JPH10255038A - Dithering method and dithering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a processing speed because an operation is not needed when a gradation value does not exist between the maximum value and the minimum value of threshold. SOLUTION: The maximum and minimum values in threshold that is included one row of a dither pattern are paid attention to in comparing the gradation value of each dot that constitutes image data with the dither pattern for dithering. When the gradation value of each dot does not exist between the maximum and minimum values of the threshold, it is decided whether a dot is hit by only comparing it with the maximum value or the minimum value. When it exists between the maximum and minimum values, it is decided whether or not a dot is hit by finding a corresponding threshold and comparing it with the threshold.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a dithering method and a dithering apparatus for speeding up processing for binarizing image data using a dither pattern.

[0002]

2. Description of the Related Art When each output dot constituting image data is represented by a binary value, a dither method is employed to represent an image having gradation. This is a method widely used in a printer or the like, and prepares data called a dither pattern in which threshold values are arranged in a matrix. The gradation value of each input dot of the image data to be processed is compared with each threshold value forming the dither pattern. If the tone value of the input dot is larger than the threshold, hit the output dot,
In other cases, binarization is performed by performing processing of not printing output dots. Such processing is called dithering.

On the other hand, in recent years, the resolution of a printer has become extremely high, and data having a lower resolution than that of the printer has been actively expanded in accordance with the resolution of the printer. At this time, by performing dithering together with the enlargement processing, a print output with rich gradation can be obtained.

[0004]

The above-mentioned conventional dithering method has the following problems to be solved. The dither pattern used for dithering has threshold values arranged in a matrix. In the case of dithering image data, a calculation process is performed to determine which threshold of the dither pattern should be compared with each input dot constituting the image, and then the tone value of the corresponding input dot is compared with the threshold. . When determining which threshold value to compare with, an arithmetic process including a predetermined division is performed based on the relationship between the position coordinates of each input dot and the length and width of the dither pattern. Therefore, such calculation processing is performed for each input dot every time.

[0005] However, when data is enlarged, such calculation processing is performed for each input dot on the enlarged image data every time, so that the amount of calculation increases significantly in accordance with the number of input dots. Arithmetic processing including division is usually relatively heavy processing, and such an increase in arithmetic processing has hindered speeding up of dithering.

[0006]

The present invention employs the following structure to solve the above problems. <Structure 1> The tone value of each dot forming the image data is compared with the corresponding threshold value forming the dither pattern to determine whether to hit the dot. The maximum value and the minimum value of the threshold values are obtained in advance, and the gradation value of each dot is set between the maximum value and the minimum value of the threshold value for the image data of the line compared with the threshold value included in the row. If not, determine whether to hit the dot by comparing the maximum value or the minimum value.If the tone value of each dot is between the maximum value and the minimum value of the threshold, A dithering method for determining whether or not to hit the dot by comparing the threshold value with the threshold value.

<Structure 2> An image data storage device for storing the gradation values of each dot forming the image data, a dither pattern storage device for storing a matrix threshold value forming the dither pattern, and one line of the dither pattern And a dither pattern maximum / minimum value storage device which previously obtains and stores the maximum value and the minimum value among the threshold values included in the image data, and a dither pattern corresponding to the gradation value of each dot of one line read from the image data storage device. If the tone value of each dot is not between the maximum and minimum values of the threshold value by comparing the maximum value and the minimum value of the threshold value in the row of the pattern, the dot is compared with the maximum value or the minimum value. A maximum value / minimum value comparing device for determining whether or not to hit a dot, and a pixel for calculating position coordinates of the corresponding threshold value when the tone value of each dot is between the maximum value and the minimum value of the threshold value. A pattern threshold value calculating device, and a dither pattern comparing device that compares a tone value of a dot with a corresponding threshold value obtained by the dither pattern threshold value calculating device and determines whether to hit the dot. Dithering device.

