JPH09200531A - Image luminosity converting device - Google Patents
Image luminosity converting deviceInfo
- Publication number
- JPH09200531A JPH09200531A JP8024643A JP2464396A JPH09200531A JP H09200531 A JPH09200531 A JP H09200531A JP 8024643 A JP8024643 A JP 8024643A JP 2464396 A JP2464396 A JP 2464396A JP H09200531 A JPH09200531 A JP H09200531A
- Authority
- JP
- Japan
- Prior art keywords
- image
- conversion
- luminosity
- lightness
- brightness
- 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.)
- Pending
Links
- 238000006243 chemical reaction Methods 0.000 claims abstract description 71
- 239000003086 colorant Substances 0.000 abstract 2
- 230000005484 gravity Effects 0.000 description 17
- 230000014509 gene expression Effects 0.000 description 12
- 238000012545 processing Methods 0.000 description 8
- 238000012937 correction Methods 0.000 description 7
- 238000010586 diagram Methods 0.000 description 5
- 238000000034 method Methods 0.000 description 5
- 238000003705 background correction Methods 0.000 description 2
- 238000007796 conventional method Methods 0.000 description 2
- 230000001186 cumulative effect Effects 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 1
- 230000001174 ascending effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000013507 mapping Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
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- Facsimile Image Signal Circuits (AREA)
- Color Image Communication Systems (AREA)
Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、画像明度変換装置
に関し、例えば、入力された元のカラー画像信号から再
びＲＧＢ信号を得て、表示やプリントすべき画像信号を
得る、明度変換装置に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image lightness conversion device, for example, a lightness conversion device for obtaining an RGB signal again from an input original color image signal to obtain an image signal to be displayed or printed.
【０００２】[0002]
【従来の技術】従来、画像明度変換装置は一般に、入力
された画像信号レベルの頻度を計測し、これに応じた明
度に変換して、適正濃度画像を得る。しかし、カラー原
稿の明るい・暗いの調子は、入力される原稿毎に異な
る。特に写真原稿は撮影の状況、現像の条件で異なり、
透過フィルムは更に濃度範囲が広いため、現像されたフ
ィルムの濃度はばらつく。印画紙や透過フィルム、ネガ
フィルム等原稿の種類により濃度範囲が異なるため、表
示装置や印字装置の表現範囲へのマッピングが必要とな
る。2. Description of the Related Art Conventionally, an image lightness conversion device generally measures the frequency of an input image signal level and converts it into a lightness corresponding to the frequency to obtain a proper density image. However, the tone of light and dark of the color original differs depending on the input original. In particular, photographic manuscripts differ depending on the shooting conditions and development conditions.
Since the transparent film has a wider density range, the density of the developed film varies. Since the density range varies depending on the type of original such as photographic paper, transparent film, and negative film, it is necessary to map it to the expression range of the display device or the printing device.
【０００３】従来法は白黒画像での処理が主であり、カ
ラー画像にその方法を適用しようとすると次の点に困難
さがある。カラー画像信号は少なくとも３次元信号であ
る。例えば３次元の信号毎に従来技術を適用しても、明
るさ変化量がそれぞれ異なると、出力される画像の色バ
ランスは入力画像とは異なってしまう。そこである１チ
ャンネルのヒストグラム（例えばＲＧＢチャンネルのう
ちＧチャンネル）から得られる変換量を、他のチャンネ
ルに適応して同一変化量とする。The conventional method is mainly used for processing a black-and-white image, and if the method is applied to a color image, the following points are difficult. The color image signal is at least a three-dimensional signal. For example, even if the conventional technique is applied to each of three-dimensional signals, the color balance of the output image is different from that of the input image if the brightness variation amounts are different. Therefore, the conversion amount obtained from a certain one-channel histogram (for example, the G channel of the RGB channels) is applied to the other channels to be the same change amount.
【０００４】しかし上記のようにしても、色の混色の場
合非直線性のため、ＲＧＢのレベルが変化すれば、色相
が異なってしまう。特にプリンタのように減法混色の場
合に著しい。そこで各チャンネル毎にヒストグラムを得
て、それぞれを適正化しても、色の歪みは線形でないた
め、やはり色相が異なってしまう。各チャンネル毎の入
出力カーブを一致させても同様である。However, even in the case of the above, due to the non-linearity in the case of the color mixture, the hue will be different if the RGB level is changed. In particular, it is remarkable in the case of subtractive color mixture like a printer. Therefore, even if a histogram is obtained for each channel and each is optimized, the color distortion is not linear, and therefore the hue is also different. The same applies when the input and output curves for each channel are matched.
