JPH08115405A - Color picture compression method - Google Patents
Color picture compression methodInfo
- Publication number
- JPH08115405A JPH08115405A JP6251781A JP25178194A JPH08115405A JP H08115405 A JPH08115405 A JP H08115405A JP 6251781 A JP6251781 A JP 6251781A JP 25178194 A JP25178194 A JP 25178194A JP H08115405 A JPH08115405 A JP H08115405A
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- Japan
- Prior art keywords
- color
- value
- representative
- picture
- pixel
- 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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- Processing Or Creating Images (AREA)
- Image Processing (AREA)
- Compression Of Band Width Or Redundancy In Fax (AREA)
- Controls And Circuits For Display Device (AREA)
Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は、カラー画像の圧縮に関
する。近年、カラー画像の表示の高品位化の要望が高ま
り、所謂フルカラー対応システムに対する要望が高まっ
て来た。一方、現状では、従来の２５６色擬似カラーデ
ィスプレイが行き渡っているため、その活用を図ること
が要求されている。このために既存のディスプレイによ
りフルカラー画像を出来る限り自然に表示する必要があ
る。このため、代表色と呼ばれる所定の数の色（例えば
２５６色）を選び、これらの色によってカラー画像を表
現する方法、即ちカラー画像圧縮方法を実現する必要が
ある。FIELD OF THE INVENTION This invention relates to color image compression. In recent years, there has been an increasing demand for high-quality display of color images, and a so-called full-color compatible system has also increased. On the other hand, at present, since the conventional 256-color pseudo color display is prevalent, it is required to utilize it. For this reason, it is necessary to display a full-color image as naturally as possible on an existing display. Therefore, it is necessary to select a predetermined number of colors called representative colors (for example, 256 colors) and implement a method for expressing a color image by these colors, that is, a color image compression method.
【０００２】[0002]
【従来の技術】カラー画像圧縮方法の一つとして、従来
より、ＬＵＴ(Look up table) が用いられている。具体
的には、原画像に観察される色（例えば、１６７７７２
１６色のフルカラー）のうち、代表色として所定の数の
色（例えば２５６色）を選び、その色のみをＬＵＴに設
定する。各画素は、ＬＵＴに格納されている何れかの色
によって表現される。なお、ＬＵＴに設定される代表色
の列はカラーマップと呼ばれる。圧縮画像によって表示
される画像において、その多くの画素は、元の色とは異
なった色によって表示され、原画像の色相感を損なうこ
とが多く、この様な欠点を回避するべく、従来より、種
々の方法が提案されている。以下に、従来技術の代表的
方法を２件例示する。2. Description of the Related Art Conventionally, an LUT (Look up table) has been used as one of color image compression methods. Specifically, the colors observed in the original image (for example, 167772
Of the 16 full colors, a predetermined number of colors (for example, 256 colors) are selected as representative colors, and only that color is set in the LUT. Each pixel is represented by any color stored in the LUT. The column of representative colors set in the LUT is called a color map. In the image displayed by the compressed image, many of the pixels are displayed in a color different from the original color, which often impairs the hue of the original image, and in order to avoid such a defect, conventionally, Various methods have been proposed. Two typical methods of the prior art will be illustrated below.
【０００３】第１は、図５に示す構成をとる（特開平４
−２９８１９６参照）。図中、１はカラー画像入力部、
２は出現色頻度計数部、３はカラーマップ作成部、４は
カラー画像変換部である。本方法では、対象となるカラ
ー画像に含まれるカラー情報の出現頻度を求め、出現頻
度の高い順に所定の数の代表色を抽出する。本方法で
は、画像の多くの範囲で観察される色は忠実に保存され
る。しかし、その他の部分の色はすべて原画像の色とか
なりかけ離れた色で再現されるので、かなりの違和感を
生じる。First, it has the configuration shown in FIG.
-298196). In the figure, 1 is a color image input section,
Reference numeral 2 is an appearance color frequency counting unit, 3 is a color map creating unit, and 4 is a color image converting unit. In this method, the appearance frequency of the color information included in the target color image is obtained, and a predetermined number of representative colors are extracted in descending order of appearance frequency. With this method, the colors observed in many areas of the image are faithfully preserved. However, the colors of the other parts are reproduced with colors that are far from the colors of the original image, which causes a considerable discomfort.
【０００４】第２は、図６に示す構成をとる（特開昭６
４−８０９９１参照）。図中、１はカラー画像入力部、
２は画像分割部、３はカラーマップ作成部、４はカラー
画像変換部である。本方法では、対象となるカラー画像
に含まれるカラー情報を色空間（例えば、ＲＧＢの三原
色の各成分を３つの座標軸とする３次元空間等）に変換
し、色空間を複数領域に分割して代表となる色を決定す
る方法も提案されている。本方法では、原画像で色相が
急激に変化する位置を検出し、その位置を境界とした領
域内に、適応的にカラーマップを決定する。その結果、
画像の全体にわたって画質が向上し、画像の転送や格納
に有用である。しかし、一つの画像に対して複数のカラ
ーマップを持つため、画像表示する場合には装置の構成
が複雑になり導入のメリットが無いのが現状である。Second, it has the configuration shown in FIG.