<Structure 3> In the structure 1, the tone value of the dot received from the image data storage device is compared with the maximum value and the minimum value of the threshold value of the corresponding row of the dither pattern, and the tone value of the dot is determined. If is not between the maximum and minimum values of the threshold, compare the gradation value with the maximum or minimum value, and determine whether or not to hit a dot by the number corresponding to the enlargement ratio. A dithering method.

<Structure 4> In the structure 2, the tone value of the dot received from the image data storage device is compared with the maximum value and the minimum value of the threshold of the corresponding row of the dither pattern, and the tone value of the dot is determined. If the value is not between the maximum and minimum threshold values, the gradation value is compared with the maximum or minimum value, and whether or not to hit a dot is determined collectively by the number corresponding to the enlargement ratio. When the tone value of the dot is between the maximum value and the minimum value of the threshold value, the tone value of each dot of the image data received from the image data storage device is held internally. A dithering apparatus characterized in that the apparatus further comprises an image data horizontal enlarging apparatus that repeatedly passes the gradation value to the dither pattern comparing apparatus by an amount corresponding to the horizontal enlarging rate.

<Structure 5> In the structure 1, the maximum value and the minimum value of the gradation value of the image data are obtained, the minimum value of the dither pattern is compared with the maximum value of the image data, and the maximum value of the dither pattern is compared with the image value. When the maximum value of the image data is smaller than the minimum value of the dither pattern, the tone values of all dots constituting the image data are determined to be equal to or less than the threshold value of the dither pattern, If it is determined that no dot is to be formed, and if the minimum value of the image data is larger than the maximum value of the dither pattern, the tone values of all the dots constituting the image data are determined to be larger than the threshold value of the dither pattern, and A dithering method characterized by determining that dots are to be formed.

<Structure 6> In Structure 2, an image data maximum value / minimum value calculating device for reading one line of image data from the image data storage device and obtaining the maximum value and the minimum value thereof is provided. The value comparison device is
In addition to comparing the minimum value of the dither pattern with the maximum value of the image data, comparing the maximum value of the dither pattern with the minimum value of the image data, and when the maximum value of the image data is smaller than the minimum value of the dither pattern, Assuming that the gradation values of all the dots constituting the image data are equal to or less than the threshold value of the dither pattern, it is determined that all the dots are not hit, and if the minimum value of the image data is larger than the maximum value of the dither pattern, the image A dithering apparatus comprising: determining that the tone value of all dots constituting data is larger than a threshold value of a dither pattern;

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below using specific examples. <Embodiment 1> FIG. 1 is a block diagram of a dithering apparatus according to Embodiment 1. Before describing this apparatus, first, normal dithering processing will be described. FIG. 2 is an explanatory diagram of a normal dithering process. The image data 15 shown in the figure is data expressing 256 gradations for each dot. This data is composed of 8 × 8 dots. On the other hand, in order to perform dithering on this image data, a 4 × 4 dot dither pattern is prepared. The dither pattern 16 has a length and width of 4 in order to correspond to image data of an 8 × 8 dot configuration.
It has a configuration in which pairs are spread. In this state, the tone value of each dot of the image data is compared with the threshold value at the corresponding location of the dither pattern. The threshold of the dither pattern is entered in each box. If the gradation value is larger than the threshold, dots are formed. Otherwise, no dot will be hit. Thereby, the binarized image data 1
7 is obtained.

FIG. 3 shows a specific operation flowchart when such a dithering process is performed. This figure 3
In steps S1 and S8, the image data is
Controls a loop for processing sequentially in the direction. Steps S2 and S7 control a loop for sequentially processing image data in the X direction. In this way, the processing is first performed one dot at a time in the X direction, and when the processing for one line of the image data is completed, the processing is shifted by one line in the Y direction and the processing is again performed one dot at a time in the X direction.

Note that, for each line, step S3
To step S6 are performed. First, a tone value of a corresponding dot of the image data is obtained. Further, in step S4, a threshold value corresponding to the dot is obtained from the dither pattern. Then, in step S5, the gradation value of the image data is compared with the threshold value. If the gradation value is larger than the threshold value, the process proceeds to step S6, and dots are formed. If the gradation value is equal to or less than the threshold value, the process proceeds to the next dot without printing a dot. In such a process, as shown in step S4, a process of obtaining the position coordinates of the corresponding threshold value of the dither pattern from the position coordinates of each dot of the image data is executed each time.

