JPH02281873A - Representing method for half tone image - Google Patents
Representing method for half tone imageInfo
- Publication number
- JPH02281873A JPH02281873A JP1103695A JP10369589A JPH02281873A JP H02281873 A JPH02281873 A JP H02281873A JP 1103695 A JP1103695 A JP 1103695A JP 10369589 A JP10369589 A JP 10369589A JP H02281873 A JPH02281873 A JP H02281873A
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- Japan
- Prior art keywords
- dither
- macro
- dither cell
- cell
- cells
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Links
- 238000000034 method Methods 0.000 title claims description 16
- 238000010586 diagram Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 2
- 230000001351 cycling effect Effects 0.000 description 1
- 229910003460 diamond Inorganic materials 0.000 description 1
- 239000010432 diamond Substances 0.000 description 1
Abstract
Description
【発明の詳細な説明】
〔産業上の利用分野〕
この発明は中間調画像の表現方法に係り、２個画像によ
り擬似的に中間調画像を表現するための、いわゆるデイ
ザ処理に関する。DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of representing a halftone image, and more particularly to so-called dither processing for representing a halftone image in a pseudo manner using two images.
この発明はこのような従来の問題点を解消すべく創案さ
れたもので、階調数を高めつつ自然な印象を与え得るデ
イザ画像を生成するための中間調画像の表現方法を提供
することを目的とする。The present invention was devised to solve these conventional problems, and aims to provide a method for expressing a halftone image to generate a dithered image that can give a natural impression while increasing the number of gradations. purpose.
中間調画像を表現する方式としてデイザ方式はよく知ら
れており、一般にｎＸｎ画素の正方形のディザセル内の
各画素の閾値を定め、このディザセルを処理対象画像に
適用して、処理対象画像を２値化する。ここに、分散型
デイザ（例：ベイヤー型）では階調数を高めようとする
と、大きなディザセルを使用することになり、エツジ等
に黒画素が集中せず、ボケな画像となるとともに組織〔
課題を解決するための手段〕
この発明に係る中間調画像の表現方法は、非長方形のデ
ィザセルおよびこのディザセルを複数隣接配列してなる
マクロディザセルを定義し、マクロディザセル単位で処
理対象画像の濃度を評価し、かつマクロディザセル内の
ディザセルについての閾値順位およびディザセル内の各
画素の閾値順位を定義するものである。The dither method is well known as a method for expressing halftone images. Generally, a threshold value for each pixel in a square dither cell of nXn pixels is determined, and this dither cell is applied to the image to be processed to convert the image to be processed into a binary image. become However, if you try to increase the number of gradations with a distributed dither (e.g. Bayer type), you will need to use a large dither cell, which will prevent black pixels from concentrating on edges etc., resulting in a blurry image and poor texture.
Means for Solving the Problems] A method for expressing a halftone image according to the present invention defines a non-rectangular dither cell and a macro dither cell formed by arranging a plurality of these dither cells adjacently, and expresses the image to be processed in units of macro dither cells. It evaluates the density and defines a threshold rank for a dither cell within a macro dither cell and a threshold rank for each pixel within the dither cell.
この発明に係る中間調画像の表現方法によれば、マクロ
ディザセル単位で処理対象画像の濃度を評価するのでデ
イザ画像のＲ［数を高めることが可能であり、かつ、マ
クロディザセル内のディザセルについての閾値順位およ
びディザセル内の各画素の閾値順位を定義するので、デ
イザ画像においてマクロディザセル内で画素が分散され
、全体的に自然な印象を与え得る。According to the method for expressing a halftone image according to the present invention, since the density of the image to be processed is evaluated in units of macro dither cells, it is possible to increase the number of R [R] of the dither image, and Since the threshold order for each pixel in the dither cell and the threshold order for each pixel in the dither cell are defined, the pixels are dispersed within the macro dither cell in the dither image, giving an overall natural impression.
次にこの発明に係る中間調画像の表現方法の実施例を図
面に基づいて説明する。Next, an embodiment of the method for expressing a halftone image according to the present invention will be described based on the drawings.
第１図は第１実施例のディザセルおよびマクロディザセ
ルを示すものであり、全体として１個のマクロディザセ
ルＭＤを、実線枠によってマクロディザセル単位内の４
ａｍのディザセルＤ１〜Ｄ４を示している。FIG. 1 shows the dither cell and macro dither cell of the first embodiment, and one macro dither cell MD as a whole is divided into four cells within a macro dither cell unit by a solid line frame.
am dither cells D1 to D4 are shown.
