JP3739519B2 - Thermal recording method and apparatus - Google Patents

Description

で求められる。なお、Ｍは第１アンシャープネス信号Ｕ¹ _ijを作成するのに用いる画素数すなわちマスクサイズであり、Ｌは（Ｍ−１）／２で定義される。
【００３１】
次いで、第１アンシャープネス信号Ｕ¹ _ijをさらに平均化して、第２アンシャープネス信号Ｕ² _ijを算出する。第２アンシャープネス信号Ｕ² _ijは、第１アンシャープネス信号Ｕ¹ _ijと同様に下記式（２）で算出される。
【数２】

【００３２】
次いで、第１アンシャープネス信号Ｕ¹ _ijと第２アンシャープネス信号Ｕ² _ijとの差を求める。そして、この差に鮮鋭度補正係数Ｋを乗算して、第１アンシャープネス信号Ｕ¹ _ijを加算することにより、すなわち、下記式（３）により、鮮鋭度補正された画像データＳ_ijが得られる。
Ｓ_ij＝Ｕ¹ _ij＋Ｋ・（Ｕ¹ _ij−Ｕ² _ij） …（３）
【００３３】
ここで、感熱記録画像の鮮鋭度は、サーマルヘッド６６（発熱素子）の温度、記録速度、感熱材料Ａのγ値等に影響され、サーマルヘッド６６の温度が高い程、記録速度が早いほど、さらに感熱材料Ａのγ値が低い程、記録画像の鮮鋭度が低下するので、必要に応じて、これらに応じて鮮鋭度補正係数Ｋを変更して鮮鋭度補正を行ってもよい。
この場合には、例えば、発熱素子の温度、記録速度、感熱材料のγ値等に応じた重み係数のテーブル（あるいは関数）を作成しておき、鮮鋭度補正時にこれを読み出して、鮮鋭度補正係数Ｋに乗算する方法等が例示される。
【００３４】
階調補正（濃度補正ともいう）とは、記録装置の状態や感熱材料Ａのγ値等に応じて画像データを補正し、適正に階調（濃度）が表現された画像を得るための補正である。
前述のように、記録装置１０は、画像データを１０ｂｉｔのデジタルデータとして受け取り、これに応じて画像記録を行う装置であるが、この装置において例えばデジタルデータで５１２の画像データが濃度（Ｄ）１．２に対応する場合には、５１２の画像データを受けた場合には、基本的に濃度１．２の画像を出力することが要求される。しかしながら、装置には個体差があり、また設置環境等も異なる。さらに、メーカや製造ロット等によっては感熱材料Ａのγ値も異なる。そのため、すべての装置が供給された画像データに応じて所定濃度の画像を出力することは不可能である。従って、階調補正を施し、画像データに応じて適正に階調が表現された感熱記録画像を形成する。
また、図示例の記録装置１０を含め、通常の感熱記録装置においては、画像データ供給源Ｒから送られた画像データは、この階調補正によって感熱記録の発熱量に応じた画像データに変換される。
【００３５】
階調補正の方法には特に限定はなく、公知の方法が各種利用可能であるが、例えば、記録装置１０によって複数の濃度の画像が記録された補正チャートを作成し、この補正チャートに記録された画像の濃度を濃度計で測定し、記録装置１０が目的とした画像濃度と、補正チャートに記録された画像濃度とから、濃度補正アルゴリズムを用いて補正テーブルすなわち階調カーブ（あるいは補正関数）を作成し、この補正テーブルを用いて画像データを変換する方法が例示される。
【００３６】
また、階調補正を施して発熱量に対応するように変換された画像データは、記録濃度が０であっても、感熱材料Ａが発色しない程度（好ましくは発色直前）の記録エネルギーをサーマルヘッド６６に供給するものであるのが好ましく、そのように前記補正テーブルを作成するのが好ましい。
このように構成することにより、記録中における各発熱素子の温度差を小さくして、サーマルヘッド６６全体の温度分布を小さくすることができ、高画質な画像が得られると共に、感熱材料Ａのベースが透明なＰＥＴフィルム等である場合には、感熱材料Ａの表面を若干だけ溶融して、光の乱反射を減少することができ、感熱材料Ａの透明度を向上することができる。
【００３７】
シェーディング補正とは、サーマルヘッド６６のグレーズ６６ａの形状バラツキ等によって生じる濃度むらを補正するものである。
前述のように、サーマルヘッド６６は発熱素子が一方向に配列されてなるグレーズを有するが、このグレーズ６６ａの形状を全画素に渡って均一にすることは困難であり、通常は、個々の画素である程度の形状バラツキを有する。また、各発熱素子の発熱量は、グレーズ６６ａ延在方向の位置によっても異なる。そのため、同一記録濃度の画像データを用いて画像記録を行っても、この形状バラツキや位置に起因する濃度むら、いわゆるシェーディングが発生する。この濃度むらを補正するために、シェーディング補正を行う必要がある。
【００３８】
シェーディング補正の方法には特に限定はなく、所定濃度の画像データに対応する発熱エネルギーをサーマルヘッド６６の全画素（発熱素子）に供給して、実際に感熱記録画像を形成して、画像濃度を濃度計等を用いて光学的に測定して、画像データが対応する記録濃度と、実際に測定された記録画像の濃度とから、形成される記録画像の濃度が均一になるように画像データを補正するシェーディング補正データ（補正係数）を各画素毎に算出してデータ記憶部８６に記憶しておき、画像データにシェーディング補正データを乗算する方法が例示される。また、同様の発熱エネルギーをサーマルヘッド６６の全画素に供給して各画素の発熱量を計測し、各画素の発熱量から同様のシェーディング補正データを算出して補正を行う方法等も例示される。
さらに、必要に応じて、画像データ（画像濃度）、サーマルヘッド６６の温度、記録速度、感熱材料Ａの温度や湿度やγ等に応じて、シェーディング補正データの補正係数（補正テーブル）を作成しておき、これらに応じてシェーディング補正データを補正してシェーディング補正を行ってもよい。
【００３９】
抵抗値補正とは、各発熱素子の抵抗値の差を補正して、適正な画像を得るための補正である。
サーマルヘッド６６に用いられる発熱素子の抵抗値は均一ではなく、製造誤差や素材のバラツキ等に起因する抵抗値のバラツキを有する。また、抵抗体である発熱素子の抵抗値は使用すなわち発熱時間および発熱エネルギー（発熱履歴）に応じて変化するが、各発熱素子の発熱履歴は均一ではなく、経時と共に抵抗値変化量にも差が生じ、抵抗値のバラツキは変動する。
このような抵抗値のバラツキに起因して、同じ時間発熱させても各発熱素子の発熱量が異なってしまい、それが記録画像の濃度むらの要因の一つとなっている。そのため、これに起因する濃度むらの補正すなわち抵抗値補正を行う必要がある。
【００４０】
抵抗値補正の方法には特に限定はなく、各発熱素子の抵抗値を実際に測定して、各発熱素子毎に抵抗値補正データ（例えば、［Ｒ／Ｒｍ］で、Ｒはその発熱素子の抵抗値を、Ｒｍは全発熱素子中の最大抵抗値を示す）を算出してデータ記憶部８６に記憶しておき、これを画像データに乗算する方法等が例示される。
また、発熱素子の抵抗値は、サーマルヘッド６６（発熱素子）の温度および画像データ（画像濃度）にも影響を受けるので、これらに応じた抵抗値補正データの補正係数のテーブル（関数）をあらかじめ作成して記憶しておき、発熱素子の温度および画像データに応じて補正係数を読み出して、この補正係数を抵抗値補正データに乗算して抵抗値補正を行ってもよい。
【００４１】
黒比率補正とは、記録パターンの変化によるサーマルヘッド電源電圧降下量変化によらず、同じ画像データを同濃度で発色するための補正である。
例えば、１ラインの画像データの中に高濃度部分が多い場合、同時に通電される発熱素子の数が多くなって電流量が増大し、例えば電源からサーマルヘッドまでの電源ケーブル等の内部抵抗によって、電流量に応じた電圧降下が発生する。このため、サーマルヘッドに供給される電源電圧が画像データの濃度に応じて各ライン毎および各発熱素子毎に変動してしまい、画像データは同一であっても記録画像には濃度差が生じるという、いわゆる黒比率むらが発生する。そのため、これに起因する濃度むらの補正すなわち黒比率補正を行う必要がある。
【００４２】
黒比率補正の方法には特に限定はなく、公知の方法が各種利用可能であり、例えば、各ライン毎に、各画素の画像データを加算して１ラインの全印加エネルギーを算出し、この全印加エネルギーに基づいて個々の画素の画像データを補正する方法、すなわち１ライン中の電圧降下量は一定であるものとして、各画素の画像データの電圧降下による熱エネルギーの損失分を補正する黒比率補正方法が例示される。
【００４３】
また、より好ましい方法としては、下記式（ａ）を用いて黒比率補正を行う方法が例示される。上記の黒比率補正方法では、１ライン中の全エネルギーに基づいて同じ補正を行っていたため、低濃度の画素は過補正になってしまうが、この方法によれば、全濃度域において、個々の画素の画像データの黒比率を最適に補正することができる。
【数３】

上記式（ａ）において、Ｎは１ラインの画素数、Ｄは画像データ、Ｍは画像データの最大値、ｋは補正係数、Ｄ（ｎ）は画素ｎの補正前の画像データ、Ｈ（Ｄ）は画像データＤに対する補正データ値、Ｄ_C （ｎ）は画素ｎの補正後の画像データを、それぞれ示す。
【００４４】
式（ａ）においては、まず、各画像データＤに対する補正データ値Ｈ（Ｄ）を算出する。例えば、画像データＤの範囲が０〜２０４７までの２０４８階調ある装置においては、これに対応する補正データ値Ｈ（０）〜Ｈ（２０４７）までの２０４８個の補正データ値を算出する。
【００４５】
このとき、補正前の画像データＤ（ｎ）が画像データＤ以上である場合には、Ｄ’（ｎ）を画像データＤとし、逆に、画像データＤ（ｎ）が画像データＤよりも小さい場合には、Ｄ’（ｎ）を画像データＤ（ｎ）とする。そして、個々の画素ｎの補正前の画像データＤ（ｎ）に対する補正データ値Ｈ（Ｄ（ｎ））を用いて、補正後の画像データＤ_C （ｎ）を算出する。
【００４６】
また、前記式（ａ）をそのまま計算すると、計算量は非常に多くなるが、以下のように計算することにより、大幅に計算量を少なくすることができる。
下記式（ｂ）に示すように、Ｃ（Ｄ）を
【数４】

と書くと、Ｈ（Ｄ）は、Ｈ（Ｄ）＝１−Ｃ（Ｄ）／（Ｎ×Ｍ）で表される。
【００４７】
ここで、Ｄ＝Ｍの場合のＣ（Ｄ）、すなわちＣ（Ｍ）は、式（ｂ）より、
【数５】

で求められる。
Ｃ（Ｍ−１）はＭ→Ｍ−１として計算するから、画像データＭの画素数をhst （Ｍ）と書くとすると、
Ｃ（Ｍ−１）＝Ｃ（Ｍ）− hst（Ｍ）
で表すことができる。
Ｃ（Ｍ−２）は、Ｍ−１，Ｍ→Ｍ−２として計算するので、