FIG. 4 is a diagram for explaining a method of calculating the coordinates of a dither pattern. The dither pattern 16 is, for example, a 4 × 4 dot matrix. On the other hand, image data 1
Reference numeral 5 is configured by arranging a large number of dots in both the X and Y directions. Here, for example, the threshold value corresponding to the dot D included in the image data 15 in FIG.
I will ask for it. Assuming that the upper left corner of the image data 15 is the origin, the position coordinates are obtained as (6, 7). As shown in the figure, the dither pattern 16 is spread over the image data without any gap. In this case, the threshold value Z corresponding to the dot D is determined by the dither pattern 16
It can be seen that it is at (2, 3) of the internal coordinates.

When the coordinates of the threshold value Z are obtained by the arithmetic processing, the coordinates are represented by the equations (1) and (2) in the figure. Equation (1) is the X coordinate inside the dither pattern 16, and Equation (2) is the Y coordinate inside the dither pattern 16. Dx obtained by equation (1)
Corresponds to the remainder obtained by dividing the X coordinate of the dot D of the image data by the width 4 of the dither pattern in the X direction.
This number is "2". Similarly, in the Y direction, the remainder is obtained by dividing the Y coordinate 7 of the dot D by the height 4 of the dither pattern. The remainder “3” is the Y coordinate inside the dither pattern with the threshold Z.

If the process of obtaining the remainder by the division is performed for all the dots of the image data, when the number of dots is large, a load on the arithmetic unit is extremely increased. In the present invention, a part of such arithmetic processing is omitted by the following method.

Returning to FIG. 1, the configuration of the apparatus for realizing the present invention will be described. In FIG. 1, this device includes a vertical counter 1, a horizontal counter 2, a vertical control device 3, a horizontal control device 4, an image data storage device 5, a dither pattern maximum minimum value storage device 6, and a maximum minimum value. Comparison device 7, dither pattern storage device 8, dither pattern threshold value calculation device 9, dither pattern comparison device 10,
It is configured by a bitmap storage device 11.

Each of the vertical counter 1, the horizontal counter 2, the vertical control device 3, and the horizontal control device 4, while taking out the tone value of a dot one by one from the image data, assigns an address for processing to proceed. The device to control. The vertical counter 1 is a counter that sequentially counts the Y-direction coordinates of image data. The vertical control device 3 is a control device for performing dithering by scanning the image data in the Y direction. The horizontal counter 2 is a counter that sequentially counts the horizontal coordinates of the image data. The horizontal control device 4 is a control device for performing dithering by scanning image data in the X direction.
Each time one dot is processed, the count value of the horizontal counter 2 increases by "1". When dithering of one row is completed, the count value of the horizontal counter 2 is returned to "0". When the counting of one row is completed, the count value of the vertical counter 1 is incremented by "1".

The image data storage device 5 stores image data to be processed. It is assumed that the tone value of a dot at an arbitrary position can be extracted from the image data storage device 5 by specifying coordinates. The dither pattern maximum value / minimum value storage device 6 is newly provided for performing the processing of the present invention. In this specific example,
It focuses on each line of the dither pattern, and stores and displays the maximum value and the minimum value of the threshold value included in that line. The dither pattern storage device 8 stores the threshold values of the matrix-like dither pattern as described above.

The dither pattern threshold value calculating device 9 is a device for calculating the coordinates of the threshold value in the dither pattern corresponding to the dot coordinates of the image data to be processed. This operation is described with reference to FIG.
This is a process for performing the calculations of the expressions (1) and (2). It is.
The maximum / minimum value comparison device 7 is a device that compares the gradation value of the dots constituting the image data with the maximum / minimum value of the threshold value stored in the dither pattern maximum / minimum value storage device 6. The dither pattern comparison device 10 is a device that compares a tone value of a dot to be processed with a threshold value calculated by the dither pattern threshold value calculation device 9. The processing executed by the maximum / minimum value comparison device 7 is a characteristic processing of the present invention. The processing executed by the dither pattern comparison device 10 is a conventional processing. Bitmap storage device 11
Stores binarized bitmap image data. The bitmap storage device 11 is, for example, a frame buffer that stores one frame of image data.
Here, a bit map is written by giving the position coordinates of the dot to be output and information indicating whether or not the dot is to be hit.

