JPS60182269A - Picture processing method - Google Patents

Abstract

PURPOSE:To obtain picture information with high picture element density by reproducing minute lines with much fidelity from picture information where the density is detected with a low picture element density to the minute lines drawn on the original picture. CONSTITUTION:When a density data is stored in each picture element of a video memory and a main scanning clock is outputted, data are transferred from a picture ROM24 to a register 25a and from operating circuits 22a, 22b, 23 to registers 25b, 25c, 25d respectively. Then picture elements A, B, C, D obtained by dividing picture elements set in four divisions while being shifted longitudinally and laterally in the rate of less than 1/2 to each picture element of the original picture element screen are obtained from the 25a-25d. The density data corresponding to the picture elements are stored in line buffers 28a, 28b, 28c, 28d by usig switching circuits 26, 27a, 27b and written in the video memory via a write circuit 29, then the density data of the small picture elements, A, B, C, D are expanded on the video memory and the picture information with four times density is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an image processing method for obtaining image information with a high pixel density from image information whose density is detected with a low pixel density.

[Technical background] Image processing devices that perform halftone dot processing on original images such as photographs, faxes, etc. detect the density of multilevel levels in predetermined pixel units and binarize the image information for the original image. The image is processed to obtain an output image. In such image processing devices, mI is used to increase the resolution of output images.
It is generally considered to increase the detection density of t, that is, increase the number of sampling pixels. However, if the number of sampling pixels is increased in this way, it will take time to detect the density of the entire original image, and as a result, the overall image processing time will be extended. Therefore, it becomes necessary to convert image information whose density is detected at a low pixel density into image information at a high pixel density.

[Prior Art and Problems] Conventionally, as an image processing method for converting predetermined image information into image information with higher pixel density, for example, Japanese Patent Laid-Open No. 55-102
There are some as disclosed in 21@ gazette.

As shown in Fig. 1, this is done by focusing on, for example, the pixel S of the sampling pixels A to S whose density has been detected, and dividing the focused pixel S into four to obtain small pixels α to δ. is newly determined in consideration of the density of pixels adjacent to the pixel S.

The density of each small pixel is determined, for example, as follows.

α= (2S+(A0B>)/4 β-(2S0(B+C))/4 γ-(2S+ (C0D>)/4 δ-(2S+ <D+A)l)/4 That is, small pixel The density of α is determined by considering the 8 degrees of sampling pixel A1B, and similarly, the density of each small pixel β, γ, and δ is
Sampling pixels B, C, C, D again, A
It is determined by considering each concentration of

According to the image processing method described above, the ia degree of a small pixel created by dividing a sampling pixel into four is calculated based on the density of the sampling pixel to which this small pixel belongs and other sampling pixels adjacent to the sampling pixel. Therefore, the original image information, that is, the image information obtained by detecting the density of the sampling pixel, is converted into image information with four times the density.

However, the line drawn on the original image is very thin, and the temperature distribution of the thin line falls within the width of one pixel (for example, about 100μ) as shown in Figure 2 (a) (two-dimensional representation), making it difficult to detect. For example, each density of the sampled pixel is
As shown in Figure (b), when A = S = 0710 B = D = 0, if image information is converted according to the image information processing method as described above, for the sampling pixel S, its small pixel Since 111 degrees of α, β, 3-γ, and δ become α-β=γ-δ = (1ox 2+(10+0)/4=7.5, the m-degree distribution after the conversion is the second As shown in Figure (C), the m degrees of each small pixel of the sampling pixel A1510 are uniformly (1, 5), resulting in a prominent distribution in that part.As a result, the width of the thin line drawn on the original image is Even if the width at half maximum in the graph of Figure 2 (a) is narrower than the width of the original sampling pixel, for example, minus on three sides, the image binarized based on the image information after the above conversion will still be the same as the original. It never became narrower than the width of the sampling pixel (see FIG. 2(d)).

