JP2004181868A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus using an electrophotographic process, which enables the output of a high-quality image by preventing the collapse of the image, while stably outputting a thin line etc. by establishing compatibility between stable toner image formation 1 in the relatively isolated case of the toner image and image output accuracy 2 in the relatively dense case of the toner image. <P>SOLUTION: In terms of an arbitrary pixel in the image to be printed, this image forming apparatus controls image exposure so as to "increase electric field strength for developing toner", in the case of a pixel which makes few "pixels to form the toner" exist in an area in a peripheral vicinity NxM, and controls the image exposure so as to "decrease the electric field strength for developing the toner", in the case of a pixel which makes many "pixels to form the toner" exist in the area in the peripheral vicinity NxM. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００７０】
この３ｘ３の補正行列は、出力画像をレーザー露光強度に変換するためのものであり、中央部が注目画素位置に対応している。ある画素に注目した時に、注目画素に対してその周辺画素が及ぼす影響を考慮し、注目画素のレーザー露光を制御する補正行列である。
【００７１】
ここで、オペレータの中央箇所以外の箇所、すなわち注目画素の周囲近傍画素に対応する値にはマイナス記号をつけている。すなわち、近隣画素の画素値に対してその大きさに応じた、しかし方向はあくまで反対の量を注目画素の画像露光量に加算することになる。すなわち、周辺近傍画素が注目画素に対して及ぼす現像電界を打ち消すような量・方向の電荷量を注目画素に対して加算する。
【００７２】
この画像露光量補正により、近隣画素のつくる現像電界の注目画素に対する影響を打ち消し、画像再現性の高いトナー画像出力を行うことが可能となる。
【００７３】
なお、ここでの値は一例にすぎず、ここに挙げる値、オペレータサイズに限るものではなく、中央あるいは注目画素位置に対応するオペレータ値のみ現像電界を大きくする方向の値であり、それ以外の各点は逆方向あるいはゼロであれば良い。
【００７４】
本実施例での露光量補正は、この補正オペレータを用いて、
▲１▼．注目画素を中心とした３ｘ３の画像データと補正オペレータの同じ位置の数値を乗算し、その後それら全てを加算する
▲２▼．その計算結果の値に対してさらに、補正を行う。本実施例では、「計算結果が負になった場合は、画像露光量＝０とする
▲３▼．上段で決定された注目画素に対するレーザー露光量強度に対し、さらに感光体の光感度・現像装置の現像特性などを含めてさらに補正を行う
という処理を行っている。
【００７５】
以下、この補正オペレータの作用について例を挙げながら示す。
【００７６】
まず孤立ドットの場合を示す。次に示すのは画像データ内の孤立ドットを中心とした３ｘ３の領域（ドット）である。それぞれのドット部に記入してある数字は出力画像の画像強度を示している。ここで数字の大小はレーザー露光の強度を基準としている。また、通常出力画像は各ドットに対して１〜８ｂｉｔデータとして取り扱われることが多いため、この例では８ｂｉｔデータの出力画像の場合を示している。
【００７７】
本実施例は、反転現像系であるため、黒部に対してレーザー露光が行われる。そのため、黒ドット部は２５５の値を持ち、白部は０の値を持つことになる。
【００７８】
【表２】

【００７９】
このような画像において、中心の黒ドットに対して、どの程度のレーザー露光強度で行えば良いかを先のオペレータを用いてオペレータ演算を行う。この孤立ドット画像では
０ｘ０＋０ｘ（−０．１５）＋０ｘ０
＋０ｘ（−０．１５）＋２５５ｘ（１）＋０ｘ（−０．１５）
＋０ｘ０＋０ｘ（−０．１５）＋０ｘ０
＝２５５
となる。すなわち、このような孤立ドットの場合には元の画像データである２５５という値が変化しない。従って、この注目画素に対してはレーザー露光強度の最大設定値そのもので出力を行うことになる。
【００８０】
また、このような孤立ドットに対して隣に位置するドットについて計算を行うと、以下のようになる。
【００８１】
【表３】

【００８２】
０ｘ０＋０ｘ（−０．１５）＋０ｘ０
＋０ｘ（−０．１５）＋０ｘ（１）＋２５５ｘ（−０．１５）
＋０ｘ０＋０ｘ（−０．１５）＋０ｘ０
＝−３８．２５
となる。
【００８３】
本実施例では、このオペレータ演算の後に、「計算結果が負になった場合は、画像露光量＝０とする」という補正を行うため、結果としてこの画素に対しての画像露光量は０となる。
【００８４】
次に、黒部と白部間の境界画素の場合を示す。
【００８５】
【表４】

【００８６】
このような画像例で中央の注目画素に対して計算を行うと
２５５ｘ０＋２５５ｘ（−０．１５）＋０ｘ０
＋２５５ｘ（−０．１５）＋２５５ｘ（１）＋０ｘ（−０．１５）
＋２５５ｘ０＋２５５ｘ（−０．１５）＋０ｘ０
≒１４０
となり、孤立ドットにおける場合の半分強の値となることがわかる。
【００８７】
電子写真プロセスにおいては、元来隣接画素の影響により、この注目画素部分はトナー現像量が増加してしまう。そのため、その増加する分をあらかじめ見越して、レーザー露光量を減らしてやるという制御を行っているのである。逆に言えば、孤立ドットなど、周辺にドットがないような条件下でトナー粒子が現像されにくいことを考慮の上に、そのような条件ではレーザー露光量を増やすという制御を行うのが本実施例の特徴である。
【００８８】
最後に、黒ベタ部における制御例を示す。次のような画像データに対して、計算を行う。
【００８９】
【表５】

【００９０】
２５５ｘ０＋２５５ｘ（−０．１５）＋２５５ｘ０
＋２５５ｘ（−０．１５）＋２５５ｘ（１）＋２５５ｘ（−０．１５）
＋２５５ｘ０＋２５５ｘ（−０．１５）＋２５５ｘ０
≒１０２
となり、黒ベタ部においては、孤立ドットにおける場合の半分以下のレーザー露光量に設定している。
【００９１】
しかし、図４に示すレーザー露光量に対する感光体表面電位と印字画像濃度の対応を示したグラフを見てもわかるように、レーザー露光量が１００以上では本実施例の画像形成装置においては、印字画像濃度は変化しない。そのため、このようにベタ黒部においてレーザー露光量を減少させるような設定で用いても、ベタ黒画像の印字濃度が低下するようなことはない。
【００９２】
また、現像装置の設定、トナー交換などにより、このレーザー露光量に対する印字画像濃度が変化した場合には、オペレータ演算後に変換テーブルを用いて補正処理を行い、その変換テーブルの値もしくは変換曲線のγ等を変化させることで、ベタ黒画像の印字濃度などを防ぐことができる。
【００９３】
本実施例ではこのような処理を行うことで、高解像度の画像出力時の課題であった
１．トナー画像が比較的孤立している場合の安定したトナー画像形成
２．トナー画像が比較的密集している場合の画像出力精度
を両立させ、良好な画像出力を得ることが可能となる。
【００９４】
（４）本実施例と従来例の比較
図５に本実施例における「出力しようとするＮｘＮドットの大きさＮと出力されるドット径」を示す。理想的な直線Ｌに対して、従来例を示す他のプロットは「トナーが比較的孤立しているパターンである小径ドット」と「トナーが比較的密集しているパターンである大径ドット」の出力が両立していないのに対し、本実施例の出力は「小径ドットの消失」も「大径ドットのつぶれ」も発生せず、良好な画像出力を行うことが可能になっている。
【００９５】
また、先に示した従来例の出力画像に対して、同じ画像を本実施例において印字比較を行った結果も図３のＢに示す。なお、本実施例と従来例のレーザー露光量の条件は、レーザー露光の最大強度を調整し「ドット密度が高い部分」での出力が同じになるように設定した。
【００９６】