FIG. 5 is an explanatory diagram of the maximum value and the minimum value of each row of the dither pattern. For example, a dither pattern 16 having a 4 × 4 matrix configuration is configured to include 16 thresholds as shown in FIG. When viewed in the X direction, there are four thresholds for one row. Therefore, the maximum value and the minimum value of the threshold value of each row of the dither pattern are extracted in advance and stored in the dither pattern maximum value minimum value storage device 6 shown in FIG. In the first row, the maximum value is “208” and the minimum value is “5”. The maximum value and the minimum value are similarly obtained for the other rows.

FIG. 6 is a diagram illustrating an example of a dither pattern and image data. As shown in this figure, when the dither pattern 16 is spread over the image data 15, each row of the image data and any row of the dither pattern correspond as shown in the figure. The dots in each row of the image data are compared to a threshold of any of the corresponding rows of the dither pattern. Here, the first dot of the first line of the image data 15 will be considered. The tone value of this leading dot is “128”. In order to determine which threshold of the dither pattern is to be compared with, the calculation for obtaining the coordinates described above is performed. However, first, the maximum value and the minimum value of the row of the dither pattern are compared. If it is larger than the maximum value, dot it. If the value is smaller than the minimum value, no dot is formed. If it is between the maximum value and the minimum value, compare which threshold value corresponds to
It is determined whether or not a dot is hit by a conventional method. When processing is performed in this manner, the image data 15 shown in FIG.
Regarding the first row, since the third dot is smaller than the minimum threshold value "5", it can be determined that the dot is not hit without performing the calculation for the corresponding threshold value. Further, since the fourth dot is larger than the maximum threshold value “208”, it can be determined that the dot is to be formed without finding a corresponding threshold value. This makes it possible to omit the coordinate calculation for obtaining the corresponding threshold for two of the four dots.

FIG. 7 shows image data 17 obtained as a result of performing the above processing. The result of this processing is the same in the case of the present invention and the case of the prior art.

FIG. 8 shows an operation flowchart of the first embodiment. In the figure, first, in step S1, the dither pattern maximum value / minimum value storage device 6 shown in FIG. 1 reads the dither pattern from the dither pattern storage device 8, and obtains the maximum value and the minimum value for each row. As described with reference to FIG. 6, the gradation value of one line of dots along the X direction of the image data corresponds to the threshold value of any one line of the dither pattern and is compared with any one of these threshold values. Is done. To check which row corresponds to the threshold, the calculation shown in FIG. 4 is performed for the Y coordinate of the target line. That is, in the present invention, the arithmetic processing as shown in FIG. 4 is performed once for the Y coordinate every time the target line is switched.

Steps S2 and S3 in FIG. 8, together with steps S10 and S11, are steps for controlling the vertical loop, ie, the Y-direction loop, and the horizontal loop, ie, the X-direction loop. As a result, the image data is processed one dot at a time in the X direction, and when the processing is completed, control is performed to shift the target one line at a time in the Y direction.

In step S4, one of the target lines
A tone value of image data is obtained for one dot.
In step S5, the maximum value of the threshold value of the row of the dither pattern is compared with the gradation value. If the tone value is larger than the maximum value, the process jumps to step S9, where dots are unconditionally hit. Otherwise, the process proceeds to step S6, where the minimum value of the threshold value of the row is compared with the gradation value. If the gradation value is equal to or smaller than the minimum value, it is determined that no dot is to be formed, the process jumps to step S10, and returns to step S4 for processing the next dot.