4-80991). In the figure, 1 is a color image input section,
Reference numeral 2 is an image division unit, 3 is a color map creation unit, and 4 is a color image conversion unit. In this method, the color information included in the target color image is converted into a color space (for example, a three-dimensional space in which each component of the three primary colors of RGB has three coordinate axes), and the color space is divided into a plurality of regions. A method of determining a representative color has also been proposed. In this method, the position where the hue changes abruptly in the original image is detected, and the color map is adaptively determined within the region bounded by the position. as a result,
The image quality is improved over the entire image, which is useful for image transfer and storage. However, since there are a plurality of color maps for one image, the configuration of the device is complicated when displaying an image, and there is no merit of introduction.
【０００５】[0005]
【発明が解決しようとする課題】従って、(1) 画像の全
体にわたって画質を保持するカラーマップを決定できな
い、(2) 画質を極力保持するために、複数のカラーマッ
プを設定しなければならない、といった問題点があっ
た。Therefore, (1) it is not possible to determine a color map that maintains image quality over the entire image, (2) multiple color maps must be set in order to maintain image quality as much as possible, There was a problem such as.
【０００６】本発明は、これらの問題点を解決し、既存
のディスプレイを用いて、フルカラー画像を表示するカ
ラー画像圧縮方法を実現することを目的とする。An object of the present invention is to solve these problems and to realize a color image compression method for displaying a full color image using an existing display.
【０００７】[0007]
【課題を解決するための手段】図１は、本発明の原理説
明図、図３は図１の処理の流れを示す図である。図１
中、１はカラー画像入力部、２は色空間分割部、３はカ
ラーマップ作成部、４はカラー画像変換部である。FIG. 1 is a diagram for explaining the principle of the present invention, and FIG. 3 is a diagram showing the flow of processing in FIG. FIG.
In the figure, 1 is a color image input unit, 2 is a color space dividing unit, 3 is a color map creating unit, and 4 is a color image converting unit.
【０００８】請求項１の発明では、画像全体のカラー情
報を一般の色空間に変換し、該色空間を所定の数の複数
部分領域に分割し、該部分領域に属する色値を代表色に
変換する。色空間の分割および代表値の決定は、全ての
画素についてその画素の色値の属する部分領域の代表色
と該画素の色値との距離の評価値の累積を求め、該累積
が小さくなるように色空間を部分領域に分割して行う。According to the first aspect of the invention, the color information of the entire image is converted into a general color space, the color space is divided into a predetermined number of partial areas, and the color values belonging to the partial areas are set as representative colors. Convert. The color space is divided and the representative value is determined by obtaining the cumulative evaluation value of the distance between the representative color of the partial area to which the color value of the pixel belongs and the color value of the pixel for all pixels, and reducing the cumulative value. The color space is divided into partial areas.
【０００９】請求項２の発明では、請求項１の発明にお
いて、分割する最初の部分領域は色空間全体とし、該部
分領域の代表色は該部分領域の平均値を用い、以下、各
部分領域毎の画素値と代表色との差を求め、この差につ
き分散を計算し、分散の大きい部分領域を選択し、該選
択された部分領域を２分割してそれぞれの代表色を決定
し、該２分割により増加した後の部分領域の数と代表色
の数が一致するまで、毎回全部分領域を対象に、領域の
分割と代表色の決定を繰り返す。According to a second aspect of the invention, in the first aspect of the invention, the first partial region to be divided is the entire color space, and the representative color of the partial region uses an average value of the partial regions. The difference between each pixel value and the representative color is obtained, the variance is calculated based on this difference, the partial region having a large variance is selected, the selected partial region is divided into two, and each representative color is determined. The division of the area and the determination of the representative color are repeated for all the partial areas every time until the number of the partial areas increased by the division into two and the number of the representative colors match.
【００１０】請求項３の発明では、請求項１または請求
項２の発明を、色空間がＲＧＢ値をそのまま３成分とす
る３次元座標で示される場合に適用する。請求項４の発
明では、請求項１または請求項２の発明を、ＲＧＢ値を
ＹＩＱの３成分とする３次元座標に変換した３次元座標
で示される場合、さらにＹＩを２成分とする２次元座標
に変換する場合に適用する。According to the invention of claim 3, the invention of claim 1 or 2 is applied to the case where the color space is represented by three-dimensional coordinates in which the RGB values are directly used as the three components. In the invention of claim 4, when the invention of claim 1 or claim 2 is expressed by three-dimensional coordinates obtained by converting RGB values into three-dimensional coordinates having three components of YIQ, two-dimensional coordinates having YI as two components It is applied when converting to coordinates.
【００１１】請求項５の発明では、請求項１ないし請求
項４のいずれかの発明について、画素の色値の属する部
分領域の代表色と該画素の色値との距離の評価値を画素
の色値の属する部分領域の代表色と該画素の色値とのユ
ークリッド距離の差値としている。According to a fifth aspect of the present invention, in any one of the first to fourth aspects of the invention, the evaluation value of the distance between the representative color of the partial area to which the color value of the pixel belongs and the color value of the pixel is determined by the pixel. The difference value is the Euclidean distance between the representative color of the partial area to which the color value belongs and the color value of the pixel.
