JPH08305843A - Method for converting pixel density of digital image - Google Patents
Method for converting pixel density of digital imageInfo
- Publication number
- JPH08305843A JPH08305843A JP7111948A JP11194895A JPH08305843A JP H08305843 A JPH08305843 A JP H08305843A JP 7111948 A JP7111948 A JP 7111948A JP 11194895 A JP11194895 A JP 11194895A JP H08305843 A JPH08305843 A JP H08305843A
- Authority
- JP
- Japan
- Prior art keywords
- pixel
- edge
- density gradient
- density
- interpolation
- 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 abstract description 40
- 238000006243 chemical reaction Methods 0.000 claims abstract description 6
- 238000010586 diagram Methods 0.000 description 7
- 238000007796 conventional method Methods 0.000 description 3
- 238000004321 preservation Methods 0.000 description 3
- 230000005540 biological transmission Effects 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 230000010365 information processing Effects 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
Classifications
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T3/00—Geometric image transformations in the plane of the image
- G06T3/40—Scaling of whole images or parts thereof, e.g. expanding or contracting
- G06T3/403—Edge-driven scaling; Edge-based scaling
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Theoretical Computer Science (AREA)
- Image Processing (AREA)
- Editing Of Facsimile Originals (AREA)
Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は、デジタル複写機、ファ
クシミリ等に関し、特に、デジタル画像処理装置におい
て高画質に画素密度変換する方法に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital copying machine, a facsimile, and the like, and more particularly to a method for converting pixel density to high image quality in a digital image processing apparatus.
【０００２】[0002]
【従来の技術】デジタル画像を表現するために様々なメ
ディアが用いられている。画素数の異なるメディア間で
画像をやり取りする際や、画像を拡大縮小する際問題と
なるのが、いかに高品質に画素密度を変換するかという
ことである。このための従来の方法としては、最近隣補
間法（Ｎｅａｒｅｓｔ Ｎｅｉｇｈｂｏｒ法）、線形補
間法（Ｂｉｌｉｎｅａｒ法）、立方体コンボリューショ
ン法（Ｃｕｂｉｃ Ｃｏｎｖｏｌｕｔｉｏｎ法）、ラグ
ランジュ補間法、スプライン補間法などがある。例え
ば、電子情報通信学会論文誌’８６／１１Ｖｏｌ．Ｊ６
９−Ｄ Ｎｏ．１１，１６１７ページ〜１６２３ページ
「画像信号の幾何学的変換のための補間フィルタと画質
に関する一考察」においては、最近隣零次補間法、最大
値零次補間法、４点線形補間法、９点２次補間法、１６
点標本化関数補間法、３次スプライン補間法の６種類の
例について説明しており、９点２次補間や３次スプライ
ン補間を用いた場合は、ある程度の画質は得られている
ようである。しかしながら、これらの従来の方法では、
各画素の画像中における意味（エッジを構成するのか、
平らな部分なのかなど）を考慮せず、全ての画素につい
て同じ処理をするため、エッジがボケたり、エッジがジ
ャギーになる、などの問題があった。換言すると、画像
中のエッジの部分（周波数の大きいところ）でも、平ら
な部分（周波数の小さいところ）でも、同じ補間処理を
施し、エッジが保存されないために、エッジがボケた
り、エッジがジャギーになってしまっていた。そこで本
発明では各画素の濃度勾配を求め、その画素、及びその
近傍にふさわしい処理を施すことによって、上記の従来
法の問題を解決するものである。Various media are used to represent digital images. A problem when exchanging images between media having different numbers of pixels and when enlarging or reducing images is how to convert the pixel density with high quality. Conventional methods for this purpose include a nearest neighbor interpolation method (Nearest Neighbor method), a linear interpolation method (Biliear method), a cubic convolution method (Cubic Convolution method), a Lagrange interpolation method, and a spline interpolation method. For example, the Institute of Electronics, Information and Communication Engineers, Journal of '86 / 11 Vol. J6
9-D No. 11, pages 1617 to 1623, "A Study on Interpolation Filter and Image Quality for Geometric Transformation of Image Signal", nearest neighbor zero order interpolation method, maximum value zero order interpolation method, four-point linear interpolation method, 9 Point quadratic interpolation method, 16
Six kinds of examples of the point sampling function interpolation method and the cubic spline interpolation method have been described. When the 9-point quadratic interpolation or the cubic spline interpolation is used, a certain level of image quality seems to be obtained. . However, with these conventional methods,
The meaning of each pixel in the image (whether it constitutes an edge,
Since it does the same processing for all pixels regardless of whether it is a flat part), there were problems such as blurring of edges and jaggies of edges. In other words, the same interpolation processing is applied to the edge part (where the frequency is high) and the flat part (where the frequency is low) in the image. It had become. Therefore, the present invention solves the above-mentioned problems of the conventional method by obtaining the density gradient of each pixel and performing appropriate processing on the pixel and its vicinity.