[Object of the Invention] The present invention has been made in view of the above, and is a high pixel density method that more faithfully reproduces a thin line drawn on an original image based on image information that detects the density at a low pixel density. The purpose of this invention is to provide an image processing method that can obtain image information.

4- Configuration of the Invention] In order to achieve the above object, the present invention converts image information obtained by detecting multi-level density for each predetermined pixel unit into image information with four times the density. At this time, a new pixel is set on the above predetermined pixel plane, with each pixel shifted by a ratio of less than one of three sides in the vertical and horizontal directions, and the density of the small pixel created by dividing this new pixel into four is calculated as described above. For a small pixel located on a plurality of predetermined pixels, it is determined based on the density of each of the plurality of pixels, while for a small pixel located on one predetermined pixel, the density is determined based on the density of the pixel and the adjacent pixel. The conversion image information is determined based on the respective densities of pixels including one pixel or two pairs of predetermined pixels among the predetermined pixels, and the densities of each of these determined small pixels are used as converted image information.

[Embodiments of the invention] Embodiments of the present invention will be described below based on the drawings.

FIG. 3 is an explanatory diagram showing an example of the image processing method according to the present invention.

In the same figure, a11 to a13, a21 to a23, a3
1 to a33 are predetermined sampling pixels for the original image, and the f1 degree of the original image is detected in units of these sampling pixels.

Here, new pixels are set on the sampling pixel plane, shifted by a quarter in both the vertical and horizontal directions with respect to each sampling pixel, and these new pixels are divided into four. Then,
The small pixels formed by this four-division are classified into the following four types.

(1) Small pixel A in the center of the original sampling pixel what is located.

(2) Small pixel B The original sampling pixel and this adjacent to the bottom of the sampling pixel The same applies to each V-pull pixel. What is located in proportion.

(3) Small pixel C The original sampling pixel and this adjacent to the right side of the sampling pixel Same as each sampling pixel. What is located in proportion.

(4) Small pixel The original sampling pixel and this Below, to the right of the sampling pixel and Adjacent sump to the lower right in the same proportion as the ring pixel. what is located.

Looking at the new pixels shifted from the original sampling pixel a22, among the four types of small pixels mentioned above, each of B, C, and D Fuchimaro is B = (a22 + a32)
/2C=(a22+a23)/2D=(a22+a32+a33+a23)/Determine according to each algorithm of 4. Further, for the small pixel A, its density is determined by an algorithm such as the one shown in FIG. 4, which performs m-degree enhancement.

Therefore, the algorithm 7 for determining the tS degree (density determination for the small pixel located at the center of the sampling pixel a22) shown in FIG. 4 will be explained.

The density distribution in the main scanning direction (horizontal direction in the drawing) centered on sampling pixel a22 is a22>a21,
a23, if the density distribution in the same sub-scanning direction (vertical direction in the drawing) is a22>a12, a32, that is, if the density of sampling pixel a22 is prominent compared to the density of surrounding sampling pixels, A= 822+ (a22-812)+ (a22-a3
2)-3(a22) -a12-a32 and A= a22+ (a22- a21) + (a22
-a23)=3 (a22) -a21-a23, whichever is larger is determined.

When the density distribution in the main scanning direction is a22<a21,a23 and the density distribution in the subscanning direction is 8-a22<a12,a32, that is, the density of sampling pixel a22 is 81 degrees compared to the surrounding sampling pixels. If A=a22+ (a22-a12) +(a22-a3
2)=3 (a22) -a12-a32 and A=a22+ (a22-a21) + (a22-a
23=3 (a22) -a21-a23, whichever is smaller is determined.

When the density distribution in the main scanning direction is a21≦a22≦a23 and the density distribution in the sub-scanning direction is a12≦a22≦a32, that is, in the main scanning direction, the density increases sequentially from the left side to the right side centering on sampling pixel a22. In the case of a density distribution in which the density gradually increases from the upper side to the lower side centering on the sampling pixel a22 in the sub-scanning direction, A = a 22 is determined.

