JP2001128005A - Picture processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a picture processing method for suppressing the occurrence or moire at the time of outputting to an output unit. SOLUTION: The periodicity of a digital picture is detected and the area of a processing object is extracted (step S1). The maximum shift quantity of a pixel in the area of the processing object is obtained based on the output pixel period of an output unit or a picture period corresponding to periodicity (step S2). The pixel in the area of the processing object is set be a pixel under consideration. When the position of the pixel under consideration is assumed to be shifted based on maximum shift quantity, a processing for obtaining the new gradation value of the noticed pixel, which corresponds to the shifted position, based on the gradation value of the nearby pixel in the shifted position, is sequentially executed by making the respective pixels as the pixels under consideration (steps S3 and S4). The digital picture substituted for the new gradation value is outputted to the output unit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing method for processing a digital image obtained by inputting a document or the like with an input device and outputting the processed digital image to an output device. The present invention relates to a technique for suppressing the occurrence of moiré.

[0002]

2. Description of the Related Art For example, a digital image of a high-definition image (for example, 200 dpi) input by an input device such as a CCD is converted to a low-resolution (for example, 72 dpi) image of a display or the like.
When outputting to a device i), it is necessary to convert a digital image to a low resolution. Further, in order to output and print a digital image to an output device such as a printing device (for example, output resolution: 400 dpi, number of screen lines: 175 lines), the digital image is converted into a halftone image by halftoning processing.

[0003]

However, when a digital image is converted to a low resolution or subjected to a halftone process as described above, moire may be generated in the output image.

In the resolution conversion, a digital image is often resampled to obtain a low-resolution image. If the high-definition image has a certain periodic image pattern, the image information of the high-definition image is lost by resampling, while the pixels that are not included in the high-resolution image in the low-resolution image after resampling. Periodic fluctuations (so-called moiré) of the density (gradation value) may occur.

FIG. 12 is a schematic diagram showing the correspondence between the period of an image pattern and the pixel period (reciprocal of resolution) of an output device. Here, it is assumed that the image pattern A has a black pattern (gradation 255) continuous in the Y direction at a two-pixel cycle in the X direction. Now, the resolution of this image A is 200 DPI
For example, in order to reduce the resolution of the image A, the image A is converted into an image B (for example, 72 DPI) by a reduction projection method. At this time, as shown in FIG. 12, the ratio of the black pattern area of the image A corresponding to one pixel of the image B differs depending on the pixel position, and the pixel values of the image B are approximately 92, 143, and 133. Therefore, despite the presence of the black pattern in the image A at a constant period, a density variation different from that of the original image occurs in each pixel value of the image B after the resolution conversion. If this density variation appears in a long cycle, it will be recognized as moire.

Further, moire generated at the time of halftoning processing is as follows.
It is thought to occur according to the following principle. In other words, moiré occurs when the halftone dot pitch and the pixel pitch of the digital image do not have a relationship of an integer ratio.

FIG. 10 shows a case where the ratio between the halftone dot pitch and the pixel pitch of the digital image has an integer ratio.
This shows an example in which a pixel DA having a gradation value of 0% density is halftone-dotted.

In this case, for example, the number of halftone dots is 175 (the number of lines per inch) and the pixel pitch is 350 DPI.
(Number of pixels per inch), the halftone dot pitch U1 (= 1/175 (inch)) and the pixel pitch U
The ratio to 2 (= 1/350 (inch)) indicates a case where U1 / U2 is 350/175 = 2/1 = 2 (integer). In this case, when each pixel in the original digital image is converted to a halftone dot, the relative positional relationship between the unit area DU of the halftone dot pattern and each pixel DA is the same in any part, and Even a pixel existing at a pixel position is halftoned so as to have the same halftone area.

However, when the ratio between the halftone dot pitch and the pixel pitch of the digital image is not a relationship of an integer ratio, the pixels of the original image have the same density (tone value) in the halftoning process. However, the result of the halftone dot conversion (the size of the halftone dot area) differs depending on the relative position of the pixel at the time of halftone dot conversion.

