JPS62256573A - Picture processor - Google Patents

Abstract

PURPOSE:To obtain a converted picture which is free from moire ahd has a gradation characteristic faithful to an original picture, by selecting a prescribed line density conversion processing from line density conversion processings of plural line density conversion processing means in accordance with a control signal generated from an image area separating means. CONSTITUTION:The original picture to be subjected to the line density conversion processing is sampled with a line density of 16 lines per 1mm by an input device 1 as a scanner with a CCD and is converted to a 4-bit digital signal to obtain sampled multilevel picture data. This multilevel picture data is inputted to a processing means 2 as an input picture signal 4. The processing means 2 separates an image area of the original picture and selects an adaptive line density conversion processing in accordance with the separation result to convert the picture to a converted picture of desired variable magnification. A converted picture signal 5 which is a one-bit digital signal as the result of this line density conversion processing is inputted to an output means 3 as a laser printer having a resolution of 16 lines per 1mm. Thus, the converted picture is obtained which has a resolvability corresponding to a desired variable magnification and has the gradation reproducing characteristic faithful to the original picture.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an image processing device, and particularly to general images that include text or line drawings, halftone photographs, and continuous tone photographs. The present invention relates to an image processing device that performs linear density conversion processing.

(Prior Art) Density conversion processing, which is the process of enlarging and reducing digital images, has traditionally been used to enable communication between different models of facsimiles with different scanning line densities, or to enable communication between different models of facsimiles with different scanning line densities, or when using character generators (character generators) in printers or displays. This has been used when outputting character patterns of various sizes from C, G), and when allocating various editing results to images of a specified size in document processing equipment.

These linear density conversions! Conventionally, processing has been performed using various conversion methods (SPC method, OR method, 9-division method, projection method, etc.) in 2!1M, but the target images were limited to images of characters or line drawings. (Information Processing Society Papers g Vol.
, 26. No. 5.9920-92 Furthermore, for halftone photographs and continuous tone photographs, a conversion method is known in which the local density is preserved by determining the density of a sampling point from nearby reference pixels.

However, recently, the document office 111ff! Focusing on the vessel,
As the demand for handling various images has increased, opportunities have increased for so-called general images in which halftone photographs and continuous tone photographs, such as newspaper photographs and gravure images, are mixed with text or line drawings.

When a conventional linear density conversion method corresponding to characters or line drawings is applied to such an image, for example, in a binary image of a halftone photograph, there is an interference between the assembly circumference m and the sampling period corresponding to the scaling factor in the density conversion process. This causes moiré (density stripes). Moiré is an interference pattern that occurs when two or more periodic patterns overlap, and appears as a density stripe pattern on an image, resulting in the disadvantage that the converted image is significantly degraded.

In addition, there has been an increasing demand for handling halftone images, especially in document processing equipment, and opportunities for using dithered images using dithering, which is a method of expressing similar gradations, have increased. Furthermore, fu? In Kushimiri communication, halftone images are also transmitted, and from the viewpoint of compression efficiency, attempts have been made to transmit dithered images. Even in such a case, a technique for linear density conversion processing for dithered images is required.

However, when performing linear density conversion processing on a dithered image using the conventional method, moiré occurs due to interference between the repetition period of the dither pattern and the sampling period corresponding to the scaling factor in linear density conversion processing. . Therefore, halftone images subjected to dither processing can only be converted images with significant image quality deterioration.

As mentioned above, character malc is a density conversion method that has been conventionally used for binary images such as line drawings. When the conversion process is performed, moiré occurs in the converted image in the areas of halftone photographs and continuous tone photographs, resulting in a significant deterioration in the image quality of the converted image.

On the other hand, when conversion processing is performed on general images using the linear density conversion method for halftone photographs and continuous tone photographs, high-frequency components are lost in text or line drawing areas, resulting in low resolution with reduced sharpness in edge areas. Only converted images were available.

(Problems to be Solved by the Invention) The present invention improves the above-mentioned conventional drawbacks, and has a high resolution characteristic for general images, and a moire image that preserves the local density of the original image. It is an object of the present invention to provide image processing that makes it possible to obtain a converted image having gradation characteristics faithful to the original image.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides an image area separation means that generates a control signal according to the characteristics of the image area, and a line W of the image. : A processing means having a small number of linear density conversion processing means for performing a linear density conversion processing, and a predetermined line density conversion processing performed by a plurality of linear density conversion processing means in accordance with a control signal generated from an image area separation means. and a selection means for selecting density conversion processing.

