JPS61218273A - Method for recording halftone - Google Patents

Abstract

PURPOSE:To attain a recording picture having a halftone with much fidelity to original picture information by selecting the density expression of the noted recording dot so that the apparent density gradation of the entire dot pattern is closest to the correction density of the noted region of the picture information. CONSTITUTION:For example, the density of all picture elements included in the noted region of the picture information is averaged to obtain a prescribed converted density. A dither value is added to the converting density. Then the apparent density gradation of the noted region in the recording picture is obtained from the dot pattern consisting of all the recording dots and the noticed recorded dot including in the noted region of the recording picture as to each density expression selected for the noted recording dot and the density expression of the noted recording dot is selected so that the difference between the said density and the corrected density is minimized. Thus, the recording picture having a halftone with much fidelity to the picture information as a whole is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a halftone recording method for digitally processing image information to obtain a recorded image expressing halftones.

"Prior Art" Generally, in computers and information devices, character information obtained from a document or the like is processed by converting it into a character code determined for each character. On the other hand, image information obtained from drawings, photographs, etc. is processed by converting the image information into electric signals for each pixel and converting them into digital signals using an image reading device such as an image line sensor. is being carried out.

A so-called dot printer, which records information by arranging minute dots in a pattern on recording paper, is widely used as a recording device for obtaining a hard copy from such text information or image information. For example, the character code is converted into this dot pattern by a character generator and then transferred to the recording device.

When recording characters, it is desirable that the dots be recorded sufficiently black so that the lines representing the characters can be clearly distinguished from the background color of the recording paper. A method of recording only either white dots or black dots is used. Note that the dots on which recording was performed will be expressed as black dots, and the dots on which recording was not performed will be expressed as white dots.

On the other hand, when recording image information with such a recording device,
First, image information is decomposed into its constituent pixels, and each pixel is converted into an electrical signal with a level corresponding to its density.

This is done using an image line sensor etc.
The output of the image line sensor is an analog image signal with a level corresponding to the density of the pixel.

This is converted into a digital image signal using an analog-to-digital converter. When image information is expressed in two types of density, such as text, white or black,
During this analog-to-digital conversion, a certain threshold level is set and the analog image signal is converted into either a digital image signal for recording white dots or a digital image signal for recording black dots. It is sufficient to perform valorization processing.

On the other hand, image information obtained from photographs, paintings, etc., for example, in the case of black and white photographs, is composed of completely black or white pixels and pixels of various densities located in between.

If such image information is subjected to binarization processing, a faithful recorded image cannot be obtained. Therefore, a multivalued digital image signal is obtained from the output of the image line sensor using an analog-to-digital converter capable of obtaining a digital output of, for example, 6 or 8 bits.

From this multivalued digital image signal, dots with a corresponding density can be recorded on the recording paper.

For example, a printer using thermal paper produces a darker or lighter color depending on the heat generated by the thermal head, so it is possible to record a color that is darker if it is produced at a higher temperature, or lighter if it is produced at a lower temperature. .

However, with regard to thermal paper, the degree of color development, that is,
It has been difficult to control the temperature accurately enough to accurately select the density gradation of each recorded dot in multiple stages. For example, thermal transfer printers using plain paper can express density by changing the diameter of the black dots themselves, but it is more difficult to accurately express many tones than with printers using thermal paper. Ta.

Therefore, in order to record halftones more accurately, recording methods called pattern method and dither method have been developed. The pattern method and dither method each have various aspects, and there are also combinations of the two, but representative examples of them are as follows.

The pattern method refers to a set of a certain number of recorded dots (hereinafter referred to as a dot pattern) that constitutes image information.
pixels. In other words, 1 that constitutes the image information
The density of each pixel is reproduced with one dot pattern. Assuming that each dot can select either white or black density expression, the apparent density gradation of the entire dot pattern can be selected in multiple stages from the combination of selected density expressions for each dot. This is what I did. (Nikkei Electronics May 7, 1984 issue, p. 171).

