JP3762567B2 - Color image forming apparatus - Google Patents

Description

【００５４】
まず彩度上昇の場合から述べる。即ちＬａｂ均等色空間上で、ａ＊軸方向、ｂ＊軸方向に原点Ｏから離れるほど鮮やかになり彩度Ｃは上がる。また、Ｌ＊軸方向に大きくなる程明るくなり、明度Ｖは大きくなる。
【００５５】
均等色空間上で、ある色αの彩度を上げる為には、色相角Ｈと明度Ｖを固定して彩度Ｃをある一定量大きくすることが望ましい。実際にはＬ＊ａ＊ｂ＊均等色空間のなかで均等に配置されている約数百色のデータを選び、その個々のパッチデータを画像入力装置１１０にて読取り、各Ｌ＊ａ＊ｂ＊データに対するＲＧＢの読取り信号を求めておく。
【００５６】
各選出データをポイントαのように、Ｌ＊ａ＊ｂ＊空間上である一定量彩度が大きくなるように動かし、そのパッチデータを前回同様に画像入力装置１１０にて読取り、彩度上昇を行ったときのＲ’Ｇ’Ｂ’データを求めておく。そして彩度を上昇させた場合の約数百色分のＲＧＢデータとＲ’Ｇ’Ｂ’データとの関係を求める。この時ハードウエアの簡略化の為に、Ｒ成分、Ｇ成分、Ｂ成分を別個に取扱い、ＲとＲ’、ＧとＧ’、ＢとＢ’との関係に簡略化させ、入力階調補正部１３にて対応可能なようにした。この場合、ハイライト部分で逆転現象が生ずるが、これはＲＧＢデータに下記に示すある一定条件を設けることで解消することが可能である。
【００５７】
・Ｒに関する条件
Ｒ＜γかつＲ＞Ｇ＋δ ｏｒ Ｒ＞Ｂ＋δの時は入力階調補正処理を実行禁止
・Ｂに関する条件
Ｂ＜εかつＢ＞Ｇ＋η ｏｒ Ｂ＞Ｒ＋ηの時は入力階調補正処理を実行禁止
・Ｇに関する条件
Ｇ＜θかつＧ＞Ｂ十κ ｏｒ Ｇ＞Ｒ＋κの時は入力階調補正処理を実行禁止
（γ、δ、ε、η、θ、κは定数）
このようにして求めた彩度上昇の場合のＲとＲ’、ＢとＢ’、ＧとＧ’の関係を図５（ａ）に示す。また、彩度低下に関しても彩度上昇と同じように求め、その関係を図５（ｂ）に示す。
【００５８】
次に、明度を上げる場合のルックアップテーブルの作り方について述べる。Ｌ＊ａ＊ｂ＊均等色空間上である色αの明度を上げる為には、色相角Ｈと彩度Ｃを固定して明度Ｖをある一定量大きくすることが望ましい。具体的には、彩度の場合と同様にＬ＊ａ＊ｂ＊均等色空間のなかで均等に配置されている約数百色のデータを選び、その個々のパッチデータを画像入力装置１１０にて読取り、各Ｌ＊ａ＊ｂ＊データに対するＲＧＢデータを求めておく。
【００５９】
各選出データをポイントαのようにＬ＊ａ＊ｂ＊空間上である一定量明度が大きくなるように動かし、そのパッチデータを前回同様に画像入力装置１１０にて読取り、明度上昇を行ったときのＲ’Ｇ’Ｂ’データを求めておく。明度を上昇させた場合の約数百色分のＲＧＢデータと、Ｒ’Ｇ’Ｂ’データとの関係を求める。彩度の場合と同様に、ハードウエアの簡略化の為にＲ成分、Ｇ成分、Ｂ成分を別個に取り扱い、ＲとＲ’、ＧとＧ’、ＢとＢ’との関係に簡略化させ入力階調補正部１３にて対応可能なようにした。このようにして求めた明度上昇の場合のＲとＲ’、ＢとＢ’、ＧとＧ’の関係を図６（ａ）に、明度低下の場合を図６（ｂ）に示す。
【００６０】
次にコントラストに関して述べる。コントラストは、画像変化のめりはり感をもとにＲとＲ’、ＧとＧ’、ＢとＢ’の関係を作る。コントラスト上昇の場合のＲとＲ’、ＢとＢ’、ＧとＧ’の関係を図７（ａ）に、コントラスト低下の場合を図７（ｂ）に示す。
【００６１】
実際にユーザが画質調整を行う場合には、まず操作パネル上の画質調整ボタンを選択すると彩度設定キー、明度設定キー、コントラスト設定キーが表示され、ユーザーの好みにあわせて上記設定キーの中から一つを選択する。ユーザーが彩度キーを選択すると、彩度に関して９段階に調整可能なようにマイナス４〜プラス４までの設定キーが表示される。表示されているマイナス４は、彩度が最も低く、ゼロに近づくほど彩度低下の割合が少なくなり、ゼロでは彩度変化がない状態となる。プラス４は、彩度がもっとも高く、ゼロに近づくほど彩度上昇の割合が少なくなる。
【００６２】
設定キーのきざみは均等である。明度設定キーを選択しても、彩度の場合と同様に、９段階の調整キーがあり、マイナス４が明度が最も低く、ゼロが明度変化無しで、プラス４が明度が最も高い設定となっている。コントラスト設定キーに関しても、彩度、明度と同様であり、９段階の調整キーがあり、マイナス４がコントラストが最も弱く、ゼロがコントラスト変化なしで、プラス４がコントラストが最も強い設定となっている。
【００６３】