【０００３】[0003]
【発明が解決しようとする課題】そこで本発明は、注目
画素の濃度勾配（微分係数）を求め、その画素がエッジ
部分であるのか否かを判断し、エッジ部分であると判断
されれば、そのエッジを保存するように画像の拡大、縮
小を行い高画質の画素密度変換方法を提供することを目
的とする。Therefore, according to the present invention, the density gradient (differential coefficient) of the pixel of interest is obtained, and it is determined whether or not the pixel is an edge portion. If it is determined that the pixel is an edge portion, It is an object of the present invention to provide a high image quality pixel density conversion method by enlarging and reducing an image so as to preserve the edge.
【０００４】[0004]
【課題を解決するための手段】請求項１記載の発明で
は、注目画素の濃度勾配を求め、各注目画素の濃度勾配
に応じた補間方法を選択することにした。According to the first aspect of the present invention, the density gradient of the target pixel is obtained, and the interpolation method according to the density gradient of each target pixel is selected.
【０００５】請求項２記載の発明では、注目画素の濃度
勾配を求め、ある画素の濃度勾配がある方向について大
きいときにはその画素をその方向のエッジとみなしエッ
ジを保存することにした。According to the second aspect of the invention, the density gradient of the pixel of interest is obtained, and when the density gradient of a certain pixel is large in a certain direction, the pixel is regarded as an edge in that direction and the edge is saved.
【０００６】請求項３記載の発明では、注目画素の濃度
勾配を求め、ある画素の濃度勾配がある方向について小
さいときにはその画素付近の濃度は平坦であるとみなし
ノイズを強調しないことにした。According to the third aspect of the present invention, the density gradient of the pixel of interest is obtained, and when the density gradient of a certain pixel is small in a certain direction, the density in the vicinity of that pixel is considered to be flat and noise is not emphasized.
【０００７】[0007]
【作用】請求項１記載の発明によれば、各画素の濃度勾
配に応じた補間方法を選択することが可能となる。According to the invention described in claim 1, it is possible to select an interpolation method according to the density gradient of each pixel.
【０００８】請求項２記載の発明によれば、ある画素の
濃度勾配がある方向について大きいときにはその画素を
その方向のエッジとみなしエッジを保存するので、高画
質な画像を得ることが可能となる。According to the second aspect of the invention, when the density gradient of a certain pixel is large in a certain direction, the pixel is regarded as an edge in that direction and the edge is stored, so that a high quality image can be obtained. .
【０００９】請求項３記載の発明によれば、ある画素の
濃度勾配がある方向について小さいときには、その画素
付近の濃度は平坦であるとみなし、ノイズを強調しない
ことにしたので高画質な画像を得ることが可能となる。According to the third aspect of the present invention, when the density gradient of a certain pixel is small in a certain direction, it is considered that the density near that pixel is flat and noise is not emphasized, so that a high quality image is obtained. It becomes possible to obtain.
【００１０】[0010]
【実施例】以下、本発明を実施例に基づいて詳細に説明
する。本発明は、注目画素の濃度勾配（微分係数）を求
め、その画素がエッジ部分であるのか否かを判断し、エ
ッジ部分であると判断されれば、そのエッジを保存する
ように画像の拡大、縮小を行って、高画質の画素密度変
換を行なうようにしたものである。本発明の概要構成
を、図１に示す。先ず、原画像の一画素ごとに濃度勾配
を求める（Ｓ１）。次に、濃度勾配と閾値を比較し、エ
ッジかどうかを判断する（Ｓ２）。その画素の濃度勾配
が、ある閾値以上であれば、エッジと判断する。エッジ
と判断された場合、そのエッジを保存する補間を行い
（Ｓ３）、エッジでないと判断された場合、既成の方法
（例えば、線形補間法など）を用いて、線形補間を行な
う（Ｓ４）。そして、これらのステップを原画像の全て
の画素について実施する（Ｓ５）。このように、注目画
素の濃度勾配を求め、各画素の濃度勾配に応じた補間方
法を選択するのが、請求項１記載の発明である。次に、
本発明の濃度勾配の計算、エッジの保存をする補間、エ
ッジでない場合の補間について、以下に詳しく説明す
る。DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. The present invention obtains a density gradient (differential coefficient) of a pixel of interest, determines whether or not the pixel is an edge portion, and if it is determined to be an edge portion, enlarges the image so as to save the edge. , And the pixel density conversion of high image quality is performed. A schematic configuration of the present invention is shown in FIG. First, the density gradient is obtained for each pixel of the original image (S1). Next, the density gradient and the threshold value are compared to determine whether the edge is an edge (S2). If the density gradient of the pixel is more than a certain threshold value, it is determined as an edge. If it is determined to be an edge, interpolation for saving the edge is performed (S3), and if it is determined not to be an edge, linear interpolation is performed using an existing method (for example, a linear interpolation method) (S4). Then, these steps are performed for all the pixels of the original image (S5). In this way, the invention according to claim 1 is to obtain the density gradient of the pixel of interest and select an interpolation method according to the density gradient of each pixel. next,
The calculation of the density gradient of the present invention, the interpolation for saving the edge, and the interpolation for the case other than the edge will be described in detail below.
