JPS6115466A - Halftone picture display device - Google Patents

Abstract

PURPOSE:To attain gradation expression to an input picture without incurring generation of moire and new noise by applying area modulation of an arithmetic means of each picture element information or a moving arithmetic means between picture element information so as to express gradation. CONSTITUTION:The picture information inputted via a one dimensioned line sensor 1 is subject to A/D conversion 3, then fed to the 1st multiplexer 4 and then inputted sequentially to five shift registers 5a-5e. Then the information of the four lines' share is read in parallel from the four shift registers not written yet among the shift registers 5a-5e and fed to an adder 7. The picture element information adding data is inputted serially to shift registers 8a-8f of six-stage constitution, the picture element information adding data of consecutive four timings are inputted to an adder 9, from which the addition data is obtained. The addition mean value expressing gradation is obtained by rounding off the low-order bit of the added value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a halftone image display device capable of displaying an image expressed in gradations using a binary image display device.

[Technical background of the invention and its problems]

2m for dot printers, etc.! 2. Description of the Related Art As a method of displaying an image having a gradation (intermediate 1jI) using an image display device, a binarization process of input image information using a systematic dither method or the like is conventionally known.

However, as is well known, the systematic dither method expresses the halftones of an image using a periodically repeated pattern. Therefore, if input image information is given that has pixel information with a periodicity close to the repetition period of the dither pattern, for example, if a halftone image or systematically dithered image is input, the display output There was a problem that moiré was likely to occur in the image.

Therefore, in the past, random dithering was added to the systematic dither pattern described above.
Add noise to make the moire less noticeable,
Alternatively, it is being considered to switch a plurality of dither patterns every dither period to prevent the occurrence of moiré. However, adding random noise to the dither pattern as described above causes new problems such as random noise occurring in the output display image, and switching noise occurring when the dither pattern is switched. occured. For example, Japanese Patent Publication No. 55-24634 discloses a method of randomly changing the threshold value of a dither matrix to prevent the occurrence of moiré, and Japanese Patent Application Publication No. 57-R19SE4 discloses a method of randomly selecting different threshold matrices. Techniques for preventing the occurrence of moiré by doing so are disclosed. However, even if such a method is used, there is a problem in that the generation of new random noise in the displayed image becomes noticeable.

[Purpose of the invention]

The present invention has been made in consideration of the above circumstances, and its purpose is to eliminate moiré from the input image even when a mesh, dot image, or dithered image information is input. To provide a highly practical halftone image display device capable of obtaining a binary display image expressing the gradation of the input image without causing noise generation or new noise generation. be.

[Summary of the invention]

When modulating input pixel information into display pixel information expressing gradation for each predetermined basic unit length, the present invention uses an additive average value of each pixel information within a basic unit length that defines one gradation, or the basic unit A moving average value between pieces of pixel information having a period that is an integer multiple or a fraction of an integer with respect to a long period is calculated, and this average value or moving average value is area-modulated to express the gradation. This is to obtain display pixel information. For example, between pixel information within a pixel basic unit that expresses the gradation indicated by the dither method, or a period that is an integer multiple ratio or an integer fraction (N times or 1/N times) of the period of the above pixel basic unit. The average value (integral value) of the pixel information having the gradation is calculated, and the output display pixel information expressing the gradation is obtained from this value. Such processing is performed by detecting that the input image has a component that is likely to cause moiré.

〔Effect of the invention〕

Thus, according to the present invention, the image information component corresponding to the basic unit period of the output image information expressing gradation is removed from the input image information through the above-described processing, so that moiré occurs in the output display image. Things will go away. However, since only the image information components that cause moiré are removed from the input image information and then the process is performed to obtain binary display pixel information that expresses gradation, new noise may also occur. do not have. Therefore, it is possible to easily obtain a binary display image having highly natural gradation expression. Further, the above-described processing can be performed based on the basic unit period expressing the gradation of the output display image, rather than the period included in the input image, so the period may be fixedly determined. Therefore, it is possible to handle any input image, such as a halftone image or an image dithered by other methods. In addition, the process can be easily executed, which brings about great practical effects.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing a first embodiment of the apparatus.

This device converts image information read and input by a one-dimensional line sensor 1 such as a COD into binary image information expressed in gradation, and converts this binary image information into a 2c1 image such as a dot printer or a thermal transfer printer. The display output device 2 is used for displaying and outputting the data. Here, the apparatus is configured to obtain the binary image information expressed in gradations using a systematic dithering method in which the size of the matrix is (4×4).