【００１２】請求項６の発明では、請求項１ないし請求
項４のいずれかの発明について、画素の色値の属する部
分領域の代表色と該画素の色値との距離の評価値を画素
の色値の属する部分領域の代表色と該画素の色値との街
区画としている。According to a sixth aspect of the present invention, in any one of the first to fourth aspects of the invention, the evaluation value of the distance between the representative color of the partial area to which the color value of the pixel belongs and the color value of the pixel The area is defined by the representative color of the partial area to which the color value belongs and the color value of the pixel.
【００１３】[0013]
【作用】請求項１の発明および請求項２の発明では、図
１の如くカラー画像入力部１から入力された原カラー画
像は、色空間分割部６に送られる。色空間分割部６は色
空間分割、ＲＧＢ変換および代表色決定の諸機能を内蔵
するもので、カラー画像のＲＧＢ値を色空間に写像し、
写像結果に基づき、全ての画素についてその画素の色値
の属する部分領域の代表色と該画素の色値との距離の評
価値の累積が小さくなるように、色空間を所定の数の複
数部分領域に分割し、各部分領域の代表色を決定する。In the first and second aspects of the invention, the original color image input from the color image input section 1 as shown in FIG. 1 is sent to the color space dividing section 6. The color space division unit 6 has various functions of color space division, RGB conversion, and representative color determination, and maps RGB values of a color image into a color space,
Based on the mapping result, the color space is set to a predetermined number of plural parts so that the cumulative evaluation value of the distance between the representative color of the partial area to which the color value of the pixel belongs and the color value of the pixel becomes small for all the pixels. The area is divided into areas, and the representative color of each partial area is determined.
【００１４】色空間分割および代表色決定の結果と原画
像とを用いて、カラーマップ作成部３でカラーマップと
して、各部分領域の通し番号と代表色の対応表を生成す
る。その結果に基づいて、続くカラー画像変換部４で、
分割された色空間内の部分領域に通し番号を付け、入力
画像の各画素を、それが属する部分領域の番号に置き換
える。このようにして得られた圧縮符号化画像（圧縮さ
れた画像）を得る。Using the result of color space division and representative color determination and the original image, the color map creation unit 3 creates a correspondence table of serial numbers of each partial area and representative colors as a color map. Based on the result, in the subsequent color image conversion unit 4,
Serial numbers are assigned to the partial areas in the divided color space, and each pixel of the input image is replaced with the number of the partial area to which it belongs. The compression encoded image (compressed image) thus obtained is obtained.
【００１５】本発明によると、全ての画素についてその
画素の色値の属する部分領域の代表色と該画素の色値と
の距離の評価値の累積が小さいため（即ち色の近似の程
度が良好であるため）、高品位の圧縮画像が得られる。According to the present invention, the cumulative evaluation value of the distance between the representative color of the partial area to which the color value of the pixel belongs and the color value of the pixel is small for all the pixels (that is, the degree of color approximation is good). Therefore, a high-quality compressed image can be obtained.
【００１６】請求項３の発明では、請求項１の発明およ
び請求項２の発明の場合と同様に、図１に示すカラー画
像入力部１から入力された原カラー画像は、色空間分割
部６に送られるが、色空間がＲＧＢ値をそのまま３成分
とする３次元座標で示される場合であり、色空間分割部
６は色空間分割および代表色決定の諸機能を内蔵するも
ので、カラー画像のＲＧＢ値を用いて、全ての画素につ
いてその画素の色値の属する部分領域の代表色と該画素
の色値との距離の評価値の累積が小さくなるように、Ｒ
ＧＢ色空間を所定の数の複数部分領域に分割し、各部分
領域の代表色を決定する。以下、請求項１の発明および
請求項２の発明の場合と同様に、色空間分割および代表
色決定の結果と原画像とを用いて、カラーマップ作成部
３でカラーマップとして、各部分領域の通し番号と代表
色の対応表を生成する。その結果に基づいて、続くカラ
ー画像変換部４で、分割された色空間内の部分領域に通
し番号を付け、入力画像の各画素を、それが属する部分
領域の番号に置き換える。このようにして得られた圧縮
符号化画像を得る。According to the third aspect of the invention, as in the case of the first aspect of the invention and the second aspect of the invention, the original color image input from the color image input section 1 shown in FIG. In the case where the color space is indicated by the three-dimensional coordinates in which the RGB values are directly used as the three components, the color space division unit 6 has various functions for color space division and representative color determination. R value of R is used to reduce the cumulative evaluation value of the distance between the representative color of the partial area to which the color value of the pixel belongs and the color value of the pixel for all pixels.
The GB color space is divided into a predetermined number of partial areas, and a representative color of each partial area is determined. Hereinafter, as in the case of the invention of claim 1 and the invention of claim 2, by using the result of color space division and representative color determination and the original image, a color map is created by the color map creation unit 3 as a color map of each partial region. Generate a correspondence table between serial numbers and representative colors. Based on the result, the subsequent color image conversion unit 4 assigns serial numbers to the partial areas in the divided color space, and replaces each pixel of the input image with the number of the partial area to which it belongs. The compression encoded image thus obtained is obtained.
