DE4447889B4 - Multiple tonal range image processing system - has host computer converting entered gray scale image into raster image expressing multiple tonal ranges, using intermediate spot pattern determined in advance - Google Patents

Abstract

The intermediate spot pattern is composed of pixels which can take only binary value densities with information indicating tonal ranges embedded in manner of arrangement of pixels in the spot pattern. This raster image thus logically expresses a large number of tonal ranges which cannot be actually expressed with pixels in binary value densities. A printer (20) receives this raster image from the host computer and converts the intermediate spot pattern in this raster image into an output spot pattern which can assume tertiary values or more in density, thus printing out a half-tone image actually expressing multiple tonal ranges.

Description

The The present invention relates to a system and method for conversion a grayscale image in a halftone image with a plurality of pixel areas composed of pixels for display of an image in multiple tonal gradations, the system being a multi-tonal image processing system is. Furthermore, the present invention relates to a corresponding Printer system, a printer driver and a computer readable Medium designed program

In the EP 0 580 151 A2 A system for generating a multi-level halftone image from a digitally sampled continuous sound image is described in which a control circuit drives look-up tables via a preference matrix to convert intensity values of the sound image to a corresponding pixel value in the halftone image. Each look-up table contains a one-dimensional transfer function, each generated such that the sum of the derivatives of the transfer functions equals the number of pixel values in a halftone cell. The magnitude of each intensity value is mapped by the transfer function into an associated output level assigned a pixel location in the halftone cell. The look-up table selection is repeated for each element of the preference matrix such that the magnitude of each different intensity value in the continuous image is mapped into a corresponding halftone cell to provide a complete multi-level halftone image.

One Dot matrix printer shapes an image by printing the pixels of a Picture in one of the binary Color values "Black" and "White". If such a Dot matrix printer forms an image with multiple tonal gradations, he uses a plurality of pixels as a unit of the presentation area the tonal gradations. This presentation area of tonal gradation is processed by means of a "dithering" method or a Grid method. In such methods, the luminosity of multiple tonal gradations from the number of black pixels in one Grid area. In these methods is the number of tone gradations the luminosity equal to the number of pixels that a display area of tonal grading, plus 1.

In In recent years, laser printer technology has become remarkable further developed. Laser printers can by controlling the laser beam energy in a pixel variations in the density of this single pixel. Laser printer, the to use this kind of density variation are available and can a big Create number of tonal variations. Use laser printers of this type a pixel information containing a plurality of bits of tone gradation data includes, and control the laser energy by generating a time accordingly the tonal gradation data for each pixel by using a digital to analogue converter.

However, these laser printers have a limited number of available tonal gradations. The limit is about 5 for a pixel size of about 40 μm ² .

By using a display area of tonal gradation formed of a plurality of dots according to the dot matrix technique coupled with the method used by laser printers, a higher number of tonal gradations can be exhibited. For example, of a 16-pixel display area in a 4 × 4 array, the tonal gradation may be represented by a figure of about 65 tonal gradations. Originally, an amount of data for representing four tone gradations is assigned to each pixel, so that the amount of data necessary to represent a tone gradation is not less than expressed in the following equation: (log 2 5) × 16 = 37.2 bits (1)

Accordingly, the amount of data necessary to represent tonal grading is more than six times the amount needed to represent 65 tonal gradations in a grayscale image, as illustrated in the following equation: log 2 65 = 6.03 bits (2)

In addition, most images are simple documents or drawings that have only the binary values "black" and "white". In these pictures, the data amount per 16 pixels for the representation of such a binary value image is expressed by the following equation: (log 2 2) × 16 = 16 bits (3)

These Quantity is two to three times smaller than the amount of data that is used to Presentation of the above Display area for Tonal gradations needed becomes.

Therefore needed the conventional multi-tone gradation image processing system that provides a display area for tonal gradations used, a multiple times larger storage capacity and a greater. Image transfer speed as a grayscale image or binary image processing system, resulting in a more expensive, conventional image processing system.

DE 36 38 852 A1 discloses an apparatus and method for recalculating the original grayscale image from a raster image originally generated from a grayscale image by means of a threshold array. On the basis of the recalculated gray scale image, certain image processing processes, such as image enlargement, can be carried out more simply and precisely.

In EP 0 580 151 A2 An apparatus and method for generating a multi-tone gradation halftone image is disclosed. By means of predetermined transfer functions, a plurality of tables are generated in which each possible gray level value is assigned a corresponding halftone value. By means of a reference matrix, a table is selected in a predetermined manner for each pixel of the gray scale image, and a halftone value is assigned to the pixel in accordance with its gray scale value. Since the halftone values can take on tertiary or higher values, the amount of data necessary for displaying the halftone image is considerably greater than in halftone images with only binary halftone values.

Therefore becomes an image output device needed that is able to use images in multiple tonal gradations of minimal amount of data without the need for increased storage capacity.

Of the The present invention is therefore based on the object, an image output device and method which are capable of producing images in multiple tonal gradations with one as possible small amount of data, which is virtually no increase in the storage capacity of the image memory requires to show.

Further It is an object of the present invention to provide a corresponding Printer system, an appropriate printer driver and a computer readable To provide a medium configured program.

These Task solves the invention by providing a system, a method, a printer system, a printer driver, and a computer-readable one Medium, as in the independent claims are defined. Further advantageous embodiments, aspects and Details of the invention are set forth in the dependent claims, the Description and the drawings indicated.

The The present invention relates to an image processing system suitable for printing or displaying images in multiple tonal gradations; more specifically, improvements to the representation of multiple Tonal gradations with a minimum amount of data. The present invention is therefore for an image output apparatus such as a printer or a CRT display, which is capable of reproducing luminosity or brightness.

Around to fulfill the task and in agreement with the purpose of the invention as embodied and broadly described herein comprises the multi-tone gradation image processing system screening means for generating a raster image in which pixels one from a Variety of given binary value densities have a gray level of associated pixels in one Grayscale image, as well as halftone conversion means for detection a spot area in a raster image which is one of a Variety of Intermediärfleckmustern corresponds to and for converting the one of a plurality of Intermediärfleckmustern in a corresponding one of a plurality of output emitter patterns, wherein the multitude of intermediate spot patterns are such speckle patterns that are a predetermined number of multiple Tonal gradations as a combination of such pixels that only binary values can accept and also in a changeable arrangement of the pixels, and the plurality of output stain patterns are such stain patterns that indeed the predetermined number of multiple tonal gradations as a combination represent such pixels, the tertiary or higher values for a density can accept.

The accompanying drawings attached to these documents and forming part of them, illustrate embodiments of the invention and, together with the description, serve to explain the Task, advantages and principles of the invention.

The The present invention will now be described with reference to the accompanying drawings explained in more detail. It demonstrate:

1 Fig. 4 is a diagram for explaining the terms used in the description of examples of preferred embodiments of the present invention;

2 (a) - 2 (d) an MGT patch pattern according to a first example of a preferred embodiment of the present invention for densities of 1 to 4 + 3/4;

3 (a) - 3 (d) an MGT patch pattern according to the first example of a preferred embodiment of the present invention for densities from 5 to 8 + 3/4;

4 (a) - 4 (d) an MGT patch pattern according to the first example of a preferred embodiment of the present invention for densities of 9 to 12 + 3/4;

5 (a) - 5 (d) an MGT patch pattern according to the first example of a preferred embodiment of the present invention for densities of 13 to 16;

6 a diagram illustrating the overview of an image editing process; which is performed by a printer in the first example of a preferred embodiment of the present invention;

7 (a) - 7 (e) Modifications of the Arrangement Which May Accept the MGT Stain Pattern in the First Example of a Preferred Embodiment of the Present Invention;

8th 10 is a block diagram illustrating a structure of the function of a whole system in the first example of a preferred embodiment of the present invention;

9 10 is a block diagram illustrating the processing operations performed by a rasterizer in a host computer in the first example of a preferred embodiment of the present invention;