【００１１】注目画素の濃度勾配の計算は、３×３のソ
ーベルオペレータを用いて行う。具体的には、図２に示
した実施例のように、３×３のマスクを注目画素にか
け、２つの方向の微分係数の２乗平均をとる。ここで図
２（ａ）は、ｘ方向の微分係数を示し、図２（ｂ）は、
ｙ方向の微分係数を示す。微分係数ｇ（ｘ，ｙ）と閾値
Ｔｈを比較し、その結果、微分係数ｇ（ｘ，ｙ）が以下
の条件式、即ち、ｇ（ｘ，ｙ）≧Ｔｈならば、エッジと
判断しｇ（ｘ，ｙ）＜Ｔｈならば、エッジでないと判断
する（但し、Ｔｈは閾値）。この結果を受けて、以下に
述べる２つの方法で補間を行う。The density gradient of the pixel of interest is calculated using a 3 × 3 Sobel operator. Specifically, as in the embodiment shown in FIG. 2, a 3 × 3 mask is applied to the target pixel and the root mean square of the differential coefficients in the two directions is calculated. Here, FIG. 2A shows the differential coefficient in the x direction, and FIG.
The differential coefficient in the y direction is shown. The differential coefficient g (x, y) is compared with the threshold value Th, and as a result, if the differential coefficient g (x, y) is the following conditional expression, that is, g (x, y) ≧ Th, it is determined to be an edge and g If (x, y) <Th, it is determined that it is not an edge (however, Th is a threshold value). Upon receiving this result, interpolation is performed by the following two methods.
【００１２】エッジの保存をする補間について説明す
る。図３に本発明の補間の仕方を一次元に簡略化して示
す。図３（ａ）は原画像の状態を表し、図３（ｂ）、及
び図３（ｃ）は、エッジの保存と補間の様子を表してい
る。ここで白丸は、原画像信号を表し、黒丸は、補間し
て得られた画像信号を表す。尚、図３は原画像を３倍に
拡大した例である。図３（ｂ）に示すように、通常はエ
ッジであっても、それを考慮せずに補間するため、原画
像にあった急峻な傾き（エッジ）は失われ、これが画像
がボケる原因となる。そこで図３（ｃ）に示すように、
原画像のエッジの傾きを保存しつつ補間する。このよう
にエッジの傾きを保存して補間すると、画像のエッジの
ボケやジャギーがなくなり、高画質な画像を得ることが
できる。また、エッジでない場合の補間について説明す
ると、原画像の注目画素がエッジでないと判断された場
合は、既成の線形補間法、あるいは、Ｃｕｂｉｃ Ｃｏ
ｎｖｏｌｕｔｉｏｎ 法などを用いて補間する。Interpolation for saving edges will be described. FIG. 3 shows a simplified one-dimensional method of interpolation according to the present invention. FIG. 3A shows the state of the original image, and FIGS. 3B and 3C show the state of edge storage and interpolation. Here, the white circles represent the original image signal and the black circles represent the image signal obtained by interpolation. Note that FIG. 3 is an example in which the original image is magnified three times. As shown in FIG. 3 (b), even if an edge is normally used, interpolation is performed without considering it, so the steep slope (edge) in the original image is lost, which is the cause of blurring of the image. Become. Therefore, as shown in FIG.
