JPH09312777A - Color information conversion processing method - Google Patents
Color information conversion processing methodInfo
- Publication number
- JPH09312777A JPH09312777A JP8123701A JP12370196A JPH09312777A JP H09312777 A JPH09312777 A JP H09312777A JP 8123701 A JP8123701 A JP 8123701A JP 12370196 A JP12370196 A JP 12370196A JP H09312777 A JPH09312777 A JP H09312777A
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- Japan
- Prior art keywords
- color
- lightness
- reproduction
- reproduced
- brightness
- Prior art date
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- Color Image Communication Systems (AREA)
- Image Processing (AREA)
- Facsimile Image Signal Circuits (AREA)
Abstract
Description
【０００１】[0001]
【発明が属する技術分野】本発明は異なる色再現範囲を
有するＣＲＴやカラープリンタ，カラーコピーなどのデ
バイス間において，カラー画像情報を移転する色情報変
換処理方法に係り，より詳細には，人間の視覚特性が彩
度差よりも明度差に敏感であることに注目し，被出力画
像の非再現色を再現可能な色に変換すると共に，階調つ
ぶれの発生を回避する色情報変換処理方法に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color information conversion processing method for transferring color image information between devices such as CRTs, color printers and color copiers having different color reproduction ranges. Focusing on the fact that the visual characteristics are more sensitive to the difference in lightness than to the difference in saturation, the present invention relates to a color information conversion processing method for converting a non-reproduced color of an output image into a reproducible color and avoiding the occurrence of gradation loss. .
【０００２】[0002]
【従来の技術】近年，カラー画像を扱うメディアは様々
な形態で発達してきている。たとえば，カラースキャナ
により文字・画像を読み取り，コンピュータのディスプ
レイ上で編集・加工し，その結果をカラープリンタなど
によりプリント出力するシステムがよく知られている。
しかし，この場合，ディスプレイ上で再現される色とプ
リント出力される色とは色再現の方法や混色系（ＲＧ
Ｂ，ＹＭＣ）の違い，および色再現範囲の不一致により
相互に異なる色となることもよく知られていることであ
る。2. Description of the Related Art In recent years, media handling color images have been developed in various forms. For example, there is well known a system in which a character or image is read by a color scanner, edited and processed on a computer display, and the result is printed out by a color printer or the like.
However, in this case, the color reproduced on the display and the color printed out are determined by a color reproduction method or a mixed color system (RG
(B, YMC), and the fact that colors differ from each other due to the mismatch of color reproduction ranges.
【０００３】このように，通常，デバイスが表現可能な
色の再現範囲はそれぞれ異なっているため，入力された
色のうち画像出力装置では出力できない色を再現可能な
色に置き換えて変換する，いわゆるカラー・ガマット圧
縮処理を行っている。As described above, since the gamut of colors that can be expressed by a device is usually different from each other, of the input colors, colors that cannot be output by an image output device are replaced with reproducible colors and converted. Performs color gamut compression processing.
【０００４】ところが，一般的に，被出力画像に非再現
色を含む場合，非再現色の周辺の色にかかわらず上記圧
縮処理がなされる。そのため，非再現色の周辺と同じ色
に再現される場合があり，その結果，階調つぶれが発生
することがあった。However, in general, when a non-reproduced color is included in an output image, the above-described compression processing is performed irrespective of colors around the non-reproduced color. Therefore, the same color as the periphery of the non-reproduced color may be reproduced, and as a result, gradation gradation may be generated.
【０００５】そこで従来は，たとえば特公平６−３６５
４８号公報の「カラー画像信号処理方法」に開示されて
いるように，明度および彩度の双方について入力カラー
画像信号によって表現される画像の特徴に適した圧縮割
合を決定し，明度および彩度の階調を保存するように出
力系の色再現範囲内に圧縮・写像を行っている。Therefore, conventionally, for example, Japanese Patent Publication No. 6-365
As disclosed in “Color Image Signal Processing Method” of JP-A-48-48, a compression ratio suitable for the characteristics of an image represented by an input color image signal is determined for both lightness and saturation, and the lightness and saturation are determined. Compression and mapping within the color reproduction range of the output system so as to preserve the gradation of
【０００６】また，上記の他に，特開昭６１−２８８６
９０号公報の「カラー画像処理方法」では，色度図上の
白色点を中心として色相を一定とし，出力系の色再現範
囲外の点を出力系の色再現範囲内に圧縮・写像を行うも
のが開示されている。[0006] In addition to the above, JP-A-61-2886.
In the "color image processing method" disclosed in Japanese Patent Publication No. 90, a hue is fixed around a white point on a chromaticity diagram, and points outside the color reproduction range of the output system are compressed and mapped within the color reproduction range of the output system. Things are disclosed.
【０００７】さらに，特開平４−２８４５７９号公報の
「カラー画像の処理方法およびその装置」では，カラー
画像情報を明度，彩度および色相に応じてコード化し，
出力系の色再現範囲外の色を色再現範囲の外縁部に変換
するものが開示されている。Further, in Japanese Patent Application Laid-Open No. 4-284579, "Color Image Processing Method and Apparatus", color image information is coded according to lightness, saturation and hue,
There is disclosed one that converts a color outside the color reproduction range of the output system to the outer edge of the color reproduction range.
