JP4453583B2 - Image processing apparatus and program - Google Patents

Description

The present invention relates to an image processing instrumentation 置及 beauty program, particularly to an image processing instrumentation 置及 beauty programs to improve the image quality of binary images obtained by the error diffusion process.

  An image processing apparatus such as a printer or a facsimile, and an image output apparatus such as a display have variations in constituent members. For this reason, the image on the recording medium or the display medium may have unevenness or streaks that do not exist in the original data, resulting in image quality deterioration of the finally obtained image. Various techniques relating to image processing for correcting the unevenness and streaks are disclosed.

  Basically, the correction signal (often multi-valued data having positive and negative values) is superimposed on the input image to make the unevenness and streaks generated in the output device inconspicuous. ing. If the input image is multivalued, this correction can be done by simply adding a correction signal to the input image.

  In recent years, pseudo halftone processing is often performed in which a multi-value input image is converted into an image having a binary value or a numerical value that can be output by an output device by a printer driver installed in a host computer. However, the unevenness and streaks are different in each output device, and there is a need to correct unevenness and streaks for images that have already been subjected to pseudo halftone processing on the output device side.

Thus, an image processing apparatus that corrects recording density unevenness that occurs when binary data is recorded with a simple configuration is disclosed (for example, see Patent Document 1).
In Patent Document 1, an average density value is obtained from the pixel values of a pixel of interest of an already binarized image and its surrounding pixels, the average density value is corrected according to the characteristics of the printing element, and the corrected average density is corrected. A technique for binarizing values by error diffusion processing is described.

Also disclosed is an image processing apparatus that solves the problem of delay in dot generation at the rising portion of the low density area and the high density area and the problem of tailing after the low density area or high density area ends (for example, (See Patent Document 2). Patent Document 2 describes a technique for reducing this dot delay and tailing by changing the quantization threshold according to the tone value of multi-value multi-tone image data input in normal error diffusion. Has been.
Japanese Patent No. 2833666 Japanese Patent No. 3554077

  The image processing apparatus described in Patent Document 1 generates a multi-valued image by once averaging the original binary image. For this reason, the value of the pixel which comprises the halftone dot etc. which are contained in the original binary image will be changed, and there existed a problem that the appearance of the original binary image and the corrected binary image will change.

  Even if the quantization threshold is changed, the image processing apparatus described in Patent Document 2 includes pixels in which dots are already formed in the data included in the binary image. Limitation will occur. Thereby, dot delay and tailing could not be improved sufficiently.

The present invention has been proposed in order to solve the above problems, it aims to provide an image processing instrumentation 置及 beauty program further further reduced dot delay and trailing in the error diffusion processing in the binary image And

In order to solve the above-described problem, the image processing apparatus according to the present invention estimates a pixel value of a target pixel when the binary image is a multi-valued image from the target pixel of the binary image and its surrounding pixels. Based on a difference between a pixel value estimating unit, a pixel value of the target pixel estimated by the pixel value estimating unit, and a pixel value of the target pixel estimated by the pixel value estimating unit and subjected to gradation correction adding the compensation signal generating means for generating a compensation signal of the target pixel, the pixel value of the pixel of interest of the binary image, the correction signal generated by the correction signal generation means, and the error diffusion correction signal, the Adding means for comparing, a binarizing means for comparing the signal generated by the adding means with a threshold value to generate a binary image signal of the pixel of interest, the signal generated by the adding means, and the binarization Binary image generated by means A binarization error signal generation unit that generates a binarization error signal that is a difference between the multilevel signal corresponding to the signal and a binarization error signal generated by the binarization error signal generation unit A storage means, and an error diffusion correction signal generation means for generating the error diffusion correction signal by multiplying the binarized error signal stored in the storage means and a predetermined error diffusion coefficient for each pixel of interest and adding them; Threshold value generating means for generating the threshold value so that the accumulated amount of the binarization error signal stored in the storage means becomes substantially constant .