Image information (time series of pixel information) input via the one-dimensional line sensor 1 is sequentially converted into a digital signal via the A/D converter 3. The first multiplexer 4 includes five shift registers 5a, 5b, 5c, and 5d provided in parallel.

5e is selected cyclically every time one line of the input image is scanned by the one-dimensional line sensor 1, and the digitalized input pixel information is sequentially input.

The second multiplexer 6 receives four lines of input images stored in each of the other four shift registers, excluding the shift register in which input image information is written under the control of the first multiplexer 4. Information is read out in parallel and this input image information is provided to an adder 7. This adder 7 sequentially obtains addition data of pixel information at the same scanning pixel position in four consecutive lines.

These five shift registers 5a, 5b, 5c,
5d.

The writing of one line of image information and the reading of four lines of image information by 5e are set according to the size of the dither matrix.

Thus, the pixel information addition data for the four lines obtained through the adder 7 is input in series to shift registers 8a, 8b, 8c, 8d, 8e, and 8f configured in six stages, and is divided into pixel units. Transferred minute by minute. Among these, the image information write data in the input stage and the shift registers 8a and 8b in the first to third stages.

The pixel information addition data output from each stage via 8C in turn, that is, the pixel information addition data at four consecutive timings, is input to the adder 9, and the addition data is obtained. This addition process of pixel information addition data at four consecutive timings is also determined according to the size of the dither matrix described above. Through the above processing, the size of the dither matrix, that is, the added value of the input pixel information within the basic pixel unit expressing the gradation, is obtained as the output of the adder 9. Note that by truncating the lower bits of this added value, the added average value of the input pixel information within the pixel basic unit expressing the gradation is determined. This processing is executed each time the input pixel information is transferred pixel by pixel, and therefore, the so-called moving addition and averaging processing for the input pixel information is performed in units of (4×4) pixels. The image data obtained as the output of the adder 9 in this way is obtained by removing the periodic component from the output pixel data that expresses the gradation using (4×4) pixels as the basic unit, as will be described later. .

On the other hand, the pixel information addition data input to the shift registers 8a, 8b, ~8f, and the pixel information addition data inputted to the shift registers 8a, 8b, ~8f, and
The pixel information addition data output with delayed pixel timing is input to an adder 10 and added together. In other words, the adder 10 calculates the sum of the pixel information addition data having a shift of one cycle of the basic pixel unit expressing the gradation. Further, the pixel information addition data which are the respective outputs of the second stage shift register 8b and the sixth stage shift register 8f are input to an adder 11 and the sum thereof is calculated. The pixel information addition data input to the adder 11 also has a shift of one cycle of the pixel basic unit expressing the gradation, but the pixel information addition data input to the adder 10 2 for each set of data
The pixel timing is delayed, that is, there is a shift of 1×2 cycles from the above cycle. In this way, there is a positional relationship with a 1X2 period shift,
A subtracter 12 calculates the difference between the outputs of the adders 10 and 11 (sum of pixel information addition data). The above difference value is input to the comparator 13, and the level setter 1
A comparison is made with a predetermined threshold value set to 4. Through this comparison and determination, it is determined whether the input image information includes a large amount of information on the basic unit period component of the dither pattern.

Further, the pixel information addition data inputted to the shift registers 8a, 8b, to 8f is inputted to a subtracter 15, and the difference from the original pixel data selected and outputted by the second multiplexer 6 is determined. This data difference value is compared with a predetermined same value set in the level setter 17 by the comparator 16. This comparative judgment also determines whether the input image information includes a large amount of information on the basic unit period component of the dither pattern.

The multiplexer 18 for output control controls the output of the adder 9 according to the comparison result of the comparator 13 or 16.
It selectively outputs the pixel information addition data in a basic unit consisting of (4×4) pixels for expressing the gradation determined by , or the original pixel data selectively output by the second multiplexer 6 . That is, when the difference value calculated by the subtracter 12.15 is larger than a predetermined threshold value, the adder 9 outputs ( 4×4) The summed average value data of pixel information between pixels is selectively output. Further, if the difference value obtained by the subtractor 12.15 is smaller than the predetermined threshold, the input image information is dithered.
The original pixel information output by the multiplexer 6 is selectively outputted, assuming that it contains almost no information on the basic unit cycle component of the pattern. Note that it is sufficient to control the selection of the multiplexer 18 by using one of the above-mentioned means.

