JPH1127534A - Image processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processor which is capable of expressing gradation more exactly. SOLUTION: Image data stored in pattern storage memory 11 are binarized by a first adding circuit 4, a binarization circuit 5, a subtraction circuit 7, a second adding circuit 8, error memory 9 and an error filter 10, an output of the binarized image data is recorded by a recording means 1, a recording result 3 as a result of the recording by the recording means 1 is read by a reading means 2 and the difference in sizes between an actual recording dot and a theoretical dot in the recording means 1 is discriminated from multilevel data in the reading means 2 and the image data in the pattern storage memory 11 by a discrimination means 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus used for a facsimile or the like.

[0002]

2. Description of the Related Art A conventional image processing apparatus will be described with reference to the drawings. In FIG. 5, a conventional image processing apparatus includes:
An input terminal 1 for inputting image information of a document decomposed in pixel units by a scanner or the like at a multi-valued level; an adder 2 for adding an image signal input from the input terminal 1 to an output from an error filter described later; A threshold value generating unit 3 for generating a threshold value for binarizing the output of the adder 2, and an output of the adder 2 based on the threshold value generated by the threshold value generating unit 3.
A comparator 4 to be converted to a value, an output terminal 5 of a binarized signal output from the comparator 4, a subtractor 6 to subtract an output from the adder 2 by an output from the comparator 4, and a plurality of peripheral pixels already binarized , An error filter 7 for performing weighted addition of error data, a recording dot correction coefficient setting unit 8 for setting a difference between an actual dot size of the recording system and a theoretical dot size, and a comparator 4. An output image memory 9 for accumulating two lines of output data in the sub-scanning direction in pixel units, and correcting the error data based on the output of the recording dot correction coefficient setting unit 8, the output of the output image memory 9, and the output of the subtractor 6. And an error memory 11 for storing two lines of error data corrected by the error data correction unit 10 in the sub-scanning direction in pixel units.
And is composed of

The operation of the conventional image processing apparatus configured as described above will be described below. The adder 2 adds the output of the error filter 7 to the image signal of the target pixel p input from the input terminal 1. Next, the comparator 4 is connected to the adder 2
Are binarized by the threshold value generated by the threshold value generation unit 3 and the result is output to the output terminal 5 and the output image memory 9. The subtracter 6 subtracts the output of the adder 2 by the output of the comparator 4 and outputs the result as error data.

Next, an error data correction unit 10 receives the error data output from the subtractor 6, a correction coefficient k described later from a recording dot correction coefficient setting unit 8, and outputs a correction coefficient k from an output image memory 9. Peripheral pixels a, b, c, d shown in FIG.
And corrects the error data of the pixel of interest. Here, as shown in FIG. 6, the correction coefficient k is a coefficient corresponding to the difference between the actual dot size of the recording system and the theoretical dot size. It is set in the correction coefficient setting unit 8.
The error data corrected here is stored in the error memory 11. As shown in FIG. 5, the error filter 7 has error data Error (a) and Error in a plurality of binarized peripheral pixels already stored in the error memory 11.
(B) Weighted addition of Error (c) and Error (d) is performed, and the result is added to the input image signal by the adder 2 as described above.

Next, the operation of the error data correction unit 10 will be described. First, FIG. 6 shows a case where all the surrounding pixels are white and the pixel of interest is black. In FIG. 6, the hatched area is an area where the actual black dot is outside the theoretical black dot. K the width of the run-off area 6, when 1 dot width theoretical area S of the shaded portion becomes S = 2k + 2k ^2. The area of the shaded area is increased by the extra black area, and it is necessary to subtract this as an error. Assuming that the black image signal level of the input image signal is W, the correction amount c
Is c = − (2k + 2k ² ) × W, and the correction error data e ′ when the error data is e
Is e ′ = e− (2k + 2k ² ) × W.

Next, FIG. 7 shows a case where the peripheral pixels are all black and the target pixel is also black. In this case as well, the spread of the dot of the target pixel is the same as in FIG. 6, but the correction amount c is effectively 0 because all the hatched portions overlap the surrounding black pixels.

Similarly, when the target pixel is p and its surrounding pixels are a, b, c, and d, the correction amount c is determined for all of these white / black combinations, and the respective correction amounts c The correction error data e ′ when the error data is e is expressed by e ′ = e + c.

[0008] The error data correction unit 10 receives the error data e of the target pixel p from the subtractor 6. At the same time, the correction coefficient k is input from the recording dot correction coefficient setting unit 8, and the pixel of interest p and its surrounding pixels a, b,
A signal indicating whether c and d are white or black is input.