ディザセルＤ１〜Ｄ４は略正六角形状の８画素のパター
ンであり、２画素を３列縦に並べ、かつ、上下方向の中
央の２画素の左右に１画素ずつ付加した形状を有する。The dither cells D1 to D4 are approximately regular hexagonal 8-pixel patterns, and have a shape in which 2 pixels are arranged vertically in 3 columns, and 1 pixel is added to each side of the 2 pixels at the center in the vertical direction.
各ディザセルにおいては、上下方向の中央の２画素の左
の画素→右の画素→最下列の右の画素→最下列の左の画
素→上下方向の中央の左に付加した画素→最上列の左の
画素→最上列の右の画素→上下方向の中央の右に付加し
た画素の順で閾値順位が定義されている。これは各ディ
ザセルについて、渦巻形のパターンを与えたことに相当
する。但し、この実施例は、ディザセルＤ１〜Ｄ、に対
して閾値順位が与えられており、ディザセルＤＩ〜Ｄ４
を循環しつつ各ディザセルに１画素ずつを与えて、マク
ロディザセル単位で濃度を表現するものであり、デイザ
画像に呉巻状のパターンが生じることはなく、自然な印
象を与える。処理対象画像はマクロディザセルの単位で
濃度を評価され、８Ｘ４＝３２Ｗｉ調の＠度表現が可能
である。発明者が実験したところによれば、自然画像の
表現には一般に３２階調以上の濃度階調を要し、３２階
調のデイザ処理であっても、従来手法のデイザ方式では
自然な印象を与えるディザ画像は生じ得ない。In each dither cell, the pixel to the left of the two pixels at the center in the vertical direction → the pixel to the right → the pixel to the right of the bottom row → the pixel to the left of the bottom row → the pixel added to the left of the center in the vertical direction → the left of the top row The threshold ranking is defined in the following order: pixel → right pixel in the top row → pixel added to the right of the center in the vertical direction. This corresponds to giving each dither cell a spiral pattern. However, in this embodiment, threshold rankings are given to dither cells D1 to D, and dither cells DI to D4
One pixel is given to each dither cell while cycling through the macro dither cells, and the density is expressed in units of macro dither cells.Therefore, the dither image does not have a cylindrical pattern, giving a natural impression. The density of the image to be processed is evaluated in units of macro dither cells, and it is possible to express 8×4=32Wi tones. According to the inventor's experiments, expressing a natural image generally requires 32 or more density gradations, and even with 32-gradation dither processing, the conventional dither method cannot produce a natural impression. A dithered image cannot occur.
ディザセルＤ Ｉ−Ｄ ４はその中心（図中Ｘ印で示す
６）が菱形の頂点に位置するように配置！！ｌれ、各デ
ィザセルの中心は、マクロディザセルの中心（図中Ｏ印
で示す。）から橿めて短距ｇｌ（２画素幅）に配置され
、ディザセルＤ Ｉ−Ｄ ４内Ｇこｍ環的に配列される
画素が極めて密な印象を与えるようになっている。Dither cell DI-D 4 is arranged so that its center (6 indicated by the X mark in the figure) is located at the apex of the diamond! ! The center of each dither cell is arranged at a short distance gl (2 pixels wide) from the center of the macro dither cell (indicated by the O mark in the figure), and The pixels are arranged in a manner that gives the impression of being extremely dense.
なお、ディザセルの形状は第２図〜第９図Ｃ；示すよう
に種々前えられ、一般に非長方形のテ°イザセルが、画
素が分散した自然な印象を与える。The shape of the dither cell can be varied as shown in FIGS. 2 to 9C; generally, a non-rectangular dither cell gives a natural impression of dispersed pixels.
第３図は１１画素からなる略正方形状のディザセルを示
し、このディザセルを４個含むマクロディザセルは、例
えば第１０図のように構成きれる。FIG. 3 shows a substantially square dither cell consisting of 11 pixels, and a macro dither cell including four dither cells can be configured as shown in FIG. 10, for example.
第１０図のマクロディザセルでは、１１Ｘ４＝４４階調
の濃度表現が可能である。The macro dither cell shown in FIG. 10 is capable of expressing density at 11×4=44 gradations.
第４図は５画素からなる十字形のディザセルを示し、こ
のディザセルな４個含むマクロディザセルは、例えば第
１１１！ｌ！ｌのように構成される。第１１図のマクロ
ディザセルでは、５ｘ４＝２０Ｆｉ調の濃度表現が可能
であり、かつデイザ画像は全体として極めて密な印象を
与える。FIG. 4 shows a cross-shaped dither cell consisting of five pixels, and a macro dither cell including four dither cells is, for example, the 111th! l! It is configured like l. The macro dither cell shown in FIG. 11 is capable of expressing 5×4=20 Fi tone density, and the dithered image as a whole gives an extremely dense impression.