As a result of the determination in steps S5 and S6, when it is determined that the gradation value is between the maximum value and the minimum value of the row, the process proceeds to step S7, where the coordinate calculation described with reference to FIG. The corresponding threshold value is found, and the threshold value is compared with the gradation value. This is the same processing as before. And
If the gradation value is larger than the threshold value, a dot is formed in step S9. In other cases, no dot is set. According to the above processing, when the gradation value is not between the maximum value and the minimum value of the threshold value of the corresponding row, the coordinates in the X direction are
It is not necessary to perform the arithmetic processing shown in FIG.

<Effect of Specific Example 1> As described above, according to this specific example, the maximum value and the minimum value are obtained for each row of the dither pattern, and the maximum value and the minimum value are determined for the dots of the corresponding line. In comparison with the gradation value, if the gradation value is not between the maximum value and the minimum value, it is unconditionally determined whether or not to hit a dot. Part of the processing including the division for obtaining the coordinates of the threshold can be omitted. As a result, the load of the arithmetic processing in the binarization processing by dithering can be reduced and the speed can be increased.

FIG. 9 is a block diagram of a dithering device according to a second embodiment. This device is provided with an image data vertical enlarging device 12 and an image data horizontal enlarging device 13 in addition to the device of the first embodiment shown in FIG. As described above, when the resolution of the printer is sufficiently higher than the original image data, the enlargement process is often performed simultaneously with the binarization process. The enlargement process is performed by comparing the tone value of one dot of the original image data with a plurality of threshold values of the dither pattern. In these cases,
By employing the method of the specific example 1, it is possible to reduce not only the processing for obtaining the threshold value from the dither pattern but also the processing for enlargement.

The image data vertical enlarging device 12 shown in FIG. 1 holds one horizontal row of the image data received from the vertical control device 3 and repeats it horizontally by the number of times corresponding to the vertical enlarging ratio. It serves to hand over to the direction control device 4. The image data horizontal enlarging device 13 internally holds the gradation value of each dot of the image data received from the image data storage device 5 and repeatedly sends the gradation value to the dither pattern comparing device 10 by the horizontal enlarging ratio. Serves to pass values. The operation of the other devices is the same as that of the first embodiment.

FIG. 10 is a view for explaining an example of a combination of enlargement and dithering. For example, the image data 15A of 256 gradations shown in the figure is converted into image data 15B that is enlarged by 16 times to 4 × 4, that is, the area. And
This image data is compared with a 4 × 4 matrix dither pattern 16. As a result, binarized image data 17 as shown in the figure is obtained. Conventionally, the tone value of each dot after the enlargement is compared with a threshold value at a corresponding position of the dither pattern 16, and if it is larger than that, the dot is hit, and otherwise the dot is not hit. Was. Therefore, as described with reference to FIG. 4, arithmetic processing including division for obtaining coordinates of a threshold value corresponding to each dot has been performed. In this specific example, attention is paid to image data 15B obtained by directly enlarging dots having the same gradation value, and the gradation value is compared with the maximum value and the minimum value of the threshold value included in the corresponding row of the dither pattern 16.

FIG. 11 is a diagram for explaining an example of ordinary binarization. FIG. 11 shows image data 15A before enlargement and 1
The image data 15B after the enlargement of the line, the dither pattern 16, and the binarized image data 17 are shown in order. In the case of ordinary binarization, as shown in FIG.
Each dot of the line is individually compared with a corresponding dither pattern threshold.

FIG. 12 is a diagram for explaining the operation of the device of the second embodiment. In the device of the specific example 2, the tone value of the dot is compared with the maximum value and the minimum value of the dither pattern for one row. Then, if it is determined that the value is larger than the maximum value as in the example of this figure, the pixel value of each dot is not compared with the threshold value,
Generate binarized image data in a lump. Since such processing is performed collectively by the enlargement ratio in the vertical and horizontal directions, there is an effect that the arithmetic processing is omitted as compared with the method of the first embodiment.