【０００８】また，図９に従来における非再現色の圧縮
方法を示す。一般的には，再現範囲の境界線に対する圧
縮角度（θ）を決め，その方向に向けて圧縮する方法
（１）と，白色点に向けて圧縮する方法（２）とがあ
る。FIG. 9 shows a conventional non-reproduction color compression method. Generally, there are a method (1) of determining a compression angle (θ) with respect to the boundary line of the reproduction range and compressing in that direction, and a method (2) of compressing toward the white point.
【０００９】[0009]
【発明が解決しようとする課題】しかしながら，上記に
示されるような従来の特公平６−３６５４８号公報や特
開昭６１−２８８６９０号公報にあっては，いずれも階
調つぶれを解消するものであるが，被出力画像の非再現
色を再現可能な色に変換するだけでなく再現可能な被出
力画像の色に対しても変換処理がなされるため，被出力
画像とは異なった色に再現されてしまう場合が生じると
いう問題点があった。However, the conventional Japanese Patent Publication No. 6-36548 and the Japanese Patent Application Laid-Open No. 61-288690 described above all dissolve gradation loss. However, since not only the non-reproduced colors of the output image are converted into reproducible colors but also the colors of the reproducible output image are converted, they are reproduced in colors different from the output image. However, there is a problem that the operation may be performed.
【００１０】また，特開平４−２８４５７９号公報のよ
うに非再現色を画像出力系の再現可能な範囲の境界線上
の様々な色に置き換えて変換しているが，望ましい圧縮
方向を決める根拠が必ずしも明確でない。また，明度の
異なる非再現色が存在する場合でも，圧縮方向が同じで
あれば階調つぶれが生じる。さらに圧縮方向が同じであ
るので，非再現色の位置によっては明度が逆転するとい
う問題点があった。Further, as in Japanese Unexamined Patent Publication No. 4-284579, the non-reproduced color is replaced with various colors on the boundary line of the reproducible range of the image output system for conversion, but there is a basis for determining a desirable compression direction. Not always clear. Further, even if there are non-reproduced colors having different lightness, gradation collapse occurs if the compression direction is the same. Further, since the compression direction is the same, there is a problem that the brightness is reversed depending on the position of the non-reproduced color.
【００１１】これ図９を用いて説明すると，ａ，ｂ，ｃ
をそれぞれ非再現色の明度，ａ’，ｂ’，ｃ’を再現先
の色の明度とした場合，ａ＞ｂ，ａ＝ｃ，ｃ＞ｂであれ
ば，ａ’＝ｂ’，ａ’＞ｃ’，ｂ’＞ｃ’というように
ａ，ｂ，ｃの間にあった階調差（明度）の関係が変化し
てしまうことが分かる。This will be described with reference to FIG. 9. a, b, c
Where a is the lightness of the non-reproduced color and a ′, b ′, c ′ are the lightnesses of the colors to be reproduced, if a> b, a = c, c> b, then a ′ = b ′, a ′ It can be seen that the relationship of gradation difference (brightness) between a, b, and c changes such that> c ′, b ′> c ′.
【００１２】本発明は，上記に鑑みてなされたものであ
って，人間の眼の知覚特性は彩度差よりも明度差に敏感
であることに注目し，被出力画像の非再現色を再現可能
な色に変換し，かつ，階調つぶれの発生を回避すること
を目的とする。The present invention has been made in view of the above, and pays attention to the fact that the human eye's perceptual characteristics are more sensitive to the lightness difference than the saturation difference, and reproduce the non-reproduced color of the output image. The purpose is to convert to a possible color and to avoid the occurrence of gradation loss.
【００１３】[0013]
【課題を解決するための手段】上記の目的を達成するた
めに，請求項１に係る色情報変換処理方法にあっては，
画像情報のうち少なくとも一部が画像出力系の色再現範
囲では再現されない非再現色である場合に，前記非再現
色を画像出力系の再現可能な色に変換する色情報変換処
理方法において，着目画素が前記画像出力系の色再現範
囲の内側か否かを判断する判断ステップと，前記判断ス
テップで色再現範囲の内側であると判断された色情報
を，色再現範囲の内側の元の色で出力し，色再現範囲の
外側であると判断された色情報を，元の色の明度情報に
より一義的に決定される明度差を用いて色再現範囲の境
界線上の色に変換して出力する色情報変換ステップとを
含むものである。According to a first aspect of the present invention, there is provided a color information conversion processing method.
In the color information conversion processing method for converting the non-reproducible color into a reproducible color of the image output system when at least part of the image information is a non-reproduced color that cannot be reproduced in the color reproduction range of the image output system, The determination step of determining whether or not the pixel is inside the color reproduction range of the image output system, and the color information determined to be inside the color reproduction range in the determination step are the original color inside the color reproduction range. The color information determined to be outside the color reproduction range is converted to a color on the boundary line of the color reproduction range by using the brightness difference uniquely determined by the brightness information of the original color and output. And a color information conversion step.