Interpolation is performed while preserving the inclination of the edges of the original image. When the inclination of the edge is stored and interpolated in this way, blurring and jaggies of the edge of the image are eliminated, and a high-quality image can be obtained. In addition, the interpolation in the case of no edge will be described. If it is determined that the pixel of interest of the original image is not an edge, an existing linear interpolation method or Cubic Co
Interpolation is performed using the nvolution method or the like.
【００１３】図４に他の実施例を示す。原画像入力部１
からの原画像信号は、原画像記憶部２に記憶される。次
に、濃度勾配計算手段３により濃度勾配が計算され（Ｓ
１）、その後、注目画素は、エッジかどうかの判断がな
される（Ｓ２）。エッジであると判断された場合は、エ
ッジ保存を考慮した補間がなされる（Ｓ３）。また、エ
ッジでないと判断された場合は、既存の方法（例えば、
線形補間法）で、補間がなされる（Ｓ４）。これらを原
画像の全ての画素について行う。全ての画素の処理が終
わっていない場合は、濃度勾配計算手段３に戻り、濃度
勾配を求め、前と同様の処理ステップを実施し、全ての
画素の処理が終わるまで続ける。全ての画素の処理が終
わったら（Ｓ５）、画像出力部４から画像を出力する。
上述したように、注目画素の濃度勾配を求め、ある画素
の濃度勾配がある方向について大きいときには、その画
素をその方向のエッジとみなし、エッジを保存するのが
請求項２記載の発明であり、また、ある画素の濃度勾配
がある方向について小さいときには、その画素付近の濃
度は平坦であるとみなし、ノイズを強調しないこととし
たのが、請求項３記載の発明である。本発明は、本発明
の主旨を満たすデジタル画像の画素密度変換方法であれ
ば、デジタル複写機、ファクシミリに限らず、デジタル
画像処理装置、情報処理装置オフィスオートーション機
器などに対して広く適用することができる。FIG. 4 shows another embodiment. Original image input section 1
The original image signal from is stored in the original image storage unit 2. Next, the concentration gradient calculation means 3 calculates the concentration gradient (S
1) After that, it is judged whether or not the pixel of interest is an edge (S2). If it is determined to be an edge, interpolation is performed in consideration of edge preservation (S3). If it is determined that the edge is not an edge, the existing method (for example,
Interpolation is performed by the linear interpolation method) (S4). These are performed for all the pixels of the original image. If all pixels have not been processed, the process returns to the density gradient calculation means 3, the density gradient is obtained, the same processing steps as before are performed, and the processing is continued until all pixels are processed. When all pixels have been processed (S5), the image output unit 4 outputs an image.
As described above, the invention according to claim 2, wherein the density gradient of the pixel of interest is obtained, and when the density gradient of a certain pixel is large in a certain direction, the pixel is regarded as an edge in that direction and the edge is saved. Further, when the density gradient of a certain pixel is small in a certain direction, the density in the vicinity of the pixel is considered to be flat, and noise is not emphasized. INDUSTRIAL APPLICABILITY The present invention is widely applicable not only to digital copying machines and facsimiles but also to digital image processing devices, information processing devices, office automation devices, etc., as long as it is a method of converting the pixel density of digital images that satisfies the gist of the present invention. You can
【００１４】[0014]
【発明の効果】本発明によれば、現在使われている様々
なメディア間でのデジタル画像の変換を極めて高画質で
行うことができる。また、記憶容量や伝送容量の制限で
粗い画像しか扱えない場合（例えば、電子スチルカメ
ラ、カラー複写機、テレビ電話など）に本発明を適用す
れば、高画質・高精細な画像を復元できる。According to the present invention, digital images can be converted with extremely high image quality between various media currently used. Further, when the present invention is applied to the case where only a rough image can be handled due to the limitation of the storage capacity and the transmission capacity (for example, an electronic still camera, a color copying machine, a videophone, etc.), a high quality and high definition image can be restored.
【００１５】[0015]
【図１】本発明の実施例を示す図。FIG. 1 is a diagram showing an embodiment of the present invention.
【図２】ソーベルオペレータの実施例を示す図。FIG. 2 is a diagram showing an example of a Sobel operator.
【図３】エッジの保存と補間の実施例を示す図。（ａ）
は原画像の状態を示す図で、（ｂ）はエッジの保存を考
慮しない普通の線形補間を示す図で、（ｃ）はエッジの
保存を考慮した線形補間を示す図。FIG. 3 is a diagram showing an embodiment of edge storage and interpolation. (A)
FIG. 4A is a diagram showing a state of an original image, FIG. 6B is a diagram showing ordinary linear interpolation not considering preservation of edges, and FIG. 7C is a diagram showing linear interpolation taking preservation of edges into consideration.