Therefore, the data (
(additional average value data or original pixel information data) is input to the comparator 19. This comparator 19 compares the input data with systematic dither matrix data preset in the memory 20 to obtain binary pixel data of the dither pattern whose basic unit is the aforementioned (4×4) pixel. It is something. This binary pixel data is supplied to the binary image display/output device 2 to output and display an image. In other words, an image expressed in gradations using a dither pattern is displayed and output.

To summarize the above, ↓ f1 Calculate the average value data between the pixel information in the basic unit of the dither pattern that performs gradation expression from the input image information, and the input image information is an image with one unit cycle of the dither pattern. When a large number of information components are included, output image information expressed in gradation by a dither pattern is obtained using the average value data, and if the input image information contains most of the image information components of the basic unit period of the dither pattern. If it is not included, the input image information itself is mixed to obtain output image information expressed in gradations using a dither pattern.

Therefore, since the above-mentioned average value data of pixel information is obtained by removing the component of the basic unit period of the dither pattern from the input iii image information, it is possible to obtain an output display image without moire. It becomes possible to obtain.

In addition, since the process simply removes the component of the basic unit period of the dither pattern from the input image information, no new noise is generated in the output display image, and the highly natural binary value expressed in gradation is generated. It becomes possible to obtain images.

Next, while analyzing the causes of moiré in conventional equipment,
The moiré suppressing effect in the apparatus according to the embodiment of the present invention will be explained.

Now, the two-dimensional image signal to be subjected to image processing is Q(x, y
), and if this is input via the one-dimensional line sensor 1, the sampled signal will be as follows.

Here, the above Xs and Vll are sample point openings in the horizontal and vertical directions by the line sensor 1.

Next, when the above-mentioned sampled image signal is resampled with the basic unit periods X and Y of the dither pattern, the signal becomes as follows.

o (x,y)ΣΣδ(x'-mxo, V-nyI
l ) n However, in the above formula, xl = kxo y is Il'WIl. When this is Fourier transformed, the following equation is obtained.

Here, the image information a (x, y) is 1/12 (maro)
The dither pattern is sampled in the X and Y directions with a period of 4 pixels each in the X and Y directions, and the spectrum in the spatial frequency plane is: This is indicated by point A in FIG. 2(d). On the other hand, the input image is 150
When a halftone image of (ring/1 nch) is given, its spectrum in the spatial frequency plane becomes as shown by point B in FIG. 2(a). In this case, the twice the spatial frequency of the dither pattern and the spatial frequency of the halftone dot image become close, and as a result, moiré occurs due to the difference (Δξ) in the spatial frequencies. The period of this moiré is (1/Δ
ξ), and when the image is displayed and output by the actual binary image display/output device 2, the period is 0.5 to several (m). Therefore, it cannot be denied that the output display image becomes very unsightly.

On the other hand, as mentioned above, for input pixel information,
When moving average processing is performed for m and n pixels in the X direction and the y direction, respectively, the average processed he signal becomes as follows.

-1) (X, V) G (ξ, η)・ml nl nl-5 inc (ξ) 5 inc (nt 77) *Σ
Σδ(ξ--, η-71) m n k)CO The distribution of the signal shown by this formula in the spatial frequency plane is
If ml and nl are respectively (4) and plotted on the above-mentioned Fig. 2 (a), the moiré suppression effect becomes clear, but here we will plot it on Fig. 2 (b) to express the effect more clearly. ) will be explained with reference to the distribution on the ξ axis.

Now, assuming that the input image is a halftone image, the distribution G (ξ', η) on the ξ axis is as shown by the solid line C in FIG. 2(b). However, when the above-mentioned moving average processing of (4×4) pixels is performed, the sinc(mt ξ)sin
The spectral distribution (second
According to the distribution indicated by the broken line in FIG. 2B, the distribution of the moving average-processed data on the ξ-axis is as indicated by the solid line E. In other words, the moving averaging process greatly suppresses the spectral components dispersed on the ξ axis of the halftone dot image.

Furthermore, as is clear from the spectral distribution on the ξ axis shown in FIG. 2(b), near the sampling frequency point of the dither pattern, the sinc
The spectral component of the term (mt ξ)sine(ns7N has a value of almost zero. This means that no matter what period of halftone dot image is input, the response of the dither pattern near the above sampling frequency to that input image This means that the frequency (Δξ) of the moire becomes low, and no noticeable moire occurs on the output display image.