【００１４】すなわち，非再現色を再現範囲の境界線上
の色に割り当てるとき，非再現色と再現先の色との明度
差が最も影響されていることに注目し，再現可能な被出
力画像の色をそのまま出力し，非再現色を，元の色の明
度によって一義的に決定される明度差を用いて望ましい
色に変換することにより，圧縮による階調つぶれが回避
され，さらに明度の逆転が生じることなく，忠実な色再
現が実現すると共に，非再現色の明度だけで，再現先の
色が容易に求められる。That is, when allocating the non-reproduction color to the color on the boundary line of the reproduction range, paying attention to the fact that the difference in brightness between the non-reproduction color and the color of the reproduction destination is most affected, and the reproducible output image is reproduced. By outputting the color as it is and converting the non-reproduced color into the desired color by using the brightness difference that is uniquely determined by the brightness of the original color, gradation collapse due to compression is avoided and further brightness reversal occurs. A faithful color reproduction is realized without any occurrence, and the color of the reproduction destination is easily obtained only by the brightness of the non-reproduction color.
【００１５】また，請求項２に係る色情報変換処理方法
にあっては，前記色情報変換ステップは，望ましい圧縮
方向になるように明度差制御の調整を決定する明度差調
整の決定ステップと，同一色相で再現範囲の境界線上の
色を決定し，変換色とする変換色決定ステップとを含む
ものである。Further, in the color information conversion processing method according to the second aspect, the color information conversion step includes a lightness difference adjustment determining step for determining lightness difference control adjustment so that a desired compression direction is obtained, And a conversion color determining step of determining a color on the boundary line of the reproduction range with the same hue and setting it as a conversion color.
【００１６】すなわち，同一色相で連続した非再現色を
再現範囲の境界線上に割り当てる主観評価の結果に基づ
いて，望ましい圧縮方向を明確にし，かつ，元の色の明
度から一定の割合で調整・圧縮し，望ましい色に変換す
ることにより，再現先の色が白っぽくなりすぎず，自然
な再現が行える。That is, the desired compression direction is clarified based on the result of the subjective evaluation in which continuous non-reproduction colors of the same hue are assigned on the boundary line of the reproduction range, and the brightness of the original color is adjusted at a constant ratio. By compressing and converting to the desired color, the reproduction destination color does not become too whitish and natural reproduction is possible.
【００１７】また，請求項３に係る色情報変換処理方法
にあっては，前記明度差調整の決定ステップは，元の色
の明度が色再現範囲の境界線の頂点の明度に対し，高い
か低いかを比較する非再現色の明度比較ステップと，前
記明度比較ステップで比較された結果に基づいて元の色
と変換後の色との明度差を調整する方向を異ならせる明
度差の方向決定ステップとを含み，元の色の明度の分布
により圧縮方向を異ならせて境界線上の色を変換するも
のである。Further, in the color information conversion processing method according to the third aspect, in the lightness difference adjustment determining step, whether the lightness of the original color is higher than the lightness of the apex of the boundary line of the color reproduction range. Lightness comparison step for comparing non-reproduced colors, and lightness difference direction determination that makes different directions for adjusting the lightness difference between the original color and the converted color based on the result compared in the lightness comparison step. Including the steps, the color on the boundary line is converted by changing the compression direction according to the distribution of the brightness of the original color.
【００１８】すなわち，元の色の明度の分布に基づいて
圧縮方向を異ならせて色変換を行うことにより，精度の
高い再現を行う。That is, highly accurate reproduction is performed by performing color conversion by changing the compression direction based on the distribution of lightness of the original color.
【００１９】[0019]
【発明の実施の形態】以下，本発明の実施の形態を添付
図面を参照して説明する。BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.
【００２０】〔実施の形態〕 （主観評価実験）まず，図１〜図３を用いて主観評価実
験について説明する。図１は，主観評価実験における任
意の非再現色の連続するカラーパッチの明度の位置や非
再現色の再現された色の圧縮方向を示す説明図，図２
は，図１のような連続したカラーパッチを用いて，主観
評価による非再現色の再現結果から回帰分析した結果を
示すグラフ，図３は，後述する（Ａ）式に基づいて処理
された結果として，非再現色から再現された色の圧縮方
向を示す説明図である。[Embodiment] (Subjective Evaluation Experiment) First, a subjective evaluation experiment will be described with reference to FIGS. FIG. 1 is an explanatory diagram showing the lightness position of a continuous color patch of an arbitrary non-reproduced color and the compression direction of a reproduced color of a non-reproduced color in a subjective evaluation experiment.
Is a graph showing the result of regression analysis from the reproduction result of the non-reproduction color by subjective evaluation using the continuous color patches as shown in FIG. 1, and FIG. 3 is the result processed based on the formula (A) described later. FIG. 3 is an explanatory diagram showing a compression direction of a color reproduced from a non-reproduction color.