以下同様にして、一般に、
【数６】

となる。
【００４８】
従って、計算手順としては、
・ステップ１
１ライン全画素のデータ値を足した値Ｓtotal と、１ラインに含まれる各画像データのヒストグラム hst（０），hst （１），…，hst （Ｍ）を求める。
・ステップ２
各画像データに対応する補正値を以下のように求める。
Ｓ（Ｍ）＝０
Ｃ（Ｍ）＝Ｓtotal
Ｓ（Ｍ−１）＝Ｓ（Ｍ）＋ hst（Ｍ）
Ｃ（Ｍ−１）＝Ｃ（Ｍ）−Ｓ（Ｍ−１）
Ｓ（Ｍ−２）＝Ｓ（Ｍ−１）＋ hst（Ｍ−１）
Ｃ（Ｍ−２）＝Ｃ（Ｍ−１）−Ｓ（Ｍ−２）
…
Ｓ（１）＝Ｓ（２）＋ hst（２）
Ｃ（１）＝Ｃ（２）−Ｓ（１）
・ステップ３
１ラインの各画素を以下のように補正する。（ｋは補正係数）
Ｄ_C （ｎ）＝Ｄ（ｎ）×｛１−ｋ×（１−Ｃ（Ｄ（ｎ））／（Ｎ×Ｍ））｝
この黒比率補正の方法は、本出願人による特願平８−２５０３６号明細書に詳述されている。
【００４９】
ところで、感熱記録装置１０では、感熱材料に記録する濃度に応じて、感熱材料Ａとサーマルヘッド６６との間の界面の摩擦力が変化する。
このため、低濃度に記録する部分から高濃度に記録する部分に変化する境界線の部分では、一瞬、感熱材料の搬送速度が速くなり、境界線の部分の記録濃度が低下して白いすじ状の濃度むらが発生するし、これとは逆に、高濃度に記録する部分から低濃度に記録する部分に変化する境界線の部分では、黒いすじ状の濃度むらが発生するという問題点がある。
【００５０】
負荷変動補正とは、上記すじ状の濃度むらが発生するのを防止するための補正処理であって、例えば予め算出してある、画像データと、感熱材料とサーマルヘッドとの間の摩擦力（搬送トルク）と、の間の関係を表す関数に基づいて、下記算出式に示されるように、前ラインの各画素に対応する摩擦力の総和から、現ラインの各画素に対応する摩擦力の総和を減算することにより、前ラインから現ラインにわたる摩擦力の変化量を算出し、この摩擦力の変化量に基づいて、各ラインの各画素毎に画像データを補正する。
【００５１】
【数７】

ここで、ｎは記録画像の行番号、ｉはｎライン目の画素番号、Ｄ’_n （ｉ）およびＤ_n （ｉ）は、それぞれ補正後および補正前のｎライン目のｉ画素目の画像データ値、ｋは補正係数、Ｈ_n はｎライン目の感熱材料とサーマルヘッドとの間の摩擦力変化を示す量、Ｍは１ラインの画素総数、ｆ（Ｄ）は画像データ値Ｄと、感熱材料とサーマルヘッドとの間の摩擦力と、の間の関係を表す関数式である。
【００５２】
なお、画像データと、感熱材料とサーマルヘッドとの間の摩擦力と、の間の関係を一次関数で近似することによって、単純に、前ラインおよび現ラインの画像データ値をそれぞれ累積加算し、これらの前ラインの累積加算値および現ラインの累積加算値の差を取るだけで負荷変動補正を施すことができるため、上記関数を用意する必要がなく、かつ、処理速度を向上させることができるという利点がある。
【００５３】
また、例えば予め算出してある、画像データと、感熱材料とサーマルヘッドとの摩擦力と、の間の関係を表す関数、および、感熱材料とサーマルヘッドとの間の摩擦力と、ゴムローラの変形量と、の間の関係を表す関数に基づいて、各ラインの各画素位置毎のゴムローラの変形量の変化量を求め、現ラインの各画素位置毎のゴムローラの変形量の変化量と前ラインの補正係数とに応じて、もしくは、現ラインの各画素位置毎のゴムローラの変形量の変化量の代わりに、各ライン毎のゴムローラの変形量の変化量の平均値と、各ラインの各画素位置毎の、各画素位置の前後ｍ画素のゴムローラの変形量の変化量の平均値と、の和を用いて、現ラインの画像データをより正確に補正するようにすることもできる。
この負荷変動補正方法については、本出願人による特願平９−５０２９５号に詳述されている。
【００５４】
温度上昇補正とは、発熱素子の温度に応じて発熱エネルギーを調整し、各発熱素子の温度履歴の差によって生じる濃度むらを補正するものである。
サーマルヘッド６６の各発熱素子の加熱は、例えば、記録画像の各画素の画像データに対応して所定時間通電することによって行われている。しかし、各発熱素子の温度は、前ラインまでの記録画像（発熱履歴）に応じて個々に異なるため、同じ画像データに応じて各発熱素子に同一時間通電しても、加熱後の発熱素子の間で温度差が生じ、濃度むらが発生する。
そのため、各発熱素子毎に、画像データや前ラインまでの発熱履歴等に基づいて発熱量を補正する、画像データの温度上昇補正を行う必要がある。
【００５５】
温度上昇補正の方法には特に限定はなく、公知の方法が各種利用可能であるが、一例として、はじめに、前処理として１画面の記録画像を所定数の画素を有する所定数の領域（ブロック）に分割して、分割された各領域毎に画像データの代表値を算出しておき、次に、この画像データの代表値とサーミスタ等により検出される温度初期値とから各領域の温度予測値を算出し、この温度予測値から各領域に対する温度補正値を算出し、各領域に対する温度補正値を補間して、１画面の記録画像の各画素に対する温度補正値を算出し、この温度補正値を用いて各画素の画像データを補正する方法が例示される。
【００５６】
より具体的には、まず、１画面の記録画像を所定数の画素を有する所定数の領域に分割、例えば、１画面の記録画像が横３０７２画素×縦４２２４画素である場合、横１２８画素×縦３２画素を有する領域によって、１画面の記録画像を横２５個×縦１３３個の各領域にメッシュ状に分割する。
次いで、領域内の所定の１画素の画像データを代表値とする方法； 領域内の画素を間引いた後の残りの所定数の画素の画像データの平均値を代表値とする方法（間引き処理）； 領域内の全画素の画像データの平均値を代表値とする方法； 等によって、分割した各領域の画像データの代表値を算出する。このようにして分割された各領域の画像データの代表値を算出する温度上昇補正の前処理が行われる。
【００５７】
次いで、各領域内の画像データの代表値と、前記サーミスタによって検出されるサーマルヘッド６６（ヒートシンクの基部６６ｄ）の温度および温度計Ｔによって検出される雰囲気温度等により検出される温度初期値とから、温度予測値を算出する。温度予測値の算出方法としては、サーマルヘッド６６の伝熱系を容量成分Ｃと抵抗成分ＲとからなるＣＲモデルによる電気系の等価回路に置換して、伝熱系の単位時間当たりの発熱量、温度、熱容量および熱抵抗を、それぞれ電気系の電流、電圧、容量および抵抗に置き換える方法等が例示される。
得られた温度予測値から、あらかじめ設定された所定の算出式を用いて各領域に対する温度補正値を算出し、領域に対する温度補正値を補間して、あらかじめ設定された算出式を用いて１画面の記録画像の各画素に対する温度補正値を算出し、これを用いて画像データの温度補正をする。
以上の温度上昇補正の方法は、本出願人による特願平８−２５０３５号明細書に詳述されている。
【００５８】
感熱記録装置においては、画像データ供給源Ｒから供給された画像データに、このような各補正を施して、サーマルヘッド６６による感熱記録に応じた感熱記録画像データとする。
ここで、本発明にかかる記録装置１０においては、上記各補正は、鮮鋭度補正および階調補正→シェーディング補正および抵抗値補正→温度上昇補正の順で、かつ階調補正以降のいずれかの補正の前もしくは後に温度上昇補正のための画像データ代表値算出処理が施される所定の順序で行われ、求められる画質レベルによっては、さらにシェーディング補正および抵抗値補正と、温度上昇補正との間で黒比率補正および負荷変動補正の少なくとも一方が行われる。
【００５９】
前述の各補正（画像処理）の説明から明らかなように、鮮鋭度補正および階調補正は、記録する画像そのものに対応して補正するものであり、供給された画像データ（図示例では、例えば１０bit(０〜１０２３）のデジタルデータ）に応じて各補正量が変動する補正、すなわち補正量が画像データで決まる補正である。
これに対し、シェーディング補正および抵抗値補正は、記録装置１０の装置固有の濃度むらを補正するもので、これを画像データに反映して補正するものである。
また、黒比率補正は、サーマルヘッド６６の電圧降下に応じた補正であり、負荷変動補正は感熱材料Ａと記録装置１０（サーマルヘッド６６）との組み合わせに応じた補正であるので、これらの補正は、できるだけ後の方に行うのがよく、サーマルヘッド６６に供給される最終的な画像データになる直前の画像データに対して行うのが好ましい。
【００６０】
なお、前述のように、温度上昇補正は雰囲気温度やサーマルヘッド６６の温度を検出し、この温度を用いてサーマルヘッド６６の温度上昇を予測し、これを基に温度補正値を算出する。従って、温度上昇補正は記録の直前、すなわち画像処理（補正）の最後に行うのが好ましく、言い換えれば、温度補正を終了したラインをすぐに記録するような（つまり、記録中に補正計算が行われている）構成にするのが好ましい。
【００６１】
そのため、階調補正や鮮鋭度補正の画像データに応じた補正より先に、シェーディング補正等の装置固有の補正を行うと、目的とする画像自身に装置特性が影響を与える結果になり、形成される画像が目的とする画像とは異なってしまう。言い換えれば、シェーディング補正等の記録装置１０に固有のスジむら等を無くすための補正が、記録画像（画像データ）そのものに応じた補正を行う前に画像データに反映されてしまい、その結果、記録画像に応じた鮮鋭度補正や階調補正も装置特性を反映してしまい、適正な補正を行うことができない。
従って、鮮鋭度補正および階調補正は、基本的に、シェーディング補正および抵抗値補正よりも先に行い、温度上昇補正は、最後の記録直前に行うのが好ましく、また、黒比率補正および／または負荷変動補正は、できるだけ遅い順番に行うのが好ましい。
【００６２】
ここで、記録される画像の階調は、感熱材料Ａの感度や階調、記録装置１０の特性によって変わる。従って、階調補正を行った後に鮮鋭度補正を行った場合、前述のシェーデング補正等と同様に感熱材料Ａと記録装置１０との組み合わせによっては、鮮鋭度補正量が変わってしまい、安定した鮮鋭度補正を行うことができなくなってしまうことがある。従ってこのような場合には、鮮鋭度補正の後で階調補正を行うのがよい。
【００６３】
ところで、階調補正においては、記録中における各発熱素子の温度差、ひいてはサーマルヘッド全体の温度分布を小さくして、高画質な感熱記録を行うため、記録濃度が０（すなわち、画像データ源から入力された画像データの値が０）の部分であっても、感熱材料Ａが発色しない程度（好ましくは発色直前）の記録エネルギーを印加するように所定の記録データ値Ｅ₀ （Ｅ₀ ＞０）に変換される。
【００６４】
このため、階調補正後に鮮鋭度補正を行った場合、図４（ａ）に示されるように、記録しようとする画像の主走査方向の１ライン中に輪郭などの濃度が高濃度側の記録データ値Ｄ_H から低濃度側の記録データ値Ｄ_L まで急激に変化する部分（以下、エッジ部という）が存在すると、鮮鋭度補正後には、図４（ｂ）に示されるように、エッジ部の濃度差が強調され、低濃度側の記録データ値Ｄ_L がＥ₀ かまたはＥ₀ に近い値である場合には、低濃度側の記録データ値Ｄ_L の強調されたピーク値Ｄ_LPがＥ₀ よりもかなり小さくなる場合が生じる恐れがある。このため、実際の記録画像において、エッジ部における熱の拡散により、この強調されたエッジ部が緩和されても、本来発色すべき箇所において十分に発色されずに非発色の部分が残存してしまうことから、図４（ｃ）に示されるように、輪郭が白く抜けたように見える偽輪郭が生じてしまい、記録画像に違和感が感じられるという問題が起こる恐れがある。
【００６５】
このような記録画像における偽輪郭の発生は、高画質な画像記録を要求される場合、特に、高精細な中間調画像の記録の場合には、大きな問題となる場合がある。特に、前述の医療用のように高精細、高画質の中間調画像が要求される用途では、画像観察の障害となり、医療のミスにもつながる重大な問題となる場合がある。
【００６６】
このような場合には、本発明においては、このように鮮鋭度補正が施された記録データＤに対し、所定値未満の記録データＤを所定値に変換する処理（以下、偽輪郭低減処理という）を施す。具体的には、前記鮮鋭度補正後の記録データＤのうち、画像データ値０に対応する記録データ値Ｅ₀ に定数ｋ（ｋ＜１）を乗じた値ｋＥ₀ より小さい記録データＤをすべてｋＥ₀ に変換することにより、偽輪郭の発生を防止する。
【００６７】
図３に、本発明の感熱記録方法の別の態様による変換処理の一例の模式図を示す。図３（ａ）は階調補正後でかつ鮮鋭度補正前における主走査方向の記録データの一例を、図３（ｂ）は（ａ）の記録データに鮮鋭度補正を施した直後の記録データの一例を、図３（ｃ）は（ｂ）の記録データに本発明の偽輪郭低減処理を施した後の記録データの一例である。図３（ｄ）は、（ｃ）の記録データのパターンに基づき形成された感熱記録画像の一例である。
以下、図３に基づいて、本発明の別の態様の感熱記録方法の一例について説明する。
まず、画像データ源から入力された画像データに階調補正を行い、図３（ａ）に示されるような主走査方向の記録データＤのパターンが得られたとする。ここで、図３（ａ）の記録データＤのパターンの中央部には、記録データ値（すなわち、濃度）が急激に変化するエッジ部が存在している。
【００６８】
次に、このようなエッジ部の存在する一連の記録データＤに対して前述の鮮鋭度補正を施すと、図３（ｂ）に示されるように、エッジ部が強調された記録データＤのパターンが得られる。すなわち、エッジ部近傍の低濃度側（画像データ値の小さい側）の画像データ値Ｄ_L がさらに小さいピーク値Ｄ_LP に強調されて変換され、エッジ部で下方（低濃度方向）にピークが形成される。一方、エッジ部近傍の高濃度側（画像データ値の大きい側）の画像データ値Ｄ_H がさらに大きいピーク値Ｄ_HPに強調されて変換され、エッジ部で上方（高濃度方向）にピークが形成される。
ここで、図３（ｂ）のデータをそのままサーマルヘッドにより記録しようとすると、図４（ｃ）に示されるように、低濃度側のピークの部分（すなわち、エッジ部）が熱の拡散にもかかわらず、発色しない場合が生じて、白く抜けて見え、偽輪郭が生じる場合があるのは前述の通りである。
【００６９】
このため、本態様では、鮮鋭度強調処理後の画像データＤに対し、以下のように変換を行い、記録データ値Ｄの最小値をｋＥ₀ とすることにより、図３（ｃ）に示されるように鮮鋭度補正後の記録データが不必要に小さい値となるのを防止して、実際の記録画像においてエッジ部の熱の拡散によって、図３（ｄ）に示されるように、偽輪郭を生じさせることなく、かつ、輪郭を鮮やかに表現することを可能にしている。
【００７０】
【数８】