以上の第１実施例およびその変形例においては、マクロ
ディザセル内の各ディザセルの閾値パターンがあらかじ
め設定きれていたが、各ディザセルの閾値パターンにラ
ンダム性を与えるとデイザ画像は一層自然な感じを与え
るものとなる。In the above-described first embodiment and its variations, the threshold pattern of each dither cell in the macro dither cell has been set in advance, but if randomness is given to the threshold pattern of each dither cell, the dithered image will have a more natural feel. Become a giver.
第１２図〜第１８図はこのランダム性を生しさせる第２
実施例を示すものであり、処理対象画像ＩＭと同一サイ
ズの参照画像ＲＩＭを生成しておき、この参照画像ＩＲ
Ｍの各画素には乱数ｒｌ＋ｒ ２ ＋・・・が与えられ
ている。処理対象面ｆｆ１１Ｍのある領域にマクロディ
ザセル間りを適用する際に、同時に参照画像の各画素の
乱数を参照する。Figures 12 to 18 show the second diagram that produces this randomness.
This shows an example, in which a reference image RIM of the same size as the processing target image IM is generated, and this reference image IR is
A random number rl+r 2 + . . . is given to each pixel of M. When applying the macro dither cell interval to a certain area of the processing target surface ff11M, the random number of each pixel of the reference image is simultaneously referred to.
この乱数は、マクロデイぜセルＭＤ内の各ディザセルＤ
１〜Ｄ４（第１５１ｍ 〜第１８１１１ ＋、：対応Ｌ
テ０〜３の数値が与えられてゎり、「０」のときＤｌ
、’ｌＪ の と き Ｄ２． ’２
Ｊ の と １Ｄ３． ｒ３」のときＤ
４が指示される。This random number is used for each dither cell D in the macro dither cell MD.
1 to D4 (151m to 18111 +,: Corresponding L
A value from 0 to 3 is given, and when it is "0", Dl
, when 'lJ D2. '2
J's and 1D3. r3” D
4 is indicated.
第１２図ではマクロディザセルＭＤ内の各画素をＰ１〜
Ｐ３２で示し、第１３図では処理対象画像ＩＭにマクロ
ディザセルＭＤを適用した状態における各画素に対応す
る乱数の例を示している。In FIG. 12, each pixel in the macro dither cell MD is
P32, and FIG. 13 shows an example of random numbers corresponding to each pixel in a state where the macro dither cell MD is applied to the image to be processed IM.
例えば、マクロディザセルＭＤの最上段の左の画素Ｐ、
に注目すると、第１３図ではこの画素に対応する乱数は
「０」である。乱数「０」はディザセルＤ、に対応し、
画素Ｐ、についてはディザセルＤｌが適用される。画素
Ｐ、の位置は、ディザセルＤ１の最上段の左の画素に対
応し、その閾値は「２０」である。従って画素Ｐ＋は閾
値「２０」により２値化される。このように各画素毎に
適用ディザセルをランダムに変更することにより、デイ
ザ画像の画素の分散がランダムになり、より自然な印象
を与え得るようになるる
乱数の発生方法としては既存の擬似乱数系列を使用する
ことは勿論可能であるが、擬似乱数においても側らかの
周期性が含まれていることが多く、ランダム性の高い自
然画法をカメラから取り込みこれを０〜３に量子化して
参照画像とすることによってより自然なデイザ画像が得
られている。For example, the top left pixel P of the macro dither cell MD,
If we pay attention to , the random number corresponding to this pixel in FIG. 13 is "0". Random number "0" corresponds to dither cell D,
Dither cell Dl is applied to pixel P. The position of pixel P corresponds to the top left pixel of dither cell D1, and its threshold value is "20". Therefore, pixel P+ is binarized using the threshold value "20". By randomly changing the applied dither cell for each pixel in this way, the pixel distribution of the dithered image becomes random, giving a more natural impression. Of course, it is possible to use pseudo-random numbers, but pseudo-random numbers often contain some periodicity, so it is necessary to take a highly random natural drawing from the camera and quantize it to 0 to 3. By using this as a reference image, a more natural dithered image is obtained.