【００１７】本発明によると、請求項１の発明および請
求項２の発明と同様にして、色の近似の程度が良好で、
高品位の圧縮画像が得られる。請求項４の発明において
も、図１の如くカラー画像入力部１から入力された原カ
ラー画像は、色空間分割部６に送られる。色空間分割部
６は色空間分割、ＲＧＢ変換および代表色決定の諸機能
を内蔵するもので、カラー画像のＲＧＢ値をＹＩＱ色空
間に写像し、写像結果に基づき、全ての画素についてそ
の画素の色値の属する部分領域の代表色と該画素の色値
との距離の評価値の累積が小さくなるように、色空間を
所定の数の複数部分領域に分割し、各部分領域の代表色
を決定する。以下請求項１ないし請求項３の発明と同様
にして、圧縮符号化画像（圧縮された画像）を得る。According to the present invention, similar to the inventions of claim 1 and claim 2, the degree of color approximation is good,
A high-quality compressed image can be obtained. Also in the invention of claim 4, the original color image input from the color image input unit 1 as shown in FIG. 1 is sent to the color space dividing unit 6. The color space division unit 6 has various functions for color space division, RGB conversion, and representative color determination. It maps RGB values of a color image into the YIQ color space, and based on the mapping result, all the pixels are The color space is divided into a predetermined number of partial areas so that the cumulative evaluation value of the distance between the representative color of the partial area to which the color value belongs and the color value of the pixel becomes small, and the representative color of each partial area is divided into decide. Hereinafter, a compression encoded image (compressed image) is obtained in the same manner as the inventions of claims 1 to 3.
【００１８】本発明では、上記の共通の効果のほかに、
ＹＩＱの３成分のうち１つの成分が他の２つに比して少
ない性質を利用して２次元色空間（ＹＩの２次元）に近
似する事が出来るため、より簡便な構成を採ることが可
能という顕著な効果がある。According to the present invention, in addition to the above common effects,
Since one component of the three components of YIQ can be approximated to a two-dimensional color space (two-dimensional of YI) by utilizing the property that one component is smaller than the other two components, a simpler configuration can be adopted. There is a remarkable effect that it is possible.
【００１９】請求項５の発明では、画素の色値の属する
部分領域の代表色と該画素の色値との距離の評価値は画
素の色値の属する部分領域の代表色と該画素の色値との
ユークリッド距離の差値であるが、その他については請
求項１の発明ないし請求項４の発明と全く同様の作用が
期待される。According to the invention of claim 5, the evaluation value of the distance between the representative color of the partial area to which the color value of the pixel belongs and the color value of the pixel is the representative color of the partial area to which the color value of the pixel belongs and the color of the pixel. Although it is a difference value of the Euclidean distance from the value, the same effects as those of the inventions of claims 1 to 4 are expected in other respects.
【００２０】請求項６の発明では、画素の色値の属する
部分領域の代表色と該画素の色値との距離の評価値は画
素の色値の属する部分領域の代表色と該画素の色値との
街区画距離であるが、その他については請求項１の発明
ないし請求項４の発明と全く同様の作用が期待される。According to the invention of claim 6, the evaluation value of the distance between the representative color of the partial area to which the color value of the pixel belongs and the color value of the pixel is the representative color of the partial area to which the color value of the pixel belongs and the color of the pixel. Although it is the distance from the value to the street division, the other operations are expected to be exactly the same as those of the inventions of claims 1 to 4.
【００２１】[0021]
【実施例】図２は本発明の実施例構成図、図４は図２の
処理の流れを示す図である。図２中、１１はＲＧＢ値変
換部で、画像記憶部１２に格納された原画像を読み出
し、ＲＧＢ値を色空間に写像した変換画像を画像記憶部
に格納するもの、１３は色空間分割および代表色決定部
で、画像記憶部に格納された変換画像を読み出し、色空
間に含まれるいかなる画像も、全ての画素についてその
画素の色値の属する部分領域の代表色と該画素の色値と
の距離の評価値の累積が小さくなるように、色空間を所
定の数の複数部分領域に分割し、各部分領域の代表色を
決定し、色空間の分割結果および各領域の代表色を色空
間分割結果および代表色記憶部１４に格納するもの、１
５は画像符号化部で、色空間分割結果および代表色記憶
部１４に格納された色空間の分割結果および各部分領域
の代表色を読み出し、各部分領域に通し番号をつけ、画
像記憶部１２に格納された原画像を読み出し、各画素を
それが属する番号に置き換えるものである。置き換えた
画像は符号化画像として画像記憶部１２に格納し、同時
に、カラーマップとして、各領域の通し番号と代表色の
対応表を生成する。生成したカラーマップは、カラーマ
ップ記憶部１６に格納する。DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 is a block diagram of an embodiment of the present invention, and FIG. 4 is a diagram showing the flow of processing of FIG. In FIG. 2, reference numeral 11 is an RGB value conversion unit, which reads the original image stored in the image storage unit 12 and stores a converted image in which RGB values are mapped in the color space in the image storage unit, and 13 is color space division and The representative color determination unit reads the converted image stored in the image storage unit, and for every image included in the color space, the representative color of the partial area to which the color value of the pixel belongs and the color value of the pixel for all the pixels. The color space is divided into a predetermined number of sub-regions, the representative color of each sub-region is determined, and the color space division result and the representative color of each region are colored so that the cumulative evaluation value of the distance becomes small. What is stored in the space division result and the representative color storage unit 14, 1
An image encoding unit 5 reads out the color space division result and the color space division result stored in the representative color storage unit 14 and the representative color of each partial region, assigns a serial number to each partial region, and stores it in the image storage unit 12. It reads the stored original image and replaces each pixel with the number to which it belongs. The replaced image is stored in the image storage unit 12 as a coded image, and at the same time, a correspondence table of serial numbers of each area and representative colors is generated as a color map. The generated color map is stored in the color map storage unit 16.