【０００５】上記の困難に対応し、入力に比べ一般的に
出力の濃度範囲は狭いため、その表現範囲を最大限利用
する。このため、色々な原稿種ごとに対しては濃度範囲
の偏りを平均化することでコントラストを得ている。In response to the above-mentioned difficulties, the density range of the output is generally narrower than that of the input, so the expression range is used to the maximum. For this reason, the contrast is obtained by averaging the bias of the density range for various document types.
【０００６】[0006]
【発明が解決しようとする課題】しかしながら、上記の
従来例では、原稿での全体が暗い、明るい、といった調
子を適正化することはできない。また、頻度の最小値・
最大値を基にしていたので、ノイズや局所的濃度に影響
され全体の調子を判断することが困難である問題を伴
う。However, in the above-described conventional example, it is not possible to optimize the tone of the whole document such as dark or bright. Also, the minimum frequency
Since it is based on the maximum value, there is a problem that it is difficult to judge the overall condition due to the influence of noise and local density.
【０００７】本発明は、入力される画像濃度がその都度
ばらついても忠実な色のままで、最大のコントラストを
得て、好ましい明るさに自動的に適正化できる画像明度
変換装置を提供することを目的とする。The present invention provides an image lightness conversion device which can obtain the maximum contrast and automatically adjust to a preferable brightness while maintaining the faithful color even if the input image density varies each time. With the goal.
【０００８】[0008]
【課題を解決するための手段】かかる目的を達成するた
め、本発明の画像明度変換装置は、各画素のＲＧＢ信号
から、画像の明度と色味の属性値を分離し、明度信号の
明度分布を変換する画像明度変換装置であり、プレスキ
ャンで測定されたカラー画像の明度を表すヒストグラム
から算出された明度変換のための変換テーブルと、ＲＧ
Ｂ信号から分離された明度信号のヒストグラムから明度
変換を行う変換手段とを有し、ヒストグラムの特徴に基
づいた明度の再変換を行うことを特徴としている。In order to achieve such an object, an image lightness conversion device of the present invention separates the lightness and tint attribute values of an image from the RGB signal of each pixel to obtain the lightness distribution of the lightness signal. Is an image lightness conversion device for converting the lightness, and a conversion table for lightness conversion calculated from a histogram representing the lightness of the color image measured by the prescan, and RG
It is characterized in that it has a conversion means for converting the brightness from the histogram of the brightness signal separated from the B signal, and re-converts the brightness based on the characteristics of the histogram.
【０００９】また、上記明度の再変換は、ヒストグラム
の最大値と最小値とから明度変換を所定の範囲に再分布
して行うか、ヒストグラムの重心値と基準画像のヒスト
グラム重心値との演算で明度変換を行うとよい。なお、
演算は線形演算、または非線形演算とするとよい。The re-conversion of the lightness is performed by redistributing the lightness conversion from the maximum value and the minimum value of the histogram into a predetermined range, or by calculating the centroid value of the histogram and the histogram centroid value of the reference image. Brightness conversion is recommended. In addition,
The calculation may be a linear calculation or a non-linear calculation.
【００１０】[0010]
【発明の実施の形態】次に添付図面を参照して本発明に
よる画像明度変換装置の実施の形態を詳細に説明する。
図１〜図８を参照すると本発明の画像明度変換装置の一
実施形態が示されている。BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of an image brightness conversion apparatus according to the present invention will be described in detail with reference to the accompanying drawings.
1 to 8, there is shown an embodiment of the image lightness conversion device of the present invention.
【００１１】図１および図２は、本発明の画像明度変換
装置を包含する画像処理部のブロック構成図である。図
２はスキャン部の回路構成例を示している。本画像処理
部は、スキャナ１１、シェーディング補正部１２、座標
変換部１３、濃度変換部１４、調子修正部１５、座標変
換部１６、色補正部１７、駆動部１８、記録部１９によ
り構成される。FIG. 1 and FIG. 2 are block configuration diagrams of an image processing unit including the image brightness conversion apparatus of the present invention. FIG. 2 shows a circuit configuration example of the scan unit. The image processing unit includes a scanner 11, a shading correction unit 12, a coordinate conversion unit 13, a density conversion unit 14, a tone correction unit 15, a coordinate conversion unit 16, a color correction unit 17, a drive unit 18, and a recording unit 19. .