(Function) By having an image area separation means that generates a tt+a signal according to the characteristics of the image area, the linear density processed by the ma linear density conversion processing means is determined according to the identification result of the image area separation means. It is possible to select a predetermined linear density conversion process from among the conversion processes and perform the process. Therefore, in the line density conversion process for text or line drawing areas in general images, it is possible to process them using the density conversion method that preserves the bit information of the original image, while for halftone photographs, continuous tone photographs, etc. In linear density conversion processing of a photographic image area, processing can be performed using a linear density conversion method that preserves the local density of the original image. Therefore, in the present invention, by applying a predetermined angle (95 degree conversion process) adapted to each area of the original image, resolution characteristics are high in text or line drawing areas, and there is no moiré in photographic image areas. , and a converted image having gradation characteristics faithful to the original image can be obtained.

(Embodiment of the Invention) Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a block diagram of an image processing apparatus according to an embodiment of the present invention. Image to be processed by linear density conversion (
The original image (hereinafter referred to as an original image) is a multivalued image sampled at a line density of 16 lines/1 by the input device 1, which is a scanner with COD, for example, and converted into a 4-bit digital signal. Data is obtained.

This multivalued image data becomes an input image signal 4 and is input to the processing means 2. The processing means 2 performs image area separation of the original image, selects an adaptive linear density conversion process according to the result, and converts the original image into a converted image with a desired magnification.

As a result of this linear density conversion processing, the converted image example @5, which has become a 1-pit digital signal, is input to the output means 3, which is a laser printer with resolution marks of 16 lines/1111 lines, and is outputted according to the desired magnification ratio. A converted image with resolution and gradation reproduction characteristics faithful to the original image can be obtained.

Next, the structure and operation of the processing means 2 will be explained in detail.

As shown in FIG. 1, the processing means 2 converts each area of the image input into the processing means 2 into characters, line drawings, halftone photographs,
An image area separation means 21 that identifies three areas of a continuous N:I photograph and generates a castle identification control signal (control signal) 28;
a second linear density converting means 23 that performs linear density conversion processing corresponding to the halftone photographic area; and a third linear density converting means 23 that performs linear density conversion processing corresponding to the continuous tone photographic area. 24, and 1-pit converted image signals 22', 23-1 output from the first, second, and third linear density conversion means 22, 23, and 24 according to the identification results of the image area separation means 21.
and a selector 25 which is a selection means for selecting and outputting a predetermined converted image signal from 24-.

That is, the original image input as the input image signal 4 from the input means 1 to the linear density conversion processing means 2 is first converted into IIt.
The 111i separating means 21 separates the image into three areas: characters or line drawings, halftone photographs, and continuous Wi-tone photographs. The image area separation means 21 generates an area identification control signal @28 based on the identification results of these three areas, and further outputs a binary image signal 26 and a halftone embroidery machine signal 27. The binarized image signal 26 is input to the first, second, and third linear density conversion means 22, 23, and 24, respectively, and is subjected to predetermined linear density conversion processing, thereby converting the 1-pit converted image signal 22.
', 23', 24' are output. That is, the first linear density converting means 22 performs a stock an conversion process corresponding to characters or line drawings, and the second linear density converting means 23 performs halftone periodic signal 27 output from the image area separating means 21. Based on this, a line density conversion process corresponding to a halftone photograph is performed, and the third linear density conversion means 24 performs a line density conversion process corresponding to a continuous tone photograph. Converted image signals 2 obtained from these first, second, and third linear density conversion means 22, 23, and 24
2-123' and 24' are input to the selector 25 and output from the image area separation means 21.
Accordingly, converted image signals 5 corresponding to each area of the original image are selected and output. Next, each configuration of this processing means 2 will be explained in more detail.

First, the configuration of the image area separating means 21 will be explained with reference to a block circuit diagram of the image area separating means 21 shown in FIG.

The image area separation means 21 extracts from the 4-pit input image signal 4,
Each area of the original image is identified into three areas: text or line drawings, halftone photographs, and continuous tone photographs, and an area identifier m signal 28 corresponding to each area is output. The image area separation means 21 includes an identification circuit 211 that detects the halftone level and outputs a binary or multi-value identification control signal (hereinafter referred to as a first identification!, II tll signal) 217, and a dither processing circuit. Under the control of the identification control signal 217 A selector 215 selects either the dithered image signal 218 or the simple binarized signal 219 and outputs it as the binarized image signal 26, detects the period of the halftone photograph peculiar to the halftone photograph, and outputs the halftone dot period signal 27. Halftone photo identification υ11
A halftone photo identification circuit 214 outputs a signal (hereinafter referred to as a second identification control signal) 220, and first and second identification control signals 217 and 220 are input, and the area identification circuit 1III
The encoder circuit 216 outputs a wJ signal 28.