本実施形態では、電子写真プロセスを用いたカラーデジタル複写機を例として説明しているが、上記の例に限定されるものではなく、画像入力装置１１０から情報を入力して、所定の画像処理を行い、その結果を出力する画像出力装置２１０として、例えば、インクジェット記録方式や昇華型の記録方式を用いた画像形成装置にも適用可能である。
【００６５】
【発明の効果】
本発明によれば、上記のように入力階調補正手段において画質調整を行うので、簡単な構成で画質調整を実現できる。また、入力階調補正手段では、ＲＧＢ画像に対して、Ｌａｂ画像への変換を行うことなく直接画質調整を行うので、回路規模を縮小させて装置の構成を簡略化することができる。
【００６６】
入力階調補正手段は変換テーブルを用いてＲＧＢデータをＲ’Ｇ’Ｂ’データに直接変換するため、回路規模をさらに縮小することが可能である。しかも、前述のように作成される変換テーブルを用いるので、簡易的に再現性良く画質調整することができる。
また本発明によれば、ハイライト部分での逆転現象を防止することができる。
【００６７】
また本発明によれば、色補正手段は変換テーブルを用いてＲＧＢデータをＣＭＹデータに直接変換するため、回路規模をさらに縮小可能である。
【図面の簡単な説明】
【図１】本発明の一実施形態に係る画像形成装置１の構成を概略的に示す図である。
【図２】画像処理装置１０の電気的な構成を示すブロック図である。
【図３】画像形成装置１の処理流れを示す図である。
【図４】Ｌ＊ａ＊ｂ＊均等色空間を示す図である。
【図５】図５（ａ）は、彩度が高い場合のＲとＲ’、ＢとＢ’、ＧとＧ’の関係を示すグラフであり、図５（ｂ）は、彩度が低い場合のＲとＲ’、ＢとＢ’、ＧとＧ’の関係を示すグラフである。
【図６】図６（ａ）は、明度が高い場合のＲとＲ’、ＢとＢ’、ＧとＧ’の関係を示すグラフであり、図６（ｂ）は、明度が低い場合のＲとＲ’、ＢとＢ’、ＧとＧ’の関係を示すグラフである。
【図７】図７（ａ）は、コントラストが高い場合のＲとＲ’、ＢとＢ’、ＧとＧ’の関係を示すグラフであり、図７（ｂ）は、コントラストが低い場合のＲとＲ’、ＢとＢ’、ＧとＧ’の関係を示すグラフである。
【符号の説明】
１ 画像形成装置
１０ 画像処理装置
１１ Ａ／Ｄ変換部
１２ シェーディング補正部
１３ 入力階調補正部
１４ 色補正部
１５ 黒生成下地除去部
１６ 空間フィルタ部
１７ 出力階調補正部
１８ 階調再現処理部
１９ 領域分離処理部
１１０ 画像入力装置
２１０ 画像出力装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color image forming apparatus such as a copying machine that digitally performs image processing and correction processing on color image information.
[0002]
[Prior art]
In order to digitally process color image information and obtain an output of a copying machine or the like, generally, the color image information of an original is decomposed into RGB (red, green, blue) components, read, and read RGB The signal is subjected to an operation for correcting the characteristic unique to the image input apparatus, converted into an L * a * b * color space, and color correction is performed. In this case, when the color reproduction range of the output image matches the color reproduction range of the input image, or when the color reproduction range of the output image is larger than the color reproduction range of the input image, the input image can be output as it is.