【００２２】以下では、色空間への変換の例として３次
元空間の場合と２次元空間の場合について夫々２例、計
４例について実際の変換式を示し、また色空間分割およ
び代表色決定、色空間におけるユークリッド距離の算出
方法、色空間における平均値の算出方法および色空間に
おける分散の算出方法につい例示し、本発明の有効性を
確認した。In the following, as an example of conversion into a color space, actual conversion formulas will be shown for two cases, three cases in the three-dimensional space and two cases in the two-dimensional space, respectively, a total of four cases, color space division and representative color determination, The Euclidean distance calculation method in the color space, the average value calculation method in the color space, and the dispersion calculation method in the color space were illustrated and the effectiveness of the present invention was confirmed.
【００２３】ＲＧＢ値の色空間への変換 〔第１の例〕ＹＩＱの３次元空間への変換の場合 ３次元空間を、互いに直交する３軸（Ｙ軸、Ｉ軸、Ｑ
軸）が成す３次元空間と捉える。本例は請求項４の発明
の第１の具体的実施例であり、図２中のＲＧＢ変換部１
１において変換が行われ、その結果を画像記憶部１２に
格納する。ＲＧＢ値のＹ座標、Ｉ座標、Ｑ座標への変換
は次式を用いておこなう。Conversion of RGB values to color space [First example] Conversion of YIQ to three-dimensional space Three-dimensional space is orthogonal to three axes (Y axis, I axis, Q)
It is regarded as a three-dimensional space formed by the axis. This example is the first specific example of the invention of claim 4, and the RGB conversion unit 1 in FIG.
The conversion is performed in 1 and the result is stored in the image storage unit 12. Conversion of RGB values into Y coordinates, I coordinates, and Q coordinates is performed using the following equation.
【００２４】Ｙ＝0.30×Ｒ＋0.59×Ｇ＋0.11×Ｂ Ｉ＝0.60×Ｒ−0.28×Ｇ−0.32×Ｂ Ｑ＝0.21×Ｒ−0.52×Ｇ＋0.31×Ｂ 〔第２の例〕ＲＧＢの３次元空間への変換の場合 ３次元空間を、互いに直交する３軸（Ｒ軸、Ｇ軸、Ｂ
軸）が成す３次元空間と捉える。本例は請求項３の発明
の具体的実施例であり、この場合、Ｒ座標、Ｇ座標、Ｂ
座標は、ＲＧＢ値をそのまま用いる。 〔第３の例〕ＹＩの２次元空間への変換の場合 色空間を、ＹＩＱ３次元空間を成す互いに直交する３軸
のうち、分布が最も少ない軸（Ｑ軸）を割愛した２軸
（Ｙ軸、Ｉ軸）が成す２次元空間と捉える。請求項４の
発明の第２の具体的実施例である。図２中のＲＧＢ変換
部１１において変換が行われ、その結果を画像記憶部１
２に格納する。ＲＧＢ値のＹ座標、Ｉ座標への変換は次
式を用いておこなう。Y = 0.30 × R + 0.59 × G + 0.11 × BI I = 0.60 × R−0.28 × G−0.32 × B Q = 0.21 × R−0.52 × G + 0.31 × B [Second Example] RGB In the case of conversion to a three-dimensional space The three-dimensional space is divided into three axes (R axis, G axis, B
It is regarded as a three-dimensional space formed by the axis. This example is a concrete example of the invention of claim 3, and in this case, R coordinate, G coordinate, B coordinate
For the coordinates, RGB values are used as they are. [Third example] Conversion of YI to two-dimensional space In the color space, the two axes (Y-axis) with the least distribution among the three axes forming the YIQ three-dimensional space and orthogonal to each other (Q-axis) are omitted. , I-axis). It is a second specific embodiment of the invention of claim 4. The conversion is performed in the RGB conversion unit 11 in FIG. 2, and the result is stored in the image storage unit 1.
2 is stored. Conversion of RGB values into Y coordinates and I coordinates is performed using the following equation.