この出力画像中で、「トナー画像が比較的密集している部分」は太線による矩形部分や自動車画像の大まかな線などであり、「トナー画像が比較的孤立している部分」は細線部分、すなわち、細線による矩形部分や、自動車画像のエンジン部分などである。
【００９７】
比較例では「トナー画像が比較的密集している部分」は適正に印字されているが、細線などの「トナー画像が比較的孤立している部分」ではトナー画像が消失するなどして、画像情報が失われているのに対して、本実施例では「トナー画像が比較的密集している部分」では従来例と全く同じように良好な印字画像が得られ、同時に「トナー画像が比較的孤立している部分」でも安定したトナー画像が得られ、画像情報を失うことなく、適正な画像出力を実現している。
【００９８】
以上に示したように、本実施例では
▲１▼．注目画素を中心とした３ｘ３の画像データと補正オペレータの同じ位置の数値を乗算し、その後それら全てを加算する
▲２▼．その計算結果の値に対してさらに、補正を行う。本実施例では、「計算結果が負になった場合は、画像露光量＝０とする
▲３▼．上段で決定された注目画素に対するレーザー露光量強度に対し、さらに感光体の光感度・現像装置の現像特性などを含めてさらに補正を行う
という処理を行うことで、
１．トナー画像が比較的孤立している場合の安定したトナー画像形成
２．トナー画像が比較的密集している場合の画像出力精度
を両立させ、良好な画像出力を得ることが可能となった。
【００９９】
［実施例２］
本実施例も実施例１と同じように、
１．出力画像の各画素に対して、該画素の近傍画素が該画素に対して形成する現像電界を打ち消すために、
２．該画素の画素値に対して、近傍画素と該画素間の距離・方向に応じた補正量を該画素近傍の距離に応じた画素が該画素に対して形成する現像電界を打ち消す方向に加算することで変化させ、
３．前段で計算された該画素の補正画素値に対し、必要であればさらに補正カーブを用いて変換し、該画素に対する露光量として用いる
処理を行うが、オペレータ演算に用いるオペレータが若干異なること、および、そのオペレータ演算後の変換テーブルを用いた補正処理が異なる。
【０１００】
それにより、「トナー画像が比較的孤立している場合」の安定した画像出力と、「トナー画像が密集している場合」にトナーが白部の画素に現像され、出力画像がつぶれることを防ぐことが可能となる。
【０１０１】
本実施例は実施例１と露光補正回路７内の補正処理が異なる以外は同じが像形成装置を用いている。以下に、その補正処理について述べる。
【０１０２】
図８は本実施例の補正処理において、露光補正回路７、補正オペレータ、が行う補正動作フロー図である。
【０１０３】
（１）本実施例の出力時の画像変換方法
本実施例の補正処理に用いるオペレータは
【０１０４】
【表６】

【０１０５】
である。また、このオペレータ演算後の補正カーブは図６に示す。
【０１０６】
実施例１の場合、オペレータ演算後の注目画素の値が負になった場合は補正後の値は０としていたために、オペレータ演算後の注目画素の値が負になるような画素は全て同じ出力値となっていた。すなわち、白画素は隣接するドットがどのようなものであっても、同じ０という値を用いていた。
【０１０７】
しかし、本実施例では実施例１とは異なり、同じ白画素であっても隣接するドットの条件により、各画素に対する露光量が異なる。例えば、近傍が全て白画素であるような白画素の場合、オペレータ演算後の値は０である。しかし、黒画素に囲まれた白画素の場合、計算値は−８となる。また、白画素の周囲に位置する黒画素の計算値は−２である。
【０１０８】
また、孤立黒画素の場合はオペレータ演算後の値は１０であり、その隣接白画素の値は−１である。周囲が全て黒部の黒画素では２となる。
【０１０９】
これらの各画素に対して補正カーブ処理をした後の値は、
・周囲が全て白画素である白画素 ４８
・孤立黒画素 ２５６
・孤立黒画素に隣接する白画素 ３２
・孤立白画素に隣接する黒画素 ３２
・黒画素に囲まれた孤立白画素 ０
・ベタ黒部 １６０
となる。すなわち、ベタ白部（４８）を基準にとると、黒画素に囲まれた孤立白画素は周囲の黒画素を含めても、よりトナーが付着しにくい電位条件にすることができる。すなわち、実施例１と同じく単に孤立黒ドットを安定して出力できるのみならず、黒画素に囲まれた白画素なども安定して出力することが可能となる。
【０１１０】
このように、本実施例では「トナーが比較的孤立した場合」および「トナーが比較的密集した場合」を共に安定して出力することが可能となり、良好な画像出力を行うことが可能となる。
【０１１１】
本発明は、実施例の「デジタル露光」の画像形成装置に限られず、「アナログ露光」の画像形成装置の場合にも同様に成り立つ。
【０１１２】
また、像担持体として感光性の無い「静電記録誘電体」を用い、この静電記録誘電体の面に電荷を選択的に飛ばして付着させ、或は静電記録誘電体の面を一様に帯電処理した後、除電針アレイや電子銃等の除電装置で選択的に除電して静電潜像を形成する「静電記録プロセス」の場合にも同様の制御を行った際には効果がある。
【０１１３】
以上、本発明の様々な例と実施例が示され説明されたが、当業者であれば、本発明の趣旨と範囲は本明細書内の特定の説明と図に限定されるのではなく、本願特許請求の範囲に全て述べられた様々の修正と変更に及ぶことが理解されるであろう。
【０１１４】
本発明の実施態様の例を以下に列挙する。
【０１１５】
〔実施態様１〕 電子写真プロセスを用いた画像形成装置であり、印字する画像内の任意の画素について、周辺近傍ＮｘＭの領域に「トナーを形成すべき画素」が少ない画素については「トナーを現像するための電界強度を増加させる」ように画像露光量を制御し、周辺近傍ＮｘＭの領域に「トナーを形成すべき画素」が多い画素については、「トナーを現像するための電界強度を減少させる」ように制御することを特徴とする画像形成装置。
【０１１６】
〔実施態様２〕 実施態様１において、前記制御を行うために、印字画像データの画素に対してオペレータ演算およびそのオペレータ演算結果に対して補正テーブルを用いた補正処理を行うことを特徴とする電子写真プロセスを用いた画像形成装置。
【０１１７】
〔実施態様３〕 実施態様２において、像担持体である感光体の膜厚変化に応じて、前記処理のオペレータあるいは補正テーブルを変化させることを特徴とする電子写真プロセスを用いた画像形成装置。
【０１１８】
〔実施態様４〕 実施態様２または３において、使用する現像装置、現像モード、現像剤、もしくは感光体などの関与パラメータに応じて前記処理の係数を変化させることを特徴とする電子写真プロセスを用いた画像形成装置。
【０１１９】
〔実施態様５〕 印字する画像内の任意の画素について、周辺近傍ＮｘＭの領域に「トナーを形成すべき画素」が少ない画素については「トナーを現像するための電界強度を増加させる」ように画像露光量を制御し、周辺近傍ＮｘＭの領域に「トナーを形成すべき画素」が多い画素については、「トナーを現像するための電界強度を減少させる」ように制御することを特徴とする電子写真プロセスを用いた画像形成方法。
【０１２０】
〔実施態様６〕 実施態様５において、前記制御を行うために、印字画像データの画素に対してオペレータ演算およびそのオペレータ演算結果に対して補正テーブルを用いた補正処理を行う電子写真プロセスを用いた画像形成方法。
【０１２１】
〔実施態様７〕 実施態様６において、像担持体である感光体の膜厚変化に応じて、前記処理のオペレータあるいは補正テーブルを変化させることを特徴とする電子写真プロセスを用いた画像形成方法。
【０１２２】
〔実施態様８〕 実施態様６または７において、使用する現像装置、現像モード、現像剤、もしくは感光体などの関与パラメータに応じて前記処理の係数を変化させることを特徴とする電子写真プロセスを用いた画像形成方法。
【０１２３】
【発明の効果】
以上に示したように、本発明では以下の手順
▲１▼．出力画像の各画素に対して、該画素の近傍画素が該画素に対して形成する現像電界を打ち消すために、
▲２▼．該画素の画素値に対して、近傍画素と該画素間の距離・方向に応じた補正量を該画素近傍の距離に応じた画素が該画素に対して形成する現像電界を打ち消す方向に加算することで変化させ、
▲３▼．前段で計算された該画素の補正画素値に対し、必要であればさらに補正カーブを用いて変換し、該画素に対する露光量として用いる
を行うという特徴により、従来発生していた課題
・ドット密度が低い部分を適正に現像されるように調整すると、ドット密度が高い部分でトナー粒子の現像量が過剰になり、出力画像がつぶれてしまう
・ドット密度が高い部分を適正に現像されるように調整すると、ドット密度が低い部分でトナー現像量が不足し、画像情報が失われてしまう
という課題を防ぎ、いずれの場合においても良好な画像性を得ることが可能となる。
【図面の簡単な説明】
【図１】実施例１の画像形成装置の概略図
【図２】従来のＮｘＮのドットを出力しようとした場合に、実際に出力されるドット径
【図３】実施例１の画像出力結果と従来例での画像出力結果（Ａ．従来例、Ｂ．本実施例）
【図４】実施例１におけるレーザー露光強度と感光体表面電位およびその際のベタ黒印字画像濃度