【００２１】ここで，上記各図に示す符号について説明
する。 Ｌ１：同一色相で非再現色である任意の連続したパラー
パッチ ｐ１〜ｐ６：パッチの明度であり，パッチ間はそれぞれ
均一である Ｌ２：同一色相で再現範囲の境界線上色で主観によって
元の色とを比較して決定されたカラーパッチｐ１’〜ｐ
６’：再現されたパッチの明度 ＧＰ：画像出力系の再現範囲の頂点の明度The symbols shown in the above figures will now be described. L1: arbitrary continuous para patches having the same hue and non-reproducible colors p1 to p6: lightness of the patches and uniform between the patches L2: the same hue and a color on the boundary line of the reproduction range, which is subjectively different from the original color The color patches p1 ′ to p determined by comparing
6 ': the brightness of the reproduced patch GP: the brightness of the apex of the reproduction range of the image output system
【００２２】また，図２に示す諸条件は以下の通りであ
る。 （１）実験データ：同一色相で非再現色である任意の連
続したカラーパッチの再現結果８５サンプル （２）説明変数：横軸（Ｌ１）：元の色の明度値 （３）目的変数：縦軸（Ｌ２）：再現先の明度値 （４）回帰分析結果の寄与率：０．９７６ （５）回帰式：Ｌ２＝０．９６×Ｌ１＋０．６The conditions shown in FIG. 2 are as follows. (1) Experimental data: Reproduction results of arbitrary continuous color patches of the same hue and non-reproduction colors 85 samples (2) Explanatory variable: Horizontal axis (L1): Lightness value of original color (3) Objective variable: Vertical Axis (L2): Lightness value of reproduction destination (4) Contribution rate of regression analysis result: 0.976 (5) Regression formula: L2 = 0.96 × L1 + 0.6
【００２３】望ましい圧縮方向を推定するために，同一
色相で，非再現色であり任意の連続するカラーパッチの
各色（図１のＬ１：ｐ１〜ｐ６）を，それぞれ画像出力
系の色再現範囲の境界線上のどの色に変換するか（図１
のＬ２：ｐ１’〜ｐ６’），主観評価に基づいて実験を
行った。In order to estimate the desired compression direction, each color (L1: p1 to p6 in FIG. 1) of an arbitrary continuous color patch which has the same hue but is a non-reproducible color is set in the color reproduction range of the image output system. Which color on the border should be converted (Fig. 1
L2: p1 ′ to p6 ′), an experiment was performed based on the subjective evaluation.
【００２４】この主観評価実験の結果によると，図３に
示すように望ましい圧縮方向は，明度の低い部分から高
い部分に向けて明度差を徐々に上げるものであった。According to the result of this subjective evaluation experiment, as shown in FIG. 3, the desirable compression direction is such that the brightness difference gradually increases from the low brightness part to the high brightness part.
【００２５】なお，図３において， ｐ１＞ｐ６のとき，ｐ１’＝Ｃ×ｐ１＋Ｄ ・・・ ・・・ ｐ６’＝Ｃ×ｐ６＋Ｄ ｐｐ１＞ｐｐ６のとき，ｐｐ１’＝Ｃ×ｐｐ１＋Ｄ ・・・ ・・・ ｐｐ６’＝Ｃ×ｐｐ６＋Ｄ したがって，明度差は， ｐ１−ｐ１’＞ｐ６−ｐ６’＞ｐｐ１−ｐｐ１’＞ｐｐ
６−ｐｐ６’ となる。In FIG. 3, when p1> p6, p1 '= C * p1 + D ... P6' = C * p6 + D When pp1> pp6, pp1 '= C * pp1 + D ... -Pp6 '= C * pp6 + D Therefore, the brightness difference is p1-p1'> p6-p6 '>pp1-pp1'> pp
6-pp6 '.
【００２６】また，実験値の回帰分析の結果，図２のグ
ラフから圧縮前後の明度差によって，次に示すような単
純な一次相関関係で表せることが分かった。ただし，明
度は白の明度値を１００として正規化した値を用いる。As a result of the regression analysis of the experimental values, it was found from the graph of FIG. 2 that the difference in brightness before and after compression can be expressed by the following simple linear correlation. However, as the lightness, a value obtained by normalizing the white lightness value to 100 is used.
【００２７】すなわち， 望ましい再現先の色の明度＝０．９６×元の色の明度＋
０．６ となり，以下のような式（Ａ）で表すことができる。That is, the brightness of the desired reproduction destination color = 0.96 × the brightness of the original color +
It becomes 0.6 and can be expressed by the following expression (A).
【００２８】 望ましい再現先の色の明度＝Ｃ×元の色の明度＋Ｄ ・・・（Ａ） ただし，Ｃ，Ｄは定数である。Desirable lightness of color to be reproduced = C × lightness of original color + D (A) where C and D are constants.
【００２９】次に，実施の形態の処理動作をフローチャ
ートに基づいて（処理動作例１），（処理動作例２），
（処理動作例３）の順に説明する。Next, the processing operation of the embodiment will be described based on the flowcharts (processing operation example 1), (processing operation example 2),
A description will be given in order of (Processing operation example 3).