【００７１】
なお、この変換は全画像データに対して行われる。また、Ｄ_m は記録データのとりうる最大値であり、適宜決定すればよい。
ここで、ｋの値としては、０．５〜０．９とするのが好ましく、さらに好ましくは０．６〜０．７であるが、使用するサーマルヘッドの性能や感熱記録材料の特性等に応じて適宜決定すればよく、特に限定されない。０．５未満では、偽輪郭が十分に除去できないことがあるので、０．９超では鮮鋭度の改善が十分に見られない場合もあり、十分な高画質が得られない場合も考えられるので好ましくない。
以上のように本態様においては、はじめに階調補正を行い、次いで鮮鋭度補正を行った後に偽輪郭低減処理を行い、その後に、シェーディング補正、抵抗値補正、または温度上昇補正のための画像データ代表値算出処理を行うのが好ましい。
【００７２】
シェーディング補正および抵抗値補正については、いずれを先に行ってもよいが、補正が画像データすなわち画像濃度に依存する場合には、画像濃度依存性が大きい方を先に行うのが好ましい。前述のように、シェーディング補正および抵抗値補正は、画像データに各画素毎（発熱素子毎）に決定された補正係数（シェーディング補正データおよび抵抗値補正データ）を乗算する補正であるので、濃度依存性の大きな補正を先に行った方が、濃度による補正への影響を小さくすることができる。一般的に、抵抗値補正よりもシェーディング補正の方が濃度依存性が大きいので、通常はシェーディング補正→抵抗値補正の順番になる。
両者の濃度依存性が等価である場合には、いずれを先に行ってもよい。また、前述のように、両補正は補正データの乗算であるので、両補正を同時に行ってもよい（好ましくは、両者の濃度依存性が等価である場合）。
【００７３】
なお、シェーディング補正データと抵抗値補正データは、共にサーマルヘッド６６に固有のものであるため、サーマルヘッド６６に応じてあらかじめ補正データを作成しておき、サーマルヘッド６６の交換時に、ＩＣカードやＦＤ等を用いて、記録装置１０（データ記憶部８６）に入力（ロード）できるようにしておくのが好ましい。
【００７４】
黒比率補正と負荷変動補正については、いずれを先に行ってもよく、感熱材料Ａと記録装置１０の組み合わせによってどちらを先に行う方がよいかを適宜決めることができる。従って、感熱材料Ａと記録装置１０との１つの組み合わせに対して、これらの補正の順序を変えて、実際にテストプリント（試し記録）を行い、良好な感熱記録の方に決定すればよい。
【００７５】
前述したように、温度上昇補正は、実際の補正量が大きいため、必ず一番最後に行う必要があるが、画像データをある大きさの領域（ブロック）に分割して、各ブロックの温度を予測計算して補正するものである。このため、各ブロックの発熱量を画像データ代表値算出処理によって求めているが、これは各ブロックの発熱量を正確に表したものでなくてはならない。従って、画像データ代表値算出処理は、必ず、階調補正を行った後に実施される必要があり、抵抗値補正や黒比率補正や負荷変動補正の前に行っておくのが好ましい。なお、この画像データ代表値算出処理は、鮮鋭度補正の前、後のいずれで行ってもよい。また、この画像データ代表値算出処理は、シェーディング補正の前、後のどちらで行ってもよく、どちらで行うかは実際に補正を行ってテストプリントして良い方に適宜決定することができる。
ここで、感熱再生画像に高画質が要求されない場合には、多少予測精度が悪化するが、抵抗値補正、黒比率補正や負荷変動補正の前でなくても階調補正後のどこかで行うことも可能である。
【００７６】
ところが、先の説明より明らかなように、黒比率補正、負荷変動補正および温度上昇補正は計算量が非常に多く、画像処理部８０の計算能力や処理タイミング（例えば、最初にすべての補正計算を終了して記録を行うのではなく、記録と計算とを平行して行う場合）によっては、補正量が大きく一番最後に行う必要のある温度上昇補正の前に黒比率補正や負荷変動補正を行うのが困難な場合がある。ここで、黒比率補正や負荷変動補正による画像データの補正量は比較的小さく、特に、サーマルヘッド６６の電源容量が大きい（つまり電源の内部抵抗が小さい）場合には、黒比率による電圧変動は小さく、また、感熱材料Ａの種類やサイズや感熱材料Ａへのサーマルヘッド６６の押圧力によっては、搬送モータのトルク変動、すなわち負荷変動は小さく、黒比率補正や、負荷変動補正による画像データの補正量は極めて小さくなる。
このため、黒比率補正および負荷変動補正のいずれか一方もしくは両方を、求める画質のレベルに応じて省略してもよい。
【００７７】
このように、画像補正（画像処理）を、鮮鋭度補正および階調補正→シェーディング補正および抵抗値補正→温度上昇補正の順で、かつ階調補正以降のいずれかの画像処理の前もしくは後に温度上昇補正のための画像データ代表値算出処理が施される所定の順序で行われ、必要に応じて、シェーディング補正および抵抗値補正と、温度上昇補正との間に黒比率補正および／または負荷変動補正が行われる本発明の記録装置１０によれば、全ての補正を適正に施し、期待される補正効果を十分に得ることができるので、適正に画像処理された感熱記録画像データによって、高画質な感熱画像を安定して記録することができる。
【００７８】
前述のように、ＣＴやＭＲＩ等の画像データ供給源Ｒからの画像データは、記録装置１０の画像処理部８０に供給される。この画像データは、画像処理部８０からデータ記憶部８６に送られ、必要に応じてフォーマットを行い、記憶される。
画像データがデータ記憶部８６に記憶されると、まず、画像処理部８０は、データ記憶部８６から必要なデータを読み出し、感熱記録の開始に先立ち、データ記憶部８６に記憶された全画像データに、鮮鋭度補正を行い、次いで階調補正を行い、または階調補正を行った後に鮮鋭度補正を行い、続いて鮮鋭度補正処理（強調）によって生じる白く抜けた偽輪郭を大幅に低減するとともに記録画像中の輪郭を鮮やかに表現するための偽輪郭低減処理を行った後に処理済の画像データをデータ記憶部８６に再び記憶する。
これらの補正処理が終了すると、感熱画像記録が開始される。画像処理部８０はデータ記憶部８６から必要なデータを読み出しながら、データ記憶部８６に記憶された画像データのうち、最初に画像記録を行う先頭のラインの画像データから、画像記録を行う順番で１ラインずつ順次、前記所定の順序でシェーディング補正、抵抗値補正および必要に応じて黒比率補正、負荷変動補正、ならびに最後に温度上昇補正を行い、サーマルヘッド６６による感熱記録に応じた感熱記録データとする。なお、この時、温度上昇補正のための画像データ代表値算出処理は、階調補正後であれば、記録開始前後のどこで行ってもよい。
【００７９】
記録制御部８４は、データ記憶部８６から、すべての補正を終了したラインの感熱記録画像データを１ラインずつ順次読み出し、読み出した感熱記録画像データに応じた記録信号（画像に応じた電圧印加時間幅）をサーマルヘッド６６に出力する。
サーマルヘッド６６の各発熱素子は、記録信号に応じて発熱し、前述のように、感熱材料Ａがプラテンローラ６０等によって矢印ｂ方向に搬送されつつ、感熱画像記録が行われる。
【００８０】
本発明の記録装置１０においては、前記所定の順番であれば、全画像データに対してすべての補正を終了した感熱記録画像データをデータ記憶部８６に記憶した後（すなわち記録する画像データを作成した後）に、データ記憶部８６から１ラインずつ読み取り、画像記録を開始してもよい。
しかしながら、上記構成、すなわち、あらかじめ鮮鋭度補正および階調補正を施した後に記録を開始し、後は記録を行いつつ補正計算を行う構成とすることにより、記録時間を大幅に短縮することができる。
【００８１】
感熱画像記録が終了した感熱材料Ａは、ガイド６２に案内されつつ、プラテンローラ６０および搬送ローラ対６３に搬送されて排出部２２のトレイ７２に排出される。トレイ７２は、ハウジング２８に形成された排出口７４を経て記録装置１０の外部に突出しており、画像が記録された感熱材料Ａは、この排出口７４を経て外部に排出され、取り出される。
【００８２】
以上、本発明の感熱記録方法および感熱記録装置について詳細に説明したが、本発明は以上の例に限定はされず、本発明の要旨を逸脱しない範囲において、各種の改良および変更を行ってもよいのはもちろんである。
【００８３】
【発明の効果】
以上、詳細に説明したように、本発明によれば、サーマルヘッドを用いる感熱記録において、施される全ての画像処理（補正）について、期待される補正効果を十分に得ることができ、従って、適正に画像処理された感熱記録画像データによって、高画質な感熱画像を安定して記録することができる。
【図面の簡単な説明】
【図１】 本発明の感熱記録装置の一例の概念図である。
【図２】 図１に示される感熱記録装置の記録部の概念図、および記録部の制御系のブロック図である。
【図３】 本発明の感熱記録方法による変換処理の一例を示す模式図である。（ａ）は階調補正後でかつ鮮鋭度補正前における主走査方向の記録データの一例、（ｂ）は（ａ）の記録データに鮮鋭度補正を施した直後の記録データの一例、（ｃ）は（ｂ）の記録データに本発明の偽輪郭低減処理を施した後の記録データの一例、（ｄ）は（ｃ）の記録データのパターンに基づき形成された感熱記録画像の一例である。
【図４】 従来の感熱記録方法による変換処理の一例を示す模式図である。（ａ）は階調補正後でかつ鮮鋭度補正前における主走査方向の記録データの一例、（ｂ）は（ａ）の記録データに鮮鋭度補正を施した直後の記録データの一例、（ｃ）は（ｂ）の記録データのパターンに基づき形成された感熱記録画像の一例である。
【符号の説明】
１０ （感熱画像）記録装置
１４ 装填部
１６ 供給搬送手段
２０ 記録部
２２ 排出部
２４ マガジン
２６ 蓋体
２８ ハウジング
３０ 挿入口
３２ 案内板
３４ 案内ロール
３６ 停止部材
４０ 吸盤
４２ 搬送手段
４４ 搬送ガイド
４８ エンドレスベルト
５０ ニップローラ
５２ 規制ローラ対
５６ クリーニングローラ対
５８，６２ ガイド
６０ プラテンローラ
６３ 搬送ローラ対
６６ サーマルヘッド
６８ 支持部材
７２ トレイ
７４ 排出口
７６ 冷却ファン
８０ 画像処理部
８４ 記録制御部
８６ データ記憶部
Ａ 感熱（記録）材料[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thermal recording method and apparatus using a thermal head.
[0002]
[Prior art]
For the recording of ultrasonic diagnostic images, image recording (hereinafter also referred to as thermal image recording) using a thermal recording material (hereinafter referred to as a thermal material) in which a thermal recording layer is formed using a film or the like as a support is used. ing.
In addition, since thermal image recording has advantages such as no need for wet development processing and easy handling, in recent years, not only small-sized image recording such as ultrasonic diagnosis but also CT diagnosis, MRI In applications where large and high-quality images are required such as diagnosis and X-ray diagnosis, use for image recording for medical diagnosis is also being studied.
[0003]
As is well known, in thermal image recording, a thermal head having a glaze in which heating elements are arranged in one direction is used to record an image by heating a thermal recording layer of a thermal material. In a state of being slightly pressed to the layer), while moving both in the direction orthogonal to the extending direction of the glaze, by applying energy to each heating element of the glaze and heating according to the recorded image, Image recording is performed by heating the heat-sensitive recording layer of the heat-sensitive material.
[0004]
[Problems to be solved by the invention]
In such a thermal recording apparatus, image data is received from an image data supply source such as a CT diagnostic apparatus or an MRI diagnostic apparatus, and the image processing apparatus performs predetermined image processing such as sharpness correction and gradation correction on the image data. The image data supplied from the image data supply source is generated by performing (correction) to obtain thermal recording image data corresponding to the thermal recording, and driving the thermal head in accordance with the thermal recording image data to generate heat in each heating element. A thermal image corresponding to the is recorded.
[0005]
  Here, as the image processing performed by the image processing apparatus of the thermal recording apparatus, specifically, sharpness correction (sharpness processing) for enhancing the outline of the image; γ value of the thermal material and the thermal recording apparatus Gradation correction to obtain an appropriate image corresponding to individual differences, etc .; Temperature rise correction to adjust the heat generation energy according to the temperature of the heating element; Shading correction to correct density unevenness caused by the glaze shape variation of the thermal head, etc. ; Resistance value correction that corrects the difference in resistance value of each heating element; Black ratio correction to develop the image data corresponding to the same density at the same density regardless of the change in thermal head power supply voltage drop due to the change in recording pattern Between the thermal head and the thermal head according to the recording densityWorldLoad fluctuation correction that corrects streaky density unevenness caused by changes in the frictional force of the surface is performed.
[0006]
In an image recording apparatus, image data is usually supplied as numerical data. In a thermal recording apparatus, image data is supplied from an image data supply source as numerical data, for example, 10-bit digital data. Various image processing is performed by performing multiplication and averaging of correction coefficients.
However, in the case of performing a combination of a plurality of image processes performed by directly changing the image data in this way, depending on the order in which the processes are performed, proper image processing cannot be performed, and an expected correction effect can be obtained. In some cases, an image having a desired image quality cannot be obtained, that is, the image quality of the recorded image is deteriorated.
[0007]
Such a decrease in the image quality of the recorded image is a serious problem in applications where high-quality image recording is required. In particular, in applications where high-quality images are required as in the medical applications described above, this is an obstacle to image observation and a serious problem that leads to a diagnostic error.
[0008]
An object of the present invention is to solve the above-mentioned problems of the prior art, and in a thermal recording apparatus using a thermal head, sufficiently obtain the expected correction effect in all image processing (correction) performed. It is possible to provide a thermal recording method capable of stably recording a high-quality thermal image by using thermal recording image data appropriately processed, and a thermal recording apparatus using the thermal recording method. It is in.
[0009]
[Means for Solving the Problems]
  In order to achieve the above object, the present invention performs predetermined image processing on image data supplied from an image data supply source, and a thermal head according to the processed image data.TheDriveFor thermal recording materialsPerform thermal recordingIn thermal recording equipmentA thermal recording method,
  The image processing, Enhance the image outlineSharpness correction andThe gradation is corrected so as to achieve a target gradation according to the characteristics of the thermal recording material and the output characteristics including individual differences of the thermal recording apparatus.Perform tone correction, thenCorrecting unevenness in density of a recorded image caused by individual differences between a plurality of heating elements included in the thermal headPerform shading correction and resistance correction, and finallyBy adjusting the heat generation energy according to the temperature of the heating element, the density unevenness caused by the difference in temperature history of each heating element is corrected.Perform temperature rise correction and before or after any processing after gradation correctionThe image to be recorded is divided into a predetermined number of areas, and a representative value of the image data is calculated for each area.There is provided a thermal recording method characterized in that the processing is performed in a predetermined order in which the representative value calculation processing of image data for temperature rise correction is performed.
[0010]
  Here, after the shading correction and the resistance value correction, before the temperature rise correction,Regardless of the change in thermal head power supply voltage drop due to the change in recording pattern, the image data corresponding to the same density is developed with the same density.Black ratio correction and / orCorrection of streaky density unevenness caused by a change in frictional force at the interface between the thermal recording material and the thermal head according to the recording densityIt is preferable to perform load fluctuation correction.
  The gradation correction is preferably performed after the sharpness correction, or the sharpness correction is preferably performed after the gradation correction is performed, and the sharpness obtained thereafter is further performed. Of the recording data after the correction processing, the recording data value E corresponding to the image data value 0₀KE multiplied by a constant k (k <1)₀All recorded data with a smaller value than kE₀It is more preferable to convert to
[0011]
In addition, the shading correction and the resistance value correction are performed with the correction having the higher image density dependency first, and when the image density dependency of both corrections is equivalent, any order or shading correction and resistance value correction are performed. It is preferable to carry out simultaneously. The black ratio correction is preferably performed before the load fluctuation correction.
[0012]
  Furthermore, the present invention provides a thermal head having a glaze formed by arranging heating elements in one direction,
  Means for bringing the glaze and the thermal recording material into contact with each other and moving the thermal head and the thermal recording material relatively in a direction perpendicular to the arrangement direction of the heating elements;
  Introduction to image data supplied from image data supply sourcesEmphasize image outlineSharpness correction andThe gradation is corrected so as to achieve a target gradation according to the characteristics of the thermal recording material and the output characteristics including individual differences of the thermal recording apparatus.Apply gradation correction, thenCorrecting unevenness in density of a recorded image caused by individual differences between a plurality of heating elements included in the thermal headApply shading correction and resistance correction, and finallyBy adjusting the heat generation energy according to the temperature of the heating element, the density unevenness caused by the difference in temperature history of each heating element is corrected.Perform temperature rise correction and before or after any processing after gradation correctionThe image to be recorded is divided into a predetermined number of areas, and a representative value of the image data is calculated for each area.Image processing means for performing representative value calculation processing of image data for the temperature rise correction;
  There is provided a thermal recording apparatus comprising recording control means for driving the thermal head based on image data processed by the image processing means.
[0013]