For example, in FIG. 11, the number of halftone dots is 17
5 lines, pixel pitch is 400DPI,
Halftone dot pitch U1 (= 1/175 inch) and pixel pitch U
3 (1/400 inch) ratio U1 / U3 is 400/1
Consider the case where 75 = 2.2, that is, not an integer. In this case, the relative position between each pixel DA of the digital image and the unit halftone dot area DU on the halftone dot pattern gradually shifts and changes at a relatively large cycle. Therefore,
The relative positions of the pixels on the halftone dot pattern may be at the position of A or may be at the position of B. Then, at the position A, the halftone dot area at the time of halftoning is small, and at the position B, the halftone dot area at the time of halftoning becomes large. Therefore, even if pixels of the same density continue in the original image, if the position of the pixel at the time of halftoning fluctuates at a relatively large cycle from A to B, etc. The point area will fluctuate. The periodic fluctuation of the halftone dot area appears to the human eye as if the density value of the image changes periodically, and is perceived as a so-called moire phenomenon.

The moiré generated by the above-described resolution conversion and halftoning causes deterioration in image quality, and becomes a major obstacle at the time of image output.

The present invention has been made in view of such circumstances, and has as its object to provide an image processing method capable of suppressing occurrence of moire at the time of output to an output device.

[0013]

The present invention has the following configuration in order to achieve the above object. In other words, the invention according to claim 1 is an image processing method for outputting a digital image to an output device, wherein a periodicity of the digital image is detected to extract a processing target area, and an output pixel period of the output device is determined. Or the maximum shift amount of the pixel in the processing target area is determined based on one of the image periods according to the periodicity, and the pixel in the processing target area is set as a target pixel,
When it is assumed that the position of the target pixel has been shifted based on the maximum shift amount, a new floor of the target pixel corresponding to the shifted position is determined based on the tone value of a neighboring pixel of the shifted position. A process for obtaining a tone value is performed by sequentially setting each pixel as a target pixel, and a digital image replaced with a new tone value is output to the output device.

According to a second aspect of the present invention, in the image processing method according to the first aspect, the maximum shift amount is obtained based on a smaller one of the output pixel cycle and the image cycle. It is characterized by being able to.

According to the third aspect of the present invention, there is provided an image processing method for outputting a digital image to an output device represented by a halftone dot, wherein the periodicity of the digital image is detected and the processing target area is detected. Is extracted, the maximum shift amount of the pixel in the processing target area is obtained based on one of the output halftone cycle of the output device or the image cycle according to the periodicity, and the pixel in the processing target area is set as a target pixel. When it is assumed that the position of the pixel of interest has been shifted based on the maximum shift amount, a new value of the pixel of interest corresponding to the shifted position is determined based on the tone value of a pixel near the shifted position. The processing for obtaining the gradation value is performed by sequentially setting each pixel as a target pixel, and a digital image replaced with a new gradation value is output to the output device.

According to a fourth aspect of the present invention, in the image processing method according to the third aspect, the maximum shift amount is determined based on a smaller one of the output halftone cycle and the image cycle. It is a feature that is required.

[0017]

The operation of the first aspect of the invention is as follows. First, the processing target area where moiré is likely to occur is detected from the periodicity of the digital image, and the maximum shift of the pixel in the processing target area is determined based on either the output pixel cycle of the output device or the image cycle according to the periodicity. Find the quantity. Then, when it is assumed that a pixel in the processing target region is a target pixel and the target pixel is shifted based on the maximum shift amount, the position after the shift is determined based on the tone value of a neighboring pixel of the position after the shift. The process of obtaining a new gradation value of the target pixel according to is performed with each pixel as the target pixel in order. Then, a digital image after processing in which the gradation value of each pixel is replaced with a new gradation value is obtained. This process breaks the periodicity between the output pixel cycle of the output device and the image cycle, so that moiré can be suppressed.