  Further, the image processing apparatus according to the present invention includes a pixel value estimating unit that estimates a pixel value of a target pixel when the binary image is a multi-valued image from the target pixel of the binary image and its peripheral pixels, Based on a difference between the pixel value of the target pixel estimated by the pixel value estimation unit and the pixel value of the target pixel estimated by the pixel value estimation unit and subjected to gradation correction, a correction signal for the target pixel is obtained. A correction signal generating means for generating; an adding means for adding the correction signal generated by the correction signal generating means; and an error diffusion correction signal; a signal generated by the adding means and a threshold value A difference between a binarization unit that generates a binary image signal of the pixel of interest, a pixel value of the pixel of interest of the binary image, and a pixel value of the binary image signal generated by the binarization unit Fluctuation signal generator that generates fluctuation signals Binarization error generation means for generating a binarization error signal that is an error between the signal generated by the addition means and the multivalue corresponding to the fluctuation signal generated by the fluctuation signal generation means; A storage unit that stores the binarization error signal generated by the binarization error signal generation unit, and a binarization error signal stored in the storage unit and a predetermined error diffusion coefficient are multiplied for each pixel of interest. Error diffusion correction signal generation means for generating the error diffusion correction signal by adding, and threshold generation means for generating the threshold value so that the accumulated amount of the binarized error signal stored in the storage means becomes substantially constant And.

  Further, the image processing apparatus according to the present invention includes a pixel value estimating unit that estimates a pixel value of a target pixel when the binary image is a multi-valued image from the target pixel of the binary image and its peripheral pixels, Based on a difference between the pixel value of the target pixel estimated by the pixel value estimation unit and the pixel value of the target pixel estimated by the pixel value estimation unit and subjected to gradation correction, a correction signal for the target pixel is obtained. A correction signal generating means for generating; an adding means for adding the correction signal generated by the correction signal generating means; and an error diffusion correction signal; an addition signal generated by the adding means; and a first and a second When the value of the addition signal is greater than or equal to the first threshold and less than the second threshold by comparing with a threshold, a binary image signal of the target pixel is output, and the value of the addition signal is the first Greater than or equal to 1 and less than the second threshold The binary signal indicating the result of comparison between the added signal and the second threshold value, and generating a binary image signal of the pixel of interest; A variation signal generation unit that generates a variation signal that is a difference between the pixel value of the target pixel and the pixel value of the binary image signal generated by the binarization unit; and the signal generated by the addition unit; A multi-value corresponding to the fluctuation signal generated by the fluctuation signal generation means, a binarization error generation means for generating a binarization error signal as an error, and a binary value generated by the binarization error signal generation means. An error for generating the error diffusion correction signal by multiplying the storage means for storing the binarization error signal and the binarization error signal stored in the storage means and a predetermined error diffusion coefficient for each pixel of interest and adding them Diffusion correction signal generating means and the storage means Threshold generating means for generating the first threshold that is a value obtained by multiplying the accumulated amount of the binarized error signal stored by (−1) and the second threshold that is larger than the first threshold; It is equipped with.

Therefore, according to the invention, the Dots delay or tailing still can be further reduced.

According to the image processing instrumentation 置及 beauty program according to the present invention, the Dots delay or tailing still can be further reduced.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a block diagram showing a configuration of an image processing apparatus according to the first embodiment of the present invention.

  The image processing apparatus according to the first embodiment performs error diffusion processing of a binary image, and is a pixel that estimates a pixel value of a target pixel when the image is a multi-value image from an input binary image signal A value estimation unit 10, a correction signal generation unit 20 that generates a correction signal for correcting unevenness and streaks of the output device based on the pixel value and the pixel position signal, and an error diffusion processing unit 30 that performs error diffusion processing It is equipped with.

  Based on the binary image signal of the pixel of interest and its surrounding pixels, the pixel value estimation unit 10 is an estimated pixel signal (8 in this embodiment) representing the pixel value of the pixel of interest when the binary image is a multi-valued image. Bit). Specifically, the pixel value estimation unit 10 stores the binary image signal of the target pixel and its peripheral pixels, obtains the average value of the multi-value image signal of the target pixel and its peripheral pixels converted to 8 bits, The average value is used as the estimated pixel signal. In addition, the pixel value estimation unit 10 may obtain a sum or a weighted sum of the multi-value image signals of the target pixel and its surrounding pixels, and the obtained value may be used as the estimated pixel signal. Furthermore, it is also possible to obtain the estimated pixel signal using a low-pass filter or using another multilevel restoration method.