Next, the principle of determining whether or not there is a periodic component that causes moiré in an input image will be explained. As shown in the embodiment described above, the value obtained by adding the pixel information between pixels having a shift of 4 pixels (one period of the dither pattern), and the value obtained by adding the pixel information between pixels having a shift of 4 pixels (one period of the dither pattern), When the subtracter 12 calculates the difference between the sum of the pixel information between the pixels having the period), the difference signal is shown as follows.

*(δ(X) + δ(X-4xQ) - δ(X-2Xo)-δ(X-6Xo)) Here, the absolute value of the Fourier transform pattern of the term enclosed in parentheses above is as shown in Figure 3. The distribution is shown by solid line F. On the other hand, if a halftone dot image as shown in FIG. 2(b) is input, the distribution of the Fourier transform pattern of the terms enclosed in parentheses () determined for this input image is shown in FIG. The center is shown by a broken line H. As is clear from the distribution characteristics shown in FIG. 3, when an image containing image information components that are likely to cause moiré is input, the response becomes high, and the difference value determined as described above increases. growing. Therefore, as shown in the above embodiment, 4
The sum of pixel information between pixels with a pixel shift (one cycle of the dither pattern) and the pixel information between pixels with a two pixel shift (1×2 cycle of the dither pattern) from each pixel above. By calculating the difference from the added value using the subtracter 12 and monitoring the value of this difference signal, it is possible to effectively determine whether or not the input image is likely to cause moiré. Then, depending on the result of this determination, if the above-mentioned moving addition and averaging process between pixel information is applied only to input images where moire is likely to occur, for example, the cause of moire, such as character pattern images and line drawings, can be eliminated. Performs averaging processing even for input images that do not have
There is no risk of causing problems such as blurring the output display image.

It should be noted that the determination as to whether or not this input image contains a cause of moiré is performed, for example, as shown in FIG. 4, a partial configuration of which is shown in FIG.
1×2 period (
Alternatively, the subtracter 21 may calculate the difference between pixels having a shift of 2 pixels). In this case, the distribution of the detection response of the judgment system becomes as shown in Fig. 5, which tends to lower the detection sensitivity and cause malfunctions due to noise compared to the above-mentioned example. Detection of point images is likewise possible. Further, in this case, there is an effect that the circuit configuration becomes extremely simple.

Furthermore, as shown in the previous example, the difference between the pixel addition data added over four lines and the original input pixel data is determined, and the value of this difference is determined. Image judgment is possible.

Next, another embodiment of the present invention will be described.

6 to 18 show an embodiment in which the present invention is applied to a color copying machine. FIG. 6 shows a schematic structure of an image input section, and FIG. 7 shows a schematic structure of an input image information processing section. are shown respectively.

In FIG. 6, a document 32 illuminated by light WA 31
A color image of
The image is inputted at 4. The color image signal inputted in this manner is amplified via a preamplifier 35, then digitally converted by an A/D converter 36, and inputted to a shading correction circuit 37 to be output to the image sensor 34.
The sensitivity unevenness of the light source 31, the illumination unevenness of the light source 31, the color filter unevenness, etc. are each corrected.

The input color image signal corrected by the shading correction circuit 37 is input to a matrix circuit 38, where it is separated into a luminance signal (2) and color difference signals CI, C2, and output.

Therefore, in order to improve the image quality of the output display image, image processing that enables highly natural gradation expression is performed only on the luminance signal (2) that has been subjected to color separation processing in the matrix circuit 38, depending on the input image. is executed selectively. still,
Regarding the color difference signals CI and C2, image signal processing is performed regardless of the input signal. FIG. 7 is a diagram showing a schematic configuration of a processing circuit for this luminance signal I. This signal processing circuit includes a block 41 that calculates the Laplacian of the luminance signal (2), a block 42 that binarizes the calculated Laplacian value, and determines and detects the combination of the binarized patterns; A block 43 for encoding values, and whether the input image formed by the luminance signal I from each output of each of these blocks 42 and 43 represents a character image, a line drawing, or a moiré image such as a halftone image. A block 44 that determines whether the image signal contains a simple periodic component, a block 45 that records this determination result and feeds it back to the block 44, and performs high-frequency correction by adding a Laplacian to the original image signal according to the determination result. and a block 46 that selects and controls whether to leave the original image signal as it is or to perform moving average addition of the previous image signal.