【図５】実施例１におけるＮｘＮのドットを出力しようとした場合に、実際に出力されるドット径
【図６】実施例２における補正テーブルの補正カーブ
【図７】実施例１の画像露光強度の補正方法において、露光補正回路７、補正オペレータ、が行う補正動作フロー図
【図８】実施例２の画像露光強度の補正方法において、露光補正回路７、補正オペレータ、が行う補正動作フロー図
【符号の説明】
１・・感光体、２・・帯電ローラ、３・・現像装置、４・・転写ローラ、５・・定着装置、６・・イメージ露光装置、７・・露光補正装置、８・・ホスト装置、Ｓ１〜Ｓ３・・バイアス印加電源、Ｃ・・プロセスカートリッジ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus and an image forming method using an electrophotographic process.
[0002]
[Prior art]
In an electrophotographic image forming apparatus, an image is formed using the following electrophotographic process.
[0003]
First, the surface of the electrophotographic photosensitive member is uniformly charged by a charging member (charging). Next, light corresponding to the image is applied to the exposed portion, and the charged charge in the portion irradiated with the light is removed. Thereby, an electrostatic latent image corresponding to the image is formed (latent image formation). Then, the developing unit develops the electrostatic latent image into a visible image (toner development). This image is transferred (transferred) to a transfer material in a transfer section and fixed (fixed).
[0004]
Generally, “latent image formation / toner development” in an electrophotographic process is realized by the following steps.
[0005]
1. By the image exposure, the charge amount at an arbitrary position in the image carrier (surface or inside) is controlled (latent image formation).
[0006]
2. The “developing electric field for developing the toner particles” is formed in the developing area by the charge latent image formed by the image exposure. The developing electric field is obtained by superposing electric fields formed by all charges in the entire region. That is, the developing electric field is not determined only by the charge amount in each region of the image carrier, and it depends on the surrounding charge distribution. That is, the developing electric field for developing the toner particles on each area on the surface of the image carrier depends not only on the amount of the charge latent image in the corresponding area but also on the amount of the surrounding charge latent image. Here, the surrounding charge distribution includes not only the charges in the image carrier, but also the charges induced in the counter electrode and the like (formation of a developing electric field).
[0007]
3. The toner particles are developed by the formed developing electric field (development of toner particles).
[0008]
As is apparent from the above process, the amount of toner development on each area of the image carrier surface is affected by not only the charge latent image in the area but also the latent image around the pixel. As a result, even if the pixels should have the same image density, the amount of toner development differs depending on the surrounding image patterns, and the output print image density / pattern may be different from the intended one.
[0009]
In particular, in the case of isolated dots or thin lines with few dots in the surrounding area and patterns in which there are dots in the surrounding area, the effect of other dots in the vicinity of each pixel is different, so that stable output of both may not be possible. Was. In particular, such a phenomenon was remarkable in a case where the distance between the adjacent pixels was short and the resolution was high, which had to be affected by the adjacent pixels.
[0010]
As an example, a case where “1200 dpi N × N dots” is output is taken as an example. Hereinafter, a pixel for forming a toner image or a toner image after formation is used. FIG. 2 shows the dot diameter of the output dot image at that time.
[0011]
by the way,
1200 dpi = 1200 dots / 25400 μm
Therefore, the size of one dot is
1 inch / 1200 dots = 25400 μm / 1200 dots = 21 μm
And the size of 10 dots should be about 210 μm.
[0012]
The straight line L shows a case where the “dot diameter to be output” linearly corresponds to the “size of the dot to be output = N”.