According to the second aspect of the present invention, the maximum shift amount is minimized by obtaining the maximum shift amount based on the smaller one of the output pixel period and the image period. it can.

According to the third aspect of the present invention, first, a processing target area in which moire is likely to occur is detected from the periodicity of the digital image, and the output halftone cycle of the output device or the periodicity thereof is determined. The maximum shift amount of the pixel in the processing target area is obtained based on one of the image periods. Then, when it is assumed that a pixel in the processing target region is a target pixel and the target pixel is shifted based on the maximum shift amount, the position after the shift is determined based on the tone value of a neighboring pixel of the position after the shift. The process of obtaining a new gradation value of the target pixel according to is performed with each pixel as the target pixel in order. Then, a digital image after processing in which the gradation value of each pixel is replaced with a new gradation value is obtained. By this processing, the periodicity between the output dot cycle of the output device and the image cycle is broken, so that moire can be suppressed.

According to the present invention, the maximum shift amount is minimized by obtaining the maximum shift amount based on the smaller one of the output halftone period and the image period. Can be.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an example of a hardware configuration of an image processing device for implementing an image processing method according to the present invention.

The apparatus of this embodiment is constituted by a computer system, and the CPU 1 takes into account processing for extracting a processing target area (processing target area extraction processing) in accordance with the processing program stored in the internal memory 3 and output equipment. In addition to image processing to suppress the occurrence of moiré (moiré suppression processing),
Image processing such as sharpness processing and processing such as halftoning are executed.

The CPU 1 and the internal memory 3 are connected to a bus line 5
Connected through. The internal memory 3 includes, in addition to the program storage unit 3a for storing the processing program, a pre-processing image storage unit 3b for storing at least a digital image (pre-processing image) before the moiré suppression processing is performed, and a moiré suppression processing. It has a processed image storage unit 3c for storing the digital image (processed image) after the application.

The CPU 1 further includes a mouse 11, which is an example of a pointing device, a storage medium driver 15 in which a storage medium 13 is loaded, an external storage device 17, a display device 19, via an input / output interface 9. , An input device 21, an image input device 23, a printing device 25, and the like.

The processing program read from the storage medium 13 loaded in the storage medium driver 15 is transferred to and stored in the program storage unit 3a, and is executed by the CPU 1.

The mouse 11 is used to indicate a destination to output an image after processing, or to input a setting value CK, which will be described later, from a graphical menu displayed on a display device 19 such as a CRT. Used.

The external storage device 17 composed of a hard disk, a magneto-optical disk, or the like is used for storing images such as images before processing and images after processing. The input device 21 composed of a keyboard or the like is used for various instructions from an operator and setting of data necessary for processing. Further, the printing device 25 is used to print the post-processing image that has been subjected to the halftone processing.

The digital image (pre-processing image) read by the image input unit 23 is stored in a pre-processing image storage section 3b in the internal memory 3, and the pre-processing image has a processing target area as described later. Extraction processing and moiré suppression processing are performed.

FIG. 2 is a functional block diagram of an image processing apparatus for executing the image processing method, and FIG. 3 is a flowchart showing one procedure of the image processing method.

This image processing apparatus is functionally divided into a processing target area extracting section 31 for executing processing target area extracting processing based on periodicity, and a moiré suppressing processing section 41 for executing moiré suppressing processing. The moiré suppression processing unit 41
Is a shift data determining unit 43 that determines shift data for each pixel in the processing target area in consideration of an output device,
A new gradation value of each pixel in the processing target area is obtained and stored in the post-processing image storage unit 3c, and the gradation value of each pixel in the pre-processing image outside the processing target area is calculated. 3
b, and a post-processing image generation unit 45 that transfers the image data as it is to the post-processing image storage unit 3c.