【００１２】図２において、スキャン部は、座標変換部
１３、調子修正テーブル１５ａ、ヒストグラム計測部１
４１、特徴検出部１４２、演算部１４３の各部で構成さ
れる。この構成により成るスキャン部において、本スキ
ャンは座標変換部１３と調子修正テーブル１５ａ間で実
行される。また、プレスキャンは、ヒストグラム計測部
１４１と特徴検出部１４２と演算部１４３とを介して実
行される。In FIG. 2, the scanning unit includes a coordinate conversion unit 13, a tone correction table 15a, and a histogram measuring unit 1.
41, a feature detection unit 142, and a calculation unit 143. In the scan unit having this configuration, the main scan is executed between the coordinate conversion unit 13 and the tone correction table 15a. Further, the pre-scan is executed via the histogram measurement unit 141, the feature detection unit 142, and the calculation unit 143.
【００１３】プレスキャンでは、測定されたカラー画像
の明度を表すヒストグラムから、明度変換のための変換
係数を算出し、調子修正の変換テーブルとする。本スキ
ャンでは、ＲＧＢ信号から分離された明度信号のヒスト
グラムから上記の変換テーブルを用いて明度変換を行
う。これらのプレスキャンと本スキャンとを組み合せ
て、各画素のＲＧＢ信号から、画像の明度と色味の属性
値を分離し、明度信号の明度分布を変換することができ
る。以下において、この内容を詳細に説明する。In the prescan, a conversion coefficient for lightness conversion is calculated from a histogram representing the lightness of the measured color image, and is used as a tone correction conversion table. In the main scan, the brightness conversion is performed using the above conversion table from the histogram of the brightness signal separated from the RGB signal. By combining these prescans and main scans, it is possible to separate the brightness and tint attribute values of the image from the RGB signals of each pixel, and convert the brightness distribution of the brightness signal. The details will be described below.
【００１４】上記構成の画像処理部において、ヒストグ
ラム測定のために、原稿の読みとりは本読みとりに先立
ちプレスキャンを行う。プレスキャンは本スキャンに比
べ走査がｎライン毎に行われる。プレスキャンされた画
像信号はＲＧＢ信号から明度と色味を表す色空間に変換
される。例えばＣＩＥ Ｌ＊ａ＊ｂ＊への変換は次の変
換を行う。In the image processing unit having the above-mentioned configuration, the reading of the document is pre-scanned prior to the main reading in order to measure the histogram. In the pre-scan, scanning is performed every n lines as compared with the main scan. The pre-scanned image signal is converted from an RGB signal into a color space representing lightness and tint. For example, the conversion to CIE L * a * b * is as follows.
【００１５】 Ｌ＊＝１１６（Ｙ／Ｙ０）1/3−１６ ａ＊＝５００［（Ｘ／Ｘ０）1/3−（Ｙ／Ｙ０）1/3］ ｂ＊＝２００［（Ｙ／Ｙ０）1/3−（Ｚ／Ｚ０）1/3］ 第１式 ここで、Ｘ０、Ｙ０、Ｚ０は標準光の刺激値である。ま
たＸＹＺは、L * = 116 (Y / Y0) 1 / 3−16 a * = 500 [(X / X0) 1 / 3− (Y / Y0) 1/3 ] b * = 200 [(Y / Y0) 1 / 3- (Z / Z0) 1/3 ] First formula Here, X0, Y0, and Z0 are stimulus values of standard light. XYZ is
【００１６】[0016]
【数１】 [Equation 1]
【００１７】次々に入力されるＬ＊ａ＊ｂ＊信号の中
で、Ｌ信号のレベル毎の画素数が次々とカウントアップ
される。図３にヒストグラム処理の手順例を示す。ま
た、図４にカウントされたヒストグラムの分布を示す。
図４において、ヒストグラム分布の横軸ｘは明度レベル
であり、ｆ（ｘ）をそのレベルｘでの頻度とする。図４
（ａ）は明るい方向に偏った明度分布を示し、図４
（ｂ）は暗い方向に偏った明度分布を示す。ヒストグラ
ムを明度順に並び替え、その特徴を検出する。その手順
を説明する。明度は最小値ｘmin からｘmax に分布して
いる。最初に入力画像の明度レベルのそれぞれ下限、上
限ｘi ，ｘj を決める。ヒストグラム分布をレベルの小
さい順にソートして、そのレベル順に頻度を加算してい
ったとき、最小の累積頻度限界ρmin は、In the L * a * b * signals that are input one after another, the number of pixels for each level of the L signal is counted up one after another. FIG. 3 shows an example of the procedure of histogram processing. Further, FIG. 4 shows the distribution of the counted histograms.