  The correction signal generation unit 20 generates a correction signal for the target pixel based on the pixel position signal indicating the position of the target pixel in the binary image and the pixel value of the target pixel generated by the pixel value estimation unit 10. .

  Here, the correction signal generation unit 20 performs gradation correction data values obtained by performing gradation correction on the estimated pixel signals generated by the pixel value estimation unit 10, and estimated pixel signal values generated by the pixel value estimation unit 10. May be obtained as a correction signal. In addition, when the binary image is one of a plurality of color components constituting one image, the correction signal generation unit 20 generates an estimated pixel signal generated by the pixel value estimation unit 10 for the binary image. A correction signal for the target pixel may be generated based on the value and at least one estimated pixel signal among the estimated pixel signals generated by the pixel value estimating unit 10 for the binary image constituting the other color component Good.

  The error diffusion processing unit 30 is a threshold generation unit 31 that generates a threshold value, and a correction signal (hereinafter referred to as an “error diffusion correction signal”) that indicates a correction value for a target pixel that is subjected to error diffusion processing next to the current target pixel. ), A correction addition unit 33 that adds an error diffusion correction signal to the correction signal, a binarization unit 34 that performs binarization processing, and an error calculation unit that calculates a binarization error signal 35 and an error storage unit 36 for storing a binarized error signal.

  FIG. 2 is a flowchart showing an error diffusion processing routine in the image processing apparatus. In the image processing apparatus configured as described above, when a binary image signal and a pixel position signal are supplied, the following processing is performed. In the binary image signal, 1 means black and 0 means white.

  When the input binary image signal that is the target pixel of the binary image is supplied, the pixel value estimation unit 10 estimates the pixel value of the target pixel when the binary image is a multi-valued image, and the estimated pixel signal Is generated (step S1). Then, the pixel value estimation unit 10 supplies the estimated pixel signal to the correction signal generation unit 20 and the threshold generation unit 31.

  The correction signal generation unit 20 generates a correction signal for the target pixel based on the pixel position signal indicating the position of the target pixel in the binary image and the estimated pixel signal generated by the pixel value estimation unit 10 (step S <b> 2), this correction signal is supplied to the threshold value generation unit 31 and the correction addition unit 33.

  Here, the correction signal is a signal having a positive or negative value. In the present embodiment, the correction signal is generated according to the pixel position signal. However, the correction signal is generated regardless of the position of the target pixel in the binary image, or the pixel regardless of the value of the estimated pixel signal. The present invention is applicable even when correction is performed only in accordance with the position signal.

  Based on the estimated pixel signal generated by the pixel value estimation unit 10 and the correction signal generated by the correction signal generation unit 20, the threshold generation unit 31 sets the average error accumulation amount in the error storage unit 36 to -1. A threshold signal is generated so as to substantially match the value multiplied by (step S3). That is, the threshold generation unit 31 generates a threshold signal so that the average error accumulation amount in the error storage unit 36 becomes substantially zero, and supplies the threshold signal to the binarization unit 34. The average error accumulation amount means the average accumulation amount of the binarized error signal stored in the error storage unit 36.

  In addition to the estimated pixel signal and the correction signal, the average error accumulation amount varies depending on a pseudo intermediate processing method such as a screen type such as an AM / FM screen, the number of screen lines, and a screen angle. For this reason, the threshold generation unit 31 may generate a threshold signal using information indicating any one of these pseudo intermediate processing methods. As a result, the average error accumulation amount can be made closer to zero. The degree of error diffusion depends on the error diffusion coefficient. Therefore, it is desirable that the threshold generation unit 31 generates a threshold signal for each error diffusion coefficient when the error diffusion coefficient is changed. The threshold generation unit 31 may use a lookup table or a lookup table with an interpolation function when performing the above-described processing.

