JPH02174464A - Recorder - Google Patents

Abstract

PURPOSE:To keep excellent picture quality by selecting a dither pattern suitable for the print density corresponding to the changeover of the print density and applying dither processing. CONSTITUTION:A dither matrix sent from a dither pattern selection circuit is stored in a RAM 21, an 8-bit picture information data is used to apply dither processing, the data is converted into a 2-bit picture signal and sent to a printer engine side. A comparator data selector 22 is reset by a horizontal synchronizing signal and a threshold level is ent to the digital comparator 23 after the dither matrix in the RAM 21 is synchronized with a picture clock. A digital comparator 23 compares a threshold level from the data selector 22 with a picture information data from a host computer to decide on/off of each picture element.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a recording device that inputs a multivalued image signal from a host computer or an external device such as an image league, and outputs a high-quality image including halftones.

[Prior Art] In recent years, printer devices using electrophotography, such as laser beam printers, have been widely used as output devices for computers. Such printer devices have many advantages such as high image quality and low noise, and are rapidly expanding in the field of desktop publishing (hereinafter referred to as DTP), especially due to their high image quality.

At the same time, with the development of host computers or controllers that control the above-mentioned printer devices, various processes have become possible in reproducing halftones.

For example, when obtaining halftones as a hard copy, the area gradation method using the dither method is currently widely used.

This means, for example, that the pixel density of a printer device is 300 dp.
i, a matrix of 8 pixels x 8 pixels is constructed, and the gradation is expressed by which pixel in this matrix is printed according to the image data. In this case, the resolution (hereinafter referred to as !a number) for expressing halftones is 37.5 lines per inch, and the number of gradations is 64 gradations. In addition, the number of lines and the number of gradations are not limited to the above values, and can be changed to, for example, 4 pixels x 4 according to the operator's needs.
Due to the pixel matrix, 75&! , 16 gradations, etc. can be adopted.

Further, the types of dithering methods are divided into distributed type and concentrated type depending on how pixels are filled.

FIG. 6 shows an example of a 4 pixel by 4 pixel dither matrix and dot pattern. FIG. 6(a) is an example of a distributed type, and FIG. 6(b) is an example of a centralized type. In the figure, the numerical values in the dither matrix indicate the order in which dots are placed, and the number of dots increases in order from data with the lowest density based on a predetermined threshold value.

[Problems to be Solved by the Invention] However, the above-mentioned conventional technology has only one dot pattern for one matrix of 8 pixels x 8 pixels or 4 pixels x 4 pixels, and the print density of the printer engine is limited. Since no consideration was given to switching, there were the following inconveniences.

For example, if the print density of the printer engine is 300 dp
For printers that have both i and 600 dpi and a 4x4 dither matrix, the printing density is set to 300 dpi.
When switching from i to 600 dpi and trying to express gradation using the same 4×4 dither matrix, the number of lines will double, allowing for more detailed expression. However, for example, when placing a dot at only one pixel in the matrix, which is the gradation of "1," it is difficult to represent this gradation because the reproducibility of each pixel decreases due to the doubling of the number of lines. Therefore, it will come out completely white.

In addition, on the contrary, when only one pixel is removed from a gradation of "15", that is, solid black, the reproducibility is low, so
It becomes black and crushed.

This reduces the number of tones that can be reproduced.

This results in an image with a strong contrast between black and white, so-called γ.

An object of the present invention is to provide a recording device that can maintain good image quality even when the print density is changed.

[Means for Solving the Problems] The present invention is capable of selectively switching between a plurality of printing densities, and has a data input unit for inputting multivalued image data, and converts the multivalued image data into a halftone image by a dithering method. A recording device that generates a plurality of print densities includes a storage means for storing optimal dither patterns for each of a plurality of print densities, and one of the dither patterns stored in the storage means is selected in response to switching of the print densities. and an image processing means that binarizes multivalued image data according to the selected dither pattern to express halftones.

[Function] In the present invention, in response to a change in print density, a dither pattern suitable for the print density is selected and dither processing is performed. Good image quality with excellent reproducibility can be maintained.

[Embodiment] FIG. 1 is a block diagram showing a first embodiment of the present invention.

The printer device according to this embodiment includes a dither pattern selection circuit 1, an image data processing circuit 2, and an image clock generation circuit 3, and dithers image information data sent from a host computer 100 to generate a halftone image. It is something that generates.

The host computer 100 sends 8-bit image information data to the printer at a predetermined timing based on a horizontal synchronization signal from the printer.

The dither pattern selection circuit l is a host computer 10
A signal specifying the print density sent from 0 (hereinafter referred to as dpi
Based on the switching signal), a dither matrix suitable for the selected print density is selected from among the dither matrices stored in the internal ROM and sent to the image data processing circuit 2.

FIG. 2 is a block diagram showing the configuration of the image data processing circuit 2. As shown in FIG.

The image data processing circuit 2 includes an internal RAM 21, a comparison data selector 22, and a digital comparator 23.
The dither matrix sent from the dither pattern selection circuit 1 is stored in the RAM 21, waits for 8-bit image information data, performs dither processing, converts it into a 2-bit image signal, and sends it to the printer engine (not shown). It is something.

The comparison data selector 22 is reset by the horizontal synchronization signal, and the dither matrix in the RAM 21 is
The digital comparator 23 sequentially synchronizes with the image clock from the first column to the second column, third column, etc.
The threshold value is sent to Note that this operation is repeated for the same line until scanning for one line is completed.