In other words, the identification circuit 211 detects the halftone level from the input image signal 4 by using a method such as detecting the density of a specific node and calculating the average density, and outputs the first identification control signal 217. It is something to do. As a result, continuous tone photographic regions can be separated within the regions of the original image. In addition, the input image signal 4 is transmitted to the dither processing circuit 212.
and is input to the simple binarization processing circuit 213, and the dither processing circuit 21 performs dither processing using, for example, a dither matrix having the threshold distribution shown in FIG. In the binarization circuit 213, the iJ7 diagram (
A simple binarization process is performed on this X-dithered image signal 21 using a dither matrix having a threshold device as shown in
8 and the simple binary signal 219 are input to the selector 215, and the ! of the first identification control signal 217 is inputted to the selector 215. , 11@ later,
In the original image, in the continuous tone photographic region of this image region, dithering i! The 1ill signal 218 and the 111 pure binary image signal 219 in other areas are selected and output as the binary image signal 26. Furthermore, the simple binarized image signal 219 is transmitted to the halftone photograph identification circuit 214.
A second identification IIJ Ill signal 220 and a halftone period signal 2 are input to the system and separate the character or line drawing area from the halftone photograph area by detecting the halftone period peculiar to the halftone photograph.
By the way, in order to separate the text or line drawing area from the halftone photo area, when detecting the halftone period of the halftone photo using the method described later, this halftone period must be detected periodically. 2 depending on whether or not
two areas can be identified. That is, the area where the halftone dot period is periodically detected is a halftone photographic area, and the area where the halftone dot period is not periodically detected is a character or line drawing area. Therefore, the halftone photo identification circuit 214 identifies the character or line drawing area and the halftone photo area by detecting the halftone period, and outputs a second identification control signal 220 corresponding to the area. It is.

Further, the first identification signal 217 and the second identification control signal 220 are input to the encoding circuit 216, and outputted from the encoding circuit 216 as the area identification control signal 28.

Here, a method for detecting the halftone period of a halftone picture in the halftone picture identification circuit 214 will be explained.

FIG. 4 shows a schematic diagram of a halftone photograph in which the halftone period is king. Figure 4 (a) shows a two-dimensional halftone photograph focusing on the pixel size, and the upper half of this figure shows the density represented by the dot diameter (Ra). The lower half of this figure shows the concentration represented by the dot diameter (Rb).

On the other hand, Fig. 4(b) shows a one-dimensional image signal obtained by scanning the halftone photograph of Fig. 4(a), and shows the upper half of Fig. 4(a) from above. The dot diameter Ra corresponds to that represented by the dot diameter Ra, and the dot diameter Ra of the lower half portion corresponds to that represented by the dot diameter Ra, respectively. Therefore, the halftone dot circumference is 1! 'J T can be detected by detecting the interval between consecutive maximum values (or minimum values) in the -dimensional image signal. Therefore, first smoothing is performed using a low-frequency pass filter to remove noise such as spike noise, and then the local maximum value (or minimum value) is detected by successively comparing the magnitude of this image signal, and the This method detects the dot period of a dot photograph. By the way, in general, halftone photographs are 501;! /
Manufactured with a dot density of inches.

Therefore, for example, in the input means 10, 16 pieces of 71 m
When inputting an image with a resolution of m, the halftone dot circumference of the halftone photo is 11
T is in the range of -C2 to 8 pixels, with the input pixel as a unit. For example, if a 1001Q/inch dot photograph is used as the original image, the detection result will be a halftone period equivalent to 4 pixels.

Next, first, second, third linear density conversion means 22.23.
24, its structure and operation will be explained in detail.

First, the first linear density converting means 22 will be explained. Fifth
As shown in Figure <a), the first density conversion means 22 is
An area determination circuit 221 that determines a reference pixel for a converted pixel, a reference pixel selection circuit 222 that determines a reference pixel, an 11 degree decompression circuit 223 that determines the density value of a reference pixel, and a simple binarization circuit that performs a simple binarization process. 224.

The first line density conversion means 22 executes the following line density conversion process corresponding to characters or line drawings.