  Furthermore, in the present embodiment, the threshold generation unit 31 generates a threshold signal so that the average error accumulation amount becomes substantially zero. However, if the average error accumulation amount is substantially constant, dot delay and tailing are performed. It can be resolved. Therefore, in order to make the average error accumulation amount substantially constant, initialization may be performed so that the average error accumulation amount in the error storage unit 36 becomes equal to the certain value.

  The correction calculation unit 32 calculates an error diffusion correction signal by performing a product-sum operation on the average error accumulation amount (binarized error signal) stored in the error storage unit 36 and the error diffusion coefficient (step S4). ).

  The correction addition unit 33 adds the input binary image signal, the correction signal generated by the correction signal generation unit 20, and the error diffusion correction signal generated by the correction calculation unit 32 to generate a correction addition signal (step S5). The correction addition signal is supplied to the binarization unit 34 and the error calculation unit 35.

  The binarization unit 34 compares the threshold signal generated by the threshold generation unit 31 with the correction addition signal generated by the correction addition unit 33. If the correction addition signal is equal to or greater than the threshold, the correction addition signal is “1”. Is less than the threshold value, “0” is generated, and a binary image signal obtained by binarizing the correction addition signal is output (step S6).

  Note that the value of the output binary image signal is the pixel value of the target pixel of the reset binary image. In addition to comparing the threshold signal and the correction value addition signal, the binarization unit 34 may binarize using any method as long as it is a general quantization method.

  The error calculation unit 35 generates a binarization error signal based on the output binary image signal generated by the binarization unit 34 and the correction addition signal generated by the correction addition unit 33 (step S7). This is supplied to the error storage unit 36. Here, the error calculation unit 35 assigns a quantization level 255 if the output binary image signal is 1, and assigns a quantization level 0 if the output binary image signal is 0, and subtracts the assigned value from the correction addition signal. To generate a binarized error signal.

  The binarization error signal calculated by the error calculation unit 35 is sequentially stored in the error storage unit 36 (step S8). This binarized error signal is read by the correction calculation unit 32 as an average error accumulation amount and used to correct the pixel of interest in the next error diffusion process.

  Finally, it is determined whether or not there is an unprocessed pixel in the input binary image signal (step S9). If there is an unprocessed pixel, the process from step S1 is executed again. Further, when there is no unprocessed pixel, this routine ends.

  FIG. 3 shows an average error accumulation amount in the error buffer (error storage unit 36) after the dots appear in a steady state, assuming that the threshold value generated by the threshold value generation unit 31 is a constant. FIG. The horizontal axis indicates the value (correction amount) of the correction signal generated by the correction signal generation unit 20, and the vertical axis indicates the average error accumulation amount. Each line shows a change in the value of the average error signal when the value of the estimated pixel signal is different.

  According to FIG. 3, the average error accumulation amount jumped greatly in the vicinity of zero where the correction amount changes from negative to positive. Thereby, it can be seen that dot delay and tailing are likely to occur at a point in the vicinity of zero where the correction amount changes from negative to positive or from positive to negative due to in-plane unevenness correction.

  Further, as both the correction amount and the estimated pixel signal value increase, the average error accumulation amount becomes a positive large value. Conversely, as the correction amount and the estimated pixel signal value both decrease, the average error accumulation amount becomes a negative large value.

  3 will be described by taking as an example a case where both the correction amount and the estimated pixel signal value are large.

  Even when a binary image signal “1” is generated by the binarization unit 34 and a dot is printed, in the case of a pixel of the input binary image signal “1”, the correction signal has an error to the surrounding pixels. Will be spread as. For this reason, errors tend to accumulate.

  For this reason, even when an already binarized image is corrected (see Patent Document 1), even if the quantization threshold is simply changed according to the input correction amount (see Patent Document 2). (1) When the change in the correction amount is large, (2) When the correction amount changes across 0, (3) When the estimated pixel signal changes without satisfying the above (1) and (2) It can be seen that dot delay and tailing occur.