When the density distribution in the main scanning direction is a21≧a22≧a23 and the density distribution in the sub-scanning direction is a12≧a22≧a32, in other words, in the main scanning direction, the density gradually decreases from left to right centering on sampling pixel a22. In the sub-scanning direction, in the case of a density distribution in which the density gradually decreases from the upper side to the lower side with the sampling pixel a22 at the center, A = a 22 is determined.

Below, the density distribution in the main scanning direction is a22>a21, a23 a22<a21, a23 a21≦a22≦a23 a21≧a22≧a23 and the density distribution in the sub-scanning direction is a22>
A=3 (a22
) −a12−832 or A=3 (a22) −a21−a23, or A=a 22 The concentration is determined based on each algorithm.

Next, Ill! of the newly set small pixel on the predetermined sampling pixel plane! An example of an apparatus that determines the degree of disease based on the above-mentioned algorithm and obtains high-density image information will be described.

FIG. 5 is a block diagram showing the basic configuration of the device.

In this process, the analog video signal obtained after optically scanning the original image and photoelectrically converting it is further A/D converted to obtain a multilevel digital video signal that is sequentially input to the video memory 10. death,
The incoming video signal is developed into a 3×3 matrix (corresponding to sampling pixels) on a video memory 10 via shift registers 11 and 12. Then, density data (4-bit data) of each sampling pixel developed on the video memory 10, that is, a
ll to a13, a21 to a23, a31 to a33
is input to an image processing circuit 20 which performs processing according to the algorithm described above.

Here, the details of the image processing circuit 20 are as shown in FIG. 6, for example. In the same figure, 21a is the input 12
This ROM21 is a ROM with a 6-bit output and a 6-bit output.
For a, each 4-bit density data of a12, a22, and a32 on the video memory 10 is input, and the 4-bit data of 3 (a22) - a12 - a32 and the 2-bit code data are output 1.
- This 2-bit code data indicates a 12-m degree distribution in the sub-scanning direction centered on a22, and has the relationship as shown in Table 1.

Table 1 21b is also a ROM with 12 bits of input and 6 bits of output.
4-bit tide data of 1, a22, and a23 are input, and 4-bit data of 3 (a22) - a21 - a23 and 2-bit code data are output. This 2-bit data indicates the density density state in the main scanning direction centered on a22, and is shown in Table 2.
The relationship is as follows.

Table 2 22a is an arithmetic circuit, and this arithmetic circuit 22a receives 4-bit data a22 and a32 (a22+a3
2)/2, and 22b is also an arithmetic circuit, and this arithmetic circuit 22b receives 4-bit data a22 and a23 and outputs (a22+823)/2. Furthermore, 23 is also an arithmetic circuit, and this arithmetic circuit 23 processes 4-bit data a22, a
23, a32 and a33 (a22+a23+
a32+a33)/4 is output. 2
4 is a ROM with 16 bits of input and 4 bits of output, and this ROM24 stores data from ROM21a and ROM21b.
2 bit data (6 bits each) and video memory 10
The 4-bit data of a22 above is input, and the 4-bit data based on the algorithm shown in FIG. 4 is output. 25a, 25b, 25c,
25d are registers, and register 25a is R.
Data from OM24, register 25b is arithmetic circuit 22
The register 25c stores data from the arithmetic circuit 22b, and the register 25d stores data from the arithmetic circuit 23 in synchronization with the same clock (C).

26 is a two-system switching circuit, and this switching circuit 26
is a switching signal (S
). 27a is a switching circuit; 28a and 28b are newly created video signals;
The switching circuit 27 is a line buffer having a capacity for one line, and the switching circuit 27 distributes data from one of the switching circuits 26 to the line buffer 28a or 28b in synchronization with O in the sub-scanning direction. It has become. Further, 27b is a switching circuit that operates in synchronization with the sub-scanning direction clock like the switching circuit 27a, and 28c and 28d are line buffers having the same capacity as the line buffers 28a and 28b. A switching circuit 27b distributes data from the system to a line buffer 28C or 28d. 29 is line buffer 28a, 28b,
This is a write circuit that sequentially writes data output from 28c and 28d into a video memory (an area different from the video memory 10) as new image data.