  Here, the image processing means further includes, after the shading correction and resistance value correction, before the temperature rise correction,Regardless of the change in thermal head power supply voltage drop due to the change in recording pattern, the image data corresponding to the same density is developed with the same density.Black ratio correction and / orCorrection of streaky density unevenness caused by a change in frictional force at the interface between the thermal recording material and the thermal head according to the recording densityIt is preferable to perform load fluctuation correction.
  The image processing means preferably performs the gradation correction after the sharpness correction, or preferably performs the sharpness correction after performing the gradation correction. Among the recorded data after the sharpness correction processing, the recorded data value E corresponding to the image data value 0₀KE multiplied by a constant k (k <1)₀All recorded data with a smaller value than kE₀More preferably, it is converted to.
[0014]
Further, the image processing means performs the correction with the higher image density dependency among the shading correction and the resistance value correction first, and when the image density dependency of both corrections is equivalent, any order or It is preferable to perform the shading correction and the resistance value correction at the same time.
The image processing means preferably performs the black ratio correction before the load fluctuation correction.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the thermal recording method of the present invention and the thermal recording apparatus of the present invention using the same will be described in detail based on preferred embodiments shown in the accompanying drawings.
[0016]
FIG. 1 shows a schematic diagram of an example of a thermal recording apparatus of the present invention that uses the thermal recording method of the present invention.
A thermal recording apparatus 10 (hereinafter referred to as recording apparatus 10) shown in FIG. 1 performs thermal image recording on a thermal recording material (hereinafter referred to as thermal material A) which is a cut sheet of a predetermined size such as B4 size. There are a loading unit 14 loaded with a magazine 24 in which the thermal material A is stored, a supply transport unit 16, a recording unit 20 for recording a thermal image on the thermal material A by a thermal head 66, and a discharge unit 22. Configured. As shown in FIG. 2, an image processing unit 80 and a recording control unit 84 are connected to the thermal head 66 of the recording unit 20, and a data storage unit 86 is connected to the image processing unit 80.
[0017]
In such a recording apparatus 10, the thermal conveying material 16 is conveyed to the recording unit 20 by the supply conveying unit 16, and the thermal head 66 is pressed against the thermal material A while the glaze extending direction (in FIGS. 1 and 2). A thermal image is recorded on the thermal material A by conveying the thermal material A in a direction orthogonal to the direction perpendicular to the paper surface and heating each heating element in accordance with the recorded image.
[0018]
The heat-sensitive material A is formed by forming a heat-sensitive recording layer on one surface of a transparent polyethylene terephthalate (PET) film or the like as a support or paper.
Such a heat-sensitive material A is usually a laminated body (bundle) of a predetermined unit such as 100 sheets and is packaged by a bag or a belt. In the illustrated example, the heat-sensitive recording layer remains in a bundle of a predetermined unit. Are stored in the magazine 24 of the recording apparatus 10 with the bottom surface being taken out from the magazine 24 one by one and used for thermal image recording.
[0019]
The magazine 24 is a housing having a lid 26 that can be freely opened and closed. The magazine 24 stores the heat-sensitive material A and is loaded into the loading unit 14 of the recording apparatus 10.
The loading unit 14 includes an insertion port 30 formed in the housing 28 of the recording apparatus 10, a guide plate 32, guide rolls 34 and 34, and a stop member 36. The magazine 24 has the lid 26 side first. The recording device 10 is inserted into the recording device 10 through the insertion port 30, and is guided to the stop plate 36 while being guided by the guide plate 32 and the guide roll 34, so that the recording device 10 is loaded at a predetermined position.
[0020]
The supply / conveyance means 16 takes out the heat-sensitive material A from the magazine 24 loaded in the loading section 14 and conveys it to the recording section 20, and is a single-wafer mechanism that uses a suction cup 40 that adsorbs the heat-sensitive material A by suction. A means 42, a conveyance guide 44, and a regulating roller pair 52 positioned at the exit of the conveyance guide 44 are included.
The conveying means 42 includes a conveying roller 46, a pulley 47 a coaxial with the conveying roller 46, a pulley 47 b and a tension pulley 47 c connected to a rotational drive source, an endless belt 48 stretched around these three pulleys, The nip roller 50 pressed by the roller 46 is configured, and the tip of the heat-sensitive material A sheeted by the suction cup 40 is sandwiched between the conveyance roller 46 and the nip roller 50 to convey the heat-sensitive material A.
[0021]
When an instruction to start recording is issued in the recording apparatus 10, the lid body 26 is opened by an unillustrated opening / closing mechanism, and a single-wafer mechanism using the suction cup 40 takes out one thermal material A from the magazine 24, and the leading end of the thermal material A Is supplied to the conveying means 42 (conveying roller 46 and nip roller 50). When the heat-sensitive material A is sandwiched between the conveying roller 46 and the nip roller 50, the suction by the suction cup 40 is released, and the supplied heat-sensitive material A is guided to the regulating roller pair 52 by the conveying means 42 while being guided by the conveying guide 44. Be transported.
Note that when the heat-sensitive material A used for recording is completely discharged from the magazine 24, the lid 26 is closed by the opening / closing means.
[0022]
The distance from the conveying means 42 to the regulating roller pair 52 defined by the conveying guide 44 is set slightly shorter than the length in the conveying direction of the thermal material A, and the tip of the thermal material A is moved by the conveying means 42. Although the control roller pair 52 is reached, the control roller pair 52 is initially stopped, and the tip of the heat-sensitive material A is stopped and positioned here.
When the leading end of the thermal material A reaches the regulating roller pair 52, the temperature of the thermal head 66 (glaze 66a) is confirmed. If the temperature of the thermal head 66 is a predetermined temperature, the thermal material A by the regulating roller pair 52 is confirmed. Is started, and the heat-sensitive material A is transported to the recording unit 20.
[0023]
FIG. 2 shows a schematic diagram of the recording unit 20.
The recording unit 20 includes a thermal head 66, a platen roller 60, a cleaning roller pair 56, a guide 58, a cooling fan 76 (see FIG. 1) and a guide 62 for cooling the thermal head 66, and an image processing unit 80 constituting a recording control system. And a recording control unit 84.
The thermal head 66, for example, performs thermal image recording with a recording (pixel) density of about 300 dpi capable of recording an image up to a maximum B4 size, and includes one heating element that performs thermal recording on the thermal material A. It has a thermal head main body 66b formed with glazes 66a arranged in a direction (perpendicular to the paper surface in FIGS. 1 and 2), and a heat sink 66c fixed to the thermal head main body 66b. The thermal head 66 is supported by a support member 68 that is rotatable about a fulcrum 68a in the direction of arrow a and in the opposite direction.
[0024]
The platen roller 60 rotates at a predetermined image recording speed while holding the heat sensitive material A in a predetermined position, and conveys the heat sensitive material A in a direction orthogonal to the main scanning direction (the direction of arrow b in FIG. 2).
The cleaning roller pair 56 is a roller pair composed of an adhesive rubber roller 56a, which is an elastic body, and a normal roller 56b. This prevents dust from adhering to the image and from adversely affecting image recording.
[0025]
In the illustrated recording apparatus 10, before the heat-sensitive material A is conveyed, the support member 68 is rotated upward (in the direction opposite to the arrow a direction), and the thermal head 66 (glaze 66 a) and the platen roller 60. There is no contact.
When the conveyance by the regulating roller pair 52 is started, the thermal material A is then sandwiched between the cleaning roller pair 56 and further conveyed while being guided by the guide 58. When the leading end of the heat sensitive material A is conveyed to the recording start position (position corresponding to the glaze 66a), the support member 68 rotates in the direction of arrow a, and the heat sensitive material A becomes the glaze 66a of the thermal head 66 and the platen roller 60. And the glaze 66a is pressed against the recording layer, and the heat sensitive material A is held at a predetermined position by the platen roller 60, while the platen roller 60 (and the regulating roller pair 52 and the conveying roller pair 63) has an arrow. It is conveyed in the b direction.
Along with this conveyance, the thermal image recording is performed on the thermal material A by heating each heating element of the glaze 66a according to the recorded image.
[0026]
As described above, the recording control system of the thermal head 66 basically includes the image processing unit 80 and the recording control unit 84. The image processing unit 80 is connected to a data storage unit 86 for storing data for various image processing (correction) performed by the image processing unit 80 and image data supplied from the image data supply source R. Is done.
Furthermore, for example, five thermistors are arranged at predetermined intervals in a portion corresponding to the glaze of the base 66d of the heat sink 66c of the illustrated thermal head 66, and the temperature of the glaze 66a (that is, the heat generated in this portion). The temperature of the element) is detected, and the detection result is sent to the image processing unit 80 as indicated by a two-dot chain line. The image processing unit 80 receives this detection result, and detects the temperature of each heating element by, for example, linear interpolation. The recording unit 20 is provided with a thermometer T that detects the ambient temperature near the thermal head 66, and sends the measurement result to the image processing unit 80.
[0027]
Image data from an image data supply source R such as CT or MRI is sent to the image processing unit 80 as 10-bit (0 to 1023) digital data, for example.
The image processing unit 80 is a combination of various image processing circuits and memories, receives image data from the image data supply source R, performs predetermined image processing (correction) on the image data, Format (enlargement / reduction, frame allocation) is performed as necessary to obtain thermal recording image data corresponding to thermal recording by the thermal head 66.
[0028]
Here, in the thermal recording apparatus according to the present invention, these correction processes are performed in the order of sharpness correction and gradation correction (density correction) → shading correction and resistance value correction → temperature rise correction, and after gradation correction. The image data representative value calculation process for temperature rise correction (for example, there is a thinning process as a representative example) is performed in a predetermined order before or after any of the image processing, but shading correction and resistance It is preferable to perform black ratio correction and / or load fluctuation correction between the value correction and the temperature rise correction. For example, in the illustrated recording apparatus 10, sharpness correction → gradation correction → image data representative value calculation processing for temperature rise correction → shading correction / resistance value correction (simultaneous) → black ratio correction → load fluctuation correction → Image processing may be performed in the order of temperature rise correction, or gradation correction → sharpness correction (including false contour reduction processing) → shading correction → image data representative value calculation processing for temperature rise correction → resistance Image processing may be performed in the order of value correction → black ratio correction → load fluctuation correction → temperature rise correction, but in the illustrated apparatus, it is preferable to perform image processing in the latter order.
[0029]
Thus, in the present invention, the order of gradation correction and sharpness correction, the order of shading correction and resistance value correction, whether or not to perform black ratio correction and load variation correction, and the order in which they are performed, and The timing (order) for performing the image data representative value calculation process for temperature rise correction is appropriately selected according to the type and size of the thermal material A, the recording device 10, the image quality required for the reproduced image, and a combination thereof. be able to.
Hereinafter, each correction process performed in the method of the present invention will be described.
[0030]
Sharpness correction (sharpness processing) is correction that enhances the sharpness of an image by enhancing the outline of a recorded image in order to obtain a clear and sharp image.
The sharpness correction can be performed by various known methods, but is performed as follows as an example.
One screen is divided into n × n pixels, and j-th image data in the extending direction of the glaze 66a in a certain pixel line i is represented by S._ijAssuming that (i = 1, 2,... N, j = 1, 2,... N), the image data S is used for sharpness correction._ijFirst, the first unsharpness signal U which is electrically blurred image data¹ _ijConvert to
This first unsharpness signal U¹ _ijIs the image data S_ijAnd the surrounding image data are obtained by averaging,
[Expression 1]