  In general, in the case of in-plane unevenness correction, the correction amount changes smoothly and continuously according to the position in the image. A sudden change in the average error accumulation amount in such a case means that the image quality is greatly deteriorated such that new unevenness is generated even though the unevenness is corrected.

  On the other hand, the threshold generation unit 31 uses not only the correction signal generated by the correction signal generation unit 20 but also the estimated pixel signal generated by the pixel value estimation unit 10, and the average error accumulation amount is substantially reduced. A threshold signal is generated so as to be zero. Thereby, even if the estimated pixel signal changes, the average error accumulation amount can be made substantially zero, so that dot delay and tailing can be suppressed.

  As described above, the image processing apparatus according to the first embodiment not only uses the correction signal for the target pixel, but also uses the pixel value of the target pixel when the binary image is a multi-valued image. By setting a threshold for binarization and performing error diffusion processing of a binary image, the average error accumulation amount of the binarization error signal generated in the error diffusion processing can be made substantially constant. As a result, dot delay and tailing that have occurred in the error diffusion process can be further suppressed.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. The same parts as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 4 is a block diagram illustrating a configuration of an image processing apparatus according to the second embodiment. The image processing apparatus according to the second embodiment performs error diffusion processing of a binary image, and based on the input binary image signal, the pixel value estimation unit 10, the pixel signal, and the pixel position signal. A correction signal generation unit 20 that generates a correction signal and an error diffusion processing unit 30A that performs error diffusion processing are provided.

  The error diffusion processing unit 30A includes a variation calculation unit 37 in the configuration of the error diffusion processing unit 30 shown in FIG. The fluctuation calculator 37 subtracts the input binary image signal from the output binary image signal generated by the binarizer 34 to generate a fluctuation signal, and supplies the fluctuation signal to the error calculator 35.

  On the other hand, the correction addition unit 33 adds the correction signal generated by the correction signal generation unit 20 and the error diffusion correction signal generated by the correction calculation unit 32 to generate a correction addition signal. The binarization unit 34 and the error calculation unit 35 are supplied.

  The error calculator 35 assigns a quantization level 255 if the fluctuation signal generated by the fluctuation calculator 37 is 1, and assigns a quantization level 0 if the output binary image signal is 0, and uses the value assigned from the corrected addition signal. By subtracting, a binarized error signal is generated. Then, the binarized error signal is supplied to the error storage unit 36. Note that the threshold generation unit 31 generates a threshold signal as in the first embodiment.

  As a result, the image processing apparatus according to the second embodiment can further suppress the dot delay and tailing that have occurred in the error diffusion processing, as in the first embodiment.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. The same parts as those in the above-described embodiment are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 5 is a block diagram illustrating a configuration of an image processing apparatus according to the third embodiment. The image processing apparatus according to the second embodiment performs error diffusion processing of a binary image, and based on the input binary image signal, the pixel value estimation unit 10, the pixel signal, and the pixel position signal. A correction signal generation unit 20 that generates a correction signal and an error diffusion processing unit 30B that performs error diffusion processing are provided.

  The error diffusion processing unit 30B has substantially the same configuration as the error diffusion processing unit 30A, but includes a threshold value generation unit 31A instead of the threshold value generation unit 31 and a binarization unit 34A instead of the binarization unit 34. . The binarization unit 34A includes a first comparison unit 41, a second comparison unit 42, an EXOR operation unit 43, and a selector 44.

  The threshold generation unit 31A generates first and second threshold signals indicating two different thresholds based on the estimated pixel signal generated by the pixel value estimation unit 10 and the correction signal generated by the correction signal generation unit 20. To do. Here, the threshold generation unit 31A generates first and second threshold signals that substantially match a value obtained by multiplying the average error accumulation amount by -1. However, the second threshold value indicated by the second threshold signal is set to a value larger than the first threshold value indicated by the first threshold signal. The threshold generation unit 31A supplies the first threshold signal to the first comparison unit 41 and the second threshold signal to the second comparison unit 42.