[0013]
However, it is difficult to stably obtain an ideal output like the straight line L in the electrophotographic process. For example, the developing electric field generated by an isolated charge latent image having a 1 × 1 dot diameter (21 μm × 21 μm) is too small, and it is difficult to stably develop and form toner particles from a developing device to a photoreceptor surface. As a result, toner particles cannot be developed for a 1 × 1 dot image.
[0014]
In the electrophotographic process, a dot image is formed by toner particles only when the dot size N is increased and the developing electric field generated by the total charge in the N × N region becomes large enough to develop the toner particles. You. For this reason, no dot is output in an area where the dot size N is small, and thereafter the dots start to be formed from the point where the dot size N has increased, and the line L is followed only after N becomes sufficiently large. .
[0015]
FIG. 2 shows such an example. A. Example where the dot exposure amount is A. In A, a dot having a size of 1 × 1, 2 × 2 cannot be developed, and a dot image starts to be formed only when 3 × 3 dots, that is, 9 dots are collected.
[0016]
Then, after 4 × 4 dots, dot images are formed along the straight line L. That is, when N is 2 or less, "dot image disappearance" occurs, and an ideal image can be formed in an area where N is 4 or more.
[0017]
However, formation of a toner image becomes unstable with 1 × 1, 2 × 2 dots, or a thin line having a width of 1 dot, which is close to an isolated dot with a small number of dot portions around.
[0018]
When such “loss of dots and lines” occurs, image information is lost. In order to prevent this, for example, it is necessary to increase the developing electric field generated by a 1 × 1 dot isolated charge latent image. However, when an attempt is made to increase the developing electric field generated by the 1 × 1 dot isolated charge latent image by increasing the image exposure amount for this purpose, the example shown in FIG. As shown in B, the 1 × 1 dot is output stably, but in a region where dots gather around the target pixel, that is, in a region where N is large, the developing electric field formed becomes excessive and I will. Therefore, for example, In B, the “output dot diameter” is larger than the straight line L.
[0019]
That is,
1. Stable toner image formation when the toner image is relatively isolated
2. Image output accuracy when toner images are relatively dense
There is a problem that it is difficult to achieve both.
[0020]
When a high-resolution image is to be formed, the size of a pixel becomes smaller and the distance between neighboring pixels becomes smaller, so that such a problem has become more prominent.
[0021]
Further, when an image carrier having a small surface energy and a small adhesive force of the toner to the image carrier is used as an image carrier, this problem becomes more remarkable, and it becomes difficult to reproduce fine dots. Similarly, when a spherical toner having a small adhesive force to the image carrier is used, the problem occurs remarkably.
[0022]
There has been proposed one that aims to correct an output image in consideration of the influence of the charge distribution of peripheral pixels (for example, see Patent Document 1). The image forming apparatus includes a step of formulating a physical relationship in an electrophotographic development process and a step of sequentially solving the equation.
[Patent Document 1]
JP-A-8-69391
[0023]
[Problems to be solved by the invention]
However, in order to cope with high-speed printing using this method, a numerical operation circuit having a very high calculation capability is required. Also, it is difficult to realize a step of formulating a physical phenomenon in the image processing apparatus into an equation in the image processing apparatus.
[0024]
The present invention has been proposed in view of the above,
1. Stable toner image formation when the toner image is relatively isolated
2. Image output accuracy when toner images are relatively dense
When a drum (OCL drum) having a small surface energy is used as an image carrier, a spherical toner is used for jumping development, for example, in an image forming apparatus of an injection charging / cleanerless system, a thin line or the like is used. This is to stabilize the output, prevent the image from being broken, and enable high-quality output.
[0025]
[Means for Solving the Problems]
The present invention relates to an image forming apparatus using an electrophotographic process, and, for an arbitrary pixel in an image to be printed, for a pixel having a small number of “pixels for which toner is to be formed” in a peripheral NxM area, “developing toner” The image exposure amount is controlled so as to "increase the electric field strength for developing the toner." For pixels having many "pixels on which toner is to be formed" in the peripheral NxM area, "decrease the electric field strength for developing the toner." The image forming apparatus is characterized in that the control is performed as described above.
[0026]
(Operation)
That is, in the present invention,
1. Stable toner image formation when the toner image is relatively isolated
2. Image output accuracy when toner images are relatively dense
Attention is paid to an arbitrary pixel in the image to be printed in order to achieve both, and for pixels around which there are few "pixels for which toner is to be formed", image exposure is performed so as to "increase the electric field strength for developing the toner". The amount is controlled, and control is performed so as to “reduce the electric field strength for developing the toner” for pixels having many “pixels on which toner is to be formed” around.
[0027]
By paying attention to any pixel in the image to be printed, and controlling the image exposure amount so as to increase the electric field strength for developing the toner for pixels having a small number of "pixels to be formed with toner" in the vicinity, In a pattern such as an isolated dot where no dot exists in the vicinity or a thin line similar to the isolated dot, the “development electric field for developing toner per pixel” is large, so that the toner image can be output without disappearing. is there.
[0028]
In the case where the dots are densely packed, the "development electric field for developing toner per pixel" is small, so that even when they are added together, it is possible to prevent the development electric field from becoming excessively large. As a result, an ideal toner image can be output.
[0029]
Similarly, by paying attention to an arbitrary pixel in the image to be printed, and by controlling the pixel having many “pixels to be formed with toner” in the vicinity so as to “reduce the electric field strength for developing the toner”, Due to the excessive developing electric field generated by the electric charge in the surrounding black pixel portion, it is possible to prevent image defects such as toner adhering to white pixels surrounded by dots.
[0030]
In addition, the amount of “charge on the surface of the photoconductor corresponding to a pixel on which toner is to be formed” excessively forming a developing electric field with respect to a peripheral pixel decreases according to the distance from the pixel. That is, dots that are very close to the pixel greatly increase the development field for the pixel. Further, if the dot is relatively far from the pixel, the developing electric field for the pixel hardly increases. That is, if a dot is present in the vicinity of the pixel for an arbitrary pixel of the output image, the charge amount on the photoconductor surface corresponding to the pixel is determined according to the distance to the dot by “developing toner. If there are no dots near the pixel, the electric field created by the charge on the photoconductor surface corresponding to the white pixel in the vicinity of the pixel, i.e., the toner particles By controlling the amount of charge on the surface of the photoconductor corresponding to the pixel so as not to be affected by the development electric field in the direction in which development is not performed, and to `` increase the electric field strength for developing the toner '',
1. Stable toner image formation when the toner image is relatively isolated
2. Image output accuracy when toner images are relatively dense
, And a good image output can be obtained.
[0031]
In order to realize such control, the present invention uses the following procedure.