Next, a correction amount c is determined from these signals, and the correction amount c and the already input error data e are added to determine correction error data e ′.

[0010]

As described above, in the prior art, the size of the recording dots is assumed to be uniform, and the size of the recording dots corresponds to the difference between the actual size of the recording dots and the theoretical size of the dots. The used coefficients are used. However, since the size of a recording dot is actually affected by the state of peripheral pixels, the above-described conventional technique cannot correct the difference between the actual recording dot size and the theoretical size. Therefore, the effect of improving the gradation expression was insufficient. The present invention
The present invention has been made in view of the above problems, and an object of the present invention is to provide an image processing apparatus that can perform gradation expression more accurately.

[0011]

In order to achieve the above-mentioned object, the invention according to claim 1 is a device for storing the difference data between the actual dot size of a recording system and the theoretical dot size and the difference between the actual dot size and the theoretical dot size. Error data, which is the difference between input image data input at a multi-valued level and output image data obtained by binarizing the input image data, is held for each state of the peripheral pixels, and the pixel to be recorded of the input image data and its peripheral pixels The correction is performed using the difference data corresponding to the state of (1). According to a second aspect of the present invention, there is provided an adding means for adding a binarized error diffusion value to input image data, a binarizing means for binarizing an output of the adding means, the binarizing means, Means for calculating error data which is the difference between the output from the adding means, and error data correcting means for correcting the error data based on the difference data between the actual dot size of the recording system and the theoretical dot size. A difference switching means for switching the difference data according to the state of the recording target pixel and its surrounding pixels, and an error data corrected by the difference data obtained by weighting the error data corresponding to the peripheral pixels of the target pixel. An error diffusion value calculating means for outputting a quantified error diffusion value to the adding means.

With this configuration, the difference data between the actual size of the recording dots and the theoretical size of the dots can be optimized according to the state of the peripheral pixels, so that the gradation expression can be performed more accurately. it can.

According to a third aspect of the present invention, in the image processing apparatus of the second aspect, the difference switching means stores the binarized data of the input image data input at the multi-value level. And a difference data storage unit that outputs difference data corresponding to each state of the recording target pixel and its surrounding pixels to the error data correction unit with reference to the data stored in the output image storage unit. .

According to such a configuration, the difference data can be output to the error data correcting means according to the state of the peripheral pixels, so that the correction of the error data can be appropriately performed according to the state of the peripheral pixels.

According to a fourth aspect of the present invention, there is provided the image processing apparatus according to the third aspect, wherein the multi-value data storing means for storing the specific multi-value data, and the recording result of outputting the multi-value data is stored. A difference determining unit that calculates difference data between the actual dot size of the recording system and the theoretical dot size using the read data and the multi-value data, and stores the difference data in the difference data storage unit. Take the configuration.

With such a configuration, since the difference data between the actual size of the recording dot and the theoretical size can be accurately calculated, the gradation expression can be performed more accurately.

According to a fifth aspect of the present invention, in the image processing apparatus according to any one of the second to fourth aspects,
When newly calculating difference data, the error data correction unit employs a configuration in which control is performed so as not to receive the previous difference data from the difference switching unit.

With this configuration, the difference data between the actual size of the recording dot and the theoretical size can be accurately calculated.

According to a sixth aspect of the present invention, in the image processing apparatus of the second to fifth aspects, the error diffusion value calculation means includes an error storage means for storing the error data corrected by the difference data; An error filter is provided which outputs a binarized error diffusion value obtained by weighting error data corresponding to a peripheral pixel of the target pixel from the error storage means to the addition means.

With this configuration, the error diffusion processing can be performed after the error data is corrected with the difference data between the actual size of the recording dot and the theoretical size, so that the gradation expression can be performed more accurately. It can be carried out.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, recording means 1
Records image data on recording paper. The reading means 2
The recording result 3 printed by the recording means 1 is read, and image information decomposed in pixel units is output at a multi-value level.

The first adder circuit 4 stores multi-valued image data output from the reading means 2 or a pattern storage memory 11 described later.
Any one of the multi-valued outputs and an error filter 10 described later.
Add the outputs from.

The binarizing circuit 5 performs binarization by comparing the output of the first adding circuit 4 with a threshold value. The output image memory 6 stores the output of the binarization circuit 5. The subtraction circuit 7 subtracts the output of the first addition circuit 4 from the output of the binarization circuit 5.