10 a flow chart illustrating the processing operations performed by the screening unit;

11 5 is a diagram illustrating an example of a positional relationship between a threshold matrix and the MGT spot to which the rasterizing unit refers;

12 Fig. 12 is a diagram illustrating another example of a positional relationship between the threshold matrix and the MGT spot to which the rasterizing unit refers;

13 a diagram illustrating an Interimiärfleckmusters in the usable maximum density, in the arrangement of 7 (a) will be shown;

14 a diagram illustrating an attribute and an order, which are set in advance for a MGT spot;

15 a diagram illustrating an example of an attribute matrix;

16 a diagram illustrating an example of an order matrix;

17 10 is a diagram illustrating an example of the relationship between a sequence, a maximum threshold, and the minimum threshold;

18 (a) - 18 (e) a specific example of the conversion of a gray scale image into a raster image;

19 10 is a block diagram illustrating a hardware construction of a halftone conversion unit in a printer in the first example of a preferred embodiment of the present invention;

20 (a) - 20 (b) a specific example of a boundary condition check which the halftone conversion unit performs;

21 10 is a block diagram illustrating a structure of the principal parts of a laser printer in a second example of a preferred embodiment of the present invention;

22 10 is a block diagram illustrating the construction of a row data buffer in the laser printer in a second example of a preferred embodiment of the present invention;

23 Fig. 12 is a diagram illustrating a MGT patch pattern for processing by a laser printer in a second example of a preferred embodiment of the present invention;

24 10 is a block diagram illustrating a structure of a pattern recognition unit in the laser printer in a second example of a preferred embodiment of the present invention;

25 10 is a block diagram illustrating a construction of an image signal modulating means in the laser printer in a second example of a preferred embodiment of the present invention;

26 10 is a block diagram illustrating the structure of a pattern recognition device in a modified structure of a second example of a preferred embodiment of the present invention;

27 FIG. 4 is a diagram illustrating a MGT speckle pattern formed in accordance with the modified structure in FIG 26 a second example of a preferred embodiment of the present invention is processed; and

28 10 is a block diagram illustrating a structure of an image signal modulating device in another modified structure of a second example of a preferred embodiment of the present invention.

• (1) einem Rasterungsmittel, welches ein Rasterbild erzeugt, in dem die zusammengehörigen Bildpunkte eine der vorgegebenen Binärwertdichten in Übereinstimmung mit der Graustufe der Bildpunkte im Graustufenbild haben, und
• (2) einem Halbtonumwandlungsmittel, welches einen Fleckbereich, der eine von vielen spezifizierten Typen von Intermediärfleckmustern aufweist, im Rasterbild entdeckt, und welches das dergestalt entdeckte Intermediärfleckmuster in das entsprechende der vielen spezifizierten Typen von Ausgabefleckmustern umwandelt.

A system according to the first aspect of the present invention is a system for converting a gray scale image into a halftone image having a spot area composed of a predetermined plurality of pixels to display an image in multiple tonal gradations, the system being a multi-tone gradation image processing system equipped with the following two elements:

• (1) a halftoning means which generates a halftone image in which the associated pixels have one of the predetermined binary value densities in accordance with the gray level of the pixels in the gray scale image, and
• (2) a halftone conversion means which detects a spot area having one of many specified types of intermediate spot patterns in the raster image, and which converts the thus-detected intermediate spot pattern into the corresponding one of the many specified types of output land patterns.

in this connection are the ones mentioned above many stain patterns such stain patterns that actually the predetermined number of multiple tonal gradations with a combination from those pixels that may take tertiary or higher density values to have.

With the term "actually represented ..." means that normally can be perceived that the indeed printed or displayed image the multiple tonal gradations correctly reproduces.

Further are the ones mentioned above many types of Intermediärfleckmustern such speckle patterns logically a predetermined number of times Tonal gradations with a combination of such pixels, the only binary values can accept and also represented by different arrangement of pixels to have. Here, the phrase "logically represented ..." means that the patch patterns The multiple tonal gradations include, even if they are the multiple Tonal gradations are not necessarily in a visually perceptible Represent way.

• (1) einer "Dither"-Matrix, die einen Fleckbereich in einer vorgegebenen Position lokalisiert hat,
• (2) einer Mehrzahl von Fleckmustertypen, die aus einer Kombination von solchen Bildpunkten zusammengesetzt sind, welche nur vorgegebene Binärwertdichten annehmen können, und welche, durch eine Veränderung in der Anordnung der Bildpunkte, eine Zahl von Tonabstufungen repräsentieren, die größer ist als die maximale Zahl der dergestalt kombinierten Bildpunkte;
• (3) einem ersten Rasterungsmittel, welches die Graustufen zumindest der Bildpunkte, die außerhalb des Fleckbereichs im oben definierten Graustufenbild liegen, unter Verwendung der "Dither"-Matrix in Binärwertdichten umwandelt; und
• (4) einem zweiten Rasterungsmittel, welches die Graustufen von zumindest einiger der Bildpunkte, die innerhalb des Fleckbereichs im Graustufenbild liegen, unter Verwendung des oben definierten Fleckmusters in Binärwertdichten umwandelt.

A multi-tone gradation image processing system according to a second aspect of the present invention is a system for converting a grayscale image into a halftone image having a spot area composed of a predetermined plurality of pixels for multi-tone gradation representation, and this system is provided with the following elements

• (1) a "dither" matrix that has located a spot area in a predetermined position,
• (2) a plurality of speckle pattern types composed of a combination of such pixels which can accept only predetermined binary value densities, and which, by a change in the arrangement of the pixels, represent a number of tonal gradations greater than the maximum number the thus combined pixels;
• (3) a first halftoning means that converts the gray levels of at least the pixels that are outside the spot area in the above-defined grayscale image to binary value densities using the "dither"matrix; and
• (4) a second rasterizer that converts the gray levels of at least some of the pixels that are within the spot area in the gray scale image to binary value densities using the above-defined spot pattern.

In a multi-tone gradation image processing system according to a The first aspect of the present invention converts a screening agent a grayscale image into a raster image, which consists of pixels with Binärwertdichten consists. The raster image contains information that is one in one Arrangement of pixels forming a predetermined intermediate spot pattern Embedded Intermediate Tone Grading Show. Therefore represented this raster image, through pixels in binary value densities, "logically" a larger number of tonal gradations, as the number of tonal gradations that actually represented can be. A halftone conversion means converts this raster image into a halftone image which "actually" represents the multiple tones, where there are pixels in densities of not less than tertiary values used.

If this system e.g. on a printing system with a host computer and a laser printer is applied, it is possible to use the host computer to provide a screening agent, and the laser printer with a Halbtonumwandlungsmittel, which immediately before printing for Application comes. With this construction are images that are in the printer saved and edited, raster images and it is possible, to use an apparatus, its storage capacity and processing speed an amount of data that is smaller than a large number of tonal gradations, which can ultimately be represented.

In a multi-tone grading image processing system according to a second aspect of the present invention, a first halftoning means converts the gray level of at least such pixels, which are outside the spot area in the grayscale image, are converted to binary value densities using the pre-prepared "dither" matrix. Further, a second rasterizer converts the gray level of at least some of the pixels within the spot area in the gray scale image into binary value densities using a pre-prepared intermediate spot pattern.

stroke diagrams and contours of graphic representations in original grayscale images converted into patterns of pixels with binary value densities, matching with the shapes of the patterns. Furthermore become halftone areas, in which intermediate gray levels in a two-dimensional Distribution of continuous change converted into a distribution of intermediate spot patterns, the logically multiple-pitches represent. Furthermore become the Intermediärfleckmuster in the converted grid as much as possible from each other isolated, so that this Pattern spatially and logically distinguished from such patterns, the stroke graphics or similar represent.