In FIG. 4, the horizontal axis x of the histogram distribution is the lightness level, and f (x) is the frequency at that level x. FIG.
FIG. 4A shows a lightness distribution that is biased in the bright direction.
(B) shows a lightness distribution biased in the dark direction. The histogram is rearranged in order of lightness, and its feature is detected. The procedure will be described. The brightness is distributed from the minimum value xmin to xmax. First, the lower and upper limits of the brightness level of the input image are determined. When the histogram distribution is sorted in ascending order of level and the frequencies are added in order of level, the minimum cumulative frequency limit ρ min is
【００１８】[0018]
【数２】 [Equation 2]
【００１９】である最大の明度値ｘi を決める。同様に
最大の累積頻度限界ρmax は、The maximum lightness value xi is determined. Similarly, the maximum cumulative frequency limit ρ max is
【００２０】[0020]
【数３】 (Equation 3)
【００２１】である最大の明度値ｘｊをを決める。上記
の第２式および第３式において、ｌ＝０〜１．０、であ
る。つぎに出力する変換明度ｘ0 を求める。出力装置の
表現範囲を与える明度範囲限界をｘ1 ，ｘ2 とすると、The maximum lightness value xj which is is determined. In the above second and third equations, l = 0 to 1.0. Next, the converted lightness x0 to be output is obtained. If the lightness range limits that give the expression range of the output device are x1 and x2,
【００２２】[0022]
【数４】 (Equation 4)
【００２３】ｘi 及びｘj の設定をすることで、頻度が
少なく目立ってない明度レベルの画像やノイズを除き、
出力装置の濃度範囲を有効に使用できる。以上により印
画紙や透過フィルム、ネガフィルム等原稿の種類により
濃度範囲が異なる原稿に対し、原稿装置や印字装置へ出
力する際、装置の表現範囲へのマッピングが可能とな
る。図５と図６（ａ）は本変換を実施しない場合の入出
力特性を示し、図６（ｂ）は本変換を実施した入出力特
性を示す。明度変換量を求めた上記の第４式は、別の実
施形態として下記の第５式のように演算しても良い。こ
の場合人間の視覚特性を考慮した変換である。By setting xi and xj, it is possible to remove an image and noise of a lightness level which is infrequent and inconspicuous,
The density range of the output device can be effectively used. As described above, when a document having a different density range depending on the type of document such as photographic paper, transparent film, or negative film is output to the document device or the printing device, mapping to the expression range of the device is possible. 5 and 6A show the input / output characteristics when this conversion is not performed, and FIG. 6B shows the input / output characteristics when this conversion is performed. The above-mentioned fourth equation for obtaining the lightness conversion amount may be calculated as the following fifth equation as another embodiment. In this case, conversion is performed in consideration of human visual characteristics.
【００２４】[0024]
【数５】 (Equation 5)
【００２５】次に明度のヒストグラムｆ（ｘ）の頻度を
重さと見て、明度ヒストグラムの重心を下記の第６式に
より求める。Next, considering the frequency of the brightness histogram f (x) as the weight, the center of gravity of the brightness histogram is obtained by the following equation (6).