As shown in FIG. 3, the processing procedure is a processing target area (an image area in which moiré may occur) in which the processing target area extracting unit 31 performs the moiré suppression processing in the image before processing. Then, an image area where an image pattern having periodicity exists is extracted (step S1). The extracted information about the processing target area is stored in the shift data determination unit 43 and the post-processing image generation unit 4 in the moiré suppression processing unit 41.
5, and periodic data (which will be described in detail later) indicating the periodicity of the image pattern in the processing target area is supplied to the shift data determining unit 43.

Next, the shift data determining unit 43 determines the given periodic data, the instructions and set values given from the input device 21, the resolution and the network of the output device such as the display device 19 and the printing device 25, and the like. The shift data for each pixel in the processing target area extracted in step S1 is determined based on the point cycle (step S2).

Then, the post-processing image generation unit 45 sets the pixel in the processing target area extracted in step S1 as a target pixel, and shifts the position of the target pixel based on the shift data determined for the target pixel. When it is assumed that the grayscale values of the neighboring pixels at the shifted position are obtained,
A new tone value of the pixel of interest corresponding to the shifted position is obtained, and the new tone value is stored as a tone value of a pixel in the processed image storage unit 3c corresponding to the pixel of interest. The process (step S3) is performed by sequentially setting each pixel in the processing target area as a target pixel (step S4). Lastly, the post-processing image generation unit 45 directly transfers the tone values of each pixel outside the processing target area in the pre-processing image from the pre-processing image storage unit 3b to the post-processing image storage unit 3c, and outputs the post-processing image. Is generated in the processed image storage unit 3c (step S5). And
The processed image is output to the display device 19 for display,
The data is output to the printing device 25 and printed.

Next, the processing contents of steps S1 to S3 in FIG. 3 will be described in detail.

[Step S1] An image area in which an image pattern having periodicity is present is extracted by examining the autocorrelation characteristics of the image before processing. For example, in the x-direction, which is a pixel column direction orthogonal to each other in a two-dimensional image before processing,
In order to check for the presence of an image pattern having periodicity along each of the y directions and to extract a processing target area,
The above characteristics are obtained by obtaining the autocorrelation data H (a) and V (a) in each of the y directions.

That is, the pixel of the image before processing is set to the central pixel (x
c, yc), the central pixel (xc,
The autocorrelation data H (a, b) and V (a, b) of the surrounding area of yc) are obtained.

H (a) = Σj ABS ｛P (xc + a + i, yc) −P (xc + i, yc)｝… (1) [i = -m to + m], [a = -wx ~ + wx)

V (b) = Σj ABS ｛P (xc, yc + b + j) -P (xc, yc + j)｝ ... (2) [j = -n to + n], [b = -wy〜 + wy)

Here, ABS ｛is a function P (x, y) for obtaining an absolute value, a gradation value m, n of a pixel (x, y) of an image before processing is a constant a for determining a difference integration area E. , b is a shift amount wx, wy for comparing autocorrelation, and a constant for determining a range W for examining the autocorrelation characteristic for one central pixel (xc, yc).

(Xc, yc) = (4, 4), m = 1 (difference integration area: 3 ×
1), wx = 2 (a = -2 to +2), and when a = + 2
FIG. 4 shows the form at the time of calculating the autocorrelation data H (a) along the x direction. (xc, yc) = (4, 4), n = 1 (difference integration area: 1 × 3), wy = 2
In the case where (b = −2 to +2), the form at the time of calculation of the autocorrelation data V (b) along the y direction when b = + 2 is shown in FIG.

Next, based on the autocorrelation data (H (a), V (b)) thus obtained, the periodicity of the image is examined.

That is, when there is an image pattern having a periodicity, the autocorrelation increases in each cycle of the image pattern (the autocorrelation data obtained by the above H (a) and V (b) decreases). Therefore, first, (A) the minimum value of the autocorrelation data is searched, and (B) whether these minimum values are below a predetermined level (threshold) and (C) whether these minimum values are regularly present. Check whether or not.