FIG. 13 is a flowchart showing the operation of the apparatus according to the second embodiment. First, step S1 in this figure is a process for obtaining the tone value of the dot of the target image data. In steps S2 and S10, a vertical enlargement loop is controlled. This loop is a loop process in which the processing of one line in the X direction for the image data before enlargement is completed, and the same output is copied by the vertical magnification when moving to the next line. Therefore, FIG.
As for the 4 × 4 magnification shown in the above, the result obtained by the processing included between the steps S2 and S10 is copied four times.

In step S3, the maximum value of the row of the dither pattern is compared with the gradation value. If the gradation value is larger than the maximum value, dots are collectively printed on one column of the enlarged bitmap (step S11). Then, the process proceeds to step S10, in which dots are collectively printed for four lines in the vertical direction by a vertical expansion loop process. If it is determined in step S3 that the gradation value is equal to or less than the maximum value of the row, the process proceeds to step S4, where the minimum value of the row is compared with the gradation value. if,
If the gradation value is equal to or less than the minimum value of the row, the process jumps from step S4 to step S10, and the process of not forming a dot is repeated for a vertical enlargement loop.

In steps S3 and S4, when it is determined that the gradation value is between the maximum value and the minimum value of the row,
Proceed to step S5, and this time step S5 and step S5
9 into a horizontal expansion loop. This is a loop for processing the same dot by the enlargement factor in the horizontal direction when the comparison between the gradation value and the threshold value is performed for one dot. The processing in this loop is a comparison processing with a conventional threshold, and in step S6, an arithmetic processing for obtaining a corresponding threshold from the dither pattern is performed. Then, in step S7, the gradation value of the image data is compared with the threshold value. If the gradation value is larger than the threshold value, the process proceeds to step S8, and a dot is formed. After that, the same result is copied by the enlargement ratio in the horizontal direction.

<Effect of Specific Example 2> When dithering is performed after enlarging the same image data, the dot gradation value is compared with the maximum value and the minimum value of the threshold of the row of the corresponding dither pattern. Therefore, as in the first embodiment, when the gradation value is not between the maximum value and the minimum value, the coordinate calculation for performing the comparison processing with the threshold value can be omitted. In addition, since the enlargement / reduction process is involved, it is possible to omit a process including a large division by copying the same result using an enlargement loop in the vertical and horizontal directions.

<Embodiment 3> FIG. 14 is a block diagram of a dithering apparatus according to Embodiment 3. This apparatus is different from the apparatus shown in FIG.
Is added. In the specific examples so far, the calculation processing is speeded up by obtaining the maximum value and the minimum value for the threshold value of each row of the dither pattern. On the other hand, the maximum value and the minimum value are also obtained for the gradation values of the image data,
By comparing with the maximum value and the minimum value of the dither pattern, the comparison operation between the gradation value and the threshold value can be significantly reduced when a certain condition is satisfied.

FIG. 15 is a diagram for explaining the operation of the third embodiment.
The outline of the operation of the third embodiment will be described with reference to FIG. FIG.
5 (a) shows a threshold value for one row of the dither pattern 16. The minimum value is 32 and the maximum value is 210. On the other hand, (b) shows the gradation values for one row of the image data. The minimum value of the gradation values in the figure is 0, and the maximum value is 31.

When comparing the image data with the dither pattern, first, the minimum value of the dither pattern is compared with the maximum value of the image data. Further, the maximum value of the dither pattern is compared with the minimum value of the image data. When the maximum value of the image data is smaller than the minimum value of the dither pattern, it can be seen that the tone values of each dot constituting the image data are all equal to or less than the threshold value of the dither pattern. Therefore, in this case, it is determined that all the dots have not been hit, and the comparison process between the tone value of each dot and the threshold can be omitted.

If the minimum value of the image data is larger than the maximum value of the dither pattern, it can be determined that all the gradation values of the image data are larger than the dither pattern. Therefore, in this case, it is determined that dots are to be formed for all the image data, and individual comparison processing can be omitted. In this specific example, the speed of the arithmetic processing is increased based on such a principle.