【００２６】[0026]
【数６】 (Equation 6)
【００２７】ここで写真画像などの画像での、好ましい
明るさを基準として求めるため、好ましい明るさの画像
を統計的に求めておき、その明るさの画像での明度ヒス
トグラムの重心を、上記第６式と同様に求める。それを
好ましい画像明るさの基準とする。入力画像の明度分布
から出力装置の表現範囲に再配分された信号は、その重
心値からの判定で好ましい明るさに、その明るさを修正
する。ここで基準となる明度重心と、プレスキャンされ
た入力画像の明度重心とから係数γを下記の第７式によ
り得る。Here, in order to obtain the preferable brightness of an image such as a photographic image as a reference, an image of the preferable brightness is statistically obtained, and the center of gravity of the brightness histogram of the image of that brightness is calculated as described above. It is calculated in the same manner as in Equation 6. It is used as a reference for a preferable image brightness. The signal redistributed from the brightness distribution of the input image to the expression range of the output device has its brightness corrected to a preferable brightness by the determination from the barycentric value. Here, the coefficient γ is obtained from the lightness center of gravity serving as the reference and the lightness center of gravity of the pre-scanned input image by the following formula 7.
【００２８】[0028]
【数７】 (Equation 7)
【００２９】入力された画像の明度ヒストグラムから得
られたデータから、出力装置の再現範囲へ、明暗の範囲
を適正に再配置し、最大のコントラストを得た第４式
を、さらに好みの明暗調子に適正化するために、第７式
の係数γを適応する。Based on the data obtained from the brightness histogram of the input image, the range of light and dark is appropriately rearranged to the reproduction range of the output device, and the fourth expression that obtains the maximum contrast is further adjusted to the desired light and dark tone. The coefficient γ of the equation (7) is adapted to optimize
【００３０】[0030]
【数８】 (Equation 8)
【００３１】図７に第８式で変換された出力データを示
す。入力画像が標準画像と一致しているときは、図７の
カーブａとなり、直線的変換であるから第４式の変換と
変わらない。入力画像が標準画像に比べ、暗いと判定さ
れた時（重心が基準より小の時）、γは１より小となる
ので図７のカーブｂとなり、カーブａより明るい方向に
修正される。入力画像が標準画像に比べ、明るいと判断
された時（重心が基準より大の時）、γは１より大とな
るので図７のカーブｃとなり、カーブａより暗い方向に
修正される。このように第８式により、印画紙や透過フ
ィルム、ネガフィルム等原稿の偏った濃度の入力原稿
を、出力装置の最適な濃度範囲に出力でき、しかも明暗
も好みの調子に適正化出来る。FIG. 7 shows the output data converted by the eighth equation. When the input image coincides with the standard image, the curve a in FIG. 7 is obtained, and since it is a linear conversion, it is the same as the conversion of the fourth expression. When it is determined that the input image is darker than the standard image (when the center of gravity is smaller than the reference), γ is smaller than 1, so the curve b in FIG. 7 is obtained, and the curve is corrected to be brighter than the curve a. When it is determined that the input image is brighter than the standard image (when the center of gravity is larger than the reference), γ is larger than 1, so the curve c in FIG. 7 is obtained, and the curve is corrected to be darker than the curve a. As described above, according to the formula (8), an input original having a biased density such as a printing paper, a transparent film, a negative film, etc. can be output within the optimum density range of the output device, and the lightness and darkness can be adjusted to a desired tone.
【００３２】以上の明度変換により求められた明度情報
は、入出力の関係を示すＲＡＭで構成されるテーブルに
記録される。入力の原稿がプレスキャンされるごとに、
ＲＡＭの内容は書き換えられる。なおプレスキャンでは
読みとりは主走査方向に１／１６画素おきなど、粗くサ
ンプリングされるので、高速に走査出来る。副走査も同
様である。The lightness information obtained by the above lightness conversion is recorded in a table composed of a RAM showing an input / output relationship. Each time the input document is prescanned,
The contents of RAM are rewritten. In the pre-scan, the reading is roughly sampled every 1/16 pixel in the main scanning direction, so that the scanning can be performed at high speed. The same applies to sub-scanning.
【００３３】明度変換量が求まりテーブルへの記録が終
了すると本スキャンがおこなわれ、次々の読みとり画像
はＲＧＢ信号から明度と色味を示す信号に変換され、そ
の明度信号は明度変換部で作成されたルックアップテー
ブルをアクセスすることにより、（ＲＡＭメモリのアド
レスに入力することで）明度変換される。変換された明
度信号と先の色味信号は画素毎に位相を揃えてもとのＲ
ＧＢ信号に逆変換される。カラー複写機の場合は濃度変
換部でＲＧＢからＹＭＣ（ＢＬＫ）に変換されて、記録
部にて表示またはプリントされる。When the lightness conversion amount is obtained and recording in the table is completed, a main scan is performed, and the next read image is converted from RGB signals into signals indicating lightness and tint, and the lightness signal is created by the lightness conversion unit. The brightness conversion is performed (by inputting the address of the RAM memory) by accessing the lookup table. The converted lightness signal and the previous tint signal have the same R when the phases are aligned for each pixel.