Is required. M is the first unsharpness signal U¹ _ijIs the number of pixels used to create a mask size, and L is defined by (M−1) / 2.
[0031]
Then the first unsharpness signal U¹ _ijIs further averaged to obtain a second unsharpness signal U² _ijIs calculated. Second unsharpness signal U² _ijIs the first unsharpness signal U¹ _ijIn the same manner as the above, it is calculated by the following formula (2).
[Expression 2]

[0032]
Then the first unsharpness signal U¹ _ijAnd the second unsharpness signal U² _ijFind the difference between Then, this difference is multiplied by the sharpness correction coefficient K to obtain the first unsharpness signal U¹ _ij, That is, the sharpness corrected image data S by the following equation (3)_ijIs obtained.
S_ij= U¹ _ij+ K ・ (U¹ _ij-U² _ij(3)
[0033]
Here, the sharpness of the thermal recording image is affected by the temperature of the thermal head 66 (heating element), the recording speed, the γ value of the thermal material A, etc. The higher the temperature of the thermal head 66, the faster the recording speed, Furthermore, since the sharpness of the recorded image decreases as the γ value of the heat-sensitive material A is lower, the sharpness correction coefficient K may be changed as necessary to perform the sharpness correction.
In this case, for example, a weight coefficient table (or function) corresponding to the temperature of the heating element, the recording speed, the γ value of the heat-sensitive material, etc. is created and read at the time of sharpness correction, and sharpness correction is performed. A method of multiplying the coefficient K is exemplified.
[0034]
Gradation correction (also referred to as density correction) is correction for obtaining an image in which gradation (density) is appropriately expressed by correcting image data in accordance with the state of the recording apparatus, the γ value of the thermal material A, and the like. It is.
As described above, the recording device 10 is a device that receives image data as 10-bit digital data and performs image recording in accordance with the 10-bit digital data. In this device, for example, 512 digital image data has a density (D) 1. .2, it is basically required to output an image having a density of 1.2 when 512 image data is received. However, there are individual differences in devices, and the installation environment and the like are also different. Furthermore, the γ value of the heat-sensitive material A varies depending on the manufacturer and production lot. Therefore, it is impossible for all apparatuses to output an image having a predetermined density according to the supplied image data. Therefore, gradation correction is performed, and a thermal recording image in which gradation is appropriately expressed according to image data is formed.
Further, in normal thermal recording apparatuses including the recording apparatus 10 shown in the figure, the image data sent from the image data supply source R is converted into image data corresponding to the heat generation amount of thermal recording by this gradation correction. The
[0035]
The gradation correction method is not particularly limited, and various known methods can be used. For example, a correction chart in which an image having a plurality of densities is recorded by the recording apparatus 10 is created and recorded on the correction chart. The density of the measured image is measured with a densitometer, and a correction table, that is, a gradation curve (or correction function) is calculated from the target image density of the recording apparatus 10 and the image density recorded in the correction chart using a density correction algorithm. And a method of converting image data using this correction table.
[0036]
Further, the image data converted to correspond to the calorific value after the gradation correction is applied to the thermal head, even if the recording density is 0, the recording energy is such that the thermal material A does not develop color (preferably just before the color development). Preferably, the correction table is generated as described above.
With this configuration, the temperature difference of each heating element during recording can be reduced, the temperature distribution of the entire thermal head 66 can be reduced, and a high-quality image can be obtained, and the base of the thermal material A can be obtained. Is a transparent PET film or the like, the surface of the heat-sensitive material A is slightly melted to reduce light irregular reflection, and the transparency of the heat-sensitive material A can be improved.
[0037]
The shading correction is to correct density unevenness caused by the shape variation of the glaze 66a of the thermal head 66.
As described above, the thermal head 66 has a glaze in which heating elements are arranged in one direction. However, it is difficult to make the shape of the glaze 66a uniform over all pixels. And have some shape variation. Further, the amount of heat generated by each heating element varies depending on the position in the extending direction of the glaze 66a. For this reason, even when image recording is performed using image data having the same recording density, density unevenness due to the shape variation and position, so-called shading occurs. In order to correct this density unevenness, it is necessary to perform shading correction.
[0038]
There is no particular limitation on the shading correction method. Heat generation energy corresponding to image data of a predetermined density is supplied to all pixels (heat generation elements) of the thermal head 66 to actually form a thermal recording image, and to adjust the image density. The image data is optically measured using a densitometer or the like, and the image data is formed so that the density of the formed recorded image is uniform from the recording density corresponding to the image data and the actually measured density of the recorded image. An example is a method in which shading correction data (correction coefficient) to be corrected is calculated for each pixel, stored in the data storage unit 86, and the image data is multiplied by the shading correction data. In addition, a method of supplying the same heat generation energy to all the pixels of the thermal head 66 to measure the heat generation amount of each pixel, calculating the same shading correction data from the heat generation amount of each pixel, and the like is exemplified. .
Furthermore, if necessary, a correction coefficient (correction table) of shading correction data is created according to the image data (image density), the temperature of the thermal head 66, the recording speed, the temperature, humidity, γ, etc. of the thermal material A. The shading correction may be performed by correcting the shading correction data in accordance with these.
[0039]
The resistance value correction is correction for obtaining a proper image by correcting a difference in resistance value of each heating element.
The resistance values of the heat generating elements used in the thermal head 66 are not uniform, and have variations in resistance values due to manufacturing errors and material variations. In addition, the resistance value of the heating element, which is a resistor, changes depending on the usage, that is, the heating time and heating energy (heating history), but the heating history of each heating element is not uniform, and the resistance value changes with time. And the variation in resistance value fluctuates.
Due to such variation in resistance value, even if heat is generated for the same time, the amount of heat generated by each heating element differs, which is one of the causes of density unevenness in the recorded image. Therefore, it is necessary to correct the density unevenness due to this, that is, to correct the resistance value.
[0040]
The resistance value correction method is not particularly limited. The resistance value of each heating element is actually measured, and resistance value correction data (for example, [R / Rm]) is used for each heating element. Examples are a method of calculating a resistance value (Rm represents a maximum resistance value in all the heating elements) and storing it in the data storage unit 86, and multiplying this by image data.
The resistance value of the heating element is also affected by the temperature of the thermal head 66 (heating element) and the image data (image density). Therefore, a correction coefficient table (function) of the resistance value correction data corresponding to these values is prepared in advance. It may be created and stored, and a correction coefficient may be read in accordance with the temperature of the heating element and image data, and the resistance value correction data may be multiplied by the correction coefficient to perform resistance value correction.
[0041]
The black ratio correction is a correction for coloring the same image data with the same density regardless of the change in the thermal head power supply voltage drop due to the change in the recording pattern.
For example, when there are many high-density parts in one line of image data, the number of heating elements that are energized at the same time increases and the amount of current increases. For example, due to the internal resistance of the power cable from the power source to the thermal head, A voltage drop according to the amount of current occurs. For this reason, the power supply voltage supplied to the thermal head fluctuates for each line and for each heating element according to the density of the image data, and even if the image data is the same, a density difference occurs in the recorded image. So-called black ratio unevenness occurs. Therefore, it is necessary to correct density unevenness due to this, that is, black ratio correction.
[0042]
The black ratio correction method is not particularly limited, and various known methods can be used. For example, for each line, the image data of each pixel is added to calculate the total applied energy of one line. A method for correcting image data of individual pixels based on applied energy, that is, a black ratio for correcting a loss of heat energy due to a voltage drop of image data of each pixel, assuming that the voltage drop amount in one line is constant A correction method is exemplified.
[0043]
Further, as a more preferable method, a method of performing black ratio correction using the following formula (a) is exemplified. In the above black ratio correction method, since the same correction is performed based on the total energy in one line, pixels with low density are overcorrected. It is possible to optimally correct the black ratio of pixel image data.
[Equation 3]