Such represents a raster image advantageously and logically both a multi-tone gradation pattern as well as the binary value patterns, such as. Line drawings within a semitone area, and such a raster image has the same amount of data as an image that exclusively Patterns in binary values represents. This dataset is smaller than a dataset in one Image, the multiple gradations through processes according to the state of Technique represents. By storing this raster image and its Processing in e.g. a printer and discovery of only intermediate spot patterns immediately before a printing process and their conversion to stain patterns, which actually multiple Represent tonal gradations, it becomes possible to produce high quality To produce prints in which advantageously both halftone images in multiple gradations as well as binary patterns for line art and similar are shown.

In an example of a preferred embodiment of the present invention Invention will be a plurality of "dither" matrix types pre-prepared to suit a plurality of types of arrangements Spot area densities in a raster image. Each of the "dither" matrices is created in accordance with a condition which the usable types of intermediate area patterns limited to those that belong to a given group of small density gradings belong, So that the Intermediärfleckmuster in a raster image in an array of related patch areas can be separated from each other. The System is constructed such that one of the plurality of types selectively on "dither" matrices used to convert a grayscale image to a raster image can be.

If a "dither" matrix of high Density selected in the spot area is the density range in which multi-tone gradation representations are achieved can be diminished, however, the resolution becomes increased in that semitone range, in which a multi-tone gradation representation is produced. If a low-density "dither" matrix has been selected, is the density range in which multi-tone gradation representations can be achieved elevated, however, the resolution becomes in that halftone area in which a multi-tone gradation representation is reduced is produced. Therefore, this system allows the selection of a suitable "dither" matrix suitable for everyone given case.

Some of the terms used in the following description will now be described with reference to FIG 1 explained. The term "grayscale image" denotes an image having many intermediate tone gradation values between the "white" level and the "black" level for each dot. The term "raster image" denotes an image having a fixed tone gradation value of either "white" level or "black" level for each pixel. The term "halftone image" denotes a type of raster image composed of halftone cells. The term "halftone cell" denotes an area 1 , as in 1 which is composed of a plurality of dots representing an intermediate tone gradation by means of the number of black dots. The term "grid mark" denotes a collection 3 of black dots in a halftone cell 1 , as in 1 shown. The term "speckle pattern" denotes the shape of a grid spot 3 , The term "grid spacing" denotes an interval d for the arrangement of halftone cells, as in 1 shown. The term "grid angle" indicates the angle θ formed by the angle of the direction of the grid marks with the horizontal direction of the paper surface.

Of the Term "MGT" is an abbreviation of "Micro Gray Technology" which to designate the image processing system according to the invention, as described in this specification.

In a preferred embodiment of the invention, the overall system comprises a host computer 10 and one with host computer 10 connected laser printer 20 , as in 8th shown (and described in detail below). host 10 reads a grayscale image ( 31 ), it turns into a raster image 39 and transfers the raster image 39 to the laser printer 20 , laser 20 converts the raster image 39 from host computer 10 in a halftone picture 40 which correctly displays the tone gradations, and prints out the resulting halftone image.

2 (a) to 5 (d) show various pre-defined speckle patterns used in this system to obtain the final halftone image from an original grayscale image.

Two Types of stain patterns are used to be in a density of 1 to 16 at density intervals of 1/4 61 tonal gradations. These are referred to as "Intermediärfleckmuster" and "Ausgabefleckmuster" and for each tonal gradation set up. These stain patterns are set up as a pattern of black dots in a range of four by four pixels, thus a total of 16 pixels. In the course of this specification will be the range of four by four pixels in which all of these Stained patterns are set up, a "MGT" stain called.

An "Intermediate Spotting Pattern" is a spotting pattern used to represent multiple tonal gradations in a grayscale image when host computers 10 a read in grayscale image 31 in a raster image 39 converts, as will be described later. This intermediate spot pattern, which assigns a "black" or "white" level to each of the 16 pixels of an MGT patch pattern, has a summed data set of 16 bits. The number of actual tonal gradations represented by the number of black pixels is thus sixteen. However, by embedding gradation data into an array of black pixels within the "Spontaneous Intermediate Spotting" pattern, this intermediate spatter pattern represents four times the number of actual tonal gradations mentioned above.

An "output spatter pattern" is a spatter pattern for converting an intermediate spatter pattern in a raster image when the printer is a raster image from a host computer 10 prints out, as described later. In other words, this output patch pattern has tone-gradation data embedded in an arrangement of black pixels of an intermediate pattern, the tone-gradation data being made kinetically as the number of black portions of a pixel at intervals of 1/4 dot, and the size of the black portion as true to the density reproduces.

2 (a) shows by way of example the four tone gradations with the densities of 1 to densities of 2 in density steps of 1/4. The number of black pixels in the intermediate spot pattern is 2, but the arrangement of the black pixels is different for each of the tone gradations embedded in this arrangement. The corresponding output patch pattern has made the embedded tone gradation kinetically through the black area of 1/4 to 1 pixel. The size of the black area represents the densities from 1 to 2 in 1/4 pixel increments.

Consequently reduces the use of an Intermediärfleckmusters in the arrangement of black pixels embedded tonal gradations the amount of data of the raster image to be processed by the printer with the final Halftone image in which an output stain pattern is used.

Further, the difference between the intermediate spot pattern and the output pad pattern is set so that the difference is less than or equal to three pixels with respect to the pattern difference and less than one pixel with respect to the density difference. Therefore, side effects are very small when the diameter of a pressure point is on the order of 40 μm ² even if a part which was not intended to be converted was mistakenly converted.

6 schematically shows the image processing operation that the printer performs in this system.

The printer 20 receives as input a raster image 39 as on the left side of 6 shown. In some cases, such a raster image includes 39 both a halftone component, such as a photograph, and a portion in black and white levels, such as line art. In such a case, the halftone image becomes an intermediate spot pattern 5 As noted above, while the black and white levels represent ordinary line drawing patterns 7 being represented.

If such a raster image 39 into a printer 20 (eg a laser printer) is input, the printer identifies 20 the intermediate spot pattern 5 within the raster image entered in this way 39 and converts interstitial patterns 5 into a corresponding output stain pattern 9 around, while the pattern 7 for line art and the like remains unchanged. The printer 20 now uses this output stain pattern 9 along with the pattern 7 as control pulses for a laser light emitting diode used as an image writing laser unit. As a result of these operations, the printed halftone image may 40 represent such halftone images as a photograph in natural reproduction with multiple tonal gradations, while the line drawings and the like are clearly represented as "black" and "white" levels.

Now it is in the processing of images by a printer 20 , as in 6 shown, necessary, in the input screen image 39 between Intermedi ärfleckmustern 5 and patterns 7 for line drawings and the like. One of the indications that may serve to make such a distinction is the difference between the two possibilities that the patterns composed of black pixels are either isolated for an individual halftone cell or that they are connected via any plurality of halftone cells. That is, a patch pattern for representing a bright halftone should generally be isolated for an individual halftone cell, as in FIG 1 shown. On the other hand, a dark pattern of black pixels should be connected to form a line drawing or the like from the starting point of the stroke to its end point. As described later in detail, therefore, the printer determines whether the pattern detected in the input raster image is isolated or connected from black pixels.

In order to enable the above-mentioned discrimination, in converting the gray-scale image to a raster image, the host computer must set the intermediate-spot patterns to be isolated from each other as much as possible. In order to accomplish this setup, certain restrictions are imposed on the arrangement of the MGT patch patterns in the image and the type of usable patch pattern. 7 (a) to 7 (g) show variations in the location of the MGT spot (the area enclosed by the thick solid line) used for this system.

7 (a) shows the densest MGT stain arrangement and 7 (g) the most spacious arrangement. 7 (b) to 7 (f) show arrangements of intermediate densities. The square shape indicated by the broken line in these figures shows the size and inclination (grating angle) of the halftone cell at the level of the single spot.

To ensure that the stain patterns in the MGT stain are isolated, the densest array of 7 (a) not the use of patterns other than those of 2 (a) - (D) and 3 (a) - (D) For example, for any density darker than 8, this arrangement can not separate the intermediate spot patterns from one another. Thus, the tonal gradations that can be represented are eight isolated and scattered tonal gradations in the range of density from 9 to the density of 16.

