JPS59189782A - Picture processing device - Google Patents

Abstract

PURPOSE:To obtain a high-quality reproduced picture by providing an output means which outputs plural threshold matrixes and constituting this means so that individual thresholds of the first and the second threshold matrixes have a prescribed relation. CONSTITUTION:Threshold data outputed from the same addresses of dither ROMs 6a and 6b which have threshold data of threshold matrixes shown in Fig. are compared with picture data in comparators 5a and 5b simultaneously, and comparison results S1 and S3 are outputted. In an AND gate 10a, an output S2 having a 1/2 picture element width is obtained by a picture element clock CLK and the output S1. Similarly, an output S4 is obtained in an AND gate 10b. An OR gate 11 combines both outputs to generate an output S5. The first half signal and the latter having the 1/2 pulse width are combined and are inputted to a printer. Consequently, laser modulation is performed in the printer 9 in accordance with the inputted pulse width to generate dots with a ternary or binary output.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an image processing device for obtaining high-quality reproduced images.

BACKGROUND OF THE INVENTION Various methods have been proposed for outputting images with halftones in digital printers and the like.

One such method is the dither method. This dithering method, as shown in FIG. This is what is output. There are various methods for creating a threshold matrix in this dither method. Among them, Bayer's pattern is one that has been known from the past. As shown in FIG. 2, this is made up of, for example, an 8×8 threshold value matrix, and if the input image density is input up to 64 levels, density expression of 65 gradations is possible.

In this Bayer pattern, the threshold values in the threshold value matrix are very dispersed, and when an image is reproduced using white and black dots, the 8×8 pattern is difficult to see and is considered to be an ideal pattern. However, if Bayer's pattern is actually used in a printer, the printer will faithfully follow this pattern.
The quality of the reproduced image differs depending on whether or not it has the ability to reproduce the image.

In other words, since the Bayer pattern has highly dispersed threshold values, the printer must always form a reproduced image with precisely sized dots. However, with regular printers, toner or ink smudges.

Due to scattering, spread of dots, responsiveness of dot writing, etc., it is difficult to reprint dots faithfully. Therefore, Bayer's pattern is not often used in conventional printers.

In addition to the Bayer pattern, a spiral pattern as shown in FIG. 3 has also been considered. In this pattern (threshold matrix), the smallest threshold is placed at the center, and larger thresholds are placed toward the periphery. Third
When the threshold matrix shown in the figure is used, since the number of black dots increases from the center of the reproduced image, the spatial frequency does not increase much and the performance of the printer can be fully utilized. However, when an image is reproduced using a threshold matrix as shown in FIG. 3, it is not possible to obtain a high-quality image due to a reduction in resolution and the like. In addition, the connected parts of the patterns become vertical and horizontal sushi, making imperfections in the image noticeable.

When the Bayer or spiral pattern described above is used in a laser beam printer, for example, the gamma characteristic (the relationship between the number of dots and the density) is affected by the performance of the printer, so it does not form a straight line as shown in Figure 4, and the reproducibility of the density is affected. indicates that it is bad.

Further, as an improved version of the above-mentioned spiral pattern, a halftone dot pattern as shown in FIG. 6(a) has been considered. As can be seen from the figure, the threshold values are arranged so that the black dots spread out at multiple locations, and are relatively low compared to the halftone dot patterns of newspapers and the like. When a threshold matrix as shown in FIG. 6(a) is used in a printer, the γ characteristic becomes a straight line as shown in FIG. 5, indicating good density reproducibility. However, the reproduced image has problems with gradation, etc., and cannot be said to be a high-quality image.

Object The object of the present invention was made in view of the above points, and is to provide an image processing device that can obtain high-quality reproduced images.

Example An embodiment of the present invention will be described below with reference to the drawings.

FIG. 7 is a control block diagram of the image processing apparatus in this embodiment.

In the figure, reference numeral 1 denotes a document, and an image of the document is irradiated by an exposure lamp (not shown) or the like, and is imaged on an image pickup device (CCD) 3 via a lens 2. 4 converts the analog image output of CCD 3 into a 6-bit digital image output (image data)
This is an A/D converter for converting. Since the A/D converter 4 has a resolution of 6 bits, it is possible to express 64 levels of gradation.

6a and 6b are ROMs having threshold data of the threshold matrix as shown in FIGS. 6(a) and 6(b), respectively;
Reading of the threshold value data of each ROM 6a, 6b is performed in synchronization with the counting operation of the address counter. This address counter 7 receives a pixel clock generated from a pixel clock generator (not shown) and a horizontal synchronization signal (BD double signal) generated from the printer 9, performs counting operations, and performs counting operations on the horizontal side of the threshold value matrix via the address bus 23. The data is extracted by sequentially accessing the directional and vertical addresses (3 bits each).The pixel clock generator and the BD multiplication signal are well known, so a detailed explanation will be omitted.

5a and 5b are comparators, and ROM6
The threshold value data outputted from the data buses 22a and 22b from the A/D converter 4 is compared with the image data outputted from the A/D converter 4, and the image is determined. When the data is threshold data, "0" is output.

The threshold data of the same address outputted from the ROMs 6a and 6b are simultaneously compared with the image data in the comparators 5a and 5b, respectively, and the respective comparison results SL and S3 are input to the synthesis circuit 8. The synthesis circuit 8 is a circuit for determining the pulse width to be output to the printer 9 based on the respective comparison results.