The block 41 that calculates the Laplacian of the luminance signal ■ is as follows:
As shown in detail in FIG. 8, the input luminance signal (2) is input to line memories 52a, 52b for each line via a multiplexer 51. An adder 53 calculates the sum of the input luminance signals for two lines stored in these line memories 52a and 52b and the current input luminance signal.
．． 54. This addition data is sent to the three-stage shift register 55a.

55b and 55c, and this shift register 55a
.

The above-mentioned addition data at three successive timings obtained as the outputs of 55b and 55c are added via the adder 5(i, 57).These addition processes result in the input image (luminance) signal shown in FIG. The added data of the (3×3) pixel valves such as By subtracting the value of the central pixel 122 of the (3×3) pixels, the Laplacian value is obtained.
As is clear from the above-mentioned example, the output of M58 is as follows.
The input image information is averaged (high frequency components are removed).

Therefore, the value of such a Laplacian is the block 42
After being inputted into the input terminal and binarized, specifically, converted into a value by extracting the value of the sign bit, it is sent to the line memories 62a, 62b, 62c via the multiplexer 61.
One line at a time is recorded. Each of these pieces of information is stored in the line memories 62a and 62b.

Three pixels are read out from 62c and input to the ROM 63 as (3×3) pixel information. Based on the information stored in the ROM 63 in advance, it is determined whether or not the input image information includes a cause of moiré based on the information of the (3×3) pixels.

On the other hand, the block 43 calculates the absolute value of the Laplacian signal and non-linearly transforms information on this absolute value.

For example, if a Laplacian signal represented by 8 bits of information is
It is converted into a compressed bit signal. The summation value for three pixels of this signal is obtained via the adder 64 and 65, and the top 4
A bit signal is output to the ROM 44.

The ROM 44 receives each output signal of the blocks 42 and 43 and comprehensively determines whether the input image information includes a moiré component. At this time, the ROM 44 uses the judgment information returned via the block 45 to
In other words, as shown in FIG. 10, the current processing target pixels are io, o.
t, when i −1, −1, i o, −1°+ i
, −1, + −i, o, and the input image information is identified.

According to such a determination result, the block 46 outputs the original input pixel signal, a signal obtained by adding the Laplacian signal of the input pixel (luminance) signal obtained in the block 41 to the original input pixel signal, or a signal obtained by averaging 9 pixels. The output signal is selectively output.

Incidentally, in parallel with such processing on the luminance signal I, the color-separated color difference signals CI and C2 are subjected to an arithmetic average of (3×3) pixels as shown in FIG. 11, and then output. Specifically, this is performed by the circuit shown in FIG. 8, and its output is similar to the output of the ROM 58.

FIG. 12 shows the configuration of a color conversion circuit which inputs each signal subjected to the above-described signal processing and obtains a signal suitable for the output characteristics of the color printer 71. That is, each of the signal components 1. CI and C2 are input to a color conversion ROM 72, and are subjected to color conversion processing according to, for example, the Neukebauer equation or the masking equation. The binary dither circuit 73 converts the signal subjected to such color conversion processing into the ROM.
Binary processing is executed in accordance with information indicating the type of input image information determined by 44. That is, when the input image shows characters or line drawings, the binarization dither circuit 13 performs fixed binarization processing on the input image information, and in other cases, binary processing is performed using the dither method.
It is designed to perform value conversion processing.

Next, the operation of the apparatus configured as described above will be explained.

As shown in Figure 13, the signal when a dot image is scanned one-dimensionally is as shown in figure (a), and the signal when a character is one-dimensionally scanned is as shown in figure (b). become.

Also, when an image such as a photograph is scanned one-dimensionally, the signal is the 13th
The result is as shown in Figure (C). As is clear from comparing these one-dimensional scanning signals, the signals of halftone dot images and character images have large local density changes, and therefore cannot be identified solely from the above-mentioned Laplacian value.

However, input images such as photographs can be identified from the Laplacian value.