Next, the operation will be explained.

Video memory 10 and shift register 11.12 to 11
In the state where 11 degree data is stored, new sampling data is written to the video memory 10 every time the main scanning direction clock is output, and the data is transferred from the ROM 24 in the image processing device 20 to the register 25a1 arithmetic circuit 22a to the register 25b1 arithmetic circuit. 22b16- to register 25C1 arithmetic circuit 23 to register 25d
Data is stored in each. At this time, register 25
The data stored in a is 11 of small pixel A in FIG.
Similarly, the register 25b, the small pixel B register 25c, and the small pixel C register 25d store St degree data corresponding to the small pixel. Then, by the operation of the switching circuit 26 in synchronization with the switching signal (S), one system of the switching circuit 26 is transferred to the register 25a.
Alternatively, the data in the register 25c is output alternately, and these data are sequentially stored in the line buffer 28a via the switching circuit 27a. That is, the data stored in the line buffer 28a via the switching circuit 27a becomes the density data corresponding to the small pixel A or the small pixel C in FIG. 3, as shown in FIG. Further, the data of the register 25b or the register 25d is alternately outputted from the other system of the switching circuit 26, and these data are outputted to the switching circuit 27.
The data are sequentially stored in the line buffer 280 via the data b. That is, the line buffer 28 is connected via the switching circuit 27b.
The data stored in c becomes density data corresponding to small pixel B or small pixel 1 (see FIG. 7). When one line of scanning is completed as described above, the line buffer 28
Density data corresponding to one line of small pixels A and C is stored in a, and density data corresponding to one line of small pixels B and D is stored in the line baranore 213c.

Then, the switching circuits 27a and 27b are switched in synchronization with the sub-scanning direction clock outputted at the start of scanning of the next line, and the image data corresponding to the small pixels Δ and C similar to the above are transferred to the line via the switching circuit 27a. buffer 2
The i opening degree data corresponding to the small pixels B and D stored in the line buffer 2 and passed through the switching circuit 271) is stored in the line buffer 2
8d. At this time, as shown in Figure 8,
When density data is stored in the line buffers 28b and 28d, the line buffer 28a
and the ig degree data stored in 28C are read out sequentially,
These density data are written into the video memory in a predetermined arrangement via the write-in circuit 29.

When the above operation is repeated until the scanning on the original image is completed, small pixels △ and 3 are stored on the video memory, respectively.
The m-degree data in 1C and D units is developed, and image information with four times the density is obtained.

If the above image processing is performed, the lines drawn on the original image will be very thin, and the density distribution of the thin lines will be as shown in Figure 9.
As shown in FIG. 9(b), each density of the detected sampling pixel falls within the width of one pixel (corresponding to FIG. 2(a)), for example, as shown in FIG. 9(b), a 11=a 21'= a 31= Oa 12=
a 22= a 32= 10a 13= a 23
= a 33 = 0, each small pixel Δ, B, C, D constituting the newly set pixel shifted from each sampling pixel a12, a22, a32 is all A=
3 (a22) -a21-a23=30B= (a2
2+ a32) / 2 =1019- C= (a22+a23)/2-5 D= (a22+a32+a33+a23)/4=5
Therefore, the concentration distribution after the conversion is shown in Figure 9 (C).
As shown in , the original sampling pixels a12, a22,
Small pixels of density 15 and density 10 are arranged alternately in the center of the horizontal direction of a32 (in this embodiment, the conversion m degree is 4 bits, so the density of density 15 or higher is limited to 15). become something. As a result, in an image that has been binarized (threshold level is appropriately determined) based on the image information after this conversion, the thin line can be reproduced with the width of the - on three sides (Figure 9 (d)) reference).