【００３０】（処理動作例１）図４は，実施の形態の処
理動作例１を示すフローチャートである。図４におい
て，この色再現処理は以下に示す手順で行われる。(Processing operation example 1) FIG. 4 is a flowchart showing a processing operation example 1 of the embodiment. In FIG. 4, this color reproduction processing is performed by the following procedure.
【００３１】まず，画像色情報を入力し（Ｓ４０１），
該画像色情報を，たとえばＬａｂ座標値に変換する（Ｓ
４０２）。続いて，非再現色であるか否かを判断する
（Ｓ４０３）。ここで非再現色であると判断した場合，
同一色相で元の色の明度より一義的に決定される明度差
を用いて変換後の色情報を決定し，再現範囲の境界線上
にある色を求める（Ｓ４０４）。First, image color information is input (S401),
The image color information is converted into, for example, Lab coordinate values (S
402). Then, it is determined whether or not the color is a non-reproduction color (S403). If it is determined that the color is a non-reproduction color,
The color information after conversion is determined using the lightness difference that is uniquely determined from the lightness of the original color in the same hue, and the color on the boundary line of the reproduction range is obtained (S404).
【００３２】一方，上記ステップＳ４０３において，非
再現色ではないと判断した場合，色再現処理を行わず，
画像出力系に出力できる色情報に変換する（Ｓ４０
５）。また，上記ステップＳ４０４を実行した後にも，
このステップＳ４０５を実行する。On the other hand, when it is determined in step S403 that the color is not a non-reproduction color, color reproduction processing is not performed,
Convert to color information that can be output to the image output system (S40
5). In addition, even after performing the above step S404,
This step S405 is executed.
【００３３】（処理動作例２）図５は，実施の形態の処
理動作例２を示すフローチャートである。ここでは，明
度差制御の調整を決定するために，前述の図４のステッ
プＳ４０４における処理を以下のように実行する。(Processing operation example 2) FIG. 5 is a flowchart showing a processing operation example 2 of the embodiment. Here, in order to determine the adjustment of the brightness difference control, the above-described processing in step S404 of FIG. 4 is executed as follows.
【００３４】まず，定数Ｃ，Ｄの値を，前述の（Ａ）式
に代入し，再現先の明度Ｌ２を求める（Ｓ５０１）。こ
れにより，図２に示すような圧縮方向となる。たとえ
ば，既に述べたように，主観評価実験の回帰分析で得ら
れた図２のグラフにより， Ｃ＝０．９６，Ｄ＝０．６ を代入する。First, the values of the constants C and D are substituted into the above equation (A) to obtain the lightness L2 of the reproduction destination (S501). As a result, the compression direction is as shown in FIG. For example, as described above, C = 0.96, D = 0.6 is substituted by the graph of FIG. 2 obtained by the regression analysis of the subjective evaluation experiment.
【００３５】次に，色再現範囲の境界線上のＬ２の色座
標を求める（Ｓ５０２）。これにより，望ましい再現
色，たとえば（Ｌ２，ａ２，ｂ２）が求まる。Next, the color coordinates of L2 on the boundary line of the color reproduction range are obtained (S502). As a result, a desired reproduction color, for example, (L2, a2, b2) is obtained.
【００３６】（処理動作例３）図６は，実施の形態の処
理動作例３を示すフローチャートである。ここでは，非
再現色の明度の位置によって明度差制御の調整を異なら
せるため，前述の図５のステップＳ５０１における処理
を以下のように実行する。(Processing operation example 3) FIG. 6 is a flowchart showing a processing operation example 3 of the embodiment. Here, in order to vary the adjustment of the lightness difference control depending on the lightness position of the non-reproduced color, the processing in step S501 of FIG. 5 described above is executed as follows.
【００３７】まず，非再現色の明度（Ｌ）と再現範囲の
頂点の明度（ＧＰ）とを比較し，ＧＰ＞Ｌである（ＧＰ
よりＬが高い）か否かを判断する（Ｓ６０１）。ここで
ＧＰ＞Ｌであると判断した場合，定数Ｃ１，Ｄ１を
（Ａ）式に代入し，再現先の明度Ｌ２を求める（Ｓ６０
２）。First, the lightness (L) of the non-reproduced color is compared with the lightness (GP) of the apex of the reproduction range, and GP> L (GP)
It is determined whether or not L is higher (S601). If it is determined that GP> L, the constants C1 and D1 are substituted into the expression (A) to obtain the lightness L2 of the reproduction destination (S60).
2).
【００３８】これにより，図７のｐ１→ｐ１’，ｐ６→
ｐ６’というような圧縮方向となる。たとえば，定数を
Ｃ１＝０．９６，Ｄ１＝０．０とすると， Ｌ２＝０．９６×Ｌ＋０．０ （Ｌは元の色の明度）となる。As a result, p1 → p1 ', p6 → in FIG.