First, the binarized image signal 26 is input to the area determination circuit 221, and the position of the converted pixel on the original image (
x, y) are determined. Then (x, y)
The reference pixel is determined by the reference pixel selection circuit 222 based on the data. Then, the density calculation circuit 223 determines the density of the converted pixel from the density of the reference pixel determined by the reference pixel selection circuit 222. Furthermore, a simple binarization processing circuit 224 performs simple binarization processing on the density value obtained by the aIf calculation circuit 223, and a converted image signal 22 corresponding to a desired magnification ratio is obtained.

The processing method for each processing circuit will be explained in detail below.

First, the position of the reference pixel (X!
, V t ) will be explained with reference to a diagram showing the positional relationship between the original pixel and the converted pixel shown in FIG. 6(a). In FIG. 6 <a>, original pixel 01
(it, jt) is represented by O, and the converted pixel Qx (I
t , Jt )tX, and shows the case of a reduced image with a variable magnification (CV) of 477. However, +
, , +, r, and J are positive integers including zero.

First, the position M(Xt
, Vt). This (Xt, Vt) is determined by the following equation.

Xt-1t/Cv・・・・・・・・・・・・・・・
・・・・・・・・・Self・・・(1) Vt-Jt/CV
・・・・・・・・・・・・・・・・・・・・・・・・
(2) Here, the reference pixel 0ft(it, jt) of the reference area is determined based on equations (1) and (2). Reference pixel O
f1 (it, jt) Lt, variable Ii1 element Qt (It
.

The original pixel o1(!Jl) is closest to the original pixel o1(!
t , j t ). Using the Gaussian symbol ([]), this reference pixel (fl, jt> is defined as it − [1t
/ (Cv +0.5)]−−(3)j s = [
Jt / (Cv +0.5>] ・−” (given as +4. In the area determination circuit 221, this 0fs(it
, jl) as the reference pixel.

Next, the reference pixel selection circuit (222) determines a reference pixel range centered on the standard reference pixel Of1 (it, jt), for example, according to the magnification ratio. In the method of determining the reference pixel according to the magnification ratio, for example, as the magnification ratio becomes smaller, the sampling points of converted pixels become wider, so the reference pixel range is enlarged. Furthermore, as the scaling factor decreases, the sampling points of converted pixels decrease, so the reference pixel range is made smaller. Therefore, in this embodiment, since the case where the scaling factor (CV) is 4/7 is explained, the reference pixel range determined according to this scaling factor is as shown by the broken line in FIG. 6(a). (2X
2>Set as pixel area. It goes without saying that this (2×2) pixel area can be selected as appropriate other than the area indicated by the broken line in FIG. 6(a).

Next, the density calculation circuit 223 calculates the selected (2×2) reference pixel 0s (it, jt) (0≦11≦1.0≦j1
≦1) concentration Do(i, j) (0≦il≦1.0≦j1
≦1), 1I of converted pixel Q1 (Is, Jt)
aDQ 1 (It, Jt)tt'1 is output. This can be determined using the following formula.

DQI(11, Jl)-Σa(it, jt)・Dot(
it, jt) /Σa(il, jt> ・・・・・・・・・ (5) However, a(!t, jt) is the conversion pixel a degree D()+(I
t, Jl) of each reference pixel (DOs(it
, jt>). In this example, sample pixel 01 (It, Jt) and each reference pixel 01 (it,
jt) and determines a(!x, jt> using a weighting function that is inversely proportional to the distance.
(is, jt)=1.

Above, the converted pixel Q1 (It
, Jt ) are determined.

Next, in the simple binarization circuit 224, the converted pixel Q1 (I
t, J+), each concentration DQt (It, Jt) is
For example, simple binarization processing is performed using the dither matrix shown in FIG. 7<b>, and one 1-bit converted image signal 22 is obtained.

Next, the second linear density converting means 23 will be explained. Fifth
As shown in FIG. 2B, the second linear density conversion means 23 includes an area determination circuit 231, a reference pixel selection circuit 232, a density aperture circuit 233, and a dither processing circuit 234.

This second linear density converting means 23 executes the following linear density converting process corresponding to the halftone photograph.

First, in the same way as explained in the first linear density conversion means 22, in the area determination circuit 231, the binarized image M number 26 color M
The quasi'JWRm element Of 2 (i 2 , j 2 ) is found.

