution mode, pixel information 1 of each color is again screen-sequentially obtained from an information source (not shown) based on the already extracted black component.
is received, and the actual transfer amount 17 is obtained by subtracting the transfer amount of the black component of each color from the pixel information 1.

The selection of the operating mode is performed by the mode controller 10.

The mode controller 10 receives control data from the host computer, on/off information of the power switch of this circuit, or other specific manual switches, etc. as control information, and selects a mode based on this control information.

There are various possible timings for selecting the black component extraction mode, such as when the power is turned on, when new printing is started, or when a specific manual switch is pressed.

The configuration and operation of this device will be explained below for each mode.

Black component extraction mode The color information storage circuit 13 receives color information 12 indicating the color of a pixel from an information source (not shown).

The table selection circuit 2 that selects the black density conversion tables 24 to 26 in accordance with the color information 12 is switched, receives pixel information 1 of each color sequentially from an information source (not shown), and selects the black density conversion tables 24 to 26 in accordance with the color information 12. 26.

After resetting the address generation circuit 5 for the black replacement processing memory 6, the mode controller 10 puts the black replacement processing memory 6 into a read/write state.

The clock of the address generation circuit 5 is connected to the pixel information synchronization clock 11, and the address of the black replacement processing memory 6 is added in synchronization with the reception of the pixel information 1.

The values output from the black density conversion tables 24 to 26 are multiplied by a preset value 9 from 0 to 1 (p in FIG. 1) in the coefficient multiplication circuit 3, and then the values are converted to black at the corresponding pixel position. It is compared with the contents of the replacement processing memory 6 by the comparison circuit 4, and the smaller value is selected and stored in the black replacement processing memory 6 at the corresponding pixel position.

These series of operations are subtractive for 3 primary colors.
Executed times.

After the third execution is completed, the contents of the black replacement processing memory 6 indicate the black density to be replaced in each pixel.

Black replacement execution mode The color information storage circuit 13 receives color information 12 indicating the color of a pixel from an information source (not shown).

After resetting the address generation circuit 5 for the black replacement processing memory 6, the mode controller 10 sets the black replacement processing memory 6 in a write-inhibited state.

The black density information 15 to be replaced is outputted from the black replacement processing memory 6 in synchronization with the reception of the pixel information 1, and the primary color separation conversion table is selected by the table selection circuit 7 according to the value of the color information storage circuit 13. 1 out of 31-33
is entered into.

The values output from the primary color separation conversion tables 31 to 33 are subtracted by pixel information 1 in a subtraction circuit 8, and the actual transfer amount 17 for that color is determined.

The actual transfer amount 17 to the printing mechanism section (not shown)
is transmitted, and one screen is printed.

These series of operations are subtractive for 3 primary colors.
Executed times.

After the third execution is completed, the contents of the black replacement processing memory 6 are sent to the printing mechanism (not shown) via the density transfer amount conversion table 14 and printed, and all operations are completed.

Although the content of the black replacement processing memory 6 is printed last in the above example, it may be printed at any time.

As described above, in this embodiment, the only memory necessary for the black replacement process is the black replacement process memory 6.
Further, since there is no need for conversion processing from three additive primary colors to three subtractive primary colors, there is no need to impose a large cost burden on the printer side.

The present invention is not limited to the above-described embodiments, but includes various modifications without departing from the spirit thereof, such as cases where the present invention is realized entirely by software.

[0047]

[Effects of the Invention] As explained above, according to the present invention, black replacement processing can be performed from subtractive three primary color information, and furthermore, black replacement processing can be performed using only one screen's worth of black replacement processing memory. The memory capacity required for processing can be significantly reduced, and black replacement processing can be performed at low cost.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing a black replacement method of the present invention.

FIG. 2 is a block diagram showing a black replacement processing circuit of the present invention.

FIG. 3 is a configuration diagram of a conventional black replacement processing circuit.

[Explanation of symbols]

1 Pixel information 4 Comparison circuit 6 Memory for black replacement processing 8 Subtraction circuit 14 Density transfer amount conversion table 24-26 Black density conversion table 31-33 Primary color separation conversion table

Claims (2)

[Claims] Claim 1: The amount of transfer of each color in a pixel composed of three subtractive primary colors is compared with the combination of the amount of transfer of each of the three subtractive primary colors to obtain black from 0 to the maximum density, and the amount obtained for each color is calculated. After obtaining the maximum possible black density, select the smallest value, and then determine the value multiplied by a predetermined constant exceeding 0 to a maximum of 1 as the black density to be replaced, and Obtain the replacement transfer amount of each color from the combination of the transfer amounts of each of the three subtractive primary colors to obtain black, subtract the replacement transfer amount from the transfer amount of each color at the pixel to obtain the actual transfer amount of each of the three subtractive primary colors, and perform the replacement. A black replacement method characterized in that after converting black density into a black transfer amount, printing is performed using four types of transfer amounts: an actual transfer amount of the three subtractive primary colors and a black transfer amount. [Claim 2] Using four colors, which are the three subtractive primary colors plus black,
In a printer that prints in a field sequential manner, there is a table that predetermines the combination of the transfer amount of each of the three subtractive primary colors to obtain black from 0 to the maximum density, and a table that specifies the transfer amount of each color of the pixel composed of the three subtractive primary colors. A black replacement processing memory for at least one screen that stores the maximum black density for each pixel obtained by referring to the table, and a maximum black density obtained by referring to the table and the contents of the black replacement processing memory at the position of the target pixel. A comparison and replacement circuit that compares and stores the smaller value in the black replacement processing memory, a predetermined table that converts black density into a black transfer amount, and a subtraction that subtracts the black transfer amount from each color transfer amount of a pixel. A black replacement processing circuit characterized by being equipped with a circuit.