JP4318136B2 - Driving method of display device - Google Patents

Description

【００２４】
ここで輝度の重みについては（２）式が成り立つ。
【００２５】
【数２】

【００２６】
さらに、消費電力が一定値になるように総表示パルス数を設定する。サブフレームの表示負荷（セル数に対する点灯セルの割合である点灯率）をα_ｉ 、単位パルス数当たりの電力をｐ(α_i )とする。ｐ(α_i )は(３)式のように近似できる。
【００２７】
【数３】

【００２８】
ｐ₀ はパネル容量の充放電に伴う無効電力であり、ｐ₁ α_i はガス放電に伴う電力である。
電力の上限をＰ_maxとすると、（４）式の拘束条件が成り立つ。Ｎはサブフレーム数を表す。
【００２９】
【数４】

【００３０】
１フレームの時間内に出力できる総表示パルス数には上限がある。その上限以下のときに（４）式の等号が成り立つように表示パルス数を決定する。（４）式を等号式として（１）式および（２）式を考慮すれば、Ｌは（５）式で表される。以下、Ｌを“仮の設定輝度”と呼称する
【００３１】
【数５】

【００３２】
（５）式の分母を（３）式を使って書き下すと
【００３３】
【数６】

【００３４】
である。（６）式において、
【００３５】
【数７】

【００３６】
とする。Ｄはフレームの表示負荷、すなわち表示負荷率である。表示負荷率の変化が大きいことと、Ｌの変化が大きいことは等価である。また、（３）式を用いるのであれば、フレームデータから直接に表示負荷率を計算してＬを求めることができる。
【００３７】
なお，１フレームの総表示パルス数には上限Ｆ_max がある。このため、Ｌは次式で定義される上限値Ｌ_maxをもつ。
【００３８】
【数８】

【００３９】
したがって、総表示パルス数の制限を考慮すると、仮の設定輝度Ｌは次式で表される。
【００４０】
【数９】

【００４１】
従来の技術として説明した単純なＡＰＣは、（９）式のＬを（１）式に適用して表示パルス数ｆ_ｉ を決定する。これに対して、本発明のＡＰＣでは（９）式のＬを直接には用いずにＬからＬ’(設定輝度）を導き、Ｌ’を用いて表示パルス数ｆ_ｉ を決定する。
【００４２】
なお，注目するフレームに対する表示パルス数ｆ_ｉの決定は、当該フレームに対応した先頭のサブフレームの表示期間以前に完了すればよい。図４の例では、注目するフレーム(ｋ)のデータ取込みを、１つ前のフレーム(ｋ−１)の表示と並行して行い、フレーム(ｋ−１)に対応した最終のサブフレームＳＦ_N の表示期間ＴＳの途中からフレーム(ｋ)に対応した先頭のサブフレームＳＦ_１ のアドレス期間ＴＡの途中までの期間に、表示パルス数ｆ_ｉの計算を行っている。
【００４３】
〔実施例１〕
実施例１のＡＰＣ動作は図５および図６で示される。ＡＰＣ演算回路７４０は、仮の設定輝度Ｌに対してローパスフィルタリングを行い、その結果および仮の設定輝度Ｌのどちらか選択する。
【００４４】
今、注目する１つのフレームの入力時刻をｔとし、フレーム周期をΔとする。まず、時刻ｔのＬ(t) について、時刻(t-Δ）のＬ(t-Δ）からＬ(t) への変化が予め設定した閾値Ｌ_ｔｈを越える大きな変化であったかどうかを調べ、大きな変化であった場合は（９）式に従って計算した通りのＬ(t) をＬ’(t) とする。変化の大きさが閾値以下であった場合は，ローパスフィルタリングで得られたＬ_ｆをＬ’(t)とする。つまり、Ｌの変化が大きいとき(表示負荷率の変化が大きいとき）には、点灯セルの輝度レベルをその変化に速く追従させ、Ｌの変化が小さいとき（表示負荷率の変化が小さいとき）には、点灯セルの輝度レベルをゆっくりとその変化に追従させる。
【００４５】
ローパスフィルタリングは次のデジタルフィルタで実現される。
【００４６】
【数１０】

【００４７】
例えば、2次のバタワースフィルタを構成する場合には、Ｑ＝Ｒ＝２であり、カットオフ周波数をω₀ ／（２π）とすれば、
【００４８】
【数１１】

【００４９】
である。ここでΩ₀ ＝ω₀ Δである。条件による場合分けをまとめると、
【００５０】
【数１２】

【００５１】
となる。なお、フィルタ動作の初期値、およびＬ(t)の変化量がＬ_ｔｈを越えた場合のフィルタ状態は、次のように更新される。
【００