In the above formula (a), N is the number of pixels in one line, D is image data, M is the maximum value of image data, k is a correction coefficient, D (n) is image data before correction of pixel n, and H (D ) Is a correction data value for the image data D, D_C(N) shows the image data after the correction of the pixel n.
[0044]
In equation (a), first, a correction data value H (D) for each image data D is calculated. For example, in an apparatus having 2048 gradations in the range of image data D from 0 to 2047, 2048 correction data values from correction data values H (0) to H (2047) corresponding thereto are calculated.
[0045]
At this time, when the image data D (n) before correction is equal to or larger than the image data D, D ′ (n) is set as the image data D, and conversely, the image data D (n) is smaller than the image data D. In this case, D ′ (n) is set as image data D (n). Then, using the correction data value H (D (n)) for the uncorrected image data D (n) of each pixel n, the corrected image data D_C(N) is calculated.
[0046]
Further, when the formula (a) is calculated as it is, the calculation amount becomes very large, but the calculation amount can be greatly reduced by calculating as follows.
As shown in the following formula (b), C (D) is
[Expression 4]

H (D) is expressed by H (D) = 1−C (D) / (N × M).
[0047]
Here, C (D) in the case of D = M, that is, C (M) is obtained from the equation (b):
[Equation 5]

Is required.
Since C (M−1) is calculated as M → M−1, if the number of pixels of the image data M is written as hst (M),
C (M-1) = C (M) -hst (M)
Can be expressed as
Since C (M-2) is calculated as M-1, M → M-2,

In the same manner, generally,
[Formula 6]

It becomes.
[0048]
Therefore, as a calculation procedure,
・ Step 1
A value Stotal obtained by adding the data values of all pixels in one line and histograms hst (0), hst (1),..., Hst (M) of each image data included in one line are obtained.
・ Step 2
A correction value corresponding to each image data is obtained as follows.
S (M) = 0
C (M) = Stotal
S (M-1) = S (M) + hst (M)
C (M-1) = C (M) -S (M-1)
S (M-2) = S (M-1) + hst (M-1)
C (M-2) = C (M-1) -S (M-2)
...
S (1) = S (2) + hst (2)
C (1) = C (2) -S (1)
・ Step 3
Each pixel in one line is corrected as follows. (K is a correction coefficient)
D_C(N) = D (n) * {1-k * (1-C (D (n)) / (N * M))}
This black ratio correction method is described in detail in Japanese Patent Application No. 8-25036 by the present applicant.
[0049]
By the way, in the thermal recording apparatus 10, the frictional force at the interface between the thermal material A and the thermal head 66 changes according to the density recorded on the thermal material.
For this reason, at the boundary line portion where the portion recorded at a low density changes to the portion recorded at a high density, the conveying speed of the heat sensitive material increases momentarily, and the recording density at the boundary line portion decreases, resulting in a white stripe shape. On the contrary, there is a problem that black streak-like density unevenness occurs at the boundary line portion that changes from the high density recording portion to the low density recording portion. .
[0050]
The load fluctuation correction is a correction process for preventing the above-mentioned stripe-shaped density unevenness from occurring. For example, the image data calculated in advance and the frictional force between the thermal material and the thermal head ( Based on the function representing the relationship between the (conveying torque) and the frictional force corresponding to each pixel of the current line from the sum of the frictional force corresponding to each pixel of the previous line, as shown in the following calculation formula: By subtracting the sum, the amount of change in friction force from the previous line to the current line is calculated, and the image data is corrected for each pixel in each line based on the amount of change in friction force.
[0051]
[Expression 7]