For example, as shown in Fig. 12, this method uses four dots (in the drawing, each dot is a white dot, a black dot is a mouth, and a black dot is Dot patterns 21 to 2. Prepare (b). By sequentially changing the combinations in which each dot is selected as white or black, five types of dot patterns 21-2s are obtained, ranging from one with no black dots to one with four black dots, as shown in the figure.

The apparent density gradation can be selected from five levels using each of these dot patterns. It goes without saying that if more dots are combined, more gradations can be expressed.

On the other hand, in the dither method, one dot is recorded for each pixel in the image information. In this method, for example, first, several types of threshold levels are provided for an analog electrical signal having a level corresponding to the density of a □ pixel, and the threshold level is changed for each pixel to obtain a binarized digital signal.

That is, for example, 1+ <L <1s <la
<i! Five threshold levels from l to I25, which are related to s, are provided. In this way, the threshold level is reached for the first pixel! , and the next pixel next to it is processed at threshold level 12, and so on, and the threshold level is changed in order. After the processing using the threshold level 15 is completed, the threshold level f is used again, and such processing is periodically repeated.

In this method, as shown in Figure 13a, the first five pixels 31 and the next five pixels 32 in the image information have different densities, and each pixel has a threshold level written below it. 1. -15 is assumed to be processed. In this case, the recorded image obtained by the dithering method described above will be as shown in the figure. That is, the area where the pixels 32 of higher density are lined up has more black dots 4, and the area where the pixels 31 of lighter density are lined up has fewer black dots 4.

"Problems to be Solved by the Invention" As described above, in the pattern method, multiple dots are used corresponding to one pixel in the image information. It has the disadvantage of being large compared to the size of .

On the other hand, in the dither method, one pixel in the image information is associated with one recorded dot of the recorded image, so that the pixels of the recorded image can be made to match the size of this recorded dot. In other words, a more detailed recorded image can be obtained.

However, for example, when recording halftones using the dither method described above for image information obtained from an image by so-called halftone dot printing, which is often used as a printing method, the halftone pitch and dither method There is a problem in that regular density unevenness, so-called moiré, occurs in recorded images due to interference with the pitch of recording density changes resulting from periodic changes in the threshold level.

The present invention has been made focusing on the above-mentioned points, and is capable of recording intermediate tones that are faithful to the original image information without causing density unevenness while reducing the size of the pixels of the recorded image. This provides a key recording method.

"Means for Solving the Problems" The halftone recording method of the present invention is a method for manually recording image information by decomposing image information into its constituent pixels and converting each pixel into an electrical signal with a level corresponding to its density. As a signal, this human drawing signal 1
One output image signal is associated with each pixel to determine its level, and recording dots with a density expression corresponding to the level of this output image signal are arranged at positions corresponding to each pixel on the recording paper.
A method is used to obtain a recorded image corresponding to the image information. here,
When determining the level of an output image signal with respect to an input image signal, a pixel in the image information and a recorded dot in the recorded image corresponding to the input image signal and the output image signal are respectively designated as a pixel of interest and a door of interest. ). Then, while setting a region of interest that includes the pixel of interest in the image information and a certain number of pixels around the pixel of interest, select the recording dot of interest in the recorded image and the density expression around the recording dot of interest. A region of interest is set that includes a certain number of completed recording dots. Next, a predetermined converted density for expressing the density of the region of interest in the image information on the recording paper is determined. A dither value predetermined based on the absolute position coordinates of the pixel of interest in the image information is added to obtain the corrected density. The density expression of the recorded dot of interest is selected so that the difference between this corrected density and the apparent density gradation of the region of interest in the recorded image is minimized, and the level of the output image signal is determined accordingly.

Specifically, for example, a predetermined converted density is obtained by averaging the density of all pixels included in the region of interest of the image information. A dither value is added to this converted density. Next, for each selectable density expression of the recorded dot of interest, the apparent density of the area of interest in the recorded image is determined from a dot pattern composed of all recorded dots included in the recorded image of interest and the recorded dot of interest. After obtaining the gradation, the density expression of the recorded dot of interest is selected so that the difference between this gradation and the corrected density is minimized.