The digital comparator 23 compares the threshold value from the comparative data selector 22 and the value of the image information data from the host computer 100, and when the value of one image information data is larger than the threshold value, it becomes "1", and the value of the image information data. When the value is smaller than the threshold value, an image signal that becomes "0" is output.

FIGS. 3(a) and 3(b) show specific examples of dither matrices selected according to the configuration described above, and FIG. 3(a) shows the dither matrix when the print density is 300 dpi. Figure 3(b) shows a print density of 600d.
The dither matrix for pi is shown. Both of these dither matrices are 4×4 matrices, and the number of lines is 75 lines for the former and 150 lines for the latter.

The numbers in each matrix are threshold values and are compared with the values of the image information data to determine whether each pixel is turned on or off.

Further, FIG. 3(e) shows the growth process of the printed dot pattern from a light tone to a dark tone using the dither matrix shown in FIG. 3(a). When the value of the above image information data is within the range indicated below each printed dot pattern.

Printing is performed as shown by each printing dot pattern, and gradation is expressed.

On the other hand, FIG. 3(d) shows the growth process of the print dot pattern from a light tone to a dark tone using the dither matrix shown in FIG. 3(b), and this figure also shows the above image information. When the data value is within the range indicated below each print dot pattern, printing is performed as indicated by each print dot pattern, and gradation is expressed.

When the print density is 300 dpi, the reproducibility is good, so dispersed dots are distributed, but when the print density is 60 dpi, the dots are dispersed.
At 0 dpi, the reproducibility is not very good, so the concentrated dot arrangement is as follows.

FIG. 4 is a block diagram showing a second embodiment of the present invention.

In this printer device, in addition to the dpi switching signal in the above embodiment, a line number designation signal is sent to the host computer 100.
is sent to the dither pattern selection circuit 1, and a dither matrix is selected based on this.

For example, when 300 dpi is designated by the dpi switching signal and 60 lines are designated by the line number designation signal, the dither pattern selection circuit l selects the 5×5 concentrated dither matrix shown in FIG. 5(a). Select.

Also, if 600 dpi is specified by the dpi switching signal and 120 lines is specified by the line number specification signal,
The dither pattern selection circuit 1 has a 5×
Select a distributed dither matrix of 5.

Furthermore, when 600 dpi is specified by the dpi switching signal, the resolution does not need to be very high and you want to increase the number of gradations, such as when reading a landscape photograph from Image League. ,
If you specify the number of lines as 60 lines, the dither pattern selection circuit l
selects the l0XIO dither matrix shown in t55 diagram (C). This quadruples the number of gradations, resulting in a smoother output image.

In addition, in the above embodiment, 300dpi and 600dpi
Although we have explained the case of selecting two types of printing densities, for example, cases of selecting from among other combinations of printing densities such as 400 dpi and 500 dpi, or selecting from among combinations of three or more types of printing densities. It goes without saying that the present invention can be similarly applied to.

The order in which the dither matrix is filled is not limited to the above-mentioned centralized or distributed type, but also depends on the printer model, such as the exposure method such as whether the printer uses image exposure or background exposure, and the print density. It may also be possible to select the most suitable one.

[Effects of the Invention] According to the present invention, since dither processing is performed by selecting an optimal dither pattern in response to switching of printing density, gradation reproduction can be achieved regardless of changes in the number of lines due to switching of printing density. This has the effect of making it possible to obtain good images with excellent quality.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the present invention. FIG. 2 is a block diagram showing the configuration of the image data processing circuit 2 provided in the first embodiment. FIGS. 3(a) and 3(b) are schematic diagrams showing specific examples of the dither matrix selected in the first embodiment, and FIG. 3(a) shows the dither matrix when the print density is 300 dpi. , Fig. 3(b) has a printing density of 600d.
The dither matrix for pi is shown. FIG. 3(C) is a schematic diagram showing the growth process of the printed dot pattern using the dither matrix shown in FIG. 3(a). FIG. 3(d) is a schematic diagram showing the growth process of the printed dot pattern using the dither matrix shown in FIG. 3(b). FIG. 4 is a block diagram showing a second embodiment of the present invention. FIG. 5(a) is a schematic diagram showing the dither matrix and the growth process of the printed dot pattern selected when the printing density is 300 dpi and the number of lines is 60 & 1 in the second embodiment. FIG. 5(b) is a schematic diagram showing the growth process of the dither matrix and print dot pattern selected when the print density is 600 dpi and the number of lines is 120 in the second embodiment. FIG. 5(C) is a schematic diagram showing a dither matrix selected when the print density is 600 dpi and the number of lines is 60 in the second embodiment. 6(a) and 6(b) are schematic diagrams showing the growth process of a typical 4×4 dither matrix and printed dot pattern; FIG. 6(a) shows a distributed type; (b) shows a centralized type. l...Dither pattern selection circuit. 2... Image data processing circuit. 3... Image clock generation circuit, 21... RAM, 22... Comparison data selector, 23... Digital comparator. 100...Host computer.

Claims (1)

[Claims] A plurality of printing densities can be selectively switched, and
A recording device having a data input section for inputting multivalued image data and generating a halftone image from the multivalued image data by a dithering method, the recording device having a memory for storing optimal dither patterns for each of a plurality of print densities. means; selection means for selecting one of the dither patterns stored in the storage means in response to switching of the printing density; binarizing the multivalued image data according to the selected dither pattern, and converting the halftones into halftones; A recording device comprising: an image processing means for expressing;