▲ 1 ▼. For each pixel of the output image, in order to cancel the developing electric field formed by the neighboring pixels of the pixel with respect to the pixel,
▲ 2 ▼. To the pixel value of the pixel, a correction amount according to the distance and direction between the neighboring pixel and the pixel is added in the direction to cancel the developing electric field formed for the pixel by the pixel according to the distance near the pixel. Change
(3). The correction pixel value of the pixel calculated in the previous stage is further converted using a correction curve if necessary, and is used as an exposure amount for the pixel.
I do.
[0032]
That is, by superimposing on the pixel a charge in a direction and amount that cancels out the developing electric field exerted on the pixel by the pixel in the vicinity of the pixel of interest, the influence of the pixel in the vicinity on the pixel is reduced. , And faithful image reproduction can be performed.
[0033]
In order to remove the influence of the pixels near the periphery on the pixels, the present invention performs a correction process using an operator operation, and then performs a correction process using a correction table.
[0034]
In addition, the amount of the developing electric field exerted on the pixel by a pixel in the vicinity of the target pixel varies depending on the thickness of the photoconductor, the photosensitivity, the distance between the developing device and the photoconductor, the setting of the developing bias, the toner type, and the like. By changing the operator of the operator calculation or the correction curve in response to these parameter changes, the thickness of the photoconductor, the light sensitivity, the distance between the developing device and the photoconductor, the setting of the developing bias, the toner type, etc. are changed. It is also possible to perform good image output.
[0035]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail using specific examples.
[0036]
[Example 1]
This embodiment is an image forming apparatus using an electrophotographic process, and performs printing on each pixel of print image data.
1. For each pixel of the output image, perform a local operator operation using an operator that arranges correction values according to the distance and direction from the pixel,
2. For the pixel value of the pixel calculated in the previous stage, the exposure amount for the pixel is determined using a correction curve.
It is characterized by:
[0037]
(1) Explanation of the implementation system
FIG. 1 is a schematic view of the image forming apparatus of the present embodiment. The image forming apparatus of this embodiment is a laser beam printer of a contact charging type, a reversal developing type, a cleanerless system, and a process cartridge type using an electrophotographic process.
[0038]
(Image carrier)
Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member as an image carrier. The image forming apparatus of this embodiment uses reversal development and uses a negative photosensitive member. This embodiment is an OPC photosensitive member having a diameter of 30 mm, and is driven to rotate in a direction of an arrow at a peripheral speed of 94 mm / sec.
[0039]
(Telephone)
Reference numeral 2 denotes a charging roller serving as a contact charging member brought into contact with the photoconductor 1. A charging bias is applied to the charging roller 2 from the charging bias power supply S1 so that the outer peripheral surface of the photoconductor 1 is uniformly charged to approximately -600V.
[0040]
(Exposure)
A scanning exposure L by a laser beam is output from an image exposure device (laser beam scanner) 6 including a laser diode and a polygon mirror to the charged surface of the photoreceptor 1.
[0041]
Reference numeral 8 denotes a host device such as an image reader / computer / facsimile transmission unit, which inputs a time-series electric digital pixel signal of target image information from the host device 8 to a control circuit unit of the image forming apparatus. The input time-series electric digital pixel signal of the target image information is first processed and corrected by the exposure correction circuit 7, and then sent to the image exposure device 6, where the scanning exposure L is intensity-modulated, and A charge distribution corresponding to the target image information is formed on the outer peripheral surface of No. 1, and an electrostatic latent image is formed. In this embodiment, image exposure is performed at an image resolution of 1200 dpi.
[0042]
(Current image)
The electrostatic latent image is developed as a developer image (toner image) by the reversal non-contact developing device 3 using a negatively chargeable magnetic one-component insulating developer (toner) 31 having an average particle diameter of 6 μm as a developer. You.
[0043]
Reference numeral 32 denotes a non-magnetic developing sleeve having a diameter of 16 mm and containing a magnet 33. The developing sleeve 32 is coated with the above-described developer 31, and is fixed to the photoconductor 1 in a state where the distance from the surface of the photoconductor 1 is fixed to 300 μm. The developing sleeve 32 is rotated at a constant speed, and a developing bias voltage is applied to the developing sleeve 32 from a developing bias power supply S2. The developer 31 is triboelectrically charged by rubbing against the elastic blade 34 and has electric charge.
[0044]
A one-component jumping development is performed between the developing sleeve 32 and the photoconductor 1 by applying a predetermined developing bias to the developing sleeve 32 and combining the developing electric fields generated by the previous image charge distribution. In this embodiment, a rectangular wave of 1.6 kVpp, 2 kHz, and Vdc = 500 V was used as the developing bias.
[0045]
(Transcription)
On the other hand, a transfer material P as a recording material is supplied from a paper supply unit (not shown), and a photosensitive member 1 and a transfer roller 4 having a medium resistance as a contact transfer unit brought into contact with the photosensitive member 1 with a predetermined pressing force. At a predetermined timing.
[0046]
A predetermined transfer bias power source is applied to the transfer roller 4 from a transfer bias application power source S3. The transfer material P introduced into the transfer portion T is conveyed by nipping the transfer portion T, and the developer image formed and carried on the surface of the photoreceptor 1 on its surface side is sequentially subjected to electrostatic force and pressing force. It is transcribed.
[0047]
(Fixed)
The transfer material P having received the transfer of the developer image is separated from the surface of the photoreceptor 1 and introduced into a fixing device 5 such as a heat fixing system, where the developer image is fixed, and as an image formed product (print, copy). It is discharged out of the device.
[0048]
(Cleanerless system)
The image forming apparatus of this embodiment is a cleaner-less apparatus that does not include a dedicated cleaning device that removes transfer residual toner remaining on the surface of the photoconductor 1 after the transfer material is separated from the surface of the photoconductor 1. The transfer residual toner remaining on the surface of the body 1 is carried to the charging section, which is the contact portion between the photosensitive body 1 and the charging roller 2, as the photosensitive body 1 continues to rotate, and further carried to the developing section. The developing device 3 cleans the image at the same time (simultaneously recovers the image) and reuses it.
[0049]
(cartridge)
The image forming apparatus according to the present embodiment includes a cartridge system in which three process devices of a photoreceptor 1, a contact charging member 2, and a developing device 3 are included in a cartridge C and can be collectively attached to and detached from the image forming apparatus main body. The device is not limited to this.
[0050]
(2) Image formation in electrophotographic process
In the above process, it is the exposure and development process that substantially forms the latent image and the toner image.
[0051]
First, the amount of charge at an arbitrary position on the surface of the photoconductor (photosensitive drum) is controlled by image exposure (latent image formation).
[0052]
Thereafter, a "development electric field for developing toner particles" is formed in the development area. At this time, the developing electric field is obtained by superposing electric fields formed by all charges in the entire region.
[0053]
That is, the developing electric field is not determined only by the charge amount in each region of the photoreceptor surface, but depends on the surrounding charge distribution. That is, the developing electric field for developing the toner particles on each area of the photoconductor surface depends not only on the amount of the latent charge image in the corresponding area but also on the amount of the surrounding latent charge image.