The compression direction is p6 '. For example, if the constants are C1 = 0.96 and D1 = 0.0, then L2 = 0.96 × L + 0.0 (L is the lightness of the original color).
【００３９】一方，上記ステップＳ６０１において，Ｇ
Ｐ＞Ｌではない（ＧＰよりＬが低い）と判断した場合，
明度が高い場合の定数Ｃ１，Ｄ１とは異なる定数Ｃ２，
Ｄ２を（Ａ）式に代入し，再現先の明度Ｌ２を求める
（Ｓ６０３）。On the other hand, in step S601, G
If it is judged that P> L is not satisfied (L is lower than GP),
A constant C2 different from the constants C1 and D1 when the brightness is high
Substituting D2 into the equation (A), the lightness L2 of the reproduction destination is obtained (S603).
【００４０】これにより，図７のｐｐ１→ｐｐ１’，ｐ
ｐ６→ｐｐ６’というような圧縮方向となる。たとえ
ば，定数をＣ２＝１．０，Ｄ２＝０．０とすると， Ｌ２＝１．０×Ｌ＋０．０ （Ｌは元の色の明度）となる。As a result, pp1 → pp1 ', p in FIG.
The compression direction is p6 → pp6 ′. For example, if the constants are C2 = 1.0 and D2 = 0.0, then L2 = 1.0 × L + 0.0 (L is the lightness of the original color).
【００４１】なお，図７において，Ｃ１，Ｃ２は任意，
ただしＣ１≠Ｃ２ ＧＰ＞ｐ１，ｐ６で，ｐ１＞ｐ６のとき， ｐ１’＝Ｃ１×ｐ１＋Ｄ１ ・・・ ・・・ ｐ６’＝Ｃ１×ｐ６＋Ｄ１ で，明度差は，ｐ１−ｐ１’＞ｐ６−ｐ６’ となり，
ＧＰ＞ｐｐ１，ｐｐ６で，ｐｐ１＞ｐｐ６のとき， ｐｐ１’＝Ｃ２×ｐｐ１＋Ｄ２ ・・・ ・・・ ｐｐ６’＝Ｃ２×ｐｐ６＋Ｄ２ で，明度差は，ｐｐ１−ｐｐ１’＞ｐｐ６’−ｐｐ６
となる。In FIG. 7, C1 and C2 are arbitrary,
However, when C1 ≠ C2 GP> p1, p6 and p1> p6, p1 ′ = C1 × p1 + D1 ... P6 ′ = C1 × p6 + D1 and the difference in brightness is p1-p1 ′> p6-p6 ′ Next to
When GP> pp1 and pp6 and pp1> pp6, pp1 ′ = C2 × pp1 + D2 ...
Becomes
【００４２】すなわち，非再現色の明度によって，同一
色相で再現範囲の境界線上の色に圧縮されることが，上
記処理動作の特徴となる部分である。That is, it is a feature of the above processing operation that the color is compressed into a color on the boundary line of the reproduction range with the same hue depending on the brightness of the non-reproduction color.
【００４３】（実施の形態の効果）次に，以上説明した
実施の形態が奏する効果について列記する。(Effects of the Embodiment) Next, the effects of the above-described embodiment will be listed.
【００４４】第１に，図４の処理動作例１で述べたよう
に非再現色の圧縮前後の明度差に注目して処理を行って
いるので，圧縮による階調つぶれが回避される。さらに
明度の逆転が生じることなく，忠実な色再現が実現す
る。また，非再現色の明度だけで，再現先の色を容易に
求めることができる。この本発明による方式を図８に示
す。First, as described in the processing operation example 1 of FIG. 4, since the processing is performed paying attention to the difference in brightness before and after the compression of the non-reproduced color, the gradation loss due to the compression can be avoided. In addition, faithful color reproduction is achieved without inversion of brightness. Further, the color of the reproduction destination can be easily obtained only by the brightness of the non-reproduction color. This method according to the present invention is shown in FIG.
【００４５】すなわち，図８において，ａ，ｂ，ｃをそ
れぞれ非再現色の明度，ａ’，ｂ’，ｃ’を再現先の色
の明度とした場合，ａ＞ｂ，ａ＝ｃ，ｃ＞ｂであれば，
ａ’＞ｂ’，ａ’＝ｃ’，ｃ’＞ｂ’というようにａ，
ｂ，ｃの間にあった階調差（明度）の関係が保持されて
いることが分かる。また，ａとｃとの彩度差はあまり感
じられないため，ａ’＝ｃ’が成り立つ。That is, in FIG. 8, when a, b, and c are lightnesses of non-reproduced colors and a ′, b ′, and c ′ are lightnesses of reproduced colors, a> b, a = c, c > B,
a '>b', a '= c', c '>b',
It can be seen that the relationship of gradation difference (brightness) between b and c is maintained. Also, since the saturation difference between a and c is not so much felt, a '= c' holds.