In other words, when the area of interest in a recorded image is viewed as a dot pattern made up of a certain number of recorded dots, the apparent density gradation of the entire dot pattern is set to be closest to the corrected density of the area of interest in the image information. , select the density expression of the recorded dot of interest.

Approximately, the sum of the density gradations for each dot obtained from the density representation of each dot making up the dot pattern may be regarded as the apparent density gradation of the entire dot pattern multiplied by the number of dots. .

At this time, it is compared with the sum of the corrected densities of all pixels included in the region of interest of the image information.

Further, for example, the number of pixels included in the region of interest of the image information and the number of recording dots included in the region of interest of the recorded image are the same, and are arranged in one-to-one correspondence. In this way, the signal processing circuit is simplified and practical.

"Operation" In the halftone recording method of the present invention, as shown in FIG. 2, each pixel 50 constituting the image information 40 is converted one by one into an electrical signal of a level corresponding to its density and digitalized. The converted image is assumed to be the input image signal 41. This human drawing signal 41 may be directly created by a computer or the like. A certain amount of this input image signal 41 is stored in a storage device. At this time, the density of the pixel of the image information is converted into a density within a range that can be expressed on the recording side, and the converted density is obtained. The details will be explained in later examples.

On the other hand, a certain amount of the output image signal 42 obtained by processing the input image signal is also stored in the storage device.

Then, the density expression of the recorded dot 53 of interest in the recorded image 43 corresponding to the pixel of interest 52 in the image information 40 is selected in the following manner.

First, for example, a region of interest 51 including a pixel of interest 52 in the image information 40 and a certain number of pixels around it, and a region of interest 56 including a recording dot of interest 53 in the recorded image 43 and the same number of recording dots around it. Set. Then, the apparent concentrations of the two are compared. First, the average value of the density of the region of interest 51 of the image information 40 is calculated in advance, and then the converted density is calculated by converting this into a density range that can be expressed on the output side.

A dither value is added to this converted density to obtain a corrected density.

This dither value is a unique value predetermined based on the position of the pixel of interest in the image information, that is, its absolute position coordinates. This value is determined so as to make density selection as uniform as possible, as will be described later. At this time, the density expression of the recording dots other than the recording dot 53 of interest in the region of interest 56 has already been selected.

Therefore, by applying all possible density expressions (for example, two types of black and white or three types of black, white, and gray) that the recorded dot 53 of interest can take, the apparent density of the entire area of interest 56 of the recorded image 43 is determined. The density expression of the recorded dot 53 of interest is selected so as to be closest to the corrected density.

To do this, predetermined input image signals and output image signals in the storage device are taken out, calculations are performed on each image signal, and the results are compared.

Furthermore, by selecting the density expression of each recorded dot included in the area of interest in the recorded image, it is possible to estimate in advance what kind of density gradation the dot pattern composed of these recorded dots will appear to have. . This may be compared with the above-mentioned corrected density.

As described above, according to the halftone recording method of the present invention, when selecting the density expression of a recording dot of interest corresponding to a pixel of interest, comparison is made in units of areas including surrounding pixels and recording dots. , it is possible to sufficiently suppress the occurrence of density unevenness in the recorded image that does not exist in the original image information. Moreover, since the average value of the density of the region of interest is not used as it is for selecting recording dots, but is corrected by adding a dither value to make it uniform, density unevenness can be further suppressed.

That is, it is possible to obtain a halftone recorded image that is extremely faithful to the original image information as a whole.

Embodiment (Explanation of Block Diagram) FIG. 1 shows a block diagram of the main parts of a recording apparatus suitable for implementing the halftone recording method of the present invention.

The input image signal lO input to this device is, for example, a 6-bit multivalued digital image signal.