The second addition circuit 8 adds the output of the judgment result storage means 13 described later and the output of the subtraction circuit 7. The error memory 9 stores the output of the second adding circuit 8. The error filter 10 performs weighted addition of error data on a plurality of neighboring pixels that have already been binarized. Pattern storage memory 1
1 stores image data of a specific pattern.

The judging means 12 converts the image data stored in the pattern storage memory 11 by the first adding circuit 4, the binarizing circuit 5, the subtracting circuit 7, the second adding circuit 8, the error memory 9, and the error filter 10. The output is binarized and the output is
The recording result 3 is read by the reading means 2. The multi-value data of the reading means 2 and the image data of the pattern storage memory 11 are used to calculate the actual recording dot size of the recording means 1 and the theoretical value. The difference between the dot sizes is determined. The judgment result storage means 13 stores the judgment result of the judgment means 12.

The operation of the image processing apparatus configured as described above will be described below. It is assumed that an appropriate value has already been stored in the determination result storage unit 13 by a method described later.

The multivalued image data read by the reading means 2 is added to the output of the error filter 10 by the first adding circuit 4. The output of the error filter 10 is obtained by adding the errors at the time of binarization of a plurality of peripheral pixels at an appropriate ratio (for example, the errors of the four peripheral pixels are each 1/4 each). The output of the error filter 10 is 0 because there is no pixel whose value has already been converted.

The output of the first adder circuit 4 is binarized by a binarization circuit 5
It is converted into a value, stored in the output image memory 6, and simultaneously output to the recording means 1 as recording image data. At the same time, the subtraction circuit 7 subtracts the output from the first addition circuit 4 and outputs the result to the second addition circuit 8 as error data. In the second adding circuit 8, the data from the determination result storage means 13 is added and stored in the error memory 9 as error data.

The decision result storage means 13 stores difference data between the actual size of the recording dots of the recording means 1 and the theoretical size, and the data differs depending on the image signals of the peripheral pixels. Reference is made to the image information of peripheral pixels from 6.

The error data stored in the error memory 9 is
As described above, the weighting is performed by the error filter 10, and the weight is added to the input image signal by the first adding circuit 4.

As described above, the error between the input image signal and the output image signal when the input image signal is binarized, and the difference between the actual recording dot size of the recording means 1 and the theoretical size are calculated. It can be spread to a plurality of peripheral pixels.

Next, the operation of storing an appropriate value in the judgment result storage means 13 will be described. First, the data of the pattern storage memory 11 is input to the first adding circuit 4 instead of the output of the reading means 2. As shown in FIG. 2, the data in the pattern storage memory 11 is multi-valued data. It is. For example, assuming that 16 levels are used as multi-value data, signals of 0, 1, 2,... 15 are continuous for 16 lines.

The operation of binarizing the data in the pattern storage memory 11 depends on whether the image signal from the reading means 2 is binarized or not. The same is true except that no addition is performed. At this time, control is performed so that the output signal of the determination result storage means 13 is set to 0. The binarized image signal is recorded by the recording means 1 and a recording result 3 is obtained.

Here, in the recording result 3, if the size of the recording dots of the recording means 1 is equal to the theoretical size, the ratio of black pixels per unit area is equal to the gradation level. For example,
In the area where the gradation 8 is recorded, １ ／ of the unit area (8 pixels when the unit area is equivalent to 4 × 4 pixels) is black. on the other hand,
If the size of the actual recording dot is larger than the theoretical size, the ratio of black pixels increases, and if the size of the actual recording dot is smaller than the theoretical size, the ratio of black pixels decreases. Thus, by calculating this, the difference between the actual size and the theoretical size of the recording dot can be known.

The calculation of the ratio of black pixels in the recording result 3 is performed by reading the recording result 3 by the reading means 2. The reading operation of the recording result 3 performed at the time of calculating the ratio of the black pixels of the recording result 3 is the same as the reading of the normal image data, but the multi-value output of the reading unit 2 is input to the determination unit 12 in this case. Is done. The judging means 12 averages the image data of a plurality of pixels in the area of the pattern storage memory 11 recorded with the pattern of the same gradation to obtain the black pixel ratio. The number of pixels required for averaging is basically determined by the maximum number of gradations of multi-value data.

In the above example, the maximum number of gradations is 16, and
In the pseudo halftone, the gray scale is represented by a white / black ratio of 16 pixels of 4 pixels × 4 pixels at minimum. Therefore, it is necessary to read 16 pixels of a minimum of 4 pixels × 4 pixels by the reading means 2 and average them.