[0003]
Recently, color digital copiers equipped with an image quality adjustment function have appeared, and it is possible to adjust the saturation, brightness, and contrast of the read image information so that the output image can be brought closer to the image of the original. Alternatively, the image of the document can be changed according to the user's preference.
[0004]
The image quality adjustment is performed in the L * a * b * uniform color space after converting the RGB signals from the scanner into L * a * b * signals, as described in JP-A-8-56290.
[0005]
[Problems to be solved by the invention]
However, in practice, the above-described calculation for correcting the characteristic unique to the image input apparatus may not be able to be completely corrected, and further correction is performed by the color correction means. Also, when image quality adjustment is performed before correction by the color correction means, saturation, brightness, and contrast must be adjusted in the L * a * b * uniform color space without completely correcting the characteristics of the image input device. In such image quality adjustment, some distortion may remain. Furthermore, since the image quality adjustment is performed on the L * a * b * uniform color space for adjusting the saturation, lightness, and contrast, a configuration for always converting the RGB signal to the L * a * b * signal is required. The circuit becomes larger and the cost increases.
[0006]
An object of the present invention is to provide a color image forming apparatus capable of adjusting saturation, brightness, contrast and the like with a simple configuration.
[0007]
Another object of the present invention is to provide a color image forming apparatus capable of easily adjusting saturation, brightness, contrast, and the like without converting an RGB image read from a document into a Lab image. .
[0008]
[Means for Solving the Problems]
  The present inventionImage input means for reading an image of a document as an RGB image decomposed into RGB components;
  Adjustment setting means for performing settings related to image quality adjustment in accordance with a user operation;
  An input gradation correction means for performing image quality adjustment on the RGB image from the image input means according to the setting of the adjustment setting means and correcting the gradation,
  A color correction unit that converts the RGB image from the input tone correction unit into a CMY image decomposed into CMY components and performs color correction;
  Image output means for performing output for printing CMY images from the color correction means,
The input tone correction means includes RGB data obtained by reading patch data of a plurality of points arranged evenly selected from an L * a * b * uniform color space by the image input means; Correction is performed by converting the RGB data from one RGB component to another according to a conversion table representing the relationship with the RGB data obtained by reading the patch data of the selected points by a certain amount by the image input means. I doThis is a color image forming apparatus.
[0011]
According to the present invention, since the image quality adjustment is performed in the input tone correction unit as described above, the image quality adjustment can be realized with a simple configuration. Further, since the input tone correction means directly adjusts the image quality without converting the RGB image into the Lab image, a circuit for converting into the Lab image is not necessary, and the circuit scale is reduced. The configuration of the apparatus can be simplified.
[0013]
  AlsoThe input tone correction means directly converts RGB data to R′G′B ′ data using a conversion table, so that it is not necessary to perform complicated arithmetic processing, and a simple circuit with a low processing speed can be used. The scale can be further reduced.
[0014]
  Moreover, as described aboveCreate conversion tables based on data calculated to optimize image quality adjustmentBecause, You can easily adjust the image quality with good reproducibility.CanThe
  Further, according to the present invention, the input gradation correction means is based on the RGB image read by the image input means.
  If R data satisfies the condition of R <γ and R> G + δ or R> B + δ, where γ and δ are constants, the input gradation correction processing is stopped,
  When G data satisfies the condition of G <θ and G> B + κ or G> R + κ, where θ and κ are constants, the input gradation correction processing is stopped,
  When the B data satisfies the condition of B <ε and B> R + η or B> G + η, where ε and η are constants, the input gradation correction process is stopped.
  According to the present invention, when the above-described conditions are satisfied, the input tone correction process is stopped, so that it is possible to prevent the reverse phenomenon from occurring in the highlight portion.
[0015]
In the invention, it is preferable that the color correction unit performs correction by converting RGB components into CMY components according to a conversion table created in advance.
[0016]
According to the present invention, since the color correction means directly converts RGB data into CMY (cyan, magenta, yellow) data using a conversion table, it is not necessary to perform complicated arithmetic processing and the circuit scale can be further reduced. is there.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram schematically showing a configuration of an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 is a copier or the like that digitally processes color images. An original table 111 and an operation unit (not shown) are provided on the upper surface of the image forming apparatus 1. An image input device 110 and an image output device 210 are provided inside.
[0018]
A double-sided automatic document feeder (RADF) 112 having a predetermined positional relationship with the upper surface is supported on the upper surface of the document table 111 so as to be freely opened and closed.