This device includes a first storage device 11 that stores this human-powered image signal 10, an arithmetic device 14 that performs processing to create an output image signal 13 from this input image signal 10, and a second storage device that stores the output image signal 13. It is composed of a storage device 15.

The first storage device 11 includes three shift registers 11□ that are connected in series and each can store one line of human-drawn image signals. ,11,0.11,. It consists of

In this figure, there are three flips 70, 11, 11, 11, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 11, 11, 11, and 11, each of the shift registers 1120 to 114° have three flips 70, each storing one input image signal 10.
-119 are shown separately. That is,
Each shift register 1120-11. o is divided into four blocks each in its longitudinal direction. Therefore, for example, flip-flop 11. The shift register 111.~113 is connected to the left side of the shift register 111.~113. is constructed by incorporating a large number of flip-flops (not shown) to store a human-generated image signal obtained by subtracting three human-generated image signals from an input image signal for one line.

The input image signal lO input to this first storage device 11 is
Flip-flop 11. Shift register 11 in order from
12, and then, if necessary, to another device (not shown).

Here, each flip-flop 11. The human drawing signals stored in . is input.

The second storage device has exactly the same configuration, and includes three shift registers 152o, 15-o, which are connected in series with each other and can each store one line of human-drawn image signals.
154o.

Each shift register is divided into four blocks in its longitudinal direction.

For example, shift register 15. , are three flip-flops 151 that can store output image signals one by one.
．． 152.15. and a shift register 1514 that stores the remaining output image signals obtained by subtracting three output image signals from one line's worth of output image signals.

The shift register 153o similarly includes the flip-flop 15.
．． ．． 155, 156 and a shift register 15.3, and the shift register 152o is composed of a flip-flop 15.156 and a shift register 15.3. ．． 15. ．． 15. and shift register 15
．． It is composed of 2. The output image signal 13 is a binary digital image signal of "0" or "1". Each flip-flop 151 to 1 of this second storage device 15
5. The output image signal stored in
Through 0, its contents are the gradation table memo of the arithmetic unit 14! It is input to J142.

The arithmetic unit 14 calculates the sum of each level of the nine human-powered image signals 10 read in this way, and further divides this by "9" to obtain the average level value, which can be expressed on the recording side. Conversion circuit 14 for converting into a range of concentrations. have. This conversion circuit 14. The output signal 20 (converted density) is sent to a comparator 148 via a dither correction circuit 143.

Also, eight flip-flops 152-15. The output image signal stored in is stored in the gradation table memory 1 of the arithmetic unit 14.
4. Manpower the □. In addition to these eight output image signals whose levels have already been determined, the gradation table memory 142 stores
When the other output image signal is selected as “1” and “0”
Data 21 and 22 corresponding to the density gradation at the time of recording are output when selected. Furthermore, this calculation device 14 includes an intermediate value calculation unit 14s that calculates the intermediate value of the output signal of these two data 21.22, and this intermediate value calculation unit 14. The comparator 14m compares the output signal of the conversion circuit 14 with the output signal of the conversion circuit 14, and outputs "1" when the latter is larger than the former, and outputs "0" when the latter is larger than the former. The output of the arithmetic unit 14 becomes the output image signal 13 and is sent to the flip-flop 15 of the second storage device 15. will be forwarded to. The output image signal 13 obtained in this way is stored in the second storage device 15 for a certain period of time, and then outputted to a printer or the like (not shown).

(Explanation of conversion circuit) Here, the conversion circuit 141 will be explained in more detail.

In FIG. 2, a human image signal 41 is obtained by photoelectrically converting the density of a pixel of interest 52 of image information 40. In FIG. Assume that the density of all pixels of this image information 40 is in the range from 0 to 2.0, as shown in FIG. 5, for example. On the other hand, the density range that can be expressed on the recording side is from 0 to 1.5.
In this case, it is necessary to convert the input image signal obtained from each pixel according to the capability of the recording side.