FIG. 6 shows that (xc, yc) = (7, 3), m = 1, wx = 5 (a = −5 to
+5) is a graph showing data indicating an example of P (x, y), H (a) and H (a). Since a = 0 is the autocorrelation between the same pixels, H (0) = 0 and the minimum value.

For the autocorrelation data H (a), the above (A)
The processing of [(H (k-1)> H (k)) and (H (k) <H (k +
1) Find the value of k that satisfies the conditions of) on the + and-sides.

In the process (B), it is determined whether H (k) satisfying the condition (A) satisfies the condition (H (k) <SL). SL is a "threshold value" at the time of the determination, for example, the region extraction sensitivity Se of the maximum value Hmax of H (a).
n (%) (for example, Sen = 60: SL = Hmax × 0.
6). The maximum value Hmax may be the maximum value of all H (a) or may be selected as follows.

For example, the maximum value of H (a) up to the first minimum value on the + side is searched for while performing the process (A) while changing k from k = 0 to the + side. ) Is used to determine the first minimum value on the + side. That is, H (a) between adjacent minimum values is used for determining the level of the minimum value.

In the process (C), for example, when the k on the + side and the k on the − side satisfying the condition (A) are set to kp, (ABS ｛kp-km｝ ≦ 1) is satisfied. It is determined by whether or not. Also, for example, for each local minimum value that satisfies the above condition (A), it is determined whether the absolute value of the mutual difference between the widths of adjacent local minimum values is 1 or less, ie, ABS ｛D ( d + 1)
-D (d)｝ ≦ 1 (d = 0, 1, 2...: D = 0 in FIG. 6). According to the latter determination, for example,
The present invention can be applied to a case where two or more minimum values exist on the + side and the − side, respectively.

Even if the minimum value of H (a) exists, if it is large to some extent (exceeds the threshold value SL) or if these minimum values are present irregularly, it is determined that there is periodicity. It is difficult to say, but the level can be determined by the above (B),
By the above (C), the regularity of the minimum value can be determined, and the presence or absence of the periodicity can be determined.

Therefore, the above (A), (B), (C)
When all of the above conditions are satisfied, there is an image pattern having periodicity in an image within the range W around the central pixel (xc, yc). For example, H (a) shown in FIG. 6 has periodicity, and H (a) shown in FIG. 7 has no periodicity.

The cycle value Th in the x direction is ((kp-km) /
2) or (D (d)).

In the above description, the presence / absence, the degree of the periodicity along the x direction, and the periodic value (Th) have been described, but the presence / absence, the degree of the periodicity, and the periodic value (Th) along the y direction are also the same. Can be obtained by the following processing.

As shown in FIG. 8, if the period value (Th) in the x direction and the period value (Tv) in the y direction are known, the period direction θ is (arctan (Tv
/ Th), and the actual period value (period value along the period direction) T on the image before processing is (Th × sin (θ)) (or Tv × cos
θ).

When the autocorrelation data S (a, b) is used, the same processing as described above is performed two-dimensionally to determine the presence or absence of the periodicity, the degree of the periodicity, and the actual periodicity on the image before processing. And the period value can be obtained, but as described above, the autocorrelation data H (a), V (b)
, The same result can be obtained at high speed.

When the autocorrelation data S (a, b) is used, the period of the actual image pattern is checked from various directions. At this time, the direction in which the period value becomes minimum is the direction of the image pattern. The direction is periodic.

As described above, a series of processing is performed by sequentially setting all pixels (or pixels at regular intervals) in the pre-processing image as the center pixel (xc, yc), thereby obtaining the pre-processing image. In, it is possible to extract all the image regions where the image patterns having periodicity exist.

The above-described period direction θ and period value T are defined as periodic data.

[Step S2] Each pixel (x,
The shift data SD of y) is defined by a shift amount dx (x, y) in the x direction and a shift amount dy (x, y) in the y direction as shown in FIG. In FIG. 9, the grid-like intersection portion is each pixel position, and the shift amount dx (xu, yu) in the x direction with respect to the pixel (xu, yu) of the image before processing and the shift amount dy (xu , y
u) indicates the shift direction and the shift amount defined by.