  The first comparison unit 41 compares the first threshold signal with the correction addition signal generated by the correction addition unit 33. If the correction addition signal is greater than or equal to the first threshold, the first comparison unit 41 is “1”, and the correction addition signal is the first. If it is less than the threshold value, “0” is generated, and this value is supplied to the EXOR operation unit 43.

  The second comparison unit 42 compares the second threshold signal with the correction addition signal generated by the correction addition unit 33. If the correction addition signal is greater than or equal to the second threshold, the second comparison unit 42 is “1”, and the correction addition signal is the second. If it is less than the threshold value, “0” is generated, and this value is supplied to the EXOR operation unit 43 and the selector 44.

  The EXOR operation unit 43 calculates an exclusive OR of signals indicating the comparison results of the first comparison unit 41 and the second comparison unit 42 and supplies the operation result to the selector 44. The exclusive OR “1” that is the output of the EXOR operation unit 43 indicates that the value of the correction addition signal is greater than or equal to the first threshold and less than the second threshold. The exclusive OR “0” indicates that the value of the correction addition signal is less than the first threshold or greater than or equal to the second threshold.

  The selector 44 sets the input binary image signal as an output binary image signal when the output of the EXOR operation unit 43 is “1”, and outputs the output of the second comparison unit 42 as an output binary when the output is “0”. Let it be an image signal.

  FIG. 6 shows that in the error buffer (error storage unit 36) after the dots appear in a steady state, assuming that the first and second threshold values generated by the threshold generation unit 31A are constants. It is a figure which shows the average error accumulation amount. According to FIG. 6, it can be seen that, unlike FIG. 3, the average error accumulation amount does not jump in the vicinity of zero where the correction amount changes from negative to positive. However, when there is a large change in the correction amount, or when the estimated pixel signal changes, dot delay or tailing occurs.

  Therefore, the image processing apparatus according to the third embodiment uses not only the correction signal of the target pixel but also the re-binarization using the pixel value of the target pixel when the binary image is a multi-valued image. The first and second threshold values are set and the error diffusion process of the binary image is performed, thereby making the average error accumulation amount of the binarized error signal generated in the error diffusion process substantially constant. As a result, dot delay and tailing that have occurred in the error diffusion process can be further suppressed. Further, even when the correction amount changes across zero, dot delay and tailing can be suppressed.

  It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that the present invention can also be applied to a design modified within the scope described in the claims.

  For example, the present invention may be installed in an image forming apparatus such as a printer or a facsimile as long as the above-described processing can be performed, or may be a program that causes a computer to execute the above-described processing.

1 is a block diagram illustrating a configuration of an image processing apparatus according to a first embodiment of the present invention. It is a flowchart which shows the error diffusion process routine in an image processing apparatus. It is a figure which shows the average error accumulation | storage amount in an error buffer after it will be in the state where a dot appears regularly when it is assumed that the threshold value produced | generated by a threshold value generation part is a constant. It is a block diagram which shows the structure of the image processing apparatus which concerns on 2nd Embodiment. It is a block diagram which shows the structure of the image processing apparatus which concerns on 3rd Embodiment. It is a figure which shows the average error accumulation | storage amount in an error buffer after it will be in the state where a dot appears regularly, when the 1st and 2nd threshold value produced | generated by a threshold value production | generation part is assumed to be a constant.

Explanation of symbols

10 pixel value estimation unit 20 correction signal generation unit 30, 30A, 30B error diffusion processing unit 31, 31A threshold generation unit

Claims (6)