The image data maximum / minimum value calculation device 14 shown in FIG. 14 reads out one line of image data from the image data storage device 5 and performs an arithmetic processing for obtaining the maximum and minimum values therein. This is the part to do.

FIG. 16 shows the operation of a device for performing normal enlargement and binarization. When binarization is performed while enlarging image data, such processing is usually performed. First, in step S1, a tone value of a corresponding dot of the image data is obtained. Steps S2 and S8 control a vertical enlargement loop, and steps S3 and S7 control a horizontal enlargement loop. In step S4, a corresponding threshold value is obtained from the dither pattern, and in step S5
Then, the gradation value of the image data is compared with the threshold value. If the gradation value is larger than the threshold value, the process proceeds to step S6, and a dot is formed. If the gradation value is equal to or smaller than the threshold value, the process proceeds directly to step S7, and no dot is formed. In this figure, the horizontal enlargement and the vertical enlargement are performed by using the conventional steps as described above.

FIG. 17 is a flowchart showing the operation of the apparatus of the third embodiment. Here, in step S1, a maximum value and a minimum value are obtained for each row of the dither pattern. This processing is as described above. Steps S2 and S9 control a vertical loop. In step S3, the maximum value and the minimum value of the gradation values for one line of the image data to be processed are obtained. Then, in step S4, the maximum value of the dither pattern is compared with the minimum value of the gradation value of the image data.

If it is determined that the minimum value of the gradation value of the image data is larger than the maximum value of the threshold value of the dither pattern, in step S10, a process is performed in which dots are printed for one line. Subsequently, the process proceeds to the vertical loop control in step S9. On the other hand, in other cases, the process proceeds to step S5, where the minimum value of the threshold value of the dither pattern and the maximum value of the tone value of the dot are compared. Here, when it is determined that the maximum value of the tone value of the dot of the image data is equal to or less than the minimum value of the threshold value, the process proceeds to step S9 without hitting a dot, and proceeds to the process in the vertical direction. Otherwise, the process proceeds to step S6, where a horizontal loop control is performed in steps S6 and S8, and a binarization process is performed for each dot in step S7. This binarization processing is the operation as described above.

<Effect of Specific Example 3> Specific Example 3 described above.
According to the method, the maximum value and the minimum value of each line of the dither pattern are obtained in advance, and the maximum value and the minimum value of the image data to be compared are obtained. The comparison between the key value and the threshold value can be omitted. As a result, the speed of the dithering process can be significantly increased.

[Brief description of the drawings]

FIG. 1 is a block diagram of a dithering device according to a first embodiment.

FIG. 2 is an explanatory diagram of a normal dithering process.

FIG. 3 is a flowchart of a normal dithering processing operation.

FIG. 4 is an explanatory diagram of a coordinate calculation method of a dither pattern.

FIG. 5 is an explanatory diagram of a maximum value and a minimum value of each row of a dither pattern.

FIG. 6 is an explanatory diagram of an example of a dither pattern and image data.

FIG. 7 is an explanatory diagram of a result of binarizing image data.

FIG. 8 is an operation flowchart of the device of the first embodiment.

FIG. 9 is a block diagram of a dithering device according to a second embodiment.

FIG. 10 is an explanatory diagram of an example of a combination of enlargement and dithering.

FIG. 11 is an explanatory diagram of an example of normal binarization.

FIG. 12 is an explanatory diagram of the operation of the device of the specific example 2.

FIG. 13 is an operation flowchart of the device of the specific example 2.

FIG. 14 is a block diagram of a dithering device according to a third embodiment.

FIG. 15 is an explanatory diagram of an operation in a specific example 3.

FIG. 16 is an operation flowchart of a device that performs normal enlargement and binarization.