Here, n is the row number of the recorded image, i is the pixel number of the nth line, D ′_n(I) and D_n(I) is the image data value of the i-th pixel of the nth line after correction and before correction, k is a correction coefficient, and H_nIs the amount indicating the change in frictional force between the thermal material of the nth line and the thermal head, M is the total number of pixels in one line, f (D) is the image data value D, and the friction between the thermal material and the thermal head It is a functional expression that expresses the relationship between force.
[0052]
In addition, by approximating the relationship between the image data and the frictional force between the thermal material and the thermal head with a linear function, the image data values of the previous line and the current line are simply cumulatively added, Since load fluctuation correction can be performed simply by taking the difference between the cumulative addition value of the previous line and the cumulative addition value of the current line, it is not necessary to prepare the above function and the processing speed can be improved. There is an advantage.
[0053]
Further, for example, a function representing a relationship between image data, frictional force between the thermal material and the thermal head, which is calculated in advance, frictional force between the thermal material and the thermal head, and deformation of the rubber roller. The amount of change in the deformation amount of the rubber roller at each pixel position of each line is obtained based on a function representing the relationship between the amount and the amount of change in the deformation amount of the rubber roller at each pixel position of the current line and the previous line. Depending on the correction coefficient of the current line, or instead of the change amount of the deformation amount of the rubber roller for each pixel position of the current line, the average value of the change amount of the deformation amount of the rubber roller for each line and each pixel of each line It is also possible to correct the image data of the current line more accurately by using the sum of the change values of the deformation amounts of the rubber rollers of m pixels before and after each pixel position for each position.
This load fluctuation correction method is described in detail in Japanese Patent Application No. 9-50295 by the present applicant.
[0054]
In the temperature increase correction, the heat generation energy is adjusted according to the temperature of the heat generating element, and the density unevenness caused by the difference in temperature history of each heat generating element is corrected.
The heating elements of the thermal head 66 are heated by energizing for a predetermined time corresponding to the image data of each pixel of the recorded image, for example. However, since the temperature of each heating element differs individually according to the recorded image (heating history) up to the previous line, even if each heating element is energized for the same time according to the same image data, A temperature difference occurs between them, and density unevenness occurs.
Therefore, for each heating element, it is necessary to perform temperature rise correction of the image data that corrects the heat generation amount based on the image data, the heat generation history up to the previous line, and the like.
[0055]
The temperature increase correction method is not particularly limited, and various known methods can be used. As an example, first, as a preprocessing, a recorded image of one screen is a predetermined number of regions (blocks) having a predetermined number of pixels. Then, the representative value of the image data is calculated for each divided area, and then the predicted temperature value of each area is calculated from the representative value of the image data and the initial temperature value detected by the thermistor or the like. The temperature correction value for each region is calculated from this temperature prediction value, the temperature correction value for each region is interpolated to calculate the temperature correction value for each pixel of the recorded image of one screen, and this temperature correction value A method of correcting the image data of each pixel by using is illustrated.
[0056]
More specifically, first, the recorded image of one screen is divided into a predetermined number of areas having a predetermined number of pixels. For example, when the recorded image of one screen is 3072 pixels wide × 4224 pixels long, 128 pixels wide × The recorded image of one screen is divided into a mesh of 25 areas × 133 areas by an area having 32 pixels vertically.
Next, a method in which image data of a predetermined pixel in a region is used as a representative value; a method in which the average value of image data of a predetermined number of remaining pixels after thinning out pixels in a region is used as a representative value (thinning processing) A method in which the average value of the image data of all the pixels in the region is used as a representative value; Pre-processing for temperature rise correction for calculating the representative value of the image data of each area divided in this way is performed.
[0057]
Next, from the representative value of the image data in each region and the temperature initial value detected by the temperature of the thermal head 66 (base of heat sink 66d) detected by the thermistor and the ambient temperature detected by the thermometer T, etc. Then, the temperature prediction value is calculated. As a method of calculating the predicted temperature value, the heat transfer system of the thermal head 66 is replaced with an equivalent circuit of an electric system based on a CR model composed of a capacitance component C and a resistance component R, and the heat generation amount per unit time of the heat transfer system. Examples include a method of replacing temperature, heat capacity, and heat resistance with electric current, voltage, capacity, and resistance, respectively.
From the obtained temperature predicted value, a temperature correction value for each region is calculated using a predetermined calculation formula set in advance, and the temperature correction value for the region is interpolated, and one screen is calculated using a preset calculation formula. The temperature correction value for each pixel of the recorded image is calculated, and the temperature correction of the image data is performed using this.
The above temperature rise correction method is described in detail in Japanese Patent Application No. 8-25035 by the present applicant.
[0058]
In the thermal recording apparatus, the image data supplied from the image data supply source R is subjected to such corrections to obtain thermal recording image data corresponding to the thermal recording by the thermal head 66.
Here, in the recording apparatus 10 according to the present invention, each of the above corrections is in the order of sharpness correction and gradation correction → shading correction and resistance value correction → temperature rise correction, and any correction after the gradation correction. Before or after the image data representative value calculation processing for temperature rise correction is performed in a predetermined order, and depending on the required image quality level, between shading correction and resistance value correction, and temperature rise correction. At least one of black ratio correction and load fluctuation correction is performed.
[0059]
As is clear from the description of each correction (image processing) described above, the sharpness correction and the gradation correction are performed in accordance with the image to be recorded, and the supplied image data (in the illustrated example, for example, 10 bits (0 to 1023 digital data), the correction amount of each correction amount varies, that is, the correction amount is determined by image data.
On the other hand, the shading correction and the resistance value correction are corrections for density unevenness specific to the recording apparatus 10 and are corrected by reflecting them in the image data.
The black ratio correction is correction according to the voltage drop of the thermal head 66, and the load fluctuation correction is correction according to the combination of the thermal material A and the recording apparatus 10 (thermal head 66). Is preferably performed as late as possible, and is preferably performed on the image data immediately before the final image data supplied to the thermal head 66 is obtained.
[0060]
As described above, the temperature rise correction detects the ambient temperature and the temperature of the thermal head 66, predicts the temperature rise of the thermal head 66 using this temperature, and calculates the temperature correction value based on this. Therefore, it is preferable that the temperature rise correction be performed immediately before recording, that is, at the end of image processing (correction). In other words, a line for which temperature correction has been completed is immediately recorded (that is, correction calculation is performed during recording). It is preferable to adopt a configuration.
[0061]
For this reason, if device-specific correction such as shading correction is performed prior to correction according to image data for gradation correction or sharpness correction, the result is that the target image itself has an effect on the device characteristics. The target image is different from the target image. In other words, the correction for eliminating the uneven stripes inherent in the recording apparatus 10 such as shading correction is reflected in the image data before performing the correction according to the recorded image (image data) itself. The sharpness correction and gradation correction according to the image also reflect the device characteristics, so that proper correction cannot be performed.
Therefore, the sharpness correction and the gradation correction are basically performed prior to the shading correction and the resistance value correction, and the temperature increase correction is preferably performed immediately before the last recording, and the black ratio correction and / or the correction is performed. It is preferable to perform the load fluctuation correction in the order as late as possible.
[0062]
Here, the gradation of the recorded image varies depending on the sensitivity and gradation of the heat-sensitive material A and the characteristics of the recording apparatus 10. Therefore, when sharpness correction is performed after tone correction, the sharpness correction amount varies depending on the combination of the heat-sensitive material A and the recording apparatus 10 as in the above-described shading correction and the like, and stable sharpness is achieved. The degree correction cannot be performed. Therefore, in such a case, it is preferable to perform tone correction after sharpness correction.
[0063]
By the way, in the gradation correction, the recording density is 0 (that is, from the image data source) in order to perform high-quality thermal recording by reducing the temperature difference of each heating element during recording, and thus the temperature distribution of the entire thermal head. Even if the input image data value is 0), a predetermined recording data value E is applied so that the recording energy is applied so that the heat-sensitive material A does not develop color (preferably just before the color development).₀(E₀> 0).
[0064]
For this reason, when sharpness correction is performed after gradation correction, as shown in FIG. 4A, the density such as the contour is recorded on the high density side in one line in the main scanning direction of the image to be recorded. Data value D_HTo low-density recording data value D_LIf there is a part that changes rapidly (hereinafter referred to as an edge part), after the sharpness correction, as shown in FIG. 4B, the density difference at the edge part is emphasized, and the recorded data value on the low density side D_LIs E₀Or E₀In the case of a value close to, the recording data value D on the low density side_LEnhanced peak value D_LPIs E₀There is a possibility that the case becomes considerably smaller than that. For this reason, in the actual recorded image, even if the emphasized edge portion is relaxed due to the diffusion of heat at the edge portion, the non-colored portion remains without being sufficiently colored at the portion where the original color should be developed. For this reason, as shown in FIG. 4C, a false contour that looks like a white outline is generated, which may cause a problem that the recorded image feels uncomfortable.
[0065]
The occurrence of false contours in such a recorded image may be a serious problem when high-quality image recording is required, particularly when recording a high-definition halftone image. In particular, in applications where high-definition and high-quality halftone images are required as in the medical applications described above, there are cases where it becomes an obstacle to image observation and a serious problem that leads to medical errors.
[0066]
In such a case, in the present invention, with respect to the recording data D that has been subjected to sharpness correction in this way, the recording data D that is less than a predetermined value is converted into a predetermined value (hereinafter referred to as false contour reduction processing). ). Specifically, the recording data value E corresponding to the image data value 0 of the recording data D after the sharpness correction.₀KE multiplied by a constant k (k <1)₀All smaller recorded data D is kE₀By converting to, generation of false contours is prevented.
[0067]
FIG. 3 shows a schematic diagram of an example of conversion processing according to another aspect of the thermal recording method of the present invention. 3A shows an example of recording data in the main scanning direction after gradation correction and before sharpness correction. FIG. 3B shows recording data immediately after sharpness correction is performed on the recording data in FIG. FIG. 3C shows an example of the recorded data after the false contour reduction processing of the present invention is applied to the recorded data of FIG. FIG. 3D is an example of a thermal recording image formed based on the recording data pattern of FIG.
Hereinafter, an example of a thermal recording method according to another aspect of the present invention will be described with reference to FIG.
First, it is assumed that tone correction is performed on image data input from the image data source, and a pattern of recording data D in the main scanning direction as shown in FIG. 3A is obtained. Here, in the central portion of the pattern of the recording data D in FIG. 3A, an edge portion where the recording data value (that is, density) changes abruptly exists.
[0068]
Next, when the above-described sharpness correction is performed on a series of recording data D having such an edge portion, as shown in FIG. 3B, the pattern of the recording data D in which the edge portion is emphasized. Is obtained. That is, the image data value D on the low density side (the side where the image data value is small) near the edge portion._LHas a smaller peak value D_LPIs emphasized and converted, and a peak is formed downward (in the low density direction) at the edge portion. On the other hand, the image data value D on the high density side (image data value larger side) near the edge portion_HHas a larger peak value D_HPThe peak is formed upward (in the high density direction) at the edge portion.
Here, if the data of FIG. 3B is recorded as it is by the thermal head, the peak portion (that is, the edge portion) on the low concentration side is also diffused by heat as shown in FIG. 4C. Regardless, as described above, there is a case where the color does not develop, the color appears to be white and a false contour may occur.
[0069]
Therefore, in this aspect, the image data D after the sharpness enhancement process is converted as follows, and the minimum value of the recording data value D is set to kE.₀Thus, as shown in FIG. 3C, the recorded data after sharpness correction is prevented from becoming an unnecessarily small value, and the heat is diffused at the edge portion in the actual recorded image. As shown in FIG. 3D, the contour can be expressed vividly without generating a false contour.
[0070]
[Equation 8]