A detailed example of the synthesis circuit 8 is shown in FIG. In the figure,
SL and S3 are outputs from the comparators 5a and 5b, respectively, and CLK is the aforementioned pixel clock with a duty ratio of 50%. Also 10a.

1Ob is an AND gate, 11 is an OR gate, and the output S5 of the OR gate 11 is input to a printer 9 (for example, a laser beam printer). FIG. 9 is a timing chart of the circuit shown in FIG. 8, and the operation of the circuit will be explained based on FIG. Output SL in synchronization with pixel clock CLK,
S3 are output from comparators 5a and 5b, respectively. AND gate 10a connects this pixel clock CLK to comparator 5a.
By performing an AND with the output Sl from , an output s2 of 1×2 pixel width (1×2 pulse width) is obtained. Similarly, the AND gate lob obtains an output S4 having a width of 1×2 pixels by ANDing the pixel clock inverted by the inverter 12 and the output S3 from the comparator 5b. or gate 11
combines the outputs of AND gates 10a and 10b to form output S5 to printer 9. In this way, in this embodiment, the first half and second half 1×2 pulse width signals outputted from the game consoles 10a and 10b, respectively, are combined and input to the blink. Therefore, in the printer 9, ``is'' the synthesis circuit 8.
The laser is modulated according to the pulse width input from the
It forms dots with ternary or binary output. In this embodiment, the diameter of the dot formed when the output of 1×2 pulse width is input to the printer 9 is half the diameter of the dot formed when the output of 1 pulse width is input. i.e. 1
When the output of X2 pulse width is input to the printer 9, it becomes a three-value output (white, gray), and the output of one pulse width is
When input to , it becomes a binary output (white, black).

Next, the threshold matrix shown in FIGS. 6(a) and 6(b) will be explained. As mentioned above, the threshold matrices shown in FIGS. 10A and 12B are stored in the ROMs 6a and 6b, respectively. Moreover, each threshold value of the threshold value matrix of FIG. 11B is obtained by interchanging the even numbers and odd numbers of the threshold value matrix of FIG. 11A. That is, they are exchanged as follows: 1←2, 3H4, 5H6---.

When an image is reproduced using a threshold matrix in which even numbers and odd numbers are exchanged in this way, there are the following advantages. Note that here, we will consider a case where image data of a uniform value is gradually increased and input. Since this embodiment uses binary and ternary output formats, when uniform image data "l" is input, first the threshold "I" of the threshold matrix shown in FIGS. 6(a) and (b) is input. When part 11 is output as 3 values and then uniform image data ゛2゛° is input, the threshold value ゛2'
' part is output as binary value. Then, when the uniform image data "3" is input, the part with the threshold value "3" is output as a ternary value, and when the next uniform image data "°4" is input, the part with the threshold value 114 I+ is output. is output as a binary value. In this way, in this embodiment, as the input image data increases, the same cylinder is output in 3 values and then in 2 values, and the number of dots is increased centering on the dark values at multiple locations. , gradation, and resolution are excellent, and the spatial frequency does not become extremely high, making it possible to avoid image unevenness.

Although this embodiment has been described using an 8×8 threshold matrix as an example, this embodiment is not particularly limited to this, and threshold matrices of other sizes may be used. Further, the threshold values of the dark value matrix may be formed sequentially without using the ROM.

Furthermore, when changing the density of the reproduced image, the threshold values may be changed without changing the original arrangement order of the threshold values by performing calculations on the basic pattern (threshold value matrix).

In this embodiment, a dithering method has been described in which one input pixel corresponds to one component of a threshold matrix, but the present invention is also applicable to a density pattern in which one input pixel corresponds to all components of a threshold matrix, or a method in between. (One input pixel is made to correspond to multiple components among all the components of the threshold matrix.

) can also be applied.

Effects As detailed above, according to the present invention, it is possible to obtain a high-quality reproduced image with excellent gradation and resolution and no image unevenness.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining the dither method, Figure 2 is a diagram for explaining the dither method, and Figure 2 is a diagram for explaining the dither method.
3 is a diagram showing a threshold matrix using a spiral pattern, FIG. 4 is a diagram showing γ characteristics when using a Bayer or spiral pattern, and FIG. 5 is a diagram showing a threshold matrix using a spiral pattern. 6(a) and 6(b) are diagrams showing the threshold matrix in this embodiment. FIG. 7 is a control block diagram of the image processing device in this embodiment. FIG. 8 9 is a detailed diagram of the synthesis circuit 8, and FIG. 9 is a timing chart of signals of each part of the synthesis circuit 8. Here, 3 is a CCD, 4 is an A/D converter, 5a, 5
b is a comparator, 6a and 6b are ROMs, 7 is an address counter, 8 is a synthesis circuit, and 9 is a printer. Applicant Canon Co., Ltd.

Claims (1)

[Claims] In an image processing apparatus that compares input image data and a threshold matrix and determines processing for each dot depending on whether it is larger or smaller than the threshold, it has an output means for outputting a plurality of threshold matrices, and each of the first threshold matrices is An image processing device characterized in that the threshold value and each threshold value of the second threshold value matrix are configured to have a predetermined relationship.