On the other hand, when examining the character images and halftone dot images, Fig. 14 shows the Laplacian obtained from the character images by 2.
As shown in FIG. 15, which shows a binarized pattern of the Laplacian obtained from the halftone dot image, the pattern is different in that the black and white pixels are continuous. 16th
Figures (a) and (b) show the number of times a periodic pattern occurs in the form of a histogram using (3×3) pixel pattern data as 9-bit data. It is shown that differences exist in the number of times the pattern occurs. That is, in the case of a character image, there are relatively few periodic components as shown in FIG. 16, and conversely, in the case of a halftone dot image, there are relatively few periodic components throughout one scanning line as shown in FIG. 16(b). Therefore, there are many periodic components.

The ROM 44 obtains such information from the block 42 and comprehensively determines the type of input image.

Then, according to the judgment and identification result, if the input image is a character/line drawing, the current image signal is added to the Laplacian.
The data is added and the high-frequency components are emphasized, the signal is binarized, and this is output and displayed. In addition, when the input image signal is a halftone image, in order to express halftones, the average value of (3×3) pixels is calculated and high-frequency component noise and frequency components that cause moiré are removed. , this is dithered and output for display. Further, if the input image is not a character/line drawing or a halftone image having moiré-generating elements, the original image signal is used as it is, subjected to normal dithering processing, and then displayed and output. In this way, a halftone image is displayed according to the type of input image.

Next, the effect of suppressing the occurrence of moiré in the output display image by averaging the (3x3) pixels on the halftone image will be described.

The dither pattern in this example is, for example, the 17th dither pattern.
When given as a diagonally arranged pattern as shown in the figure, the dither pattern period is 5.7 (= 4
V'T). If the responsiveness on the Fourier transform plane at this time is calculated in the same manner as in the previous embodiment, it will be shown by point J in FIG. 18.

On the other hand, when the color input image is information read from a color printed matter, the angle of the halftone dots of the image differs depending on the printing color plate. However, in general, the magenta and black color plates with the highest contrast of the input image have a dither pattern arranged in the 45° direction, similar to the monochrome color plate. For other color plates, dither patterns are arranged in directions shifted by 15° or 30°. Therefore,
150 dither patterns arranged in the above 456 directions
When finding the response of the halftone dot of (line/1nch),
On the Fourier transform surface, it becomes as shown by the dot in FIG. 18(a).

Therefore, when the response of the signal obtained by moving and averaging between (3×3) pixels as in the above-mentioned embodiment is plotted on the ξ axis, the distribution is shown in FIG. 18(b). Therefore, the response to the halftone dot image becomes as shown by distribution M in the figure, and the frequency 5 component indicating the periodicity of the halftone dot image is suppressed to approximately zero. Therefore, as in the embodiments described above, moiré in the output display image is effectively suppressed, and it is possible to obtain an output display image with highly natural halftone expression.

As described above with respect to the two embodiments, according to the present invention, when an input image includes a frequency component having periodicity that causes moire, the moire is generated by averaging the input pixel information. Since only possible frequency components are removed, moire appearing in the output display image can be removed without introducing new noise. Therefore, a highly natural binary display image expressing gradations can be easily and effectively obtained. In addition, the above-described processing can be executed by fixedly determining the processing pixel unit according to the basic unit period for expressing the gradation of the image to be output and displayed, so the hardware configuration is simple.
Effects such as high practicality can be achieved.

Note that the present invention is not limited to the embodiments described above. In the embodiment, the moving average value between the pixel information of the basic unit period expressing the gradation was calculated, but for example, the average value of the moving sum between the pixels having a period that is an integer multiple of the basic unit period is calculated. It's okay. Of course, it is also possible to determine the type of input image using other methods. Furthermore, it is not necessary to say that the basic unit period of the dither pattern is not limited to the example described above. In short, the present invention can be implemented with various modifications without departing from the gist thereof.

[Brief explanation of the drawing]