[0071]
This conversion is performed on all image data. D_mIs the maximum value that the recording data can take and may be determined as appropriate.
Here, the value of k is preferably 0.5 to 0.9, and more preferably 0.6 to 0.7. However, in terms of the performance of the thermal head used, the characteristics of the thermal recording material, and the like. It may be determined appropriately depending on the situation and is not particularly limited. If it is less than 0.5, the false contour may not be removed sufficiently. If it exceeds 0.9, the sharpness may not be sufficiently improved, and sufficient image quality may not be obtained. It is not preferable.
As described above, in this aspect, first, gradation correction is performed, then sharpness correction is performed, and then false contour reduction processing is performed, and then image data for shading correction, resistance value correction, or temperature rise correction is performed. It is preferable to perform a representative value calculation process.
[0072]
  Either shading correction or resistance value correction may be performed first. However, when the correction depends on image data, that is, image density, it is preferable to perform the one having higher image density dependency first. As described above, the shading correction and the resistance value correction are corrections in which image data is multiplied by a correction coefficient (shading correction data and resistance value correction data) determined for each pixel (for each heating element). If the correction with large characteristics is performed first,InTherefore, the influence on the correction can be reduced. In general, since shading correction is more dependent on density than resistance value correction, the order is usually shading correction → resistance value correction.
  If both concentration dependencies are equivalent, either may be performed first. Further, as described above, since both corrections are multiplications of correction data, both corrections may be performed at the same time (preferably, when both density dependencies are equivalent).
[0073]
  Shading correction data and resistancevalueSince both the correction data are unique to the thermal head 66, the correction data is prepared in advance according to the thermal head 66, and when the thermal head 66 is replaced, the recording apparatus 10 is used by using an IC card or FD. It is preferable that data can be input (loaded) into the (data storage unit 86).
[0074]
Either the black ratio correction or the load fluctuation correction may be performed first, and which one should be performed first can be appropriately determined depending on the combination of the thermal material A and the recording apparatus 10. Therefore, for one combination of the heat-sensitive material A and the recording apparatus 10, the order of these corrections may be changed, and a test print (trial recording) may be actually performed to determine better heat-sensitive recording.
[0075]
As described above, since the actual temperature correction amount is large, it must be performed last, but it is necessary to divide the image data into areas (blocks) of a certain size and adjust the temperature of each block. Predictive calculation is to be corrected. For this reason, the heat generation amount of each block is obtained by the image data representative value calculation process, but this must accurately represent the heat generation amount of each block. Therefore, the image data representative value calculation process must be performed after tone correction, and is preferably performed before resistance value correction, black ratio correction, and load fluctuation correction. This image data representative value calculation process may be performed either before or after sharpness correction. Further, this image data representative value calculation process may be performed before or after shading correction, and which one can be performed can be determined as appropriate depending on the actual correction and test printing.
Here, when high image quality is not required for the heat-sensitive reproduced image, the prediction accuracy is somewhat deteriorated, but it is performed somewhere after the gradation correction even before the resistance value correction, the black ratio correction and the load fluctuation correction. It is also possible.
[0076]
However, as is clear from the above description, the black ratio correction, the load fluctuation correction, and the temperature rise correction have a large amount of calculation, and the calculation capability and processing timing of the image processing unit 80 (for example, all correction calculations are first performed). Depending on the case where recording and calculation are performed in parallel instead of recording after completion, the black amount correction or load fluctuation correction is performed before the temperature rise correction that is required to be performed at the end with a large correction amount. It can be difficult to do. Here, the correction amount of the image data by the black ratio correction and the load fluctuation correction is relatively small. In particular, when the power supply capacity of the thermal head 66 is large (that is, the internal resistance of the power supply is small), the voltage fluctuation due to the black ratio is Depending on the type and size of the heat-sensitive material A and the pressing force of the thermal head 66 on the heat-sensitive material A, the torque fluctuation of the carry motor, that is, the load fluctuation is small, and the image data of the black ratio correction or the load fluctuation correction is reduced. The correction amount is extremely small.
Therefore, either one or both of the black ratio correction and the load fluctuation correction may be omitted according to the required image quality level.
[0077]
Thus, image correction (image processing) is performed in the order of sharpness correction and gradation correction → shading correction and resistance value correction → temperature rise correction, and before or after any image processing after gradation correction. The image data representative value calculation processing for the rise correction is performed in a predetermined order, and if necessary, the black ratio correction and / or the load fluctuation between the shading correction and the resistance value correction and the temperature rise correction. According to the recording apparatus 10 of the present invention in which correction is performed, all corrections can be appropriately performed, and the expected correction effect can be sufficiently obtained. A stable thermal image can be recorded stably.
[0078]
As described above, the image data from the image data supply source R such as CT or MRI is supplied to the image processing unit 80 of the recording apparatus 10. This image data is sent from the image processing unit 80 to the data storage unit 86, where it is formatted and stored as necessary.
When the image data is stored in the data storage unit 86, first, the image processing unit 80 reads out necessary data from the data storage unit 86, and all image data stored in the data storage unit 86 prior to the start of thermal recording. In addition, sharpness correction is performed, and then gradation correction is performed, or sharpness correction is performed after gradation correction is performed, and subsequently, white outlines generated by sharpness correction processing (emphasis) are greatly reduced. At the same time, the processed image data is again stored in the data storage unit 86 after performing false contour reduction processing for vividly expressing the contour in the recorded image.
When these correction processes are completed, thermal image recording is started. The image processing unit 80 reads out necessary data from the data storage unit 86, and among the image data stored in the data storage unit 86, from the image data of the first line on which image recording is performed first, in the order of image recording. Thermal recording data corresponding to the thermal recording by the thermal head 66, one line at a time, shading correction, resistance correction, black ratio correction, load fluctuation correction, and finally temperature rise correction as necessary. And At this time, the image data representative value calculation process for temperature rise correction may be performed anywhere before and after the start of recording as long as the gradation correction is performed.
[0079]
The recording control unit 84 sequentially reads out the thermal recording image data of the lines for which all corrections have been completed from the data storage unit 86 line by line, and records signals corresponding to the read thermal recording image data (voltage application time corresponding to the image). Width) is output to the thermal head 66.
Each heating element of the thermal head 66 generates heat in response to the recording signal, and as described above, thermal image recording is performed while the thermal material A is conveyed in the direction of arrow b by the platen roller 60 or the like.
[0080]
In the recording apparatus 10 of the present invention, if the predetermined order, the thermal recording image data in which all corrections have been completed for all image data is stored in the data storage unit 86 (that is, image data to be recorded is created). After that, the image storage may be started by reading the data storage unit 86 line by line.
However, the recording time can be greatly shortened by adopting the above-described configuration, that is, the recording is started after sharpness correction and gradation correction are performed in advance, and thereafter the correction calculation is performed while recording. .
[0081]
The thermal material A for which thermal image recording has been completed is transported to the platen roller 60 and the transport roller pair 63 while being guided by the guide 62 and discharged to the tray 72 of the discharge unit 22. The tray 72 protrudes to the outside of the recording apparatus 10 through a discharge port 74 formed in the housing 28, and the heat-sensitive material A on which an image is recorded is discharged to the outside through the discharge port 74 and is taken out.
[0082]
The thermal recording method and thermal recording apparatus of the present invention have been described in detail above. However, the present invention is not limited to the above examples, and various improvements and modifications can be made without departing from the scope of the present invention. Of course it is good.
[0083]
【The invention's effect】
As described above in detail, according to the present invention, the expected correction effect can be sufficiently obtained for all image processing (correction) performed in the thermal recording using the thermal head. High-quality thermal images can be stably recorded with thermal recording image data that has been appropriately image-processed.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of an example of a thermal recording apparatus of the present invention.
2 is a conceptual diagram of a recording unit of the thermal recording apparatus shown in FIG. 1, and a block diagram of a control system of the recording unit.
FIG. 3 is a schematic diagram showing an example of conversion processing by the thermal recording method of the present invention. (A) is an example of recording data in the main scanning direction after gradation correction and before sharpness correction, (b) is an example of recording data immediately after sharpness correction is performed on the recording data of (a), (c) ) Is an example of recording data after the false contour reduction processing of the present invention is applied to the recording data of (b), and (d) is an example of a thermal recording image formed based on the pattern of the recording data of (c). .
FIG. 4 is a schematic diagram showing an example of conversion processing by a conventional thermal recording method. (A) is an example of recording data in the main scanning direction after gradation correction and before sharpness correction, (b) is an example of recording data immediately after sharpness correction is performed on the recording data of (a), (c) ) Is an example of a thermal recording image formed based on the recording data pattern of (b).
[Explanation of symbols]
10 (Thermal image) recording device
14 Loading section
16 Supply / conveyance means
20 Recording section
22 Discharge section
24 Magazine
26 Lid
28 Housing
30 insertion slot
32 Information board
34 Guide roll
36 Stopping member
40 sucker
42 Conveying means
44 Transport guide
48 Endless Belt
50 Nip rollers
52 Regulating Roller Pair
56 Cleaning roller pair
58, 62 guide
60 Platen roller
63 Conveyor roller pair
66 Thermal Head
68 Support member
72 trays
74 Discharge port
76 Cooling fan
80 Image processing section
84 Recording controller
86 Data storage
A Heat-sensitive (recording) material

Claims (12)

This is a thermal recording method in a thermal recording apparatus that performs predetermined image processing on image data supplied from an image data supply source and drives a thermal head to perform thermal recording on a thermal recording material in accordance with the processed image data. And
In the image processing, first, sharpness correction for emphasizing the contour of an image and correction of gradation so that a target gradation is obtained according to output characteristics including characteristics of the thermal recording material and individual differences of thermal recording apparatuses. to perform gradation correction, thereafter, subjected to individual differences shading correction and the resistance value correction for correcting the density unevenness of the printed image caused by among a plurality of heating elements the thermal head is provided, the temperature of the end to the heating element Accordingly, the temperature rise correction is performed to adjust the heat generation energy to correct the density unevenness caused by the difference in the temperature history of each heat generating element , and the image to be recorded is recorded before or after any processing after the gradation correction. performed in a predetermined order to perform a representative value calculation process of the image data for a predetermined number of divided into regions and calculates a representative value of the image data for each the respective areas the temperature increase correction Thermal recording method comprising Rukoto. A black ratio that causes image data corresponding to the same density to be developed at the same density after the shading correction and the resistance value correction and before the temperature rise correction , regardless of a change in the thermal head power supply voltage drop due to a change in recording pattern. 2. The thermal sensitivity according to claim 1, wherein load fluctuation correction is performed to correct streaky density unevenness caused by a change in frictional force at an interface between the thermal recording material and the thermal head in accordance with correction and / or recording density. Recording method.   The thermal recording method according to claim 1, wherein the gradation correction is performed after the sharpness correction.   The thermal recording method according to claim 1, wherein the sharpness correction is performed after the gradation correction.   For shading correction and resistance value correction, correction with higher image density dependency is performed first, and when the image density dependency of both corrections is equivalent, arbitrary order or shading correction and resistance value correction are performed simultaneously. The thermal recording method according to claim 1.   The thermal recording method according to claim 2, wherein the black ratio correction is performed before the load fluctuation correction. A thermal head having a glaze in which heating elements are arranged in one direction;
Means for bringing the glaze and the thermal recording material into contact with each other and moving the thermal head and the thermal recording material relatively in a direction perpendicular to the arrangement direction of the heating elements;
The image data supplied from the image data supply source has the target gradation according to the sharpness correction that emphasizes the outline of the image and the output characteristics including the characteristics of the thermal recording material and individual differences of the thermal recording apparatus. After that , the gradation correction for correcting the gradation is performed, and then the shading correction and the resistance value correction for correcting the density unevenness of the recorded image caused by individual differences between the plurality of heating elements included in the thermal head are performed. Adjusting the heat generation energy according to the temperature of the heat generating element to perform temperature increase correction for correcting density unevenness caused by the difference in temperature history of each heat generating element, and before any processing after gradation correction or representative value calculation processing of the image data for the temperature rise corrected image to be recorded after divided into a predetermined number of areas to calculate a representative value of the image data for each the respective areas Image processing means for performing,
A thermal recording apparatus comprising: a recording control unit that drives the thermal head based on the image data processed by the image processing unit. After the shading correction and resistance value correction, and before the temperature increase correction, the image processing means further stores the same image data corresponding to the same density regardless of the change in the thermal head power supply voltage drop due to the change in the recording pattern. Correction of black ratio for color development and / or load fluctuation correction for correcting streaky density unevenness caused by change in frictional force at the interface between the thermal recording material and the thermal head according to the recording density The thermal recording apparatus according to claim 7.   9. The thermal recording apparatus according to claim 7, wherein the image processing unit performs the gradation correction after the sharpness correction.   The thermal recording apparatus according to claim 7 or 8, wherein the image processing unit performs the sharpness correction after the gradation correction.   The image processing means performs the correction with the higher image density dependency among the shading correction and the resistance value correction first, and when the image density dependency of both corrections is equivalent, any order or shading correction is performed. The thermal recording apparatus according to any one of claims 7 to 10, wherein the correction and the resistance correction are performed simultaneously.   The thermal recording apparatus according to claim 8, wherein the image processing unit performs the black ratio correction before the load fluctuation correction.

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