It is converted back to a GB signal. In the case of a color copying machine, the density conversion unit converts RGB to YMC (BLK) and the recording unit displays or prints.
【００３４】他の実施形態として、入力画像の明度ヒス
トグラムの重心と好ましい画像での重心から出力信号を
つぎのように求める。入力画像の明度信号と明度ヒスト
グラムの重心とが、明度信号≦明度ヒストグラムの重
心、の関係の時は第９式による。As another embodiment, the output signal is obtained from the center of gravity of the brightness histogram of the input image and the center of gravity of the preferable image as follows. When the brightness signal of the input image and the center of gravity of the brightness histogram satisfy the relationship of brightness signal ≦ center of gravity of the brightness histogram, Expression 9 is used.
【００３５】[0035]
【数９】 [Equation 9]
【００３６】入力画像の明度信号と明度ヒストグラムの
重心とが、明度信号＞明度ヒストグラムの重心、の関係
の時は第１０式による。When the brightness signal of the input image and the center of gravity of the brightness histogram have a relationship of brightness signal> center of gravity of the brightness histogram, equation 10 is used.
【００３７】[0037]
【数１０】 (Equation 10)
【００３８】図８に第９式および第１０式により変換さ
れた出力データを示す。入力画像が標準画像と一致して
いるときは、図８のカーブａとなり、直線的変換である
から、第４式の変換と変わらない。入力画像が標準画像
に比べ、暗いと判断された時（重心が基準より小の
時）、図８のカーブｂとなり、カーブａより、明るい方
向に修正される。入力画像が標準画像に比べ、明るいと
判断された時（重心が基準より大の時）、図８のカーブ
ｃとなり、カーブａより暗い方向に修正される。第８式
の実施形態に比べ、カーブが重心値を境に折れ線近似さ
れている。従って第８式に比べ、精度は落ちるが、高速
に演算出来る。また対数演算器が不要なので、安価に達
成出来る。このように第９、１０式により、印画紙や透
過フィルム、ネガフィルム等原稿の偏った濃度の入力原
稿を、出力装置の最適な濃度範囲に出力でき、しかも明
暗も好みの調子に適正化出来る。FIG. 8 shows the output data converted by the ninth and tenth expressions. When the input image coincides with the standard image, the curve a in FIG. 8 is obtained, and the conversion is linear, which is the same as the conversion of the fourth expression. When it is determined that the input image is darker than the standard image (when the center of gravity is smaller than the reference), the curve b in FIG. 8 is obtained, and the curve a is corrected to be brighter. When it is determined that the input image is brighter than the standard image (when the center of gravity is larger than the reference), the curve c in FIG. 8 is obtained, and the curve is corrected to be darker than the curve a. Compared with the embodiment of the eighth formula, the curve is approximated by a polygonal line with the center of gravity as a boundary. Therefore, as compared with the formula (8), the accuracy is lowered, but the calculation can be performed at high speed. Moreover, since a logarithmic calculator is unnecessary, it can be achieved at low cost. As described above, according to the ninth and tenth formulas, an input original having an uneven density such as a printing paper, a transparent film, and a negative film can be output within the optimum density range of the output device, and the brightness and darkness can be adjusted to a desired tone. .
【００３９】ここで写真画像などの画像での、好ましい
明るさを基準として、基準画像の明度ヒストグラムの重
心を求めたが、カラー複写機のように、印画紙モード、
透過フィルムモード、透過ネガフィルムモード、イラス
トモードのように、モードを選択し、それぞれに合った
色処理等の処理を選択出来る場合は、それぞれのモード
をカテゴリとして分類し、カテゴリごとの好ましい明る
さ基準を、上式と同様に求めておく。複写機ユーザはモ
ードを選択すると同時にカテゴリの明るさ重心が選ばれ
る。上記出力演算はそれぞれのカテゴリの重心値で演算
される。Here, the center of gravity of the brightness histogram of the reference image was determined with reference to the preferable brightness of an image such as a photographic image.