[0019]
The double-sided automatic document feeder 112 first conveys a document so that one side of the document faces the image input device 110 at a predetermined position on the document table 111. After the image reading on the one surface is completed, the document is reversed and conveyed toward the document table 111 so that the other surface faces the image input device 110 at a predetermined position on the document table 111. In addition, the double-sided automatic document feeder 112 discharges the original after one-sided image reading has been completed for one original, and performs a double-sided conveyance operation for the next original. The above document transport and front / back reversing operations are controlled in relation to the overall operation of the image forming apparatus 1.
[0020]
The image input device 110 is disposed below the document table 111 in order to read an image of the document conveyed on the document table 111 by the double-sided automatic document feeder 112. The image input device 110 includes a document scanning body 301 that reciprocates in parallel along the lower surface of the document table 111, an optical lens 115, and a CCD (Charge) that is a photoelectric conversion element.
Coupled Device) line sensor 116.
[0021]
The document scanning body 301 includes a first scanning unit 113 and a second scanning unit 114. The first scanning unit 113 includes an exposure lamp 302 that exposes the document surface and a first mirror 303 that deflects a reflected light image from the document in a predetermined direction, and is constant with respect to the lower surface of the document table 111. While reciprocally moving in parallel at a predetermined scanning speed. The second scanning unit 114 has a second mirror 304 and a third mirror 305 that deflect the reflected light image from the original deflected by the first mirror 303 of the first scanning unit 113 further in a predetermined direction. The first scanning unit 113 reciprocates in parallel while maintaining a constant speed relationship.
[0022]
The optical lens 115 reduces the reflected light image from the original deflected by the third mirror 305 of the second scanning unit 114 and forms the reduced light image at a predetermined position on the CCD line sensor 116. .
[0023]
The CCD line sensor 116 sequentially photoelectrically converts the formed light image and outputs it as an electrical signal. The CCD line sensor 116 is a three-line color CCD that can read a black-and-white image or a color image and output line data that is color-separated into RGB color components. The document image information converted into an electrical signal by the CCD line sensor 116 is further transferred to an image processing apparatus 10 described later in FIGS. 2 and 3 and subjected to predetermined image data processing.
[0024]
Next, the configuration of the image output apparatus 210 and the configuration of each unit related to the image output apparatus 210 will be described.
[0025]
Below the image output device 210 is provided a paper feed mechanism 211 that separates the sheets (recording media) P stacked in the paper tray 306 one by one and supplies them to the image output device 210. . The sheets P separated and supplied one by one are transported to the image output device 210 with timing controlled by a pair of registration rollers 212 arranged in front of the image output device 210. Further, the paper P on which an image is formed on one side is conveyed again and supplied to the image output device 210 in accordance with the image formation timing of the image output device 210.
[0026]
A transfer / conveying belt mechanism 213 is disposed below the image output device 210. The transfer / conveying belt mechanism 213 has a configuration in which the sheet P is electrostatically adsorbed and conveyed to the transfer / conveying belt 216 stretched between the driving roller 214 and the driven roller 215 so as to extend substantially in parallel. Yes. A pattern image detection unit is provided in the vicinity of the lower side of the transfer / conveying belt 216.
[0027]
Further, a fixing device 217 for fixing the toner image transferred and formed on the paper P onto the paper P is disposed on the downstream side of the transfer / conveying belt mechanism 213 in the paper transport path. The paper P that has passed through the nip between the pair of fixing rollers of the fixing device 217 is discharged onto a paper discharge tray 220 attached to the outer wall of the image forming apparatus 1 by a discharge roller 219 via a conveyance direction switching gate 218. .
[0028]
The switching gate 218 selectively selects a conveyance path of the fixed sheet P between a path for discharging the sheet P to the main body of the image forming apparatus 1 and a path for resupplying the sheet P toward the image output apparatus 210. To switch to. The paper P whose transport direction has been switched again toward the image output device 210 by the switching gate 218 is turned upside down via the switchback transport path 221 and then supplied again to the image output device 210.
[0029]
Further, above the transfer conveyance belt 216 in the image output device 210, the first image formation unit Pa, the second image formation unit Pb, the third image formation unit Pc, and the fourth image are adjacent to the transfer conveyance belt 216. The image forming units Pd are arranged in order from the upstream side of the sheet conveyance path.
[0030]
The transfer / conveying belt 216 is driven in the direction indicated by the arrow Z in FIG. 1 by the driving roller 214 and carries the paper P fed through the paper feeding mechanism 211 as described above, and the paper P is fed to the image forming unit Pa. To Pd sequentially.