With the in 7 (b) . 7 (c) and 7 (d) In the arrangement shown, the patterns in the 45 tonal gradations may have densities from 1 to densities of 12, as in FIG 2 (a) to 4 (d) shown to be used. With the in 7 (e) and 7 (f) The patterns of the 53 tone gradations with densities of 1 to densities of 14, as shown in FIG 2 (a) to 5 (b) shown to be used. With the most spacious, in 7 (g) Finally, all 61 patterns of the 53 tone gradations with densities from 1 to densities of 14 can be used.

such becomes with increasing density in the arrangement of the MGT patches the Decrease the number of types of usable stain patterns. That means that the area on tones, where a fine representation of multiple tonal gradations is achieved is limited to a range of bright tones. In contrast to becomes, the more spacious the formation of MGT patches is the area of suitable Types of stain patterns expanded to ever greater densities. This means, that the Range of tones, where a fine representation of multiple tonal gradations is achieved is extended to the area of darker tones. In addition, will the influence be small, since a representation of multiple tonal gradations stronger of bright tones as of dark tones affected even if the area in which a representation of multiple Tonal gradations can be generated, limited to a range of bright tones.

on the other hand A denser arrangement of patches means a reduction the size of the halftone cells. More specifically, the grating pitch becomes narrower and the resolution higher. in the In contrast, a more spacious arrangement means an enlargement of the Size of the halftone cells. More specifically, the grating pitch gets wider and the resolution gets lower.

Consequently The density of the patch arrangement produces changes in the ability to Tonal gradation representation and inverse inverse resolution to each other. Therefore it is desirable to Case-by-case basis to determine which of the patch arrangements used should be, so that the elected Stain arrangement of image quality the original grayscale image and the image quality or the like of the desired Pressure is appropriate.

Next, the details of this system will be explained with reference to FIG 8 (a) to 20 (b) described.

8 (a) to (E) illustrate the overall structure of the functions of this system.

The host computer 10 has a grayscale input unit 11 which receives grayscale image data line by line as input from an image scanner or the like, and via rasterization unit 13 representing the input grayscale image 31 converted into raster data.

Screening unit 13 converts, as described above, the halftone component of the gray scale image 31 using an intermediate spot pattern in a raster image 39 around.

Screening unit 13 uses two types of threshold matrices (described below) that reside in the main memory device 15 are stored, as well as the Intermediärfleckmuster from the 2 (a) to 5 (d) , The laser printer 20 has the halftone conversion unit 21 which is a raster image 39 from the host computer 10 receives and the raster image into a halftone image 40 converts, as well as over printing unit 23 which is the halftone image 40 prints. Halbtonumwandlungseinheit 21 converts an Intermediärfleckmuster, the in from the host computer 10 skillful raster image 39 is included in an output dot pattern as described above.

Now the editing process is performed by the screening unit 13 of the host computer 10 is carried out with reference to 9 to 18 (e) described in detail.

As in 9 shown uses the screening unit 13 a maximum threshold value matrix 33 , a minimum threshold matrix 35 , or Intermediärfleckmuster 37 to the entered grayscale image 31 on, thus the grayscale image 31 in raster image 39 converting. Here is the maximum threshold value matrix 33 a conversion matrix that provides an indication of the density threshold for specifying "black" for individual pixels of the gray scale image 31 contains. Furthermore, the minimum threshold matrix is 35 a conversion matrix that provides an indication of the density threshold for specifying "white" for individual pixels of the gray scale image 31 contains.

The sizes of the maximum threshold matrix 33 and the minimum threshold matrix 35 are determined by the arrangement of in 7 (a) determined until (g) shown MGT spots. More specifically, the sizes of the maximum threshold value matrix 33 and the minimum threshold matrix 35 set in such a manner that the stain pattern, in accordance with the arrangement of the stains in 7 (a) - (g) automatically results from the use of maximum threshold value matrix 33 and minimum threshold matrix 35 on the individual, from the thick, solid line in grayscale image 31 limited areas, as in 9 shown.

More specifically, their sizes are four by four pixels in the array of 7 (a) , six times six pixels in the arrangement in 7 (b) , ten times ten pixels in the arrangement in 7 (c) and 7 (d) , 25 times 25 pixels in the arrangement in 7 (e) and 7 (f) , as well as eight by eight pixels in the arrangement in 7 (g) ,

10 illustrates the flow of processing operations of rasterization unit 13 be performed.

First, the grayscale (density) of grayscale image 31 with the maximum threshold of the corresponding pixel in the maximum threshold matrix 33 compared (S1). If the result of the comparison is that the gray level is larger than the maximum threshold value (S3), the pixels are specified as "black" (S15). If the gray level is equal to or less than the maximum threshold, the gray level with the minimum threshold of the corresponding pixel in the minimum threshold matrix 35 compared (S5). If the result of this comparison indicates that the gray level is smaller than the minimum threshold value (S7), the pixels are specified as "white" (S17).

If the gray level is not larger as the maximum threshold and not smaller than the minimum threshold, it is determined if the pixels are any element of the MGT spot are or not (S9). If this process leads to the result that certain Pixels are not some element of the MGT patch, the Pixels specified as "white". If the pixels are the elements of the MGT spot will be on that Intermediärfleckmuster resorted which corresponds to the density of the MGT spot (S11), and it is decided whether a particular pixel, in accordance with this Intermediärfleckmuster, is specified as "black" or "white" (S13, S15 and S17).

Now will be a detailed description regarding the steps S8 to S13 carried out.

11 and 12 show the positional relationship between the MGT spot and the threshold matrix. The rectangular areas indicated by hatching are the MGT spots, and the rectangular area enclosed by a thick line is a threshold matrix. 11 shows the positional relationship to the arrangement of the spots in 7 (b) , and 12 shows the positional relationship in the 7 (g) shown spot arrangement.

A judgment as to whether or not the pixels are any element of the MGT spot in step S8 must be made on the basis of the position of the MGT spot in the threshold matrix, as in FIG 11 and 12 shown. More specifically, if any pixel in the threshold pixel matrix associated with a particular pixel is included in the MGT spot, it is considered to be an element of the MGT spot.

13 to 17 show examples of the stain arrangement 7 (b) are taken as how the maximum threshold value matrix and the minimum threshold value matrices are determined.

First, as in 13 1, the maximum density pattern is selected from among the intermediate spot patterns that may be used for the spot array used. In the case of in 7 (b) The spot pattern shown becomes the intermediate spot pattern with the density 12 out 4 (d) selected.

Likewise, as in 14 shown assigned an attribute and an order in advance to each MGT spot. Here, the term "attribute" means an identification number for each pixel assigned to each pixel in sequential order starting with the pixel in the upper left corner, as also shown in the figure. Also, the term "order" means the sequential order in which the spot is filled with black pixels. The order is set up so that black pixels are placed in an array beginning with the pixel nearest in the position to the center of the spot and along a spiraling route and uniformly in the upper, lower, leftward and rightward directions goes. By filling the black pixels in accordance with this order, a speckle pattern having a turbine shape is obtained, as in FIG 2 (a) to 5 (d) shown.

Next, the attribute / order of the 14 for the black pixels for the Intermediärfleckmuster in the maximum density of 13 in the position of the MGT spot in the threshold matrix 11 set up. Through this process, the attribute matrix shown in 15 , and the order matrix shown in 16 , receive. In the attribute matrix of 15 For example, if a particular number identifying the attributes is assigned only to pixels corresponding to the maximum density intermediate spot pattern, and no particular number is assigned to any other pixels ("RAW") in the matrix. In the order matrix of 16 will be the default order 14 assigned to the pixel corresponding to the maximum density intermediate dot pattern, and a larger number indicating the order is assigned to each pixel by a suitable method (for example, in an arbitrary manner at the discretion of the user).