The above-described averaging and determination result storage processing will be described with reference to FIG. First, the recording result is read for one line, and an average value is calculated (S1). If the average value is not 0 (S2), the recording result is read for four lines (S3).
Further, the recording result is read for eight lines, an average value is calculated, and this is defined as Xa (S4). Next, data is read from the pattern storage memory 11 and is set as Xb (S
5). When the difference D between Xb and Xa is calculated, this is the difference between the actual dot size of the printing system and the theoretical dot size (S6). This difference D is stored in the address Xb of the determination result storage means 13 (S7). Xb is 15
If it becomes, the process is terminated (S8). If it is not 15, the recording result is read for one line and an average value is calculated (S9). If the average value is 0, the process returns to the beginning (S10). If the average value is not 0 (S10), the recording result is read again for one line, and the average value is calculated (S9).

Next, reading of the pattern storage memory will be described with reference to FIG. First, the pattern storage memory 1
One byte is read from 1 (S51). If the read data is not 0 (S52), the data is substituted for Xb (S53). Further, one byte is read from the pattern storage memory 11 (S54), and if this is equal to the Xb, reading is performed again (S55).

Here, if the average value of the area of the gradation level 8 is, for example, 9, the actual size of the recording dot at the gradation level 8 is 9/8 times the theoretical size. This information is associated with the peripheral pixel information (in this case, the pattern when the gradation level 8 is binarized by error diffusion with the size of the recording dot being the same as the theoretical size),
It is stored in the judgment result storage means 13.

Although the patterns stored in the pattern storage memory 11 are all possible gradation patterns in the above example, the patterns can be simplified depending on the degree of influence of peripheral pixels.

[0041]

As is apparent from the above description, according to the present invention, the difference between the actual recording dot size and the theoretical dot size is actually measured for each state of the peripheral pixels, and this difference is measured during error diffusion processing. Since the correction can be performed, the gradation expression can be performed more accurately.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an image processing apparatus according to the present invention.

FIG. 2 is an address configuration diagram of a pattern storage memory.

FIG. 3 is a flowchart of an averaging and determination result storing process.

FIG. 4 is a flowchart of reading from a pattern storage memory.

FIG. 5 is an overall configuration diagram of a conventional image processing apparatus.

FIG. 6 is a block diagram showing the spread of dots.

FIG. 7 is a block diagram showing the spread of dots.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 recording means 2 reading means 3 recording result 4 first addition circuit 5 binarization circuit 6 output image memory 7 subtraction circuit 8 second addition circuit 9 error memory 10 error filter 11 pattern storage memory 12 judgment means 13 judgment result storage means

Claims (6)

[Claims] 1. An image processing apparatus according to claim 1, wherein difference data between the actual dot size of the recording system and the theoretical dot size is held for each state of a recording target pixel and its surrounding pixels, and input image data to be inputted at a multi-level level. An image processing apparatus for correcting error data, which is a difference from output image data obtained by binarizing input image data, using difference data corresponding to a state of a pixel to be recorded of the input image data and surrounding pixels. . 2. An adding means for adding a binarized error diffusion value to input image data, and a binarizing means for binarizing an output of the adding means.
Means for calculating error data, which is the difference between the output of the binarizing means and the adding means, based on difference data between the actual dot size of the recording system and the theoretical dot size. Error data correcting means for correcting the error data, a difference switching means for switching the difference data according to the state of the recording target pixel and its surrounding pixels, and an error data corrected by the difference data to the surrounding pixels of the pixel of interest. An error diffusion value calculation unit that outputs a binarized error diffusion value obtained by weighting the error data corresponding to the error data to the addition unit. 3. The difference switching means includes: an output image storage means for storing binarized data of input image data input at a multi-value level; and a recording object with reference to the data stored in the output image storage means. 3. The image processing apparatus according to claim 2, further comprising: difference data storage means for outputting difference data corresponding to each state of the pixel and its surrounding pixels to the error data correction means. 4. A multi-value data storing means in which specific multi-value data is stored, and an actual dot of a printing system using the multi-value data and data obtained by reading a print result of outputting the multi-value data. 4. The image processing apparatus according to claim 3, further comprising: difference determination means for calculating difference data between the size of the dot and the theoretical dot size and storing the difference data in the difference data storage means. 5. The apparatus according to claim 2, wherein the error data correction means performs control not to receive the previous difference data from the difference switching means when newly calculating difference data. An image processing device according to any one of the above. 6. An error diffusion value calculation means, comprising: an error storage means for storing error data corrected by the difference data; and a binarization error weighted from the error storage means to error data corresponding to a peripheral pixel of a target pixel. The image processing apparatus according to claim 2, further comprising: an error filter configured to output the diffusion value to the adding unit.