【００２５】Ｙ＝0.30×Ｒ＋0.59×Ｇ＋0.11×Ｂ Ｉ＝0.60×Ｒ−0.28×Ｇ−0.32×Ｂ 〔第４の例〕ｘｙ２次元空間への変換の場合 色空間を、次式で示す２軸（ｘ軸、ｙ軸）が成す２次元
空間と捉える。請求項１の発明および請求項２の発明の
具体的実施例である。図２中のＲＧＢ変換部１１におい
て変換が行われ、その結果を画像記憶部１２に格納す
る。Y = 0.30 × R + 0.59 × G + 0.11 × B I = 0.60 × R−0.28 × G−0.32 × B [Fourth example] In the case of conversion to an xy two-dimensional space It is regarded as a two-dimensional space formed by the two axes shown (x axis and y axis). It is a concrete embodiment of the invention of claim 1 and the invention of claim 2. Conversion is performed in the RGB conversion unit 11 in FIG. 2, and the result is stored in the image storage unit 12.
【００２６】ｘ＝（Ｒ＋Ｇ＋Ｂ）／３ ｙ＝（Ｒ−Ｂ）／２ 以上の各例においては、以下の手段（手順）を共通して
用いる。 〔第１の手段〕色空間分割および代表色決定の手段 (1) 色空間での画素分布を一つの部分領域とみなす。こ
の部分領域の代表色として該部分領域の平均値を用い
る。 (2) 部分領域数が代表色の所定数と一致するまで、(3)
から(6) まで繰り返す。 (3) 各部分領域毎の画素値と代表色との差を求め、この
差につき分散を求める。 (4) これまでに得られた全ての部分領域の中で (3)で得
られた分散値が最も高い部分領域を２分割の対象として
選択し、２つの部分領域に分割する。そして該部分領域
内でユークリッド距離が最も大きい２色を仮に２分割後
の新しい２つの部分領域のそれぞれの代表色とする。 (5) (4)で得られた２つの部分領域のいずれかに属する
各点は、その点と代表色のうちユークリッド距離が小さ
い方の領域に属しているとみなして、２つの領域それぞ
れの平均値を計算し、それを新しい代表色とする。 (6) (5)における平均値計算後の新しい代表色が平均値
計算前の古い代表色と一致するまで (5)の過程を繰り返
す。 〔第２の手段〕色空間におけるユークリッド距離の算出
方法 (1) 色空間が３次元の場合 ある二つの色Ｃ1 ＝（Ｘ1,Ｙ1,Ｚ1 ）およびＣ2 ＝（Ｘ
2,Ｙ2,Ｚ2 ）の距離ｄは次式により求められる。X = (R + G + B) / 3 y = (RB) / 2 In the above examples, the following means (procedures) are commonly used. [First means] Color space division and representative color determination means (1) The pixel distribution in the color space is regarded as one partial area. The average value of the partial area is used as the representative color of the partial area. (2) Until the number of partial areas matches the specified number of representative colors, (3)
Repeat from to (6). (3) The difference between the pixel value of each partial area and the representative color is obtained, and the variance is obtained from this difference. (4) Of all the partial areas obtained so far, the partial area having the highest variance value obtained in (3) is selected as the target of the two divisions and divided into two partial areas. Then, the two colors having the largest Euclidean distance in the partial area are assumed to be representative colors of the two new partial areas after being divided into two. (5) Each point that belongs to either of the two partial areas obtained in (4) is regarded as belonging to the area with the smaller Euclidean distance of that point and the representative color, and Calculate the average value and use it as the new representative color. (6) The process of (5) is repeated until the new representative color after the average value calculation in (5) matches the old representative color before the average value calculation. [Second means] Calculation method of Euclidean distance in color space (1) Two colors C 1 = (X 1 , Y 1 , Z 1 ) and C 2 = (X
The distance d of ( 2 , Y 2 , Z 2 ) is obtained by the following equation.
【００２７】ｄ＝｛（Ｘ1 −Ｘ2 ）2 ＋（Ｙ1 −Ｙ2 ）
2 ＋（Ｚ1 −Ｚ2 ）2 ｝1/2 (2) 色空間が２次元の場合 ある二つの色Ｃ1 ＝（Ｘ1,Ｙ1 ）およびＣ2 ＝（Ｘ2,Ｙ
2 ）の距離ｄは次式により求められる。D = {(X 1 -X 2 ) 2 + (Y 1 -Y 2 )
2 + (Z 1 -Z 2) 2} 1/2 (2) of the two is when the color space is two-dimensional color C 1 = (X 1, Y 1) and C 2 = (X 2, Y
2 ) The distance d is calculated by the following equation.
【００２８】 ｄ＝｛（Ｘ1 −Ｘ2 ）2 ＋（Ｙ1 −Ｙ2 ）2 ｝1/2 〔第３の手段〕色空間における平均値の算出方法 (1) 色空間が３次元の場合 ある領域に属する色をＣi ＝（Ｘi,Ｙi,Ｚi ）(i=1,N）
（Ｎは自然数）とすると、この領域の平均値Ｃm ＝（Ｘ
m,Ｙm,Ｚm ）は次式により求められる。D = {(X 1 -X 2 ) 2 + (Y 1 -Y 2 ) 2 } 1/2 [Third Means] Calculation Method of Average Value in Color Space (1) Color space is three-dimensional In some cases, a color belonging to a certain area is C i = (X i, Y i, Z i ) (i = 1, N)
(N is a natural number), the average value C m = (X
m, Y m, Z m ) is calculated by the following equation.