Next, by applying, for example, a relationship as in 17 shown on the order matrix 16 the maximum threshold MAX and the minimum threshold MIN are determined for each pixel of the matrix. This process becomes the maximum threshold matrix 33 and the minimum threshold matrix 35 receive.

The following results are made by performing the machining operations 10 obtained, the maximum threshold value matrix 33 and the minimum threshold matrix 35 which are obtained as described above.

Those parts, such as line drawings consisting solely of black and white levels in the original grayscale image, are converted to a raster image that faithfully represents the black and white levels of line drawings and the like, since the "black" level is always greater than that Maximum threshold MAX, as in 17 shown, and the "white" level is always smaller than the minimum threshold MIN in 17 ,

on the other hand become such parts, which in the original grayscale image in halftone are converted into raster images in the manner described below.

When the gray level (density) of a halftone portion is above the maximum density in the usable intermediate spot pattern (a density of 12 in this example), all the pixels in the maximum dense intermediate spot pattern are black, and those pixels outside the intermediate spot pattern are white in accordance with their respective gray levels or black. This means that all the pixels have atomic numbers 1 to 12 are black while the pixels are with ordinal numbers 13 and greater white or black, respectively in correspondence with their gray levels.

Moreover, in case the gray level (density) of a halftone portion is not in any respect larger than the maximum density of the usable intermediate spot pattern (with density of 12), only the pixels inside the determined intermediate spot pattern in the maximum density are white or black in accordance with their respective gray levels, and such pixels outside the particular intermediate spot pattern are certainly white. This means that only the pixels with ordinal numbers 1 to 12 in the arrangement matrix 16 in accordance with their respective gray levels are white or black, but such pixels with ordinal numbers 13 and bigger certainly are white. This means that black pixels are formed only in the MGT spot (ie, lattice spot).

If a grating stain is formed only in a MGT spot, the stain pattern is determined as follows. If the gray level of a pixel is greater than the maximum threshold MAX or less than the minimum threshold MIN, the particular pixel is specified as "black" or "white" as previously described with reference to FIG 10 described (S15 and S17 in 10 ). On the other hand, when the gray level of a pixel is between the maximum threshold MAX and the minimum threshold MIN, reference is made to an intermediate spot pattern (S11) in accordance with the representative gray level of the MGT spot, and the pixel is marked "white" in accordance with the determined intermediate spot pattern. or "black" (S13, S15 and S17).

The transformation in the MGT spot made in the latter case is particularly described with reference to FIG 18 ,

18 is an original grayscale image, as shown, with a tonal range for 256 tonal gradations. In general, the amount of tone scale values between adjacent pixels of a halftone image changes by 1 or less, as in FIG 18 (a) shown. The tone gradation values for this original grayscale image are converted to grayscale to a degree corresponding to the densities (for a total of 65 gradations between density 0 and density 16), which for the intermediate dot pattern of the 2 to 5 be used as in 18 (b) shown.

When the in 17 maximum threshold and minimum thresholds shown on the grayscale image 18 (b) For example, those pixels positioned near the outer boundary and having high atomic numbers may be set to "black" or "white," but those pixels positioned in the region near the center where they have low atomic numbers , can not be set to either "white" or "black" as indicated by "?" in 18 characterized. In such case, therefore, the representative gray level is determined for this MGT spot. For example, the gray level 6 + 1/4 of the pixel P5 having the attribute number 5 in the MGT spot is used as the representative gray level.

Next, reference will be made to the intermediate spot pattern corresponding to this representative gray level 6 + 1/4. This is a patchwork pattern like in 18 (d) shown. According to the stain pattern in 18 (d) is for everyone with "?" marked pixel via "black" or "white" decided. As a result of this operation, a raster image as in 18 (e) to be obtained.

• (1) Ein Halbtonanteil eines Graustufenbilds, der irgendeine Graustufe unterhalb der Maximaldichte in einem verwendbaren Intermediärfleckmuster hat, wird in ein Halbtonbild in multiplen Tonabstufungen umgewandelt, solange es nicht irgendwelche abrupten Wechsel in der Graustufe enthält (z.B. die Kante oder ähnliches einer Figur).
• (2) Ein Halbtonanteil, der irgendeine Graustufe oberhalb der Maximaldichte eines verwendbaren Intermediärfleckmusters hat, wird in ein Rasterbild umgewandelt, wobei eine Technik angewandt wird, die ähnlich den Rasterungsoperationen gemäß dem Stand der Technik ist.
• (3) Ein abrupter Wechsel in der Graustufe, der am Rand oder ähnlichem einer graphischen Figur in einem Halbtonanteil auftritt, wird originalgetreu durch einen Wechsel in der Zahl der schwarzen Bildpunkte dargestellt, der in Übereinstimmung mit diesem Wechsel ist.
• (4) Strichzeichnungen und ähnliches werden originalgetreu in zwei Tonabstufungen dargestellt (d.h. schwarz und weiß).

The above-described editing process converts a grayscale image into a raster image. This conversion has the features described below.

• (1) A halftone portion of a gray scale image having any gray level below the maximum density in a usable intermediate spot pattern is converted to a halftone image in multiple tone gradations unless it contains any abrupt changes in the gray level (eg, the edge or the like of a figure).
• (2) A halftone portion having any gray level above the maximum density of a usable intermediate spot pattern is converted into a halftone image using a technique similar to the prior art halftoning operations.
• (3) An abrupt change in the gray scale occurring at the edge or the like of a graphic figure in a halftone portion is faithfully represented by a change in the number of black pixels that is in accordance with this change.
• (4) Line drawings and the like are faithfully reproduced in two tone gradations (ie, black and white).

Now, referring to 19 to 20 (b) a detailed description of the halftone conversion unit 21 in the laser printer 20 out 6 given.

19 illustrates the hardware construction of halftone conversion unit 21 ,

The data is in the same horizontal positions on seven consecutive lines in one of the host computers 10 received raster image will be in seven shift registers 41 to 53 each with six memory elements read. The data is synchronized with a given clock and then to the back memories of the shift registers 41 to 53 pushed. In the following part of the description, the data in the fifth memory (the hatched mark) of the fourth row, that is, in shift registers 47 read line as the data for use as the subject of the current conversion process and referred to as "object data".

selector 55 takes the data from four memory gates, from the second to the sixth memory, each of the seven shift registers 41 to 53 and selects a record of four consecutive lines of input data (ie, data of four by four pixels that are the same size as a MGT spot) and transmits them to decoders 59 , In this case, selector relocated 55 said four lines line by line across said seven lines. That is, the selector 55 transfers a record from the top four rows of shift registers 41 to 47 , a record for the second four lines, calculated from the top line, of shift registers 43 to 49 , a record for the third four lines, calculated from the top line of shift registers 45 to 51 , and a record for the bottom four rows of shift registers 47 to 53 , to the decoder 59 , synchronized with the above-mentioned select clock.

A boundary conditioner 57 takes the data from the first, second, sixth and seventh memory of the seven shift registers 41 to 53 as read in, and checks, as described above, the boundary conditions for the discovery of an Intermediärfleckmusters.

The boundary condition check is an AND operation check to determine if the black pixels are in the decoder 59 transmitted four times four pixels are connected to the black pixels on the outer boundary of this area or not. For example, in the in 20 (a) In the case shown, the black pixels in the area are not connected to the black pixels on the outer boundary, but isolated from them, and accordingly the black pixels in this area are detected as an intermediate spot pattern. On the other hand, in the case according to 20 (b) the black pixels in the area connected to the black pixels on the outer boundary as indicated by reference "E" so that the black pixels in this area are not detected as those.

The limit conditioner 57 carries out such a limit condition test. Furthermore, the boundary conditioner inspector checks 57 in this embodiment, only the left and right boundary conditions, but does not check the upper and lower boundary conditions, as based on the in 19 shown construction can be detected. The results of these boundary condition tests are sent to decoders 59 transfer.