This figure 5 shows the conversion method. For example, from the pixel density on the horizontal axis of 0.8, the converted density on the vertical axis is 0.6.
It can be seen that In this example, it is sufficient to simply multiply the density of the pixel by three-quarters.

Here, it is assumed that each pixel included in the region of interest 51 of the image information 40 in FIG. 2 has a different density. Find the sum of the levels of the nine input image signals obtained from each of these pixels, then divide by "9", and then convert using the conversion method shown in Figure 5 to obtain the average density of the area of interest as the converted density. It can be calculated.

For this purpose, the conversion circuit 141 is configured by combining an addition circuit and a multiplication circuit that calculates the sum of the levels of each human image signal and performs processing for conversion. It goes without saying that either the calculation for calculating the sum of the human image signals or the conversion process may be performed first.

(Description of Recording Method) FIG. 2 is an explanatory diagram illustrating the correspondence between image information 40, input image signal 41, output image signal 42, and recorded image 43 in the method of this embodiment. The image information 40 is decomposed into each pixel 50 that constitutes it. Here, a region of interest 51 including nine pixels is set. Among these pixels, the pixel in the lower right corner is the pixel whose density expression is currently determined on the output side, and is referred to as the pixel of interest 52.

The arithmetic unit 14 determines the level of the output image signal 42 based on the human image signal 41 obtained by converting the pixel 52 of interest into a digital signal with a level corresponding to its density. Depending on the level of this output image signal 42, a recorded dot 53 of interest is recorded. This recorded image 43 also has image information 40
One recording dot 55 is recorded in one section. At this time, recorded image 4
3, a region of interest 56 including nine recording dots 55 is also set. The area of interest 56 of this recorded image 43 is based on the image information 40.
A recording dot located in exactly the same positional relationship as the region of interest 51 and corresponding to the pixel of interest 52 is called a recording dot of interest 53. It is this recording dot 53 of interest that has now been selected for density expression.

FIG. 3 is an explanatory diagram illustrating the operation of shifting one output image signal for each input image signal over time.

The region of interest 51 of the image information 40 (FIG. 3a) is sequentially shifted to the right (in the direction of arrow 58) by the width of one pixel, and correspondingly, the region of interest 56 of the recorded image 43 (FIG. 3b) is shifted to the right (in the direction of arrow 58). Also 1
The recording dots are sequentially shifted to the right by the width of the recording area. After repeating this to the right end, press down (arrow 59)
The same thing is done by shifting one step (width of one pixel) in the direction).

The level of the output image signal is determined one by one using the @ number.

(Description of operation of storage device) FIG. 4 shows how the human image signal obtained from the image information 40 shown in a of FIG. 3 is transferred in the first storage device 11 shown in FIG. FIG.

First, in FIG. 4a, the position coordinates of each pixel of the image information 40 of FIG. 3a are arranged and displayed in association with each other.

These position coordinates are 1, 2, 3...
...P, and the positions in the sub-scanning direction (direction of arrow 59 in Figure 3a) are set to [2, 3 in order from the top], then this is (m, n
).

The part surrounded by the broken line in this figure corresponds to the region of interest 51'.

Assuming that the display of each position coordinate represents an input image signal corresponding to each pixel, this human-powered image signal is stored in the first storage device 11 in FIG. 1 (1, 1>, (2,
I), <3.1)... (P.

1), (1,2), (2,2)... (P
, 2), (1, 3), . . . (P, 3), at a certain point the human-powered image signal will be stored as shown in FIG. In this b, the parts surrounded by solid lines are the shift registers 111 in FIG.
It corresponds to 114°.

That is, at this time, the nine flip-flops 11. of FIG. .about.119 store the next input image signals surrounded by the broken line 6I in FIG. 4, respectively.

(2,1), (3,1), (4,1>(2,2>, (3,2), (4,2) (2,3), (3,3), (4,3 ) Comparing this with the image information 40 in FIG. 3, it can be seen that the human image signal corresponding to each pixel in the region of interest 51' surrounded by the broken line is stored here.