To determine such shift data SD,
For example, there is a method of randomly determining as follows. In addition to the method of randomly determining the shift data SD as described below, there is a method of using or fixing a periodic function.

In this case, dx (x, y) = dPm × R (−1.0 to +1.0) dy (x, y) = dPm × R (−1.0 to +1.0)

However, dPm is a function for generating a random number between the maximum shift amount R (−1.0 to +1.0) and −1.0 to +1.0.

It should be noted that R (-1.0 to Rx) in determining dx (x, y)
+1.0) and R (-1.0 to +1.0) when determining dy (x, y) are separate, and the determined values of dx (x, y) and dy (x, y) are Are not necessarily the same.

As described above, by randomly determining dx (x, y) and dy (x, y), the shift direction and the shift amount can be determined at random.

The maximum shift amount dPm required for determining the shift data SD is determined as follows. dPm = ± CK × min {T _I , T _A }

Where CK is a set value set in the range of 0 <1.0 min {} is a function TI for selecting a smaller cycle T _I is a cycle value T of the image pattern obtained as described above T _A is the pixel period or halftone period of the output device.

Incidentally, it has been found from experiments by the inventors that under the general conditions, the set value CK = 0.5 can suppress the moire most. However, depending on the conditions, moire may not be suppressed as desired with the value. In such a case, the operator may use the mouse 11 to indicate a different set value CK.

The moiré suppression processing by the shift processing is performed as described above. By setting the set value CK for adjusting the maximum shift amount dPm by an operator, a moiré suppression image with a desired moiré suppression degree is obtained. be able to. Further, by minimizing the maximum shift amount dPm, it is possible to minimize the deterioration in the image quality of the output image based on the digital image.

[Step S3] The new tone value Q (xu, yu) of the target pixel (xu, yu) corresponding to the shifted position is obtained by interpolating the tone values of the neighboring pixels at the shifted position. Ask. As this interpolation method, a general bilinear method or the like can be adopted.

As described above, by performing the shift processing on the pixels of the original digital image, the periodicity generated between the output pixel cycle of the output device such as the display device 19 and the image cycle is broken, and moiré is generated. The density fluctuation which occurs in a relatively long cycle, which causes the above, can be suppressed. Therefore, with respect to the digital image after the processing, it is possible to suppress the moire that has conventionally occurred when a high-resolution digital image is converted into a low-resolution digital image and output.

Similarly, at the time of the halftoning process, by performing a shift process on the pixels of the original digital image, the relative pattern between the periodic pattern and the halftone pattern of the original digital image is obtained. Moire generated due to the positional relationship can be suppressed.

Note that the output device is not the display device 19,
In the case of the printing device 25, the above-described maximum shift width d
T _A in the equation for calculating Pm is the dot period, which is the output dot period.

[0071] Further, when the value of the period direction theta and halftone angle theta _A image pattern in this case becomes different conditions, viewed from the image pattern when the halftone angle theta _A look larger. Therefore, if the difference between those angles is θ _D , the above T
_A may be replaced with the following value T _A '. T _A '= T _A / cos θ _D

In the above-described embodiment, the operator is allowed to select the set value CK for setting the maximum shift amount dPm.

In the embodiment, when the maximum shift amount is obtained, the maximum shift amount is obtained based on the smaller period of the output pixel (dot) period or the image period. However, the maximum shift amount is obtained based on only one period. You may ask for it.
Even in this case, the periodicity between the output pixel (dot) cycle and the image cycle can be broken, so that moire can be suppressed.

[0074]

As is apparent from the above description, if the invention described in claim 1 is applied to a digital image, the periodicity that has occurred between the output pixel cycle of the output device and the image cycle is broken, and For the processed digital image, it is possible to suppress moire that has conventionally occurred when a high-resolution digital image is converted into a low-resolution digital image and output.