The decoder 59 has a built-in logic circuit that determines if the data for the four is from the selector 55 entered lines of any of the Intermediärfleckmuster the 2 to 5 match or not, and the data for the four from the selector 55 input lines are fed into this logic circuit. The logic circuit judges only which one of the intermediate spot patterns corresponds to the input data or none if the logic circuit of the boundary condition checker 57 has received a detection signal and if the logic circuit has determined that the data corresponds to an intermediate spot pattern. The logic circuit outputs the relevant object data in the input data as converted data of the corresponding pixels in an output pad pattern corresponding to the intermediate spot pattern found as correct correspondence. Otherwise, this logic circuit outputs the item data as such without any conversion.

As mentioned above, each time the record for the four lines is synchronized with the select clock in the decoder 59 is inputted, the data of the subject pixels are outputted after being converted in accordance with the output spot pattern as described above, or as they are without any conversion. The data of the object pixels output from the logic circuit with respect to the data set for the four lines of the four kinds are once in the decoder 59 saved. After that passes decoder 59 the final item data, either as converted data, if that data contains any data that has been converted in accordance with the output pad pattern, or as unchanged target data as they are, if no converted data is included, to the picture signal modulating unit 61 out. Then modulates image signal modulation unit 61 a laser drive signal in accordance with the final data inputted on the subject pixels to form a print-ready image.

When next becomes a laser printer in a second preferred embodiment of the present invention.

These preferred embodiment is a simplified system compared to the preferred above embodiment a reduced number of different intermediate spot patterns having.

21 shows the structure of a data processing unit of a laser printer according to the second preferred embodiment. As in 21 As shown, this printer is equipped with a main memory device 71 for storing image data and the like, a central processing unit (CPU) 72 , a data receiving unit 73 for receiving image data from the host computer, a program storage device 74 , which is a program for commanding the CPU 72 with respect to the operations to be performed, a row data buffer 75 for storing the data of four adjacent lines, a DMA device 76 (hereinafter referred to as image data DMA) which extracts the image data from the main memory device 71 reads and reads the data so read to row data buffers 75 transfers, a horizontal position counter 77 representing the position of the line data buffer 75 specified pixel, a pattern recognition device 78 , Which based on the pixel data from row data buffer 75 or recognizes a particular intermediate spot pattern from the data patterns of the pixels in the vicinity of the pixel data, a pixel signal modulating device 79 which signals in accordance with the result of a pattern recognition device 78 modulated assessment of an arrangement 80 a laser light emitting diode and an amplifier unit which generates a laser beam for horizontally scanning a laser printer in the photosensitive material, a scan start position detecting device 81 for detecting the start position for starting a scanning operation with the laser beam, and a clock generation unit 82 which generates a clock (hereinafter referred to as a dot clock) proportional to the distances of the scanned pixels and the generated clock to horizontal position counters 77 supplies.

22 Fig. 10 is a block diagram illustrating the detailed construction of row data buffers 75 in this embodiment.

In 22 denotes reference numeral 101 random access memory (hereinafter referred to as RAM) capable of writing and reading 8 bits as a word at an arbitrarily selected address. The reference number 102 denotes a counter indicating the initial value of the RAM address at the start time of a scan operation and a circular count for the scan start position signal 113 where five (the number of words in a row) is used as a divisor. The reference number 103 denotes an address counter indicating the number of read operations and the number of RAM write operations 101 one; and the counting output 108 is connected to the address input on the RAM 101 , The address counter 103 is with the counting output 112 from start address counter 102 reassigned at each scan start position signal. In the RAM 101 For example, read operations are performed four times for every eight periods of the dot clock, and a write operation is performed once for each of the data occupying the same horizontal position and the newest line formed by image data DMA 76 from the main storage device 71 was read out. The reference number 110 denotes a shift register number counter which has a circular count process with the number of read operations and the number of RAM write operations 101 performing 5 as a divider. This shift register number counter 110 is determined by a scan start position signal 113 initialized to zero.

The reference numerals 104 . 105 . 106 . 107 and 111 are registers for 16 bits, 15 bits, 14 bits, 13 bits, and 12 bits, respectively, and these registers shift the data one bit at a time into a higher memory element in each period of the dot clock. In addition, the least significant eight bits of each shift register are indicated by the shift register number counter 110 , with the values of a RAM data input / output bus 109 at the time of a read or write operation in RAM 101 initialized.

At the As described above, the bit arrangement P0 to 4 and 0 to 3 in a range of five including four pixels including the pixels at the output position in real time with each dot clock are read out of the bit arrangements in which the four most significant ones Bits of each shift register are arranged.

23 presents a table with an intermediate spot pattern to be detected by the printer and its associated output pad pattern. The difference between the intermediate spot pattern and the output spot pattern is arranged to be within three pixels with a difference in pattern and within a pixel with a difference in density in the same manner as in the above-described embodiment. Due to this property, if any, only a side effect of virtually imperceptible size will occur if the diameter of a dot is on the order of 40 μm ² , even if a conversion operation has been erroneously performed on a portion other than for any conversion was provided. In addition, since the black pixel pattern surrounded by a white area in a MGT spot is specified as an intermediate spot pattern, no conversion is made and thus no side effect is generated, which is a continuous boundary line such as a straight line, a curved line, the edge of a That are otherwise prone to the most obvious side effects produced by erroneous conversion.

24 Fig. 10 is a circuit diagram illustrating an example of the circuit of the pattern recognition apparatus 78 ,

As in 23 5, the pixels included in an intermediate spot pattern are subjected to conversion to an output spot pattern of two lines perimeter, and the pattern recognition apparatus 78 consists of two circuits, namely two pattern recognition circuits for each one of the two lines.

The reference number 201 is a circuit for identifying white pixels in an MGT spot common to all the intermediate spot patterns, and this circuit produces a "1" in the output 202 of the identified result, if the condition is true, but "0" if the condition wrong is. The reference number 203 denotes a decoder circuit for each component owning each intermediate spot pattern. The entire output of this decoder circuit is multiplied by the output 202 of the identified result to find a product thereof, and if the output 202 of the identified result is "false", each one of the decoded outputs will be "false". A pattern recognition device 78 gives the decoded output 204 to the image modulating device 79 out.

25 Fig. 10 is a block diagram illustrating the image signal demodulating apparatus 79 ,

The reference number 301 indicates a ROM (read only memory). The decoding signal 302 that of pattern recognition device 78 is output is applied to a line selection signal, and the corresponding 8-bit-wise pattern data stored in each line is read out. The reference number 303 denotes an eight-bit shift register, and a shift operation becomes during the period in which the shift operation specifying input 304 "true" is from a shift clock 309 which has a period of 1/4 of the data transfer time of one dot (hereinafter referred to as quadruple clock). Furthermore, the shift register 303 always initialized so that it is the value of the ROM data bus 313 assumes whenever the input specifying the shift operation 304 "wrong is.

The input specifying the shift operation 304 receives as input a signal obtained by delaying the logical sum of all decoded signals by a proportion for one period of the pixel clock 312 by means of a pulse width extension circuit 307 and then expanding the period from "true" to a period equivalent to two periods of the dot clock. The signal is also in the selection input 305 of the selector 306 entered, and if the selection input 305 "true", the selector selects 306 the output of shift registers 303 , or if the selection input 305 is false, the selector selects 306 a signal obtained by delaying the pixel values P2 and 1 associated with the output positions by one period of the dot clock by means of a D-type (master / slave) flip-flop register 311 was obtained. This signal is output as a modulated signal 306 of the modulated signal. This modulated signal drives the laser light emitting diode 60 ,

When next becomes a modified structure of the second preferred embodiment of the present invention.

26 illustrates the construction of a pattern recognition device in this modified structure. This pattern recognition device has over the in 24 shown an additional output position detection circuit. The description in the following section will be made mainly with respect to this output position detection circuit.