[0054]
In addition, the charge distribution around this area includes charges induced by a developing bias applied to the developing device (formation of a developing electric field).
[0055]
Then, the toner particles are developed by the finally formed developing electric field, and a toner image is formed (development of toner particles).
[0056]
Thus, "the developing electric field for developing the toner particles on each area of the photoconductor surface depends not only on the amount of the latent charge image in the corresponding area but also on the amount of the surrounding latent charge image". As a result, the amount of toner development on the photoreceptor surface varies depending on the surrounding image pattern, and the output printed image may be different from the intended one.
[0057]
In particular, in the case of high resolution, since the distance between adjacent pixels is short, the pixel is easily affected by the developing electric field generated by the adjacent pixels. For this reason, the above-described isolated dots at the time of high resolution or the disappearance of the fine lines occur.
[0058]
In order to show such a problem in the related art, an output using the conventional example in which only the exposure amount correction is applied without performing the calculation using the neighboring pixel value in the exposure correction circuit 7 of the present embodiment is performed. The example of FIG. 2 shows “N × N dot size N and output dot diameter”. A, eg. B.
[0059]
Example. With the laser exposure of A, dots having the size of 1 × 1, 2 × 2 cannot be developed, and a dot image starts to be formed only when 3 × 3 dots, that is, 9 dots are collected. After 4 × 4 dots, dot images are formed along the straight line L. However, if N is 2 or less, "dot image disappearance" occurs, and image information disappears.
[0060]
In order to prevent this, it is necessary to increase the developing electric field generated by the 1x1 dot isolated charge latent image. Therefore, an example in which the developing electric field generated by the 1x1 dot isolated charge latent image is increased by increasing the image exposure amount . In the case of B, 1 × 1 dots are output stably, but in a region where dots gather, that is, in a region where N becomes large, the developing electric field formed becomes excessive. Therefore, for example, In B, the “dot diameter to be output” is large as a whole, and an “image in which the line is thickly collapsed” has a large amount of toner attached to the image to be originally output.
[0061]
Specific examples. FIG. 3A shows an output image in the case of A. This image shows a rectangle having a 1, 2, 3, 4 dot width and a general line image. From this image, it can be seen that the rectangular portion drawn by a thin line of 1 dot width disappears, and the thin line portion also disappears in the general line image, and image information is lost.
[0062]
(3) Method of Correcting Image Exposure Intensity of This Embodiment
In order to solve such a problem, in the present embodiment, in the exposure correction circuit 7, the image exposure intensity of each pixel is subjected to intensity correction so as to cancel the influence of the neighboring pixels, and then the sensitivity of the photoconductor is further increased. Intensity correction is performed according to the characteristics.
[0063]
Hereinafter, the correction method of this embodiment will be specifically described. FIG. 7 is a flowchart of a correction operation performed by the exposure correction circuit 7 and a correction operator in the image exposure intensity correction method.
[0064]
As described above, in the electrophotographic process, there occurs a phenomenon that "even if the exposure and charge distribution of the dot portions on the photoconductor surface are equal, the toner development amount and the dot shape are different due to the influence of adjacent pixels".
[0065]
Therefore, if the image formation is performed ignoring the influence of the image distribution in the peripheral portion, if the image exposure is performed based on the isolated dots, the toner development amount becomes excessive when dots exist in the peripheral portion. In some cases. Conversely, if image exposure is performed based on a state in which dots are concentrated, a situation may occur in which the amount of toner development decreases in isolated dots and the like.
[0066]
In order to solve such issues,
▲ 1 ▼. For each pixel of the output image, in order to cancel the developing electric field formed by the neighboring pixels of the pixel with respect to the pixel,
▲ 2 ▼. To the pixel value of the pixel, a correction amount according to the distance and direction between the neighboring pixel and the pixel is added in the direction to cancel the developing electric field formed for the pixel by the pixel according to the distance near the pixel. Change
(3). The correction pixel value of the pixel calculated in the previous stage is further converted using a correction curve if necessary, and is used as an exposure amount for the pixel.
It is effective.
[0067]
That is, by superimposing on the pixel a charge in a direction and amount that cancels out the developing electric field exerted on the pixel by the pixel in the vicinity of the pixel of interest, the influence of the pixel in the vicinity on the pixel is reduced. , And faithful image reproduction can be performed.
[0068]
In order to realize such control, in the present embodiment, an operator operation is performed on the output image data using a 3 × 3 operator as described below, so that the pixel of interest and the neighboring pixels around the pixel of interest are By performing laser exposure control in consideration of the influence, better image control is enabled.
[0069]
[Table 1]

[0070]
This 3 × 3 correction matrix is for converting an output image into laser exposure intensity, and the center portion corresponds to the pixel position of interest. This is a correction matrix for controlling the laser exposure of the target pixel in consideration of the influence of the peripheral pixels on the target pixel when the target pixel is focused.
[0071]
Here, a minus sign is attached to a portion other than the central portion of the operator, that is, a value corresponding to a pixel in the vicinity of the target pixel. That is, an amount corresponding to the size of the pixel value of the neighboring pixel but in the opposite direction is added to the image exposure amount of the target pixel. That is, the amount of charge in the direction and amount that cancels the development electric field exerted on the target pixel by the peripheral neighboring pixels is added to the target pixel.
[0072]
By this image exposure amount correction, it is possible to cancel the influence of the developing electric field generated by the neighboring pixels on the target pixel, and to perform toner image output with high image reproducibility.
[0073]
Note that the value here is merely an example, and is not limited to the values listed here and the operator size.Only the operator value corresponding to the center or the target pixel position is a value in the direction in which the developing electric field is increased. Each point may be in the opposite direction or zero.
[0074]
Exposure amount correction in this embodiment is performed using this correction operator.
▲ 1 ▼. The 3 × 3 image data centered on the target pixel is multiplied by the numerical value at the same position of the correction operator, and then all of them are added.
▲ 2 ▼. The value of the calculation result is further corrected. In the present embodiment, “If the calculation result is negative, the image exposure amount is set to 0.
(3). The laser exposure intensity for the target pixel determined in the upper stage is further corrected including the photosensitivity of the photoconductor and the development characteristics of the developing device.
Is performed.
[0075]
Hereinafter, the operation of the correction operator will be described with reference to examples.
[0076]
First, the case of an isolated dot will be described. The following is a 3 × 3 area (dot) centered on an isolated dot in the image data. The number written in each dot part indicates the image intensity of the output image. Here, the magnitude of the number is based on the intensity of the laser exposure. In addition, since a normal output image is often handled as 1 to 8 bit data for each dot, this example shows an output image of 8 bit data.
[0077]
In the present embodiment, since a reversal development system is used, laser exposure is performed on a black portion. Therefore, the black dot portion has a value of 255, and the white portion has a value of 0.