【００２９】[0029]
【数１】 [Equation 1]
【００３０】(2) 色空間が２次元の場合 ある領域に属する色をＣi ＝（Ｘi,Ｙi ）(i=1,N）（Ｎ
は自然数）とすると、この領域の平均値Ｃm ＝（Ｘm,Ｙ
m ）は次式により求められる。(2) When the color space is two-dimensional: Colors belonging to a certain area are C i = (X i, Y i ) (i = 1, N) (N
Is a natural number), the average value C m = (X m, Y
m ) is calculated by the following equation.
【００３１】[0031]
【数２】 [Equation 2]
【００３２】〔第４の手段〕色空間における分散の算出
方法 (1) 色空間が３次元の場合 ある領域に属する色をＣi ＝（Ｘi,Ｙi,Ｚi ）(i=1,N）
（Ｎは自然数）、そして、この領域の平均値をＣm ＝
（Ｘm,Ｙm,Ｚm ）とすると、この領域の分散σは次式に
より求められる。[Fourth Means] Calculation Method of Variance in Color Space (1) When Color Space is Three-Dimensional A color belonging to a certain area is C i = (X i, Y i, Z i ) (i = 1, N)
(N is a natural number), and the average value of this region is C m =
Assuming that (X m, Y m, Z m ), the variance σ of this region is obtained by the following equation.
【００３３】[0033]
【数３】 (Equation 3)
【００３４】(2) 色空間が２次元の場合 ある領域に属する色をＣi ＝（Ｘi,Ｙi ）(i=1,N）（Ｎ
は自然数）、そして、この領域の平均値をＣm ＝（Ｘm,
Ｙm ）とすると、この領域の分散σは次式により求めら
れる。(2) When the color space is two-dimensional: Colors belonging to a certain area are C i = (X i, Y i ) (i = 1, N) (N
Is a natural number), and the average value of this region is C m = (X m,
Y m ), the variance σ of this region is obtained by the following equation.
【００３５】[0035]
【数４】 [Equation 4]
【００３６】[0036]
【発明の効果】以上説明した様に、本発明によれば、
(1) 画像の全ての画素についてその画素の色値の属する
部分領域の代表色と該画素の色値との距離の評価値の累
積を考慮するので、画像の全体にわたって均一に画質を
保持するカラーマップを決定することができ、(2) 画像
のすべての点を同時に考慮して代表色を決定するので、
一枚の画像につきただ一つのみカラーマップを設定でき
る。As described above, according to the present invention,
(1) For all pixels of the image, the cumulative evaluation value of the distance between the representative color of the partial area to which the color value of the pixel belongs and the color value of the pixel is considered, so that the image quality is uniformly maintained over the entire image. Since the color map can be determined, and (2) the representative color is determined by simultaneously considering all points of the image,
Only one color map can be set per image.
【００３７】その結果、カラー画像（例えば、１６７７
７２１６色のフルカラー）の原画を従来の方法よりも自
然に疑似カラー（例えば２５６色）に圧縮する事が出
来、既存の設備の有効利用を図ることが出来る。As a result, a color image (eg, 1677)
The original image of 7216 full colors can be compressed into a pseudo color (for example, 256 colors) more naturally than the conventional method, and the existing equipment can be effectively used.
【図１】 本発明の原理説明図である。FIG. 1 is a diagram illustrating the principle of the present invention.
【図２】 本発明の実施例構成図である。FIG. 2 is a configuration diagram of an embodiment of the present invention.
【図３】 処理の流れ１である。FIG. 3 is a process flow 1;
【図４】 処理の流れ２である。FIG. 4 is a process flow 2;
【図５】 従来技術の構成１である。FIG. 5 is Configuration 1 of the related art.
【図６】 従来技術の構成２である。FIG. 6 is a configuration 2 of the related art.
１ カラー画像入力部 ２ 出現色頻度計数部 ３ カラーマップ作成部 ４ カラー画像変換部 ５ 画像分割部 ６ 色空間分割部 １１ ＲＧＢ値変換部 １２ 画像記憶部 １３ 色空間分割および代表色決定部 １４ 色空間分割結果および代表色記憶部 １５ 画像符号化部 １６ カラーマップ記憶部 1 Color Image Input Unit 2 Appearance Color Frequency Counting Unit 3 Color Map Creating Unit 4 Color Image Converting Unit 5 Image Dividing Unit 6 Color Space Dividing Unit 11 RGB Value Converting Unit 12 Image Storage Unit 13 Color Space Dividing and Representative Color Determining Unit 14 Colors Space division result and representative color storage unit 15 Image encoding unit 16 Color map storage unit
───────────────────────────────────────────────────── フロントページの続き (51)Int.Cl.6 識別記号 庁内整理番号 ＦＩ 技術表示箇所 Ｇ０９Ｇ 5/06 9377−5Ｈ Ｈ０４Ｎ 1/41 Ｃ Ｇ０６Ｆ 15/66 ３３０ Ｂ ─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. 6 Identification code Office reference number FI Technical display location G09G 5/06 9377-5H H04N 1/41 C G06F 15/66 330 B
Claims (6)
数の複数部分領域に分割し、該部分領域に属する色値を
該部分領域毎に定めた代表色に変換するカラー画像圧縮
方法であって、 前記カラー画像中の各画素についてその画素の色値の属
する部分領域の代表色と該画素の色値との距離の評価値
を求め、前記カラー画像中の全画素の該評価値を累積し
て求まる累積値が小さくなるように色空間を部分領域に
分割していくことを特徴とするカラー画像圧縮方法。1. A color image compression method for dividing a color space of a color image into a plurality of partial areas corresponding to a representative color and converting a color value belonging to the partial area into a representative color defined for each partial area. Then, for each pixel in the color image, an evaluation value of the distance between the representative color of the partial area to which the color value of the pixel belongs and the color value of the pixel is obtained, and the evaluation values of all the pixels in the color image are calculated. A color image compression method, characterized in that a color space is divided into partial areas so that a cumulative value obtained by cumulatively becomes small.