【００４６】第２に，図５の処理動作例１で述べたよう
に主観評価に基づいて，望ましい非再現色の圧縮方向が
明確化され，かつ，元の色の明度から一定の割合で調整
・圧縮するので，再現先の色が白っぽくなりすぎず，自
然な再現を行うことができる。Secondly, as described in the processing operation example 1 of FIG. 5, the desirable compression direction of the non-reproduction color is clarified based on the subjective evaluation, and the brightness of the original color is adjusted at a constant rate. -Because it is compressed, the destination color does not become too whitish and can be reproduced naturally.
【００４７】第３に，図６の処理動作例１で述べたよう
に非再現色の明度の分布によって圧縮方向を異ならせて
いるので，精度の高い再現を行うことができる。Thirdly, as described in the processing operation example 1 of FIG. 6, since the compression direction is made different depending on the distribution of the brightness of the non-reproduced color, highly accurate reproduction can be performed.
【００４８】なお，これらの処理はきわめて単純な処理
なので，実現が非常に容易であり，非再現色を含む自然
画の処理においても，良好な画像に再現されることを確
認することできた。Since these processes are extremely simple processes, it is very easy to realize, and it has been confirmed that good images can be reproduced even in the process of natural images including non-reproduced colors.
【００４９】[0049]
【発明の効果】以上説明したように，本発明に係る色情
報変換処理方法（請求項１）によれば，非再現色を再現
範囲の境界線上の色に割り当てるとき，非再現色と再現
先の色との明度差が最も影響されていることに注目し，
再現可能な被出力画像の色をそのまま出力し，非再現色
を，元の色の明度によって一義的に決定される明度差を
用いて望ましい色に変換するため，圧縮による階調つぶ
れが回避され，さらに明度の逆転が生じることなく，忠
実な色再現が実現すると共に，非再現色の明度だけで，
再現先の色を容易に求めることができる。As described above, according to the color information conversion processing method (Claim 1) of the present invention, when the non-reproduction color is assigned to the color on the boundary line of the reproduction range, the non-reproduction color and the reproduction destination are set. Note that the difference in brightness from the color of is most affected,
The reproducible color of the output image is output as it is, and the non-reproduced color is converted into the desired color by using the brightness difference that is uniquely determined by the brightness of the original color, so gradation collapse due to compression is avoided. ， Faithful color reproduction is realized without further inversion of lightness, and only the lightness of non-reproduced color
The color to be reproduced can be easily obtained.
【００５０】また，本発明に係る色情報変換処理方法
（請求項２）によれば，同一色相で連続した非再現色を
再現範囲の境界線上に割り当てる主観評価の結果に基づ
いて，望ましい圧縮方向を明確にし，かつ，元の色の明
度から一定の割合で調整・圧縮し，望ましい色に変換す
るため，再現先の色が白っぽくなりすぎず，自然な再現
を行うことができる。Further, according to the color information conversion processing method of the present invention (claim 2), the desirable compression direction is obtained based on the result of the subjective evaluation in which the continuous non-reproduction colors of the same hue are assigned on the boundary line of the reproduction range. Since the brightness of the original color is clarified, and the brightness of the original color is adjusted / compressed at a fixed ratio and converted to the desired color, the color of the reproduction destination does not become too whitish and natural reproduction can be performed.
【００５１】また，本発明に係る色情報変換処理方法
（請求項３）によれば，元の色の明度の分布に基づいて
圧縮方向を異ならせて色変換を行うため，精度の高い再
現を行うことができる。Further, according to the color information conversion processing method (claim 3) of the present invention, since the color conversion is performed by changing the compression direction based on the distribution of the lightness of the original color, highly accurate reproduction is possible. It can be carried out.
【図１】実施の形態に係る主観評価実験における任意の
非再現色の連続するカラーパッチの明度の位置や非再現
色の再現された色の圧縮方向を示す説明図である。FIG. 1 is an explanatory diagram showing a position of lightness of a continuous color patch of an arbitrary non-reproduced color and a compression direction of a reproduced color of a non-reproduced color in a subjective evaluation experiment according to the embodiment.
【図２】図１のような連続したカラーパッチを用いて，
主観評価による非再現色の再現結果から回帰分析した結
果を示すグラフである。FIG. 2 uses a continuous color patch as in FIG.
It is a graph which shows the result of regression analysis from the reproduction result of the non-reproduction color by subjective evaluation.
【図３】実施の形態に係る（Ａ）式に基づいて処理され
た結果として，非再現色から再現された色の圧縮方向を
示す説明図である。FIG. 3 is an explanatory diagram showing a compression direction of a color reproduced from a non-reproduction color as a result of processing based on the expression (A) according to the embodiment.
【図４】実施の形態の処理動作例１を示すフローチャー
トである。FIG. 4 is a flowchart showing a processing operation example 1 of the embodiment.
【図５】実施の形態の処理動作例２を示すフローチャー
トである。FIG. 5 is a flowchart showing a processing operation example 2 of the embodiment.
【図６】実施の形態の処理動作例３を示すフローチャー
トである。FIG. 6 is a flowchart showing a processing operation example 3 of the embodiment.