[0031]
The image forming portions Pa, Pb, Pc, and Pd have substantially the same configuration, and include photosensitive drums 222a, 222b, 222c, and 222d that are rotationally driven in the direction of arrow F shown in FIG.
[0032]
The chargers 223a to 223d for uniformly charging the photosensitive drums 222a to 222d and the electrostatic latent images formed on the photosensitive drums 222a to 222d are developed around the photosensitive drums 222a to 222d, respectively. Developing devices 224a to 224d, transfer members 225a to 225d for transferring the developed toner images on the photosensitive drums 222a to 222d to the paper P, and a cleaning device 226a for removing the toner remaining on the photosensitive drums 222a to 222d. To 226d are sequentially arranged along the rotation direction of the photosensitive drums 222a to 222d.
[0033]
Laser beam scanner units 227a to 227d are provided above the photosensitive drums 222a to 222d, respectively. The laser beam scanner units 227a to 227d include a semiconductor laser element (not shown) that emits light modulated according to image data, and a polygon mirror (deflecting device) for deflecting the laser beam from the semiconductor laser element in the main scanning direction. ) 240a to 240d, fθ lenses 241a to 241d and mirrors 242a to 242d and 243a to 243d for imaging the laser beams deflected by the polygon mirrors 240a to 240d on the surfaces of the photosensitive drums 222a to 222d. .
[0034]
The laser beam scanner 227a has a pixel signal corresponding to the black component image of the color original image, the laser beam scanner 227b has a pixel signal corresponding to the cyan component image of the color original image, and the laser beam scanner 227c has a pixel signal. The pixel signal corresponding to the magenta color component image of the color original image is input to the laser beam scanner 227d, and the pixel signal corresponding to the yellow color component image of the color original image is input thereto.
[0035]
As a result, electrostatic latent images corresponding to the color-converted document image information are formed on the photosensitive drums 222a to 222d. The developing device 224a contains black toner, the developing device 224b contains cyan toner, the developing device 224c contains magenta toner, and the developing device 22 contains yellow toner. The electrostatic latent images on the photosensitive drums 222a to 222d are developed with the toners of these colors. As a result, the document image information is reproduced as a toner image of each color by the image output device 210.
[0036]
Further, a sheet adsorbing charger 228 is provided between the first image forming portion Pa and the sheet feeding mechanism 211, and the adsorbing charger 228 charges the surface of the transfer conveyance belt 216 to supply the sheet. The paper P supplied from the mechanism 211 can be transported without shifting between the first image forming portion Pa and the fourth image forming portion Pd in a state where the paper P is reliably adsorbed on the transfer transport belt 216.
[0037]
On the other hand, a static eliminator 229 is provided between the fourth image forming unit Pd and the fixing device 217 almost directly above the drive roller 214. The static eliminator 229 is applied with an alternating current for separating the sheet P electrostatically attracted to the conveying belt 216 from the transfer conveying belt 216.
[0038]
In the image forming apparatus 1 having the above configuration, cut sheet-like paper is used as the paper P. When the paper P is fed out from the paper tray 306 and supplied into the guide of the paper feed conveyance path of the paper feed mechanism 211, the leading end of the paper P is detected by a sensor (not shown) and output from this sensor. Based on the detected signal, the pair of registration rollers 212 are temporarily stopped.
[0039]
The sheet P is fed onto the transfer / conveying belt 216 rotating in the direction of the arrow Z in FIG. 1 in time with each of the image forming units Pa to Pd. At this time, since the transfer conveyance belt 216 is charged by the charging charger 228 as described above, the sheet P is stably conveyed and supplied while passing through the image forming portions Pa to Pd. Is done.
[0040]
In each of the image forming units Pa to Pd, each color toner image is formed and superimposed on the support surface of the paper P that is electrostatically adsorbed and conveyed by the transfer conveyance belt 216. When the transfer of the image by the fourth image forming unit Pd is completed, the sheet P is sequentially peeled off from the transfer / conveying belt 216 by the discharging unit 229 from the leading end portion thereof and guided to the fixing device 217. Finally, the paper P on which the toner image is fixed is discharged onto a paper discharge tray 220 from a paper discharge port (not shown).
[0041]
In the above description, the laser beam scanner units 227a to 227d scan and expose the laser beam to perform optical writing on the photosensitive member. However, instead of the laser beam scanner unit, imaging with a light emitting diode array is performed. You may use the LED (Light Emitting Diode) head for optical writing which consists of a lens array. The LED head is smaller than the laser beam scanner unit and has no moving parts and is silent. Therefore, it can be suitably used in a tandem digital color image forming apparatus that requires a plurality of optical writing units.