If you can select a mode, such as transmissive film mode, transmissive negative film mode, or illustration mode, and select a process such as color processing that matches each mode, classify each mode as a category and set the preferred brightness for each category. The standard is obtained in the same manner as the above formula. The copier user selects the mode and simultaneously the center of gravity of the brightness of the category is selected. The output calculation is performed with the barycentric value of each category.
【００４０】本発明によれば、カラー写真原稿など、入
力される画像濃度がその都度ばらついた入力でも、色相
の変化を起こさないで忠実な色のまま、最大のコントラ
ストを得て出力でき、そのうえ明るさの調子を示す基準
を決めて、好ましい明るさに自動的に適正化できる。According to the present invention, even if the input image density such as a color photographic original varies from time to time, the faithful color can be output without changing the hue and the maximum contrast can be obtained and output. It is possible to automatically adjust to a desired brightness by setting a standard indicating the brightness condition.
【００４１】[0041]
【発明の効果】以上の説明より明らかなように、本発明
の画像明度変換装置は、各画素のＲＧＢ信号から、画像
の明度と色味の属性値を分離し、明度信号の明度分布を
変換する。この明度変換は、プレスキャンで測定された
カラー画像の明度を表すヒストグラムから算出された明
度変換のための変換テーブルと、ＲＧＢ信号から分離さ
れた明度信号のヒストグラムから行う。よって上記の再
変換によれば、カラー画像信号を色の３属性を表す色空
間から明度と色味を表す属性に変換して、その明度成分
の画像レベルごとの頻度を測定し、その分布の特徴量を
利用して適切な明度変換を行い、入力されたカラー画像
の明度を適正に変えることが可能となる。As is apparent from the above description, the image lightness conversion apparatus of the present invention separates the lightness and tint attribute values of an image from the RGB signal of each pixel and converts the lightness distribution of the lightness signal. To do. This lightness conversion is performed from a conversion table for lightness conversion calculated from a histogram representing the lightness of the color image measured by the prescan, and a histogram of the lightness signal separated from the RGB signals. Therefore, according to the above-mentioned re-conversion, the color image signal is converted from the color space showing the three attributes of color into the attributes showing the lightness and the tint, the frequency of the lightness component for each image level is measured, and its distribution It is possible to appropriately change the lightness of the input color image by performing appropriate lightness conversion using the feature amount.
【図１】本発明の画像明度変換装置を包含する画像処理
部の実施形態を示すブロック構成図であるFIG. 1 is a block configuration diagram showing an embodiment of an image processing unit including an image lightness conversion device of the present invention.
【図２】図１の濃度変換部のより詳細な構成例を示すブ
ロック図である。FIG. 2 is a block diagram showing a more detailed configuration example of a density conversion unit in FIG.
【図３】ヒストグラム処理の手順例を示すフローチャー
トである。FIG. 3 is a flowchart illustrating a procedure example of histogram processing.
【図４】カウントされたヒストグラムの分布図であり、
（ａ）が明るい画像の場合、（ｂ）が暗い画像の場合で
ある。FIG. 4 is a distribution chart of counted histograms,
(A) is a bright image, and (b) is a dark image.
【図５】本変換を実施しない場合の入出力特性を示す図
である。FIG. 5 is a diagram showing input / output characteristics when this conversion is not performed.
【図６】入出力特性を示す図であり、（ａ）が本変換を
実施しない場合、（ｂ）が本変換を実施した場合であ
る。6A and 6B are diagrams showing input / output characteristics, where FIG. 6A shows the case where the main conversion is not executed, and FIG. 6B shows the case where the main conversion is executed.
【図７】第８式で変換された出力データを示す。FIG. 7 shows output data converted by Expression 8.
【図８】第９式および第１０式で変換された出力データ
を示す。FIG. 8 shows output data converted by Expressions 9 and 10.