【図４】本発明の他の実施例を示す図。FIG. 4 is a diagram showing another embodiment of the present invention.
【００１６】[0016]
１ 原画像入力部 ２ 原画像記憶部 ３ 濃度勾配計算手段 ４ 画像出力部。 1 original image input unit 2 original image storage unit 3 density gradient calculating means 4 image output unit
Claims (3)
て、注目画素の濃度勾配を求め、各画素の濃度勾配に応
じた補間方法を選択することを特徴とするデジタル画像
の画像密度変換方法。1. An image density conversion method for a digital image, characterized in that, in the pixel density conversion method for a digital image, a density gradient of a pixel of interest is obtained and an interpolation method corresponding to the density gradient of each pixel is selected.
て、注目画素の濃度勾配を求め、ある画素の濃度勾配が
ある方向について大きいときには、その画素をその方向
のエッジとみなし、エッジを保存することを特徴とする
デジタル画像の画像密度変換方法。2. A method of converting a pixel density of a digital image, wherein a density gradient of a pixel of interest is obtained, and when the density gradient of a pixel is large in a certain direction, the pixel is regarded as an edge in that direction and the edge is saved. A method for converting the image density of a characteristic digital image.
て、注目画素の濃度勾配を求め、ある画素の濃度勾配が
ある方向について小さいときには、その画素付近の濃度
は平坦であるとみなし、ノイズを強調しないことを特徴
とするデジタル画像の画像密度変換方法。3. A method of converting a pixel density of a digital image, wherein a density gradient of a pixel of interest is obtained, and when the density gradient of a certain pixel is small in a certain direction, it is considered that the density near the pixel is flat and noise is not emphasized. An image density conversion method for a digital image, characterized in that
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP7111948A JPH08305843A (en) | 1995-05-10 | 1995-05-10 | Method for converting pixel density of digital image |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP7111948A JPH08305843A (en) | 1995-05-10 | 1995-05-10 | Method for converting pixel density of digital image |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH08305843A true JPH08305843A (en) | 1996-11-22 |
Family
ID=14574167
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP7111948A Pending JPH08305843A (en) | 1995-05-10 | 1995-05-10 | Method for converting pixel density of digital image |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH08305843A (en) |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6760489B1 (en) | 1998-04-06 | 2004-07-06 | Seiko Epson Corporation | Apparatus and method for image data interpolation and medium on which image data interpolation program is recorded |
| US7039254B1 (en) | 1999-08-05 | 2006-05-02 | Sanyo Electric Co., Ltd. | Image interpolating method |
| JP2006228107A (en) * | 2005-02-21 | 2006-08-31 | Yamaha Corp | Image processing method and device |
| CN100367800C (en) * | 2004-12-24 | 2008-02-06 | 精伦电子股份有限公司 | Image processing method and apparatus based on sensing resolution |
| US7429994B2 (en) | 2000-06-20 | 2008-09-30 | Mitsubishi Denki Kabushiki Kaisha | Image processing method and apparatus, and image display method and apparatus for changing edge sharpness |
| JP2012506646A (en) * | 2008-09-22 | 2012-03-15 | サムスン エレクトロニクス カンパニー リミテッド | Video interpolating apparatus and method using region segmentation |
-
1995
- 1995-05-10 JP JP7111948A patent/JPH08305843A/en active Pending
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6760489B1 (en) | 1998-04-06 | 2004-07-06 | Seiko Epson Corporation | Apparatus and method for image data interpolation and medium on which image data interpolation program is recorded |
| US7039254B1 (en) | 1999-08-05 | 2006-05-02 | Sanyo Electric Co., Ltd. | Image interpolating method |
| US7429994B2 (en) | 2000-06-20 | 2008-09-30 | Mitsubishi Denki Kabushiki Kaisha | Image processing method and apparatus, and image display method and apparatus for changing edge sharpness |
| CN100367800C (en) * | 2004-12-24 | 2008-02-06 | 精伦电子股份有限公司 | Image processing method and apparatus based on sensing resolution |
| JP2006228107A (en) * | 2005-02-21 | 2006-08-31 | Yamaha Corp | Image processing method and device |
| JP4734952B2 (en) * | 2005-02-21 | 2011-07-27 | ヤマハ株式会社 | Image processing method and apparatus |
| JP2012506646A (en) * | 2008-09-22 | 2012-03-15 | サムスン エレクトロニクス カンパニー リミテッド | Video interpolating apparatus and method using region segmentation |
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