The second storage device 1 shown in FIG. 1 stores the output image signal.
5 operates in exactly the same way.

Therefore, the third rI! Pixel of interest 6 of image information 40 shown in J
When an input image signal corresponding to .3 is applied to the flip-flop 111 of the first storage device 11 shown in FIG. If the output image signal whose level is determined according to the input image signal is manually generated, each flip-flop stores image information and all image signals corresponding to the area of interest in the recorded image. become.

Incidentally, the image signal 63 of the pixel of interest in the region of interest 51' in FIG. 3 corresponds to the human image signal (4, 3) shown in FIG. 4.

(Operation of dither correction circuit) In the halftone recording method of the present invention, a dither value is added to the converted density thus obtained to calculate a corrected density.

The dither value is determined as follows.

First, as shown in FIG.
A matrix consisting of 4 pixels horizontally is divided vertically and horizontally as one IJ sock section. Then, for the 16 pixels included in each section, a unique dither N062 is applied to the relative position coordinates within that section 60. The dither numbers are assigned so as to be distributed as much as possible within this section. and,
A dither value is determined corresponding to this dither NO. This dither value ranges from "-0,07" to "0.07'," for example, as shown in FIG. It is determined in "Ol" increments.

As a result, for example, if the pixel of interest is at (6,7) of the absolute position coordinates 64 indicated by the arrow 63 in FIG.
2, 3) are the relative position coordinates 61 within the section 60. A dither value N062 is obtained from the relative position coordinates 61, and a dither value 67 is determined using FIG. As is clear from FIG. 6, after all, specific dither numbers and dither values are specified in advance for the absolute position coordinates 64 of all pixels in the image information, so the dither values are immediately determined from the absolute position coordinates. You can make a table.

FIG. 8 is a block diagram of a dither correction circuit 143 using this dither table ROM.

When the main scanning synchronization signal is counted by the counter 191, the coordinates in the arrow direction 71 (main scanning direction) in FIG.
When counting by 2, the coordinates in the arrow direction 72 (sub-scanning direction) in FIG. 6 are output from the counter 192. The output signals from the counters 191 and IL correspond to absolute position coordinates, and when this signal is input to the address of the dither table ROM 1431 storing the dither table, the corresponding dither values 14 and 3 are output. Conversion concentration 143. When inputting the dither value 14.2 and the dither value 14.2 to the address of the correction ROM 14sz, the sum of the two becomes 145. is output.

Here, as shown in FIG. 6, a region of interest 73 is determined,
Assuming that the absolute position coordinates of the pixel of interest 74 are (4, 3), this region of interest 73 is included in the upper left corner section. The relationship between the absolute position coordinates of each pixel included in this section, the dither number, and the dither value is shown in Table 1.

Table 1 Therefore, the relationship between the density of each pixel in the region of interest 73, the converted density, and the corrected density is as shown in Table 2.

As described above, the corrected density can be determined using a relatively simple circuit configuration.

(Operation of arithmetic device) When the input image signals are input manually in this way, each of the input image signals (2, 1) (2, 1) (4) surrounded by the broken line in Figure 4
.

Here, the positional coordinates of the input image signal corresponding to the pixel of interest are (4, 3) as explained in Fig. 4, and the average level of the human input image signal in this area of interest including this is shown below. Described. At this time, the density of the pixel of interest in the image information is 0.8
The converted concentration calculated using the table in FIG. 5 is 0.6 as shown in Table 3. Then, from Table 2, the corrected density by adding that dither value is 0.56 as shown in Table 1.
It is.

Also, when the level of the output image signal corresponding to the recorded dot of interest is selected as "1" (recording density 1 is displayed in Table 1) and when it is selected as "0" (recording density 0 is displayed in Table 1). ), the density gradation of the dot pattern obtained by the combination of output image signals at that time is listed in the bottom column of Table 1.