Pixel value estimating means for estimating the pixel value of the target pixel when the binary image is a multi-valued image from the target pixel of the binary image and its surrounding pixels;
The pixel value of the pixel of interest estimated by the pixel value estimating means, compensation signal of the pixel of interest on the basis of the gradation-corrected pixel value of the pixel of interest is estimated by the pixel value estimating means, of the difference a compensation signal generating means for generating a,
Adding means for adding the pixel value of the target pixel of the binary image, the correction signal generated by the correction signal generating means, and the error diffusion correction signal;
Binarization means for comparing the signal generated by the addition means with a threshold value to generate a binary image signal of the pixel of interest;
A binarization error signal generation unit that generates a binarization error signal that is a difference between the signal generated by the addition unit and the multilevel signal corresponding to the binary image signal generated by the binarization unit. When,
Storage means for storing the binarization error signal generated by the binarization error signal generation means;
An error diffusion correction signal generating means for generating the error diffusion correction signal by multiplying the binarization error signal stored in the storage means and a predetermined error diffusion coefficient for each pixel of interest and adding them;
Threshold generation means for generating the threshold so that the accumulated amount of the binarization error signal stored in the storage means is substantially constant;
An image processing apparatus.   Pixel value estimation means for estimating the pixel value of the target pixel when the binary image is a multi-valued image from the target pixel of the binary image and its surrounding pixels;
  Based on a difference between the pixel value of the target pixel estimated by the pixel value estimation unit and the pixel value of the target pixel estimated by the pixel value estimation unit and subjected to gradation correction, a correction signal for the target pixel is obtained. Correction signal generating means for generating,
Adding means for adding the correction signal generated by the correction signal generating means and the error diffusion correction signal;
Binarization means for comparing the signal generated by the addition means with a threshold value to generate a binary image signal of the pixel of interest;
Fluctuation signal generating means for generating a fluctuation signal that is a difference between the pixel value of the target pixel of the binary image and the pixel value of the binary image signal generated by the binarization means;
A binarization error generation unit that generates a binarization error signal that is an error between the signal generated by the addition unit and the multivalue corresponding to the variation signal generated by the variation signal generation unit;
  Storage means for storing the binarization error signal generated by the binarization error signal generation means;
  Error diffusion correction signal generation means for generating the error diffusion correction signal by multiplying and adding the binarized error signal stored in the storage means and a predetermined error diffusion coefficient for each pixel of interest;
  Threshold generation means for generating the threshold so that the accumulated amount of the binarization error signal stored in the storage means is substantially constant;
  An image processing apparatus.   Pixel value estimation means for estimating the pixel value of the target pixel when the binary image is a multi-valued image from the target pixel of the binary image and its surrounding pixels;
  Based on a difference between the pixel value of the target pixel estimated by the pixel value estimation unit and the pixel value of the target pixel estimated by the pixel value estimation unit and subjected to gradation correction, a correction signal for the target pixel is obtained. Correction signal generating means for generating,
Adding means for adding the correction signal generated by the correction signal generating means and the error diffusion correction signal;
When the addition signal generated by the adding means is compared with the first and second threshold values and the value of the addition signal is equal to or greater than the first threshold value and less than the second threshold value, A value image signal is output, and if the value of the addition signal is not less than the first threshold value and less than the second threshold value, a binary signal indicating the comparison result between the addition signal and the second threshold value is output. Thus, binarization means for generating a binary image signal of the pixel of interest,
Fluctuation signal generating means for generating a fluctuation signal that is a difference between the pixel value of the target pixel of the binary image and the pixel value of the binary image signal generated by the binarization means;
A signal generated by the adding means, a multi-value corresponding to the fluctuation signal generated by the fluctuation signal generating means, and a binarization error generating means for generating a binarization error signal which is an error;
  Storage means for storing the binarization error signal generated by the binarization error signal generation means;
  Error diffusion correction signal generation means for generating the error diffusion correction signal by multiplying and adding the binarized error signal stored in the storage means and a predetermined error diffusion coefficient for each pixel of interest;
  The first threshold value, which is a value obtained by multiplying the accumulated amount of the binarization error signal stored in the storage means by (−1), and the second threshold value greater than the first threshold value are generated. Threshold generation means;
  An image processing apparatus. Said threshold generating means, the image according to any one of claims 1 to 3 for generating a threshold value based pixel value of the pixel of interest estimated by the pixel value estimating means and to said compensation signal Processing equipment. The threshold generation means generates the threshold so that the accumulated amount of the binarization error signal stored in the storage means becomes substantially zero.
The image processing apparatus according to claim 1 . An image processing program for causing a computer to function as each unit of the image processing apparatus according to any one of claims 1 to 5 .

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