The reference number 403 indicates a counter that performs a circular counting process with one dot clock 409 (hereinafter referred to as horizontal position counter), where 4 is used as a divider. The horizontal position counter 403 is initialized to zero by a scan position start signal 410 , The least significant portion of the count output of this horizontal position counter 403 is denoted by the reference numeral 405 displayed while the higher part of the count output by the reference numeral 406 is shown.

The reference number 404 denotes a counter, which, with 4 as a divisor, a circular counting process for image reading of line buffer 75 (hereinafter referred to as vertical position counter) generates horizontal synchronizing signals. The horizontal position counter 404 is initialized at the time of starting a printing operation. The least significant proportion of the count output from this horizontal position counter 404 is denoted by reference numerals 407 , the higher proportion of counting output by reference numerals 408 displayed.

The reference number 402 denotes a "logical product" element which judges whether the positions of the coordinates for output P0 and 0 from the line buffer are any multiples of 4 in both the horizontal direction and the vertical direction or not, and the reference number 401 is another "logical product" element that judges whether the positions of the coordinates for output P1, 0 from the line buffer 75 are any multiples of 4 both in the horizontal direction and in the vertical direction or not.

The structure described in this modified example is capable of reducing the number of MGT patch patterns as compared with the previous embodiment as in FIG 27 to increase (ie, increase the number of patch patterns corresponding to densities of 1/4 to 3/4) by the output of the logical product of the detected outputs from these two "logical product" elements 401 and 402 and the identified outputs from the two identifying circuits mentioned above 201 and 201 as input to the above-mentioned decoder circuits 203 and 203 is applied.

28 shows an image signal modulating device 79 in another modified structure of the second embodiment. The picture signal module is formed in connection with a conversion range limiting circuit, the structure of 25 will be added. The following is a description of an image signal modulating circuit mainly with regard to this conversion range limiting circuit.

The reference number 505 denotes a DMA device (hereinafter referred to as mask data DMA) which applies a word of the mask data to the shift register each time 501 transfers when the shift register 501 consumed a word. The reference number 503 indicates an initialization signal for shift registers 501 and the reference numeral 504 indicates an initializing data bus.

in this connection mean the ones mentioned above Mask data such data that a given mask pattern in one to one match for every pixel in the image data used as the object of a transformation, where mask data of value "1" is a conversion the associated pixels of the image data, and wherein mask data of value "0" indicate that no image data conversion should be done.

The shift register 501 performs a shift operation for each dot clock and outputs one bit at a time of the mask data. With the logical product of the bit of mask data thus output and the output of pulse-stretching circuit 307 as a select signal, it is possible not to cause a conversion of such a region having a shape in accordance with the mask pattern. Because of this property, it is possible to surely eliminate the side effects of modulation.

Farther can be one of those similar Function be realized by such a method, the one Line dot counter to disposal represents and the counted Value compares with a preset value, with a value to be converted Area is discovered.

The Examples of preferred embodiments described above are applied to laser printers applied, but it goes without saying that a similar effect by using a similar circuit for controlling an electron beam in a cathode ray display tube unit or similar can be caused.

As described above the present invention is the representation of multiple tone gradations with a small amount of data.

The above description of preferred embodiments of the invention was presented for purposes of illustration and description. she is not exhaustive or for limiting the invention to the precise form disclosed Intended, and modifications and modifications are in the light the above teaching possible or like by running of the invention. The embodiments have been chosen and described the principles of the invention and its practical application to explain and to enable the skilled person the invention in various embodiments and with different, for the certain intended uses, modifications to use. It is intended that the scope of the invention through the attached claims and their equivalents be determined.

In a preferred manner, therefore, the screening agent closes 13 , a "dither" matrix, which in a process in which the rasterizer 13 the grayscale image 31 into the raster image 39 converts the detected spot area has been located in a predetermined position and the individual Intermediärfleckmuster 5 in the raster image as far as possible separated from each other. The "dither" matrix includes: a maximum threshold matrix 33 which determines maximum thresholds for individual pixels to set the gray level to the larger of the binary value densities, and a minimum threshold matrix 35 which determines minimum threshold values for individual pixels to set the gray level defined above to the lesser of the binary density values defined above, wherein both maximum thresholds and minimum thresholds have a smaller value for pixels within the detected spot area than a value for pixels outside the detected spot area. The "dither" matrix also includes: a maximum threshold matrix 33 which sets maximum thresholds for individual pixels to set the gray level to the greater of the binary density values defined above, and a minimum threshold matrix 35 which sets minimum thresholds for individual pixels to set the gray level to the lesser of the binary density values defined above, the maximum thresholds and minimum thresholds being set such that the maximum thresholds are greater than the minimum thresholds for at least some pixels in the detected spot area and both thresholds are identical are for any pixels except those in the detected spot area, and the halftone means 13 an intermediate spot pattern 5 from a variety of Intermediärfleckmustern 37 which corresponds to a representative gray level in the detected spot area if any pixel in the detected spot area has an intermediate gray level whose density is not based on either the maximum threshold matrix 33 or the minimum threshold matrix 35 and the density of a pixel having an intermediate gray level in accordance with the selected intermediate spot pattern 5 sets. The screening agent 13 selects a gray level of a given pixel in a neighborhood of a central position in the detected spot area and uses the selected gray level as a representative gray level.

A plurality of "dither" matrices are prepared beforehand in accordance with a plurality of density-differing arrays in the detected spot area on the raster image, each of the plurality of "dither" matrices being predetermined in accordance with a condition in which a usable one Type of intermediate stain patterns 5 is limited to a type belonging to a predetermined small range of densities, so that the plurality of intermediate spot patterns 37 on the raster image 39 is isolated under an arrangement of the associated detected spot area, and the halftoning means 13 the grayscale image 31 into the raster image 39 converts, selectively using one of a variety of "dither" matrices.

The plurality of "dither" matrices has a maximum threshold value matrix 33 which sets maximum thresholds for individual pixels to set the gray level to the larger of the binary value densities, and a minimum threshold matrix 35 which sets minimum threshold values for the individual pixels to set the gray level to the lesser of the binary value densities defined above, the maximum thresholds and the minimum thresholds being set such that the maximum thresholds are greater than the minimum thresholds for at least some of the pixels in the detected spot area, and the thresholds for pixels other than those in the detected spot area are identical, and the halftoning means 13 an intermediate spot pattern corresponding to a representative gray level in the detected spot area 5 from a variety of Intermediärfleckmustern 37 if any pixel in the detected spot region has an intermediate gray level, its density is not based on either the maximum threshold matrix 33 or the minimum threshold matrix 35 can be set, and it sets the density of an intermediate density pixel in accordance with the thus-selected intermediate spot pattern 5 firmly.

A system for converting a gray-scale image into a halftone image having a spot area of a predetermined plurality of pixels for multi-tone gradation representation, which system is a multi-tone gradation image processing system, is characterized by: a rasterization process for generating a raster image from an associated pixel; one of the predetermined binary value densities in accordance with a gray level of the pixels in the gray scale image 31 and a halftone conversion process for detecting a spot area having an intermediate spot pattern 5 from a variety of Intermediärfleckmustern 37 has, in a raster image 39 and for converting the one intermediate spot pattern 5 a variety of Intermediärfleckmustern 37 of the detected spot area into an associated output pad pattern 9 among a plurality of output patch patterns, wherein the plurality of output patch patterns are those patch patterns which actually represent a predetermined plurality of multiple tonal gradations by combining pixels capable of accepting tertiary or higher density values, and the plurality of intermediate patch patterns 37 are such speckle patterns that logically represent a plurality of multiple tonal gradations by combining pixels that can only accept binary value densities, and also by changing the arrangement of the pixels.