In FIG. 9(A), a region of interest 51 of image information corresponding to this third table is displayed. It is assumed that a portion with a high hatching density has a high concentration. Further, FIG. 5B shows a recording dot pattern in the case of a recording density of 1 in Table 1, and FIG. The only difference between the two is the recorded dot 53 of interest.

Table 3 Conversion circuit 14 shown in Figure 1. converts the nine input image signals shown in Table 3, and the resulting data is "0.
6'' is determined and then passed through the dither correction circuit 143 to the comparator 14.6''.
Transfer to.

Similarly, the gradation table memo 1J that processes the output image signal
142 (FIG. 1) outputs density gradations of 22 and 21 of the dot pattern obtained by the combination of output image signals for recording density 1 and recording density 0 shown in Table 3, respectively. The values are "0.70" and "0.55" for each concentration in Table 3. An intermediate value between these two values is calculated by an intermediate value calculator 14. Find it by

This calculation may be performed, for example, by halving the sum of both.

It is clear that this intermediate value is "0.625". In addition to this, the output of the dither correction circuit 143 (Fig. 1)
0.56'', this value is lower than this intermediate value.

Comparator 14. is the intermediate value calculator 14. The output of “0.625
” as the threshold level and the dither correction circuit 143
Processes the output “0.56” and changes the value of the output image signal 13 to “
0''. As a result, the dot pattern shown in FIG. 9(C) is selected.

Here, as shown in FIG. 10, processing of an input image signal corresponding to a pixel at the upper left corner of image information will be described.

At this time, input image signals other than those of the pixel of interest 52 are
It is not stored in the flip-flops 11□-11 in FIG. Of course, the flip-flop 15. which stores the output image signal. ~159 has nothing stored at all. Therefore, in advance, each shift register 11° to 11. and 1
5. ~15. Clear all to zero. In this way, each flip-flop acts in the same way as a blank space, and the above-described operation can be performed without any trouble.

According to the method of the embodiment described above, for example, the density of recording dots is 1 per inch (25.4 mm).
If a recording device with 00 to 150 dots is used and the area of interest contains a total of 25 recording dots (5 vertically and 5 horizontally), the image obtained from the original with halftone dot printing will be When information is recorded in halftones, the occurrence of moiré can be sufficiently effectively suppressed.

"Modification" Incidentally, in the present invention, a memory device configured with a random access memory, etc., for example, is used as a storage device for storing human-powered image signals and output image signals, and input/output of each image signal is performed. The calculation may be performed by a microprocessor.

Further, any input image signal may be used, such as one read by an image line sensor or one stored in a storage device such as a disk attached to a convenience store or the like.

In addition, the density expression of recording dots is black, gray, and white.
If the color of the seeds can be recorded, three types may be selected, or if the size and shape of the dots can be changed, more types may be selected.

Further, the pixel of interest does not necessarily have to be located at the lower right corner of the region of interest of the image information. As shown in FIG. 11, the region of interest 51
There is no problem even if the pixel of interest 52 is located at the lower center corner of the image.

Further, the number of pixels included in the region of interest in the image information and the number of recorded dots included in the region of interest in the recorded image do not necessarily have to match. It is sufficient that the average value of the density of pixels in the region of interest in the image information can be obtained. Of course, the shape of the region of interest in this image information does not necessarily have to be rectangular.

On the other hand, regarding recording dots, we treated the area of interest as a type of dot pattern, and an example was shown in which the apparent density gradation of this dot pattern was used. The density gradation obtained by expressing the density of each recorded dot may be added as is and regarded as the number of dots times the apparent density gradation of the dot pattern. Further, the size and shape of the region of interest and the size and shape of one section for setting the dither value may be set arbitrarily.