1 to 5 show a first embodiment of the present invention, FIG. 1 is a schematic configuration diagram of the embodiment device, and FIG. 2(a)
(b) is a diagram showing the signal response in the Fourier transform plane to explain the moire suppression effect; Figure 3 is a diagram showing the detection response of frequency components that may cause moire in the input image; FIG. 4 is a diagram showing an example of the main part configuration of the input image type determination circuit, FIG. 5 is a diagram showing the response of the circuit shown in FIG. 4, and FIGS.
6 shows the configuration of the image input section, FIG. 7 shows the configuration of the signal processing section, and FIG. 8 shows the configuration of the circuit block for calculating the Laplacian of the input pixel signal. , FIG. 9 is a diagram showing pixels to be subjected to Laplacian processing, FIG. 10 is a diagram showing corresponding pixel positions of information used in identification judgment of input image information, and FIG. 11 is a diagram showing a high-pass cut filter ( 12 is a diagram showing the configuration of the binary image converter, FIG. 13 is a diagram showing differences in one-dimensional image input signals due to differences in input images, and FIGS. 14 and 15 are diagrams showing differences in one-dimensional image input signals depending on input images. Figure 16 is a diagram showing the properties of the Laplacian binarization pattern of the input image, Figure 16 is a diagram comparing the frequency of appearance of each periodic component of characters, line drawings, and halftone dot images, and Figure 17 is a diagram showing the appearance frequency of each periodic component of the output image. FIG. 18, which is a diagram showing the pattern, is a diagram showing the response of the signal on the Fourier transform plane. DESCRIPTION OF SYMBOLS 1... One-dimensional line sensor, 2... Binary image display output device, 3... A/D converter, 4, 6.18... Multiplexer, 5a, 5b, ~5e... 1 Line shift register, 7.9, 10.11... Adder, 8a
, 8b, ~8f...shift register, 12.15
...Subtractor, 13.16...: Comparator, 14.17.
...Level setter, 20...Dither pattern memory. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure s2 (a) Figure 3 Figure 4 Figure 1 Figure 5 Figure 6 Figure 8 Figure 9 Figure 10 Figure 11 jl! Figure 12 Figure 13 (a) (b)
(c)-m-. $ 14 Figure (a) (b) (c) No. 15
figure

Claims (7)

[Claims] (1) When input pixel information is modulated into display pixel information expressing gradation for each predetermined basic unit length, the average value of each pixel information within the basic unit length that defines one gradation, or the basic unit A moving average value of pixel information having a cycle that is an integral multiple of a long cycle is obtained, and display pixel information expressing the gradation is obtained by area-modulating the additive average value or the moving average value. A halftone image display device characterized by: (2) Determine the average value of each pixel information within a basic unit length that defines one gradation, or the moving average value of pixel information having a period that is an integral multiple of the period of the basic unit length, The process of obtaining display pixel information expressing the gradation by area-modulating the average value or the moving average value is performed when input image information has an integer multiple ratio with respect to the period of the basic unit length indicating the gradation. The halftone image display device according to claim 1, wherein the halftone image display device is executed by detecting the presence of pixel information having a period. (3) Determine the average value of each pixel information within the basic unit length that defines one gradation, or the moving average value of pixel information having a period that is an integral multiple of the period of the basic unit length, The process of obtaining display pixel information expressing the gradation by area modulating the average value or the moving average value is performed when the difference between the average value or the moving average value and the input pixel information is larger than a predetermined value. A halftone image display device according to claim 1, which is executed at times. (4) Determine the average value of each pixel information within a basic unit length that defines one gradation, or the moving average value of pixel information having a period that is an integral multiple of the period of the basic unit length, The process of obtaining display pixel information expressing the gradation by area-modulating the average value or the moving average value is performed so that the difference between the pixel information having a shift of 1/2 cycle of the basic unit length indicating the gradation is The halftone image display device according to claim 1, which is executed when the value is larger than a predetermined value. (5) Calculate the average value of each pixel information within the basic unit length that defines one gradation, or the moving average value of pixel information having a period that is an integral multiple of the period of the basic unit length, The process of obtaining display pixel information expressing the gradation by area modulating the additive average value or the moving additive average value is performed by adding the sum value between the pixel information having a period shift of the basic unit length indicating the gradation, and the above-mentioned Claim 1: The method is executed when the difference between the pixel information having a shift of 1/2 cycle of the basic unit length for each pixel and the added value is larger than a predetermined value.
The halftone image display device described in . (6) Determine the average value of each pixel information within a basic unit length that defines one gradation, or the moving average value of pixel information having a period that is an integral multiple of the period of the basic unit length, The process of area modulating the average value or the moving average value to obtain display pixel information expressing the gradation is selectively performed on the luminance signal component of color input image information depending on the input image. and the process is executed for color difference signals regardless of the input image.
The halftone image display device described in . (7) Determine the average value of each pixel information within a basic unit length that defines one gradation, or the moving average value of pixel information having a period that is an integral multiple of the period of the basic unit length, The process of obtaining display pixel information expressing the gradation by area modulating the average value or the moving average value is performed by determining that the input image information is not a character image or a line image. The halftone image display device according to item 1.