[0078]
[Table 2]

[0079]
In such an image, operator calculation is performed using the previous operator to determine what laser exposure intensity should be used for the central black dot. In this isolated dot image
0x0 + 0x (-0.15) + 0x0
+ 0x (-0.15) + 255x (1) + 0x (-0.15)
+ 0x0 + 0x (-0.15) + 0x0
= 255
It becomes. That is, in the case of such an isolated dot, the value of 255 as the original image data does not change. Therefore, the target pixel is output with the maximum setting value of the laser exposure intensity itself.
[0080]
Further, when calculation is performed for a dot located adjacent to such an isolated dot, the result is as follows.
[0081]
[Table 3]

[0082]
0x0 + 0x (-0.15) + 0x0
+ 0x (-0.15) + 0x (1) + 255x (-0.15)
+ 0x0 + 0x (-0.15) + 0x0
= -38.25
It becomes.
[0083]
In the present embodiment, after this operator operation, a correction is made that “if the calculation result is negative, the image exposure amount is set to 0”. As a result, the image exposure amount for this pixel is 0. Become.
[0084]
Next, a case of a boundary pixel between a black part and a white part will be described.
[0085]
[Table 4]

[0086]
Performing calculations on the center pixel of interest in such an image example
255x0 + 255x (-0.15) + 0x0
+ 255x (-0.15) + 255x (1) + 0x (-0.15)
+ 255x0 + 255x (-0.15) + 0x0
$ 140
It can be seen that the value is slightly more than half the value in the case of an isolated dot.
[0087]
In the electrophotographic process, the amount of developed toner in the target pixel portion increases due to the influence of the neighboring pixels. Therefore, control is performed to reduce the laser exposure amount in anticipation of the increase. Conversely, taking into account that toner particles are unlikely to be developed under conditions where there are no dots around, such as isolated dots, control is performed to increase the laser exposure under such conditions. This is a feature of the example.
[0088]
Finally, an example of control in the solid black section will be described. The calculation is performed on the following image data.
[0089]
[Table 5]

[0090]
255x0 + 255x (-0.15) + 255x0
+ 255x (-0.15) + 255x (1) + 255x (-0.15)
+ 255x0 + 255x (-0.15) + 255x0
$ 102
In the solid black portion, the laser exposure amount is set to be less than half of that in the case of an isolated dot.
[0091]
However, as can be seen from the graph showing the correspondence between the photoconductor surface potential and the print image density with respect to the laser exposure amount shown in FIG. The image density does not change. Therefore, even if the setting is made so as to reduce the laser exposure amount in the solid black portion, the print density of the solid black image does not decrease.
[0092]
Further, when the print image density corresponding to the laser exposure amount changes due to the setting of the developing device, toner exchange, etc., correction processing is performed using the conversion table after the operator calculation, and the value of the conversion table or the γ of the conversion curve is used. The print density of a solid black image can be prevented.
[0093]
In the present embodiment, by performing such processing, there is a problem in outputting a high-resolution image.
1. Stable toner image formation when the toner image is relatively isolated
2. Image output accuracy when toner images are relatively dense
, And a good image output can be obtained.
[0094]
(4) Comparison between the present embodiment and the conventional example
FIG. 5 shows “the size N of the N × N dots to be output and the output dot diameter” in the present embodiment. Other plots showing the conventional example with respect to the ideal straight line L are “small-diameter dots, a pattern in which toner is relatively isolated” and “large-diameter dots, a pattern in which toner is relatively dense”. While the outputs are not compatible, the output of the present embodiment does not cause “disappearance of small-diameter dots” or “crush of large-diameter dots”, and can output good images.
[0095]
FIG. 3B also shows the result of comparison of the output image of the conventional example shown above with the same image in this embodiment. The laser exposure conditions of the present example and the conventional example were set so that the maximum intensity of the laser exposure was adjusted and the output at the “dot density high portion” was the same.
[0096]
In this output image, “a portion where the toner images are relatively dense” is a rectangular portion with a thick line or a rough line of an automobile image, and “a portion where the toner image is relatively isolated” is a thin line portion, That is, a rectangular portion formed by a thin line, an engine portion of an automobile image, and the like.
[0097]
In the comparative example, the “part where the toner image is relatively dense” is printed properly, but in the “part where the toner image is relatively isolated” such as a thin line, the toner image disappears. In contrast to the loss of information, in the present embodiment, in the “part where the toner images are relatively dense”, a good printed image is obtained in exactly the same way as in the conventional example, and at the same time, A stable toner image is obtained even in the "isolated portion", and an appropriate image output is realized without losing image information.
[0098]
As described above, in this embodiment,
▲ 1 ▼. The 3 × 3 image data centered on the target pixel is multiplied by the numerical value at the same position of the correction operator, and then all of them are added.
▲ 2 ▼. The value of the calculation result is further corrected. In the present embodiment, “If the calculation result is negative, the image exposure amount is set to 0.
(3). The laser exposure intensity for the target pixel determined in the upper stage is further corrected including the photosensitivity of the photoconductor and the development characteristics of the developing device.
By performing the process of
1. Stable toner image formation when the toner image is relatively isolated
2. Image output accuracy when toner images are relatively dense
And a good image output can be obtained.
[0099]
[Example 2]
This embodiment is also similar to the first embodiment,
1. For each pixel of the output image, in order to cancel the developing electric field formed by the neighboring pixels of the pixel with respect to the pixel,
2. To the pixel value of the pixel, a correction amount according to the distance and direction between the neighboring pixel and the pixel is added in the direction to cancel the developing electric field formed for the pixel by the pixel according to the distance near the pixel. Change
3. The correction pixel value of the pixel calculated in the previous stage is further converted using a correction curve if necessary, and is used as an exposure amount for the pixel.
Processing is performed, but the operator used for the operator calculation is slightly different, and the correction processing using the conversion table after the operator calculation is different.
[0100]
As a result, stable image output in the case "the toner image is relatively isolated" and development of the toner in the white pixels in the case "the toner image is dense" prevent the output image from being crushed. It becomes possible.
[0101]
This embodiment is the same as Embodiment 1 except that the correction processing in the exposure correction circuit 7 is different, but uses an image forming apparatus. Hereinafter, the correction process will be described.
[0102]
FIG. 8 is a flowchart of a correction operation performed by the exposure correction circuit 7 and a correction operator in the correction processing of this embodiment.
[0103]
(1) Image conversion method at the time of output of the present embodiment
The operator used for the correction processing of this embodiment is
[0104]
[Table 6]

[0105]
It is. FIG. 6 shows the correction curve after the operator calculation.
[0106]
In the case of the first embodiment, when the value of the pixel of interest after the operator operation becomes negative, the corrected value is set to 0, and therefore all the pixels having the negative value of the pixel of interest after the operator operation are the same. Output value. That is, the same value of 0 is used for the white pixel regardless of the type of the adjacent dot.