[0042]
FIG. 2 is a block diagram showing an electrical configuration of the image processing apparatus 10. Image data read by the image input device 110 is first converted into a digital signal by an A / D (analog / digital) converter 11. The digital signal is subjected to shading correction in the shading correction unit 12 to remove various distortions generated in the illumination system, imaging system, and imaging system of the image input device 110. The corrected signal is adjusted in color balance by the input tone correction unit 13 and at the same time is converted from a reflectance signal to a signal that can be easily handled by the image processing system such as a density signal.
[0043]
Next, the color correction unit 14 performs a process of removing color turbidity based on the spectral characteristics of the CMY color material including unnecessary absorption components in order to faithfully realize the color. The black generation background removal unit 15 generates a black (K) signal from the CMY three-color signals after color correction, and generates a new CMY signal by subtracting the K signal obtained by black generation from the original CMY signal. The CMY three-color signal is converted into a CMYK four-color signal.
[0044]
Next, the obtained four-color signal is subjected to a spatial filter process using a digital filter in the spatial filter processing unit 16, and a process for preventing the blur and graininess of the output image by correcting the spatial frequency characteristics. Done. The output tone correction unit 17 converts a signal such as a density signal into a halftone dot area ratio that is a characteristic value of the image output device 210. The gradation reproduction processing unit 18 finally divides the image into pixels to generate halftones, and performs processing so that each gradation can be reproduced.
[0045]
In addition, after the above-described color correction processing, in the region separation processing unit 19, in order to improve the reproducibility of black characters or color characters in a character and photo mixed original, an image region of black characters (including color characters in some cases) is created. Extracted. The extracted image region is emphasized by high frequency by the spatial filter processing unit 16. At the same time, the halftone generation process is configured to select a binarization process or a multi-value process on a high-resolution screen suitable for high-frequency reproduction.
[0046]
On the other hand, for the region determined to be a photograph by the region separation processing unit 19, the spatial filter processing unit 16 performs low-pass filter processing for removing the input halftone component. At the same time, in the halftone generation process, a binarization process or a multi-value process is performed on the screen with an emphasis on gradation reproducibility. The image data subjected to the above-described processes is temporarily stored in the storage means, read out at a predetermined timing, and sent to the image output device 210.
[0047]
FIG. 3 is a diagram illustrating a processing flow of the image forming apparatus 1. The simple image quality adjustment of the present invention is performed by the input gradation correction unit 13 described above.
[0048]
When the user selects the simple image quality adjustment key on the operation panel, the RGB signals read by the image input device 110 are converted into L * a * b * signals after processing such as shading correction as shown in FIG. The RGB signal is directly sent to the input tone correction unit 13 where the RGB signal is converted into an R′G′B ′ signal by a look-up table for image quality adjustment. The look-up table is a conversion table that is stored in advance in memory and optimally adjusts image quality such as saturation, brightness, and contrast, and converts RGB signals to R′G′B ′ signals. After that, the R′G′B ′ signal undergoes the same color correction, black generation background removal processing, region separation processing, spatial filter processing, output gradation correction processing, and gradation reproduction processing (halftone generation) as in normal copying. Output.
[0049]
On the other hand, in the case of normal copying (when simple image quality adjustment is not executed), the RGB signals read by the image input device 110 are sent to the input tone correction unit 13 after processing such as shading correction, and calculation processing is performed. Color correction, black generation, background removal processing, region separation processing, spatial filter processing, output gradation correction processing, and gradation reproduction processing (halftone generation) are performed and output without any change.
[0050]
Hereinafter, color correction performed by the color correction unit 14 will be described. The color correction unit 14 grasps the characteristics of the image input apparatus 110 and the characteristics of the image output apparatus 210, and performs correction in consideration of the characteristics of both. Specifically, first, patches of approximately several thousand colors of L * a * b * data prepared in advance are read by the image input device 110, and the relationship between the L * a * b * signal and the RGB signal is obtained. Next, the image output device 210 outputs CMY data of about several thousand colors, and the output result is measured by a spectrophotometer to obtain the relationship between L * a * b * data and CMY data. Based on the relationship between the RGB signal and the L * a * b * signal thus obtained and the relationship between the L * a * b * signal and the CMY signal, a direct relationship between RGB and CMY is obtained by neurolearning. The color correction table shown is obtained. The data used to create the color correction table is evenly arranged in the L * a * b * space.