According to the second aspect of the present invention, by minimizing the maximum shift amount, it is possible to minimize the deterioration in the image quality of the output image based on the digital image.

Further, when the invention according to claim 3 is applied to a digital image, the periodicity generated between the output dot period of the output device and the image period is broken, and the digital image after the processing is processed. Can suppress moiré, which has conventionally occurred at the time of printing after halftone processing for converting a high-resolution digital image to a low-resolution one.

According to the fourth aspect of the invention, the maximum shift amount can be minimized, and the deterioration of the image quality of the output image based on the digital image can be minimized.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of a hardware configuration of an image processing apparatus that performs an image processing method according to the present invention.

FIG. 2 is a functional block diagram of an image processing apparatus that performs the image processing method of the present invention.

FIG. 3 is a flowchart illustrating one procedure of an image processing method.

FIG. 4 is a diagram showing an example of a form at the time of calculating autocorrelation data along the x direction.

FIG. 5 is a diagram showing an example of a form at the time of calculating autocorrelation data along the y direction.

FIG. 6 is a diagram showing an example of a gradation value of each pixel of an image before processing, data showing autocorrelation data along the x direction obtained from the gradation value, and graphing the autocorrelation data.

FIG. 7 is a diagram illustrating an example of autocorrelation data along the x direction having no periodicity.

FIG. 8 is a diagram showing a relationship between a periodic value along the x direction and a periodic value along the y direction and actual periodic directions and periodic values.

FIG. 9 is a diagram illustrating shift directions and shift amounts of shift data.

FIG. 10 is a diagram showing a dot cycle and a pixel position.

FIG. 11 is a diagram illustrating a dot cycle and a pixel position.

FIG. 12 is a diagram illustrating a relationship between an image pattern and an output pixel cycle.

[Explanation of symbols]

11 ... mouse 19 ... display 21 ... input device 23 ... image input unit 25 ... printing apparatus dx ... x-direction shift amount dy ... y-direction shift amount SD ... shift data dPm ... maximum shift width CK ... set value T _I ... Image cycle T _A … output pixel (dot) cycle

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C062 AB16 AB22 AB23 AB42 AC07 AC21 AC58 BA00 5C077 LL03 NN04 PP03 PP15 PP20 PP27 PP28 PP43 PP57 PP58 PP68 PQ20

Claims (4)

[Claims] 1. An image processing method for outputting a digital image to an output device, comprising detecting a periodicity of the digital image, extracting a processing target area, and responding to an output pixel cycle of the output device or the periodicity. It is assumed that the maximum shift amount of the pixel in the processing target region is obtained based on one of the image periods, and the position of the target pixel is shifted based on the maximum shift amount with the pixel in the processing target region as a target pixel. Then, based on the tone value of the neighboring pixel at the position after the shift, a process of obtaining a new tone value of the target pixel according to the shifted position is performed by sequentially setting each pixel as the target pixel, An image processing method comprising: outputting a digital image replaced with a new gradation value to the output device. 2. The image processing method according to claim 1, wherein the maximum shift amount is obtained based on a smaller one of the output pixel period and the image period. 3. An image processing method for outputting a digital image to an output device represented by a halftone dot, comprising detecting a periodicity of the digital image, extracting a processing target area, and outputting an output halftone period of the output device. Alternatively, the maximum shift amount of the pixel in the processing target area is obtained based on one of the image periods according to the periodicity, and the pixel in the processing target area is set as a target pixel, and the pixel of interest is determined based on the maximum shift amount. When it is assumed that the position is shifted, a process of obtaining a new tone value of the pixel of interest corresponding to the shifted position based on the tone value of a pixel near the shifted position is performed on each pixel. An image processing method, wherein the digital image is sequentially output as a target pixel, and a digital image replaced with a new gradation value is output to the output device. 4. The image processing method according to claim 3, wherein the maximum shift amount is obtained based on a smaller one of the output halftone period and the image period.