なお乱数の分布状態によっては、濃度の帰りが生じる可
能性があるが、乱数の発生頻度を均一化すれば、このよ
うな障害は完全に防止できる。例えば、参照画ＩＲＩＭ
の各マクロディザセル対応領域毎に０〜３の乱数の個数
が均一となるように乱数を分散させることによって発生
頻度は均一になる。またこのように発生頻度を均一化す
るための乱数の分布が各マクロデイぜセル毎に同一であ
るとデイザ画像に周期性が生じることになるが、この乱
数の分布をマクロディザセル毎に乱数に基づいて変化き
せれば、このような周期性も解消される。なお乱数出現
頻度の均一化は必ずしもマクロディザセル単位で１テう
必要はなく、複数のマクロディザセルを含む領域毎に均
一化してもよい。It should be noted that depending on the distribution state of random numbers, there is a possibility that concentration returns may occur, but if the frequency of occurrence of random numbers is made uniform, such troubles can be completely prevented. For example, the reference image IRIM
By distributing the random numbers so that the number of random numbers 0 to 3 is uniform for each macro dither cell corresponding area, the frequency of occurrence becomes uniform. Also, if the distribution of random numbers to equalize the frequency of occurrence is the same for each macro dither cell, periodicity will occur in the dither image, but if the distribution of random numbers is changed to random numbers for each macro dither cell, periodicity will occur. If changes can be made based on this, such periodicity will be eliminated. Note that the random number appearance frequency does not necessarily have to be made uniform for each macro dither cell, but may be made uniform for each area including a plurality of macro dither cells.
前述のと８つ、この発明に係る中間調画像の表現力ｔム
は、非長方形のディザセルおよびこのディザセルを複数
隣接配列してなるマクロディザセルを定義し、マクロデ
ィザセル単位で処理対象画像の濃度を評価し、かつマク
ロディザセル内のディザセルについての閾値順位および
ディザセル内の各画素の閾値順位を定義するので、マク
ロデイぜセルにより階調数を増しながら各局部において
は密なドツト表現が可能であり、分解能の高い自然な擬
似中間調表現を実現し得る。In addition to the above, the expressive power of the halftone image according to the present invention is achieved by defining a non-rectangular dither cell and a macro dither cell formed by arranging a plurality of these dither cells adjacently, and expressing the image to be processed in macro dither cell units. Since the density is evaluated and the threshold order of the dither cells within the macro dither cell and the threshold order of each pixel within the dither cell are defined, it is possible to express dots densely in each local area while increasing the number of gradations using the macro dither cell. Therefore, it is possible to realize a natural pseudo-halftone expression with high resolution.
ざらにマクロディザセル内のディザセルの閾値順位を乱
数系列に基づいて設定することにより、−層自然な中間
調表現が可能になる。By roughly setting the threshold ranking of dither cells within a macro dither cell based on a random number series, -layer natural halftone expression can be achieved.
流側においてマクロディザセルを処理対象画像に適用し
た例を示す概念図、第１４図は同実施例の参照画像を示
す概念図である。FIG. 14 is a conceptual diagram showing an example in which a macro dither cell is applied to an image to be processed on the downstream side, and FIG. 14 is a conceptual diagram showing a reference image of the same embodiment.
ＭＤ・・マクロディザセル、Ｄ、〜Ｄ４・・ディザセル
、ＩＭ・・処理対象画像、ＲＩＭ・・・参照画像、ｒｌ
＋ ｒ２・乱数。MD... Macro dither cell, D, ~D4... Dither cell, IM... Image to be processed, RIM... Reference image, rl
+ r2・Random number.
Claims (8)
数隣接配列してなるマクロディザセルを定義し、前記デ
ィザセル内の各画素について閾値順位を定義するととも
に前記マクロディザセル内のディザセルの閾値順位を定
義し、前記マクロディザセル内の各画素について、ディ
ザセルをディザセルの閾値順位に従って循環しつつ、各
ディザセル内の閾値順位に従って各画素の閾値を定義し
、前記マクロディザセル単位で画像の各画素を２値化す
ることを特徴とする中間調画像の表現方法。(1) Define a non-rectangular dither cell and a macro dither cell formed by arranging a plurality of these dither cells adjacently, define a threshold order for each pixel in the dither cell, and define a threshold order of the dither cells in the macro dither cell. , for each pixel in the macro dither cell, define the threshold value of each pixel according to the threshold order in each dither cell while circulating the dither cells according to the threshold order of the dither cells, and convert each pixel of the image into a binary value in units of the macro dither cell. A method of expressing halftone images characterized by
る特許請求の範囲第１項記載の中間調画像の表現方法。(2) The method for expressing a halftone image according to claim 1, wherein the dither cell has a substantially regular hexagonal shape.
許請求の範囲第２項記載の中間調画像の表現方法。(3) The method for expressing a halftone image according to claim 2, wherein the dither cell is composed of 8 pixels.