１１ スキャナ １２ シェーディング補正部 １３ 座標変換部 １４ 濃度変換部 １５ 調子修正部 １６ 座標変換部 １７ 色補正部 １８ 駆動部 １９ 記録部 11 Scanner 12 Shading Correction Section 13 Coordinate Conversion Section 14 Density Conversion Section 15 Tone Correction Section 16 Coordinate Conversion Section 17 Color Correction Section 18 Drive Section 19 Recording Section
Claims (5)
色味の属性値を分離し、明度信号の明度分布を変換する
画像明度変換装置において、 プレスキャンで測定されたカラー画像の明度を表すヒス
トグラムから算出された明度変換のための変換テーブル
と、 ＲＧＢ信号から分離された明度信号のヒストグラムから
前記明度変換を行う変換手段とを有し、 ヒストグラムの特徴に基づいた明度の再変換を行うこと
を特徴とする画像明度変換装置。1. An image lightness conversion device for separating the lightness and tint attribute values of an image from the RGB signal of each pixel and converting the lightness distribution of the lightness signal, wherein the lightness of a color image measured by prescan is A conversion table for brightness conversion calculated from the represented histogram, and a conversion unit for performing the brightness conversion from the histogram of the brightness signal separated from the RGB signal are provided, and the brightness is reconverted based on the characteristics of the histogram. An image brightness conversion device characterized by the above.
の最大値と最小値とから前記明度変換を所定の範囲に再
分布して行うことを特徴とする請求項１記載の画像明度
変換装置。2. The image brightness conversion apparatus according to claim 1, wherein the brightness conversion is performed by redistributing the brightness conversion into a predetermined range from the maximum value and the minimum value of the histogram.
の重心値と基準画像のヒストグラム重心値との演算で前
記明度変換を行うことを特徴とする請求項１記載の画像
明度変換装置。3. The image lightness conversion device according to claim 1, wherein the lightness conversion is performed by calculating the barycentric value of the histogram and the histogram barycentric value of the reference image.
する請求項３記載の画像明度変換装置。4. The image brightness conversion apparatus according to claim 3, wherein the calculation is a linear calculation.
とする請求項３記載の画像明度変換装置。5. The image brightness conversion device according to claim 3, wherein the calculation is a non-linear calculation.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP8024643A JPH09200531A (en) | 1996-01-18 | 1996-01-18 | Image luminosity converting device |
| DE1997101527 DE19701527C2 (en) | 1996-01-18 | 1997-01-17 | Device for improving the picture quality |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP8024643A JPH09200531A (en) | 1996-01-18 | 1996-01-18 | Image luminosity converting device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH09200531A true JPH09200531A (en) | 1997-07-31 |
Family
ID=12143827
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP8024643A Pending JPH09200531A (en) | 1996-01-18 | 1996-01-18 | Image luminosity converting device |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH09200531A (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
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| US7142712B2 (en) | 2001-06-14 | 2006-11-28 | Matsushita Electric Industrial Co., Ltd | Automatic tone correction apparatus, automatic tone correction method, and automatic tone correction program storage mediums |
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-
1996
- 1996-01-18 JP JP8024643A patent/JPH09200531A/en active Pending
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|---|---|---|---|---|
| US6738527B2 (en) | 1997-06-09 | 2004-05-18 | Seiko Epson Corporation | Image processing apparatus, an image processing method, a medium on which an image processing control program is recorded, an image evaluation device, and image evaluation method and a medium on which an image evaluation program is recorded |
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| US7508548B2 (en) | 1997-06-09 | 2009-03-24 | Seiko Epson Corporation | Image processing method and image processing apparatus |
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| US8681380B2 (en) | 1997-06-09 | 2014-03-25 | Seiko Epson Corporation | Image processing apparatus, an image processing method, a medium on which an image processing control program is recorded, an image evaluation device, an image evaluation method and a medium on which an image evaluation program is recorded |
| US8867099B2 (en) | 1997-06-09 | 2014-10-21 | Seiko Epson Corporation | Image processing apparatus, an image processing method, a medium on which an image processing control program is recorded, an image evaluation device, an image evaluation method and a medium on which an image evaluation program is recorded |
| US7142712B2 (en) | 2001-06-14 | 2006-11-28 | Matsushita Electric Industrial Co., Ltd | Automatic tone correction apparatus, automatic tone correction method, and automatic tone correction program storage mediums |
| US7359571B2 (en) | 2002-02-19 | 2008-04-15 | Fujifilm Corporation | Method, apparatus and program for image processing |
| US8363125B2 (en) | 2008-12-19 | 2013-01-29 | Ricoh Company, Limited | Image processing apparatus, image processing method, and computer program product |
| JP2010251883A (en) * | 2009-04-13 | 2010-11-04 | Ricoh Co Ltd | Image processor, image processing method, program, and recording medium |
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