FIG. 17 is an operation flowchart of the device of the third embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 vertical counter 2 horizontal counter 3 vertical control device 4 horizontal control device 5 image data storage device 6 dither pattern maximum / minimum value storage device 7 maximum / minimum value comparison device 8 dither pattern storage device 9 dither pattern threshold value calculation device Reference Signs List 10 dither pattern comparison device 11 bitmap storage device

Claims (6)

[Claims] 1. A method for comparing a tone value of each dot forming image data with a corresponding threshold value forming a dither pattern to determine whether or not to hit the dot. The maximum value and the minimum value among the included thresholds are obtained in advance, and for the image data of the line to be compared with the threshold included in the row, the gradation value of each dot is determined by the maximum value and the minimum value of the threshold. If not, determine whether to hit the dot by comparing the maximum value or the minimum value, and if the tone value of each dot is between the maximum value and the minimum value of the threshold, A dithering method comprising determining whether or not to hit the dot by comparing with a corresponding threshold value. 2. An image data storage device for storing a tone value of each dot forming image data, a dither pattern storage device for storing a matrix threshold value forming a dither pattern, and a dither pattern included in one row. And a dither pattern maximum / minimum value storage device which previously obtains and stores the maximum value and the minimum value among the threshold values to be obtained, and a dither pattern corresponding to the tone value of each dot of one line read from the image data storage device. If the tone value of each dot is not between the maximum and minimum values of the threshold value compared to the maximum and minimum values of the row, the dot is hit by comparing with the maximum or minimum value. A maximum value / minimum value comparison device for determining whether or not the dot value is between the maximum value and the minimum value of the threshold, and a dither pattern for calculating position coordinates of the corresponding threshold. A threshold value calculating device, and a dither pattern comparing device that determines whether to hit the dot by comparing the tone value of the dot with a corresponding threshold value obtained by the dither pattern threshold value calculating device. Dithering device. 3. The method according to claim 1, wherein a tone value of the dot received from the image data storage device is compared with a maximum value and a minimum value of a threshold value of a corresponding row of the dither pattern, and the tone value of the dot is determined. If the threshold value is not between the maximum value and the minimum value, compare the gradation value with the maximum value or the minimum value, and determine whether or not to hit a dot by the number corresponding to the enlargement ratio. Characteristic dithering method. 4. The method according to claim 2, wherein the tone value of the dot received from the image data storage device is compared with a maximum value and a minimum value of a threshold value of a corresponding row of the dither pattern, and the tone value of the dot is determined. If the threshold value is not between the maximum value and the minimum value, the gradation value is compared with the maximum value or the minimum value to determine whether or not to hit a dot by a number corresponding to the enlargement ratio at a time. The minimum value comparing device, and when the tone value of the dot is between the maximum value and the minimum value of the threshold value, the tone value of each dot of the image data received from the image data storage device is held internally, A dithering device, comprising: an image data horizontal enlarging device that repeatedly passes a gradation value to a dither pattern comparing device by an amount corresponding to a horizontal enlarging ratio. 5. The method according to claim 1, wherein a maximum value and a minimum value are obtained for the gradation value of the image data, and the minimum value of the dither pattern is compared with the maximum value of the image data. If the maximum value of the image data is smaller than the minimum value of the dither pattern, it is determined that the tone values of all dots forming the image data are equal to or less than the threshold value of the dither pattern.
If it is determined that all the dots are not hit, and if the minimum value of the image data is larger than the maximum value of the dither pattern, it is determined that the tone values of all the dots constituting the image data are larger than the threshold value of the dither pattern.
A dithering method characterized by determining that dots are formed for all image data. 6. The image data maximum value minimum value calculation device according to claim 2, further comprising: an image data maximum value minimum value calculation device for reading out one line of image data from the image data storage device and obtaining a maximum value and a minimum value thereof. The comparison device compares the minimum value of the dither pattern with the maximum value of the image data, compares the maximum value of the dither pattern with the minimum value of the image data, and determines that the maximum value of the image data is smaller than the minimum value of the dither pattern. In this case, it is assumed that the tone values of all the dots constituting the image data are equal to or less than the threshold value of the dither pattern.
If it is determined that all the dots are not hit, and if the minimum value of the image data is larger than the maximum value of the dither pattern, it is determined that the tone values of all the dots constituting the image data are larger than the threshold value of the dither pattern.
A dithering device, which determines that dots are to be formed for all image data.