[0107]
However, in this embodiment, different from the first embodiment, even for the same white pixel, the exposure amount for each pixel differs depending on the condition of the adjacent dot. For example, in the case of white pixels whose neighborhood is all white pixels, the value after the operator operation is 0. However, in the case of a white pixel surrounded by black pixels, the calculated value is -8. The calculated value of the black pixel located around the white pixel is -2.
[0108]
In the case of an isolated black pixel, the value after the operator operation is 10, and the value of the adjacent white pixel is -1. The value is 2 for black pixels whose periphery is all black.
[0109]
The value after performing the correction curve processing for each of these pixels is
・ White pixels 48 whose periphery is all white pixels
.Isolated black pixels 256
A white pixel 32 adjacent to an isolated black pixel 32
A black pixel 32 adjacent to an isolated white pixel 32
・ Isolated white pixel 0 surrounded by black pixels
・ Solid black part 160
It becomes. That is, on the basis of the solid white portion (48), the potential condition can be set such that the isolated white pixel surrounded by the black pixel does not easily adhere to the toner, even if the surrounding black pixel is included. That is, similarly to the first embodiment, not only can an isolated black dot be stably output, but also a white pixel surrounded by black pixels can be stably output.
[0110]
As described above, in the present embodiment, it is possible to stably output both “when the toner is relatively isolated” and “when the toner is relatively dense”, and it is possible to perform good image output. .
[0111]
The present invention is not limited to the "digital exposure" image forming apparatus of the embodiment, and is similarly applicable to the "analog exposure" image forming apparatus.
[0112]
In addition, an "electrostatic recording dielectric" having no photosensitivity is used as an image carrier, and electric charges are selectively skipped and adhered to the surface of the electrostatic recording dielectric, or the surface of the electrostatic recording dielectric is removed. When the same control is performed in the case of the “electrostatic recording process” in which the charge is selectively processed and the charge is selectively removed by a charge removing device such as a charge removing needle array or an electron gun to form an electrostatic latent image, effective.
[0113]
Although various examples and embodiments of the present invention have been shown and described, those skilled in the art will appreciate that the spirit and scope of the present invention is not limited to the specific description and figures herein. It will be appreciated that various modifications and changes are set forth which are all set forth in the following claims.
[0114]
Examples of embodiments of the present invention are listed below.
[0115]
[Embodiment 1] An image forming apparatus using an electrophotographic process, in which, for an arbitrary pixel in an image to be printed, a pixel having a small number of "pixels to be formed with toner" in a peripheral NxM area is "developed with toner". The image exposure amount is controlled so as to “increase the electric field strength for developing the toner.” For the pixels having many “pixels on which toner should be formed” in the NxM area near the periphery, “the electric field strength for developing the toner is reduced”. The image forming apparatus is controlled as described above.
[0116]
Second Embodiment In the first embodiment, in order to perform the control, an operator operation is performed on pixels of the print image data and a correction process using a correction table is performed on a result of the operator operation. An image forming apparatus using a photographic process.
[0117]
[Embodiment 3] An image forming apparatus using an electrophotographic process according to Embodiment 2, wherein the operator of the processing or the correction table is changed in accordance with a change in the thickness of the photoconductor as the image carrier.
[0118]
[Embodiment 4] The electrophotographic process according to Embodiment 2 or 3, wherein the coefficient of the processing is changed in accordance with the parameters involved such as a developing device, a development mode, a developer, or a photoconductor. Image forming apparatus.
[0119]
[Embodiment 5] Regarding an arbitrary pixel in an image to be printed, an image such that “an electric field strength for developing the toner is increased” is set for a pixel having a small number of “pixels for forming toner” in a peripheral NxM area. Electrophotography wherein the amount of exposure is controlled, and control is performed so as to "reduce the electric field strength for developing the toner" for a pixel having a large number of "pixels for which toner is to be formed" in a peripheral NxM area. Image forming method using a process.
[0120]
[Embodiment 6] In Embodiment 5, in order to perform the control, an electrophotographic process is used in which an operator operation is performed on pixels of print image data and a correction process is performed on a result of the operator operation using a correction table. Image forming method.
[0121]
[Embodiment 7] An image forming method using an electrophotographic process according to Embodiment 6, wherein the operator of the processing or the correction table is changed in accordance with a change in the film thickness of the photoconductor as the image carrier.
[0122]
[Embodiment 8] The electrophotographic process according to embodiment 6 or 7, wherein the coefficient of the processing is changed according to the involved parameters such as a developing device, a developing mode, a developer, or a photoreceptor to be used. Image forming method.
[0123]
【The invention's effect】
As described above, in the present invention, the following procedures
▲ 1 ▼. For each pixel of the output image, in order to cancel the developing electric field formed by the neighboring pixels of the pixel with respect to the pixel,
▲ 2 ▼. To the pixel value of the pixel, a correction amount according to the distance and direction between the neighboring pixel and the pixel is added in the direction to cancel the developing electric field formed for the pixel by the pixel according to the distance near the pixel. Change
(3). The correction pixel value of the pixel calculated in the previous stage is further converted using a correction curve if necessary, and is used as an exposure amount for the pixel.
Problem that occurred in the past
・ If the adjustment is performed so that the low dot density area is properly developed, the output amount of the toner particles becomes excessive in the high dot density area, and the output image is crushed.
-If the adjustment is performed so that the high dot density area is properly developed, the toner development amount is insufficient in the low dot density area, and image information is lost.
In any case, good image quality can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an image forming apparatus according to a first embodiment.
FIG. 2 shows a dot diameter actually output when a conventional N × N dot is output.
FIG. 3 shows an image output result of the first embodiment and an image output result of the conventional example (A. Conventional example, B. This embodiment)
FIG. 4 shows the laser exposure intensity, photoconductor surface potential, and solid black print image density at that time in Example 1.
FIG. 5 is a diagram illustrating a dot diameter actually output when NxN dots are to be output in the first embodiment.
FIG. 6 shows a correction curve of a correction table according to the second embodiment.
FIG. 7 is a flowchart of a correction operation performed by an exposure correction circuit 7 and a correction operator in the image exposure intensity correction method according to the first embodiment.
FIG. 8 is a flowchart of a correction operation performed by an exposure correction circuit 7 and a correction operator in the image exposure intensity correction method according to the second embodiment.
[Explanation of symbols]
1. photoconductor, 2. charging roller, 3. developing device, 4. transfer roller, 5. fixing device, 6. image exposure device, 7. exposure correction device, 8. host device, S1 to S3: bias power supply, C: process cartridge

Claims (1)

An image forming apparatus using an electrophotographic process. For an arbitrary pixel in an image to be printed, for a pixel having a small number of “pixels for which toner is to be formed” in a peripheral NxM area, a “field intensity for developing toner” is used. The amount of image exposure is controlled so as to “increase”, and control is performed so as to “reduce the electric field strength for developing the toner” for pixels having many “pixels on which toner is to be formed” in the NxM area near the periphery. An image forming apparatus comprising:

Images