"Effects of the Invention" According to the halftone recording method of the present invention as explained above, the pixels of the recorded image can be made sufficiently small, and moiré does not occur even when the image information obtained from halftone dot printing is recorded. This makes it possible to obtain a halftone recorded image that is extremely faithful to the image information as a whole. Furthermore, by correcting using the dither value, it is possible to suppress the wavy pattern (due to typhoid fever) that would otherwise occur in the recorded image.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the main parts of a recording apparatus suitable for carrying out the halftone recording method of the present invention, and FIGS. 2 and 3 are explanatory diagrams for explaining the procedure of the halftone recording method of the present invention. FIG. 4 is an explanatory diagram of the operation of the storage device in FIG. 1, FIG. 5 is a graph showing a method of converting an input image signal, and FIGS. 6 and 7 are explanatory diagrams of the operation of calculating a dither value from absolute position coordinates. FIG. 8 is a concrete block diagram of the dither correction circuit, FIG. 9 is an explanatory diagram explaining the method of selecting the density expression of the output signal, FIG. 10 is an explanatory diagram of the operation at the start of image information processing, and FIG. 11 12 is an explanatory diagram showing an example of a dot pattern using a known pattern method. FIG. 13 is an explanatory diagram showing an example of a known dither method. It is an explanatory diagram. 40... Image information, 41... Input image signal, 42... Output image signal, 43... Recorded image, 51... Image Area of interest of information, 52... Pixel of interest of image information, 53... Recorded dot of interest of recorded image, 56...
...Recorded image area of interest, 64...Absolute position coordinates, 67...Dither value. Applicant: Fuji Xerox Co., Ltd. Representative
People Patent Attorney Yudai Ume Yamauchi
2 Figure 4 Figure 5 Pixel density Figure 7 Disa-N. Figure 8 Figure 9 Figure 10 Figure 11 and Figure 12

Claims (1)

[Claims] 1. Image information is decomposed into its constituent pixels, each pixel is converted into an electrical signal of a level corresponding to its density, and the input image signal is defined as an input image signal. The level of the output image signal is determined by assigning one output image signal to the output image signal, and recording dots expressing density according to the level of the output image signal are arranged at positions corresponding to each of the pixels on the recording paper. In a device that obtains a recorded image corresponding to information, when determining the level of an output image signal with respect to the input image signal, pixels in the image information and the recorded image corresponding to the input image signal and the output image signal, respectively. When the recorded dots in the image information are defined as a pixel of interest and a recording dot of interest, a region of interest is set that includes the pixel of interest in the image information and a certain number of pixels around this pixel of interest, while the recording dot of interest in the recorded image is set. A method for setting a region of interest including a dot and a certain number of recording dots around the recording dot of interest for which density expression has already been selected, and expressing the density of the region of interest in the image information on the recording paper. A corrected density is obtained by adding a dither value predetermined based on the absolute position coordinates of the pixel of interest in the image information to a predetermined converted density, and this corrected density and the apparent density of the area of interest in the recorded image are calculated. A halftone recording method characterized in that the level of the output image signal is determined by selecting the density expression of the recorded dot of interest so that the difference in tone is minimized. 2. Obtain a predetermined converted density by averaging the densities of all pixels included in the area of interest in the image information, and add a dither value to this to obtain a corrected density. For each case, the apparent density gradation of the area of interest in the recorded image is obtained from the dot pattern consisting of all recorded dots included in the area of interest of the recorded image and the recorded dot of interest, and this apparent density and 2. The halftone recording method according to claim 1, wherein the density expression of the recorded dot of interest is selected so that the difference from the corrected density is minimized. 3. Calculate the sum of the corrected densities of all pixels included in the area of interest of the image information, and calculate the density gradation of the dot pattern consisting of all the recorded dots and dots of interest included in the area of interest of the recorded image. The recorded dot of interest is calculated from the sum of the density gradations of each dot obtained from the density expression of each dot, and the difference between the sum of the density gradations of each dot of this dot pattern and the sum of the corrected densities is minimized. 2. The halftone recording method according to claim 1, wherein a density expression of . 4. A patent claim characterized in that the number of pixels included in the area of interest of the image information and the number of recorded dots included in the area of interest of the recorded image are the same, and are arranged in a one-to-one correspondence. A halftone recording method according to any one of the first to third aspects of the range.