心間距離が最小となるようにディザセルを４個配列して
なることを特徴とする特許請求の範囲第２項記載の中間
調画像の表現方法。(4) The method for expressing a halftone image according to claim 2, wherein the macro dither cell is formed by arranging four dither cells such that the distance between the centers of the dither cells within the macro dither cell is the minimum. .
乱数系列に基づいて設定することを特徴とする特許請求
の範囲第１項ないし第４項のいずれか１項に記載の中間
調画像の表現方法。(5) The threshold ranking of dither cells within a macro dither cell is
5. The method for representing a halftone image according to claim 4, wherein the setting is performed based on a random number series.
基づいて生成することを特徴とする特許請求の範囲第５
項記載の中間調画像の表現方法。(6) The random number series is generated based on the density of a highly random natural image.
How to express halftone images as described in Section 1.
確率が均一となるよう設定することを特徴とする特許請
求の範囲第５項記載の中間調画像の表現方法。(7) The method for expressing a halftone image according to claim 5, wherein the random number series is set so that the probability of appearance of each random number in the macro dither cell is uniform.
とを特徴とする特許請求の範囲第７項記載の中間調画像
の表現方法。(8) A method for expressing a halftone image according to claim 7, characterized in that the random number series is sequentially changed based on the random number series.
Priority Applications (7)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP1103695A JP2928786B2 (en) | 1989-04-24 | 1989-04-24 | Expression method of halftone image |
| US07/512,258 US5201013A (en) | 1989-04-24 | 1990-04-20 | Dither processing method |
| EP90107677A EP0394929B1 (en) | 1989-04-24 | 1990-04-23 | Dither image processing method |
| DE69022469T DE69022469T2 (en) | 1989-04-24 | 1990-04-23 | Shivering image processing method. |
| KR1019900005781A KR0173456B1 (en) | 1989-04-24 | 1990-04-24 | Dither image processing method |
| US07/881,730 US5315669A (en) | 1989-04-24 | 1992-05-08 | Dither processing method |
| US08/247,397 US5438634A (en) | 1989-04-24 | 1994-05-23 | Dither processing method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP1103695A JP2928786B2 (en) | 1989-04-24 | 1989-04-24 | Expression method of halftone image |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH02281873A true JPH02281873A (en) | 1990-11-19 |
| JP2928786B2 JP2928786B2 (en) | 1999-08-03 |
Family
ID=14360915
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP1103695A Expired - Lifetime JP2928786B2 (en) | 1989-04-24 | 1989-04-24 | Expression method of halftone image |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2928786B2 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7139103B1 (en) | 1998-12-28 | 2006-11-21 | Ricoh Company, Ltd. | Screening method and a screening apparatus |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS57142072A (en) * | 1981-02-27 | 1982-09-02 | Canon Inc | Video signal processor |
| JPS57185768A (en) * | 1981-05-12 | 1982-11-16 | Ricoh Co Ltd | Binary tone processing method for analog picture signal |
| JPS59163959A (en) * | 1983-03-08 | 1984-09-17 | Fujitsu Ltd | Intermediate tone picture converting system |
| JPS6115467A (en) * | 1984-06-30 | 1986-01-23 | Toshiba Corp | Thermal transfer color printer |
| JPS63164758A (en) * | 1986-12-26 | 1988-07-08 | Fuji Xerox Co Ltd | Image processor |
| JPS63245174A (en) * | 1987-03-31 | 1988-10-12 | Toshiba Corp | Picture processing unit |
-
1989
- 1989-04-24 JP JP1103695A patent/JP2928786B2/en not_active Expired - Lifetime
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS57142072A (en) * | 1981-02-27 | 1982-09-02 | Canon Inc | Video signal processor |
| JPS57185768A (en) * | 1981-05-12 | 1982-11-16 | Ricoh Co Ltd | Binary tone processing method for analog picture signal |
| JPS59163959A (en) * | 1983-03-08 | 1984-09-17 | Fujitsu Ltd | Intermediate tone picture converting system |
| JPS6115467A (en) * | 1984-06-30 | 1986-01-23 | Toshiba Corp | Thermal transfer color printer |
| JPS63164758A (en) * | 1986-12-26 | 1988-07-08 | Fuji Xerox Co Ltd | Image processor |
| JPS63245174A (en) * | 1987-03-31 | 1988-10-12 | Toshiba Corp | Picture processing unit |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7139103B1 (en) | 1998-12-28 | 2006-11-21 | Ricoh Company, Ltd. | Screening method and a screening apparatus |
Also Published As
| Publication number | Publication date |
|---|---|
| JP2928786B2 (en) | 1999-08-03 |
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