Claims (15)

System for converting a grayscale image ( 31 ) into a halftone image ( 40 ) having a spot area composed of a predetermined plurality of pixels for displaying an image in multiple tonal gradations, the system being a multi-tone gradation image processing system, characterized by: a screening means ( 13 ) for generating a raster image ( 39 ), in which pixels have a binary value density of a plurality of predetermined binary value densities, which corresponds to a gray level of corresponding pixels in the gray scale image ( 31 ), and a halftone conversion means ( 21 ) for the detection of a spot area corresponding to an intermediate spot pattern ( 5 ) of a plurality of intermediate spot patterns ( 37 ) from the raster image ( 39 ) and the conversion of the one detected intermediate spot pattern ( 5 ) from a multiplicity of intermediate spot patterns ( 37 ) in a corresponding Augabefleckmuster ( 9 ) of a plurality of output spot patterns, wherein the plurality of intermediate spot patterns ( 37 ) are such speckle patterns that logically represent a predetermined number of multiple tonal gradations with a combination of such pixels that can accept only binary values and also in a variable array of pixels, where the plurality of output spot patterns are those speckle patterns that are actually the predetermined number of multiple tonal gradations with a combination of pixels that may take on tertiary or higher values of density, and wherein the pixels of the halftone image are represented by a Output device can be output directly. System for converting a grayscale image ( 31 ) into a halftone image ( 40 ) having a spot area consisting of a plurality of pixels for multiple tonal gradation representation, the system being a multi-tone grading image processing system, characterized by: a "dither" matrix having a spot area located at a predetermined position, a plurality of Speckle patterns formed by combining pixels that can only accept predetermined binary value densities, and which logically represent tonal gradations in a larger number than the maximum number of combined pixels by varying the arrangement of the pixels; a first halftoning means for converting a gray level of pixels located at least outside the detected spot area in the gray scale image into the binary value densities using the "dither" matrix, and second halftoning means for converting a gray level of at least some pixels located within the detected spot area in the gray scale image into the above defined binary value densities, using the detected patch patterns, and wherein the pixels of the halftone image can be output directly by means of an output device. A system according to claim 1 or 2, wherein the spot area comprises a predetermined central area and a predetermined edge area, and that the arrangement of the pixels coincides with a change in the image due to the intermediate spot patterns (Fig. 3 7) so that the pixels to be changed are one pixel of either the predetermined central area or the predetermined margin when the tone scale value changes by one. A system according to claim 1 or 2, wherein each of the intermediate spot patterns ( 37 ) consists of data determined by bits whose number is the same as the number of pixels of the spot area, and that each of the output patch patterns consists of data determined by bits whose number is n times (n≥2 and integral) of the number of pixels of the spot area. System according to one of claims 1 to 4, wherein the difference between the actual by the Intermediärfleckmuster ( 37 ) and the density actually represented by the corresponding output spot pattern, within one pixel, expressed in density difference. Method of converting a grayscale image into a raster image with a spot area of a predetermined plurality of pixels for displaying an image in a plurality of tonal gradations, the method being a multi-tone gradation image processing method is, comprising the steps: Providing a "dither" matrix whose detected spot area is in a predetermined position, Providing a variety of patch patterns, logically the number of multiple tonal gradations express with a combination of those pixels that only binary values can accept, and this also in a changed Arrangement of pixels, where the number of multiple tonal gradations is larger as the number of pixels, Converting a gray level into binary values by means of the "dither" matrix, wherein the gray level of the pixels to be converted is that outside of the detected Fleckbereiches are located in the gray scale image, and Convert a gray level in binary by means of the detected stain pattern, wherein the gray level to be converted of the pixels that are within the detected spot area in the Grayscale image are located. The method of claim 6, wherein the pixels of the Halftone image by means of an output device can be output directly are. A printer system in which a host computer is connected to a printer, wherein a greyscale image in the host computer is converted into a raster image having a spot area defined by a predetermined plurality of pixels for printing an image in multiple tone gradations, comprising: a rasterizer ( 13 ) for generating a raster image ( 39 ), in which pixels have a binary value density of a plurality of predetermined binary value densities, which corresponds to a gray level of corresponding pixels in the gray scale image ( 31 ), wherein the screening agent ( 13 ) is formed in the host computer, and a halftone conversion means ( 21 ), to receive the raster image from the rasterizer ( 13 ), to discover a spot area corresponding to an intermediate spot pattern ( 5 ) of a plurality of intermediate spot patterns ( 37 ) from the raster image ( 39 ) and the conversion of the one detected intermediate spot pattern ( 5 ) from a multiplicity of intermediate spot patterns ( 37 ) into a corresponding output stain pattern ( 9 ) from a plurality of output patch patterns, the halftone conversion means ( 21 ) is formed in the printer, wherein: the plurality of intermediate spot patterns ( 37 ) Logically, a predetermined number of multiple tonal gradations with a combination of such pixels, which can accept only binary values, and in a variable arrangement of pixels represent, and the plurality of output spot patterns actually represent the predetermined number of multiple tone gradations with a combination of pixels that may take tertiary or higher values of density. The system of claim 8, wherein the pixels of the Halftone image by means of an output device can be output directly are. Printer driver installed in a computer to convert a grayscale image ( 31 ) into a raster image ( 40 ) having a spot area consisting of a plurality of pixels for expressing an image in multiple tone gradations, the printer driver comprising: a "dither" matrix having a spot area located at a predetermined position, a plurality of patch patterns containing the patch patterns are logically expressing the number of multiple tonal gradations with a combination of those pixels that can accept only binary values, and this also in an altered array of pixels, wherein the number of multiple tonal gradations is greater than the number of pixels, a first screening means for converting a gray level into binary values by means of the "dither" matrix, wherein the gray level to be converted is from the pixels located outside the detected spot area in the gray scale image, and second screening means for converting a gray level into binary values using the patch patterns used the umzuwan is gray levels of the pixels located within the detected spot area in the gray scale image. A printer driver according to claim 10, wherein the pixels of the halftone image can be output directly by means of an output device are. Computer readable medium with a computer program, to translate a grayscale image inside a computer of the computer into a raster image with a spot area from a given one Variety of pixels to express an image in multiple Make tonal gradings, comprising the following steps: Provide a "dither" matrix whose detected spot area is in a predetermined position, Providing a variety of speckle patterns that are such speckle patterns, logically the number of multiple tone gradations with a combination of those Express pixels, the only binary values can accept and this also in a changed Arrangement of pixels, where the number of multiple tonal gradations is larger as the number of pixels, Converting a gray level into binary values by means of the "dither" matrix, wherein the gray level of the pixels to be converted is that outside of the detected Fleckbereiches are located in the gray scale image, and Convert a gray level in binary by means of the patch patterns used, wherein the gray level to be converted of the pixels that are within the detected spot area in the Grayscale image are located. The computer readable medium of claim 12, wherein the pixels of the halftone image by means of an output device can be dispensed directly. Printer driver installed in a computer where a grayscale image in the computer is in a halftone image is converted, with a spot area, by a predetermined Variety of pixels is defined, expressing an image in multiple tonal gradations, with the printer driver having: a Raster device for generating a raster image in which pixels a density of a plurality of predetermined binary value densities corresponding to one Gray levels of corresponding pixels in the grayscale image have, where the raster image has a plurality of intermediate spot patterns, wherein: the Variety of Intermediärfleckmustern logically a predetermined number of tonal gradations with a combination from the pixels, the only binary values can accept and this also in a changed Arrangement of the pixels, and a difference between the actual Expression density and logical expression density by the intermediate spot pattern within a pixel, expressed in density difference, lies. A computer readable medium having a computer program for making on a computer a grayscale image within the computer into a halftone image having a spot area defined by a predetermined plurality of pixels for printing an image in multiple tonal gradations, the computer program comprising the steps of: Generating a raster image in which pixels have a density of a plurality of predetermined binary value densities corresponding to a gray level of corresponding pixels in the gray scale image, the raster image having a plurality of intermediate spot patterns; Converting the plurality of intermediate spot patterns into a plurality of output spot patterns to form an actual output image, wherein: the plurality of intermediate spot patterns logically express a predetermined number of multiple tone gradations with a combination of the pixels that can accept only binary values, and so on changed arrangement of pixels, and a difference between the actual expression density and the logical expression density by the intermediate spot pattern within a pixel expressed in the density difference.