の代表色は該部分領域の平均値を用い、以下、各部分領
域毎の画素値と代表色との距離の評価値を求めて、該評
価値の分散を計算し、分散の大きい部分領域を選択し、
該選択された部分領域を２分割してそれぞれの代表色を
決定し、該２分割により増加した後の部分領域の数が所
定数になるまで、毎回全部分領域を対象に、領域の分割
と代表色の決定を繰り返すことを特徴とするカラー画像
圧縮方法。2. The first partial area to be divided is the entire color space, the representative color of the partial area is an average value of the partial areas, and the pixel value and the representative color of each partial area are described below. The evaluation value of the distance between and is calculated, the variance of the evaluation value is calculated, and the partial area with a large variance is selected,
The selected partial area is divided into two to determine the respective representative colors, and the area division is performed for all the partial areas each time until the number of partial areas increased by the two divisions reaches a predetermined number. A color image compression method characterized by repeating determination of a representative color.
するカラー画像圧縮方法。3. The color image compression method according to claim 1 or 2, wherein the color space of the color image is an RGB color space.
空間であることを特徴とするカラー画像圧縮方法。4. The color image compression method according to claim 1, wherein the color space of the color image is a YIQ color space or a YI two-dimensional color space.
いて、 画素の色値の属する部分領域の代表色と該画素の色値と
の距離の評価値は画素の色値の属する部分領域の代表色
と該画素の色値とのユークリッド距離の差値であること
を特徴とするカラー画像圧縮方法。5. The evaluation value of the distance between the representative color of the partial area to which the color value of the pixel belongs and the color value of the pixel is the partial area to which the color value of the pixel belongs, according to any one of claims 1 to 4. A color image compression method, which is a difference value of a Euclidean distance between a representative color and a color value of the pixel.
いて、 画素の色値の属する部分領域の代表色と該画素の色値と
の距離の評価値は画素の色値の属する部分領域の代表色
と該画素の色値との街区画距離であることを特徴とする
カラー画像圧縮方法。6. The evaluation value of the distance between the representative color of the partial area to which the color value of the pixel belongs and the color value of the pixel is the partial area to which the color value of the pixel belongs. A color image compression method, which is a city block distance between a representative color and a color value of the pixel.
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|---|---|---|---|
| JP25178194A JP3674965B2 (en) | 1994-10-18 | 1994-10-18 | Color image compression method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP25178194A JP3674965B2 (en) | 1994-10-18 | 1994-10-18 | Color image compression method |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH08115405A true JPH08115405A (en) | 1996-05-07 |
| JP3674965B2 JP3674965B2 (en) | 2005-07-27 |
Family
ID=17227835
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP25178194A Expired - Fee Related JP3674965B2 (en) | 1994-10-18 | 1994-10-18 | Color image compression method |
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| Country | Link |
|---|---|
| JP (1) | JP3674965B2 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009001549A1 (en) * | 2007-06-28 | 2008-12-31 | Konica Minolta Business Technologies, Inc. | Image processing method, image processing device, image data compressing device and computer program |
| JP2010074406A (en) * | 2008-09-17 | 2010-04-02 | Konica Minolta Business Technologies Inc | Image processing method, image processing apparatus, and image processing program |
-
1994
- 1994-10-18 JP JP25178194A patent/JP3674965B2/en not_active Expired - Fee Related
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009001549A1 (en) * | 2007-06-28 | 2008-12-31 | Konica Minolta Business Technologies, Inc. | Image processing method, image processing device, image data compressing device and computer program |
| JP4831233B2 (en) * | 2007-06-28 | 2011-12-07 | コニカミノルタビジネステクノロジーズ株式会社 | Image processing method, image processing apparatus, image data compression apparatus, and computer program |
| US8320669B2 (en) | 2007-06-28 | 2012-11-27 | Konica Minolta Business Technologies, Inc. | Image processing method, image processing apparatus, image data compression device, and computer program |
| JP2010074406A (en) * | 2008-09-17 | 2010-04-02 | Konica Minolta Business Technologies Inc | Image processing method, image processing apparatus, and image processing program |
| US8306321B2 (en) | 2008-09-17 | 2012-11-06 | Konica Minolta Business Technologies, Inc. | Image processing method of compressing image data to be suitable for data transmission |
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