【図７】実施の形態の処理動作例３に係り，非再現色の
明度の位置によって非再現色から再現された色の圧縮方
向が異なることを示す説明図である。FIG. 7 is an explanatory diagram according to the processing operation example 3 of the embodiment and showing that the compression direction of the color reproduced from the non-reproduction color differs depending on the lightness position of the non-reproduction color.
【図８】本発明に係る非再現色の圧縮方法を示す説明図
である。FIG. 8 is an explanatory diagram showing a non-reproduction color compression method according to the present invention.
【図９】従来における非再現色の圧縮方法を示す説明図
である。FIG. 9 is an explanatory diagram showing a conventional non-reproduction color compression method.
Ｌ１ 同一色相で非再現色である任意の連続したパラー
パッチ ｐ１〜ｐ６ パッチの明度 Ｌ２ 同一色相で再現範囲の境界線上色で主観によって
元の色とを比較して決定されたカラーパッチ ｐ１’〜ｐ６’ 再現されたパッチの明度 ＧＰ 画像出力系の再現範囲の頂点の明度L1 Same continuous hue and non-reproducible color continuous patch p1 to p6 Lightness of the patch L2 Color on the boundary line of the reproduction range of the same hue Color patch determined by subjective comparison with the original color p1 ′ to p6 'Brightness of the reproduced patch Brightness of the vertex of the reproduction range of the GP image output system
Claims (3)
力系の色再現範囲では再現されない非再現色である場合
に，前記非再現色を画像出力系の再現可能な色に変換す
る色情報変換処理方法において，着目画素が前記画像出
力系の色再現範囲の内側か否かを判断する判断ステップ
と，前記判断ステップで色再現範囲の内側であると判断
された色情報を，色再現範囲の内側の元の色で出力し，
色再現範囲の外側であると判断された色情報を，元の色
の明度情報により一義的に決定される明度差を用いて色
再現範囲の境界線上の色に変換して出力する色情報変換
ステップと，を含むことを特徴とする色情報変換処理方
法。1. Color information conversion for converting the non-reproducible color into a reproducible color of the image output system when at least a part of the image information is a non-reproduced color that cannot be reproduced in the color reproduction range of the image output system. In the processing method, a determination step of determining whether or not the pixel of interest is inside the color reproduction range of the image output system, and color information determined to be inside the color reproduction range in the determination step Output in the original color inside,
Color information conversion that converts color information that is judged to be outside the color reproduction range into a color on the boundary line of the color reproduction range using the brightness difference that is uniquely determined by the brightness information of the original color and outputs A color information conversion processing method comprising:
縮方向になるように明度差制御の調整を決定する明度差
調整の決定ステップと，同一色相で再現範囲の境界線上
の色を決定し，変換色とする変換色決定ステップと，を
含むことを特徴とする請求項１に記載の色情報変換処理
方法。2. The color information converting step includes a brightness difference adjustment determining step of determining adjustment of brightness difference control so as to obtain a desired compression direction, and a color on the boundary line of the reproduction range having the same hue, and converting. The color information conversion processing method according to claim 1, further comprising: a conversion color determining step for determining a color.
色の明度が色再現範囲の境界線の頂点の明度に対し，高
いか低いかを比較する非再現色の明度比較ステップと，
前記明度比較ステップで比較された結果に基づいて元の
色と変換後の色との明度差を調整する方向を異ならせる
明度差の方向決定ステップとを含み，元の色の明度の分
布により圧縮方向を異ならせて境界線上の色を変換する
ことを特徴とする請求項２に記載の色情報変換処理方
法。3. The lightness difference adjustment step comprises a non-reproduction color lightness comparison step of comparing whether the lightness of the original color is higher or lower than the lightness of the apex of the boundary line of the color reproduction range,
Compression according to the distribution of the brightness of the original color, including the step of determining the direction of the brightness difference for adjusting the direction in which the brightness difference between the original color and the converted color is adjusted based on the result of the comparison in the brightness comparison step. The color information conversion processing method according to claim 2, wherein the color on the boundary line is converted in different directions.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP8123701A JPH09312777A (en) | 1996-03-19 | 1996-05-17 | Color information conversion processing method |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP8-63226 | 1996-03-19 | ||
| JP6322696 | 1996-03-19 | ||
| JP8123701A JPH09312777A (en) | 1996-03-19 | 1996-05-17 | Color information conversion processing method |
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| Publication Number | Publication Date |
|---|---|
| JPH09312777A true JPH09312777A (en) | 1997-12-02 |
Family
ID=26404311
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP8123701A Pending JPH09312777A (en) | 1996-03-19 | 1996-05-17 | Color information conversion processing method |
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| Country | Link |
|---|---|
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| US6282313B1 (en) | 1998-09-28 | 2001-08-28 | Eastman Kodak Company | Using a set of residual images to represent an extended color gamut digital image |
| US6285784B1 (en) | 1998-09-28 | 2001-09-04 | Eastman Kodak Company | Method of applying manipulations to an extended color gamut digital image |
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| US6763135B1 (en) | 1999-09-21 | 2004-07-13 | Minolta Co., Ltd. | Image processing apparatus |
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