In this embodiment, the density of a small pixel located at the center of the original sampling pixel is determined based on the density of the sampling pixel and each sampling pixel adjacent to it vertically, horizontally, etc. For example, 20-△-9(a22)-(a11+a12+a13-I-
a 21+ a 23+ a 31+ a 32+ a
33). Furthermore, in this example,
The m anti-emphasis of the small pixel A located at the center of the original sampling pixel is determined by considering the density distribution in the vertical and horizontal directions of the sampling pixel, but it is also determined by considering the density distribution in both diagonal directions. Further, the density of the small pixel A may not be emphasized and A=a22 may be always set.

Furthermore, in this embodiment, a new pixel is set on a predetermined sampling pixel plane by shifting a quarter of each sampling pixel vertically and horizontally, but the present invention is not limited to this. For example, as shown in FIG. 10, a new pixel may be set that is shifted vertically and horizontally at a ratio of -4 for each sampling pixel, and furthermore, the above shifting ratio is less than one of the three. If so, it can be anything you like.

Here, if the newly set pixel is shifted by -3 as shown in Fig. 10, the 11 degrees of the small pixels A, B, C, and D obtained by dividing the newly set pixel into four will be the small pixel For △, B, and C, by performing weight calculations that take into account the ratio of the original sampling pixels to which each small pixel belongs, the small pixel A
may be determined by considering the bias within the sampling pixel to which this small pixel A belongs.

[Effects of the Invention] As explained above, according to the present invention, a new pixel is set on a predetermined pixel plane with respect to each pixel shifted by a ratio of less than one of three sides in each direction, and The density of a small pixel created by dividing a new pixel into four is determined based on the density of each of the plurality of pixels for the small pixel located on the predetermined plurality of pixels, while The located small pixel is determined based on the density of the pixel, which includes the pixel and a predetermined pixel adjacent to this pixel, or the density of the pixel above the pixel, so that From the image information that detects the density of a thin line at a low pixel density, it is now possible to obtain high pixel density image information that more faithfully reproduces the thin line, which more faithfully reproduces the original image without reducing processing speed. It becomes possible to realize an image processing device that can

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the state of pixel division in a conventional image processing method, FIG. 2 is an explanatory diagram when thin lines drawn on an original image are processed by the conventional method, and FIG. 3 is an image according to the present invention. An explanatory diagram showing an example of the state of pixel division in the processing method, FIG. 4 is an explanatory diagram showing an algorithm for determining the density of the small pixel A in FIG. 3, and FIG. 5 is an explanatory diagram showing an algorithm for determining the density of the small pixel A in FIG. 6 is a block diagram showing the details of the image processing circuit in FIG. 5, and FIG. 7 is a block diagram showing the basic configuration of the device shown in FIG.
a, a timing chart showing the output state of 27b,
FIG. 8 shows line buffers 28a, 281), 2 in FIG.
8c. FIG. 9 is an explanatory diagram showing an example of the state when thin lines drawn on an original image are processed by the image processing method according to the present invention, and FIG. 10 is an image processing method according to the present invention. FIG. 7 is an explanatory diagram showing pixel divisions in another embodiment of the circuit. 21a, 21b124-ROM 22a 122b, 23-... Arithmetic circuit 25a,
25t), 25c, 25d...Register 2G,
27a, 27b...Switching circuit 28a, 2
8b, 28c, 28d... Line buffer 29... Write circuit patent applicant Fujitsu Limited 24-

Claims (1)

[Claims] When converting the image information obtained by detecting the multilevel density for each predetermined pixel unit into an image and information with four times the density, each pixel is Set a new pixel shifted by less than one on each side, and divide this new pixel into four to create a small pixel of 81 degrees.For small pixels located above the predetermined plurality of pixels, While it is determined based on the density of each pixel, for a small pixel located above one predetermined pixel, the density is determined based on the density of the pixel and the predetermined pixel adjacent to this pixel. An image processing method characterized in that the density of each sub-pixel is determined based on the density of each pixel of (2), and the density of each small pixel thus determined is used as converted image information.