[0051]
In this way, matrix coefficients are not used for color correction, and since the individual RGB data read from the image input device 110 has one-to-one CMY data, reproducibility by color correction is very good. It is. In addition, since the color correction unit 14 converts from RGB to CMY, adjustment of image quality such as saturation, brightness, and contrast is not performed in the L * a * b * uniform color space, and the input tone correction unit 13 is adjusted. Thus, simple image quality adjustment similar to color correction can be performed. Since the input tone correction unit 13 uses a look-up table calculated so that image quality adjustment is optimized in advance, each image quality adjustment can be easily performed with good reproducibility.
[0052]
Next, a method for creating a lookup table used in the input tone correction unit 13 will be described. In the L * a * b * uniform color space shown in FIG. 4, all colors can be expressed, and the saturation, lightness, and hue are expressed by the following equations.
[0053]
[Expression 1]

[0054]
First, let's start with the case of increasing saturation. That is, in the Lab uniform color space, the distance from the origin O increases in the a * axis direction and the b * axis direction, and the saturation C increases. Further, the larger the value in the L * -axis direction, the brighter the brightness V becomes.
[0055]
In order to increase the saturation of a color α in the uniform color space, it is desirable to fix the hue angle H and lightness V and increase the saturation C by a certain amount. Actually, data of about several hundred colors arranged uniformly in the L * a * b * uniform color space is selected, and individual patch data is read by the image input device 110, and each L * a * b is read. * Find RGB read signals for data.
[0056]
Each selected data is moved so that a certain amount of saturation in the L * a * b * space is increased as indicated by point α, and the patch data is read by the image input device 110 in the same manner as the previous time to increase the saturation. The R′G′B ′ data when it is performed is obtained in advance. Then, the relationship between the RGB data for about several hundred colors and the R′G′B ′ data when the saturation is increased is obtained. At this time, in order to simplify the hardware, the R component, the G component, and the B component are handled separately, and the relationship between R and R ′, G and G ′, and B and B ′ is simplified to correct the input gradation. Part 13 can be used. In this case, the reverse phenomenon occurs in the highlight portion, but this can be solved by setting certain conditions shown below in the RGB data.
[0057]
・ Conditions regarding R
When R <γ and R> G + δ or R> B + δ, execution of input tone correction processing is prohibited
・ Conditions related to B
When B <ε and B> G + η or B> R + η, execution of input tone correction processing is prohibited
・ G conditions
When G <θ and G> B + κ or G> R + κ, execution of input gradation correction is prohibited
(Γ, δ, ε, η, θ, κ are constants)
FIG. 5A shows the relationship between R and R ′, B and B ′, and G and G ′ in the case of increasing saturation. Further, the saturation reduction is obtained in the same manner as the saturation increase, and the relationship is shown in FIG.
[0058]
Next, how to create a lookup table for increasing the brightness will be described. In order to increase the brightness of the color α in the L * a * b * uniform color space, it is desirable to fix the hue angle H and the saturation C and increase the brightness V by a certain amount. Specifically, as in the case of saturation, data of about several hundred colors arranged uniformly in the L * a * b * uniform color space is selected, and the individual patch data is sent to the image input device 110. The RGB data for each L * a * b * data is obtained.
[0059]
When each selected data is moved so as to increase a certain amount of lightness in the L * a * b * space like point α, and the patch data is read by the image input device 110 in the same manner as the previous time, and the lightness is increased. R'G'B 'data is obtained. The relationship between the RGB data for about several hundred colors and the R'G'B 'data when the brightness is increased is obtained. As in the case of saturation, the R component, G component, and B component are handled separately for simplification of hardware, and the relationship between R and R ′, G and G ′, and B and B ′ is simplified. The input tone correction unit 13 can handle this. FIG. 6A shows the relationship between R and R ′, B and B ′, and G and G ′ in the case of increasing the brightness, and FIG. 6B shows the case of decreasing brightness.
[0060]
Next, the contrast will be described. Contrast creates the relationship between R and R ', G and G', and B and B 'based on the feeling of the image change. FIG. 7A shows the relationship between R and R ', B and B', and G and G 'when the contrast is increased, and FIG. 7B shows the case when the contrast is decreased.
[0061]
When the user actually adjusts the image quality, when the image quality adjustment button on the operation panel is first selected, the saturation setting key, brightness setting key, and contrast setting key are displayed. Select one from When the user selects the saturation key, setting keys from minus 4 to plus 4 are displayed so that the saturation can be adjusted in 9 levels. The displayed minus 4 has the lowest saturation. The closer to zero, the lower the saturation reduction rate. At zero, there is no saturation change. Plus 4 has the highest saturation, and as it approaches zero, the rate of increase in saturation decreases.