Next, in the reference pixel selection circuit 232, the halftone dot circumference IQ
Based on the size of the standard reference pixel Of2 (i2.j2)
A self-illuminated pixel range centered on is determined. For example, 1
In the case of a halftone photograph of 00 lines/inch, the reference pixel range is (4
Since this is the size of the X4) pixel area, this (4×4) pixel size range is extracted as the reference pixel. If self-illuminated pixels are extracted within this range, the local density of the original image can be preserved, so that the density information of the original image can be faithfully obtained. In this embodiment, for example, it is possible to extract the reference pixel area within the range indicated by the broken lines A and B in FIG. 6(b), but which range is selected is completely arbitrary.

Next, in the concentration calculation circuit 233, the selected (4×4)
Reference pixel 02 (t2.j2) (0≦12≦3.0
≦j2≦3) DO2(i2.j2) (0≦12≦3.
0≦j2≦3), find the average density in the reference area, and use that value as a density OQ2 (
r2. J2).

This can be calculated using the following formula.

DQ2 (Iz, J2)-ΣDO2(i2.j2
)7M ・・・・・・・・・(6) However, M is the total number of pixels in the reference pixel area (16 in this example)
), and A represents a set of reference pixels.

As described above, each density DQ of the converted image is calculated from the original image according to the magnification ratio.
2 (12, J2) is determined.

Next, in the dither processing port V8234, the density DQ2 (12, J2) of the converted image (9) determined above is processed by a 4×4 dither matrix having a threshold device shown in FIG. 7(C), for example. Dither processing is performed to obtain a 1-bit converted image signal 23. This dither processing circuit 234
The dither matrix thresholding device used in this study is of the dot concentration type. Although a dither matrix thresholding device can have a dot-distributed threshold arrangement, a dot-concentrated thresholding device is preferred for halftone photographs.

Next, the third linear density converting means 24 will be explained. Fifth
As shown in FIG. Reference pixel selection circuit 242. II Enguchi circuit 243. It is composed of a dither processing circuit 244.

This third coarse density conversion means 24 executes the following linear density conversion process corresponding to continuous tone photographs.

First, in the same manner as described with respect to the first linear density conversion means 22, the area determination circuit 241 determines the standard reference pixel Of3 (is, j3) from the binary image signal @26.

Next, the reference pixel selection circuit 242 selects the base rF−reference pixel 0
A reference pixel range is determined based on the size of the dither matrix of the dither processing circuit 212, with f(i, j) as the center. In this embodiment, since the dither processing circuit 212 performs dither processing using the (4×4) dither matrix shown in FIG. 7(a), the reference pixel selection circuit 242 uses the standard reference pixel Of3 (i3. pixel 03 (i3.j3) as the center and surrounding 16 pixels as reference pixel 03 (i3.j3).
). In this embodiment, it is conceivable to extract the reference pixel area within the range indicated by the broken lines A and B in FIG. 6(C), for example, but which range is selected is completely arbitrary.

Note that the range of reference pixels selected by the reference pixel selection circuit 242 changes depending on the size of the dither matrix in the dither processing circuit 212. For example, dither processing circuit 2
If the size of 12 dither matrices is (2×2), 13 quasi-reference pixels Or3 (i3.j3)
Reference pixel 03 (i3.j3
) is determined as

If the reference pixels are extracted within this range, all the dot data of one unit of the dither matrix can be extracted, so the local m1 degree of the original image can be preserved and the density information of the original image can be faithfully obtained.

moreover,! Once the calculation circuit 243 selects (4X
4) Reference pixel 03 (i3.j3) (0≦i3
Concentration DO3 (i3゜j3) of <3.0≦j3≦3>
From 0≦13≦3, 0≦j3≦3), find the average density in the reference area and convert the value to the converted pixel Q2 (12, J2) (
7) Let ilfiDQ3([3, J3). This can be determined using the following formula.

DQ3 (13, J3) - ΣDO3 (i3.j3)
7M ・・・・・・・・・(7) However, M represents the total number of pixels in the reference pixel area (16 in this example), and A
represents a set of reference pixels.

As described above, each 'm degree D of the converted image from the original image according to the magnification ratio is
Q3 (13, J3) is determined.

Next, in the dither processing circuit 244, the density DQ3 (131J3) of the converted image determined above is dithered by a (4×4) dither matrix having a threshold device shown in FIG. 7(d), for example. A 1-pit converted image signal 24 is obtained.

The dither matrix threshold device used in this dither processing circuit 244 is of a dot concentration type. The dither matrix threshold device can also be a dot-distributed threshold device.

These first, second and third density conversion means 22°23.2
4, the converted image signals 22', 23',
24- is input to the selector 25. This selector 2
5, the optimal converted image signals 22', 23- for each area of the image (characters or line drawings, halftone photographs, continuous tone photographs) are determined by the area identification control signal 28 output from the image area separation means.
．． 24- is selected, and the converted image signal 5 is output. Therefore, the selector 25 outputs a converted image signal 5 corresponding to each area of the original image, which has been subjected to linear density conversion processing suitable for that area.

The converted image signal 5 output from the selector 25 and subjected to the density conversion process corresponding to each region of the original image becomes an input signal to the output means 3, and this output means outputs the converted image according to the magnification. A recording is made.

In this way, according to the image processing ¥K I related to this embodiment, characters or line drawings are 1M! When performing linear density conversion processing at an arbitrary magnification ratio on general images, including single-point photographs and continuous tone photographs, it is possible to output image output signals that have undergone linear density conversion processing corresponding to each area of the image. Since the color density can be selected, it is possible to obtain a density conversion means that has high resolution, is free from moiré, and has gradation reproduction characteristics that are faithful to the original image.

Furthermore, in this image processing device, a predetermined linear density conversion process corresponding to each area can be selected from the density conversion processes processed by a plurality of linear density conversion means, so it can be applied to a variety of images. This makes it possible to realize a low-cost, highly versatile image processing device.

In the image processing apparatus of the present invention, various embodiments can be considered without departing from the above idea. For example, the two-in or multi-value identification method of the area separation means 21 may separate continuous tone photographic areas from the original image by pattern matching. On the other hand, in the halftone photograph identification method, by detecting the halftone dot period two-dimensionally, it becomes possible to determine the halftone dots of the diagonal pattern, and more accurate identification becomes possible.

Furthermore, by determining the output dither pattern as a diagonal pattern based on the result, it is possible to obtain a converted image that is more faithful to the original image. Furthermore, the line density 'ti conversion process performed by the first line density conversion means 22 corresponding to a character or line drawing area is not necessarily limited to this example,
For example, the density conversion process can be performed using various methods such as the 9-division method and the projection method.

[Effect of the invention 1 As described above, in the document image processing device of the present invention,
Even if ordinary images (text or line drawings, halftone photographs, continuous tone photographs) are subjected to C linear density conversion processing at any magnification ratio, the resolution is high in the text or line drawing areas, and there is no moiré in the halftone image areas. This has the advantage that it is possible to obtain a converted image with gradation recirculation characteristics faithful to the original image without the occurrence of .

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a linear density conversion processing means of an image processing apparatus according to an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of an image processing apparatus according to an embodiment of the present invention, FIG. 3 is a block diagram showing the configuration of an image area separation means according to an embodiment of the present invention, FIG. 4 is a schematic diagram of a halftone photograph,
FIG. 5 is a block circuit diagram showing the configuration of each linear density converting means included in the linear density converting means of the present invention, FIG. FIG. 7 is a diagram showing an example of a dither matrix used in the image processing 1ffi of the present invention. 2...Line density conversion processing means, 21...@area separation means, 22...First linear density conversion means, 23...Second line! Degree conversion means, 24...Third linear density conversion means, 2
5... Selection means (selector), 211... Identification circuit, 212... Dither processing circuit, 213... Single lit
! 2 +tll conversion circuit, 214... Halftone photo identification circuit, 215... Selector, 216... Encoding circuit,
221, 231.241... area determination circuit, 222,
232.242... Reference pixel selection circuit, 223, 23
3,243...Concentration 8Ii calculation circuit, 224...IJ
I wear binarization circuit, 234.244... dither processing circuit

Claims (3)

[Claims] (1) An image area separation means that generates a control signal according to the characteristics of each area of an image; a processing means having a plurality of linear density variation processing means that performs a plurality of linear density conversion processes; and the image area separation means. an image processing apparatus comprising: a selection means for selecting a predetermined linear density conversion process from among the linear density conversion processes processed by the plurality of linear density conversion process means according to a control signal generated from the image processing apparatus; . (2) The image processing apparatus according to claim 1, wherein the processing means includes first, second, and third linear density conversion processing means. (3) The first line density conversion processing means has a function of performing line density conversion processing corresponding to characters or line drawings, and the second line density conversion processing means performs line density conversion processing corresponding to halftone photographs. The image processing apparatus according to claim 2, wherein the third linear density conversion processing means has a function of performing linear density conversion processing corresponding to continuous tone photographs. .