[0062]
Setting key increments are equal. Even if the brightness setting key is selected, there are 9 levels of adjustment keys, as in the case of saturation, with minus 4 being the lowest brightness, zero being no brightness change, and plus 4 being the highest brightness setting. ing. Contrast setting keys are also the same as saturation and lightness, and there are nine adjustment keys. Minus 4 is the weakest contrast, zero is no contrast change, and plus 4 is the strongest contrast. .
[0063]
In the present embodiment, a color digital copying machine using an electrophotographic process has been described as an example. However, the present invention is not limited to the above example, and predetermined image processing is performed by inputting information from the image input device 110. As the image output device 210 that performs the operation and outputs the result, for example, it can be applied to an image forming device using an ink jet recording method or a sublimation recording method.
[0065]
【The invention's effect】
  BookAccording to the invention, since the image quality adjustment is performed in the input tone correction means as described above, the image quality adjustment can be realized with a simple configuration. Further, the input tone correction means directly adjusts the image quality without converting the RGB image into a Lab image, so that the circuit scale can be reduced and the configuration of the apparatus can be simplified.
[0066]
  EnterSince the force gradation correcting means directly converts RGB data into R′G′B ′ data using a conversion table, the circuit scale can be further reduced.In addition, since the conversion table created as described above is used, the image quality can be easily adjusted with good reproducibility.
  Further, according to the present invention, it is possible to prevent the reverse phenomenon at the highlight portion.
[0067]
Further, according to the present invention, since the color correction unit directly converts RGB data into CMY data using a conversion table, the circuit scale can be further reduced.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a configuration of an image forming apparatus 1 according to an embodiment of the present invention.
2 is a block diagram showing an electrical configuration of the image processing apparatus 10. FIG.
FIG. 3 is a diagram illustrating a processing flow of the image forming apparatus 1;
FIG. 4 is a diagram illustrating an L * a * b * uniform color space.
FIG. 5A is a graph showing the relationship between R and R ′, B and B ′, and G and G ′ when saturation is high, and FIG. 5B is low saturation. It is a graph which shows the relationship of R and R ', B and B', and G and G 'in the case.
6A is a graph showing the relationship between R and R ′, B and B ′, and G and G ′ when the lightness is high, and FIG. 6B is a graph when the lightness is low. It is a graph which shows the relationship between R and R ', B and B', G and G '.
FIG. 7A is a graph showing the relationship between R and R ′, B and B ′, and G and G ′ when the contrast is high. FIG. 7B is a graph when the contrast is low. It is a graph which shows the relationship between R and R ', B and B', G and G '.
[Explanation of symbols]
1 Image forming device
10 Image processing device
11 A / D converter
12 Shading correction part
13 Input tone correction unit
14 color correction unit
15 Black generation ground removal part
16 Spatial filter section
17 Output tone correction unit
18 gradation reproduction processor
19 Region separation processing unit
110 Image input device
210 Image output device

Claims (3)

Image input means for reading an image of a document as an RGB image decomposed into RGB components;
Adjustment setting means for performing settings related to image quality adjustment in accordance with user operations;
An input gradation correction means for performing image quality adjustment on the RGB image from the image input means according to the setting of the adjustment setting means and correcting the gradation,
A color correction unit that converts the RGB image from the input tone correction unit into a CMY image decomposed into CMY components and performs color correction;
Image output means for performing output for printing CMY images from the color correction means ,
The input tone correction means includes RGB data obtained by reading patch data of a plurality of points arranged evenly selected from an L * a * b * uniform color space by the image input means; Correction by converting from RGB component to another RGB component according to a conversion table showing the relationship with the RGB data obtained by reading the patch data of the selected point by a certain amount by the image input means color image forming apparatus and performs. The input tone correction means is based on the RGB image read by the image input means.
If R data satisfies the condition of R <γ and R> G + δ or R> B + δ, where γ and δ are constants, the input gradation correction processing is stopped,
When G data satisfies the condition of G <θ and G> B + κ or G> R + κ, where θ and κ are constants, the input gradation correction processing is stopped,
2. The color image formation according to claim 1, wherein the input gradation correction processing is stopped when the B data satisfies the condition of B <ε and B> R + η or B> G + η with ε and η as constants. apparatus. It said color correction means, by converting the RGB components into CMY components according to the conversion table prepared in advance, a color image forming apparatus according to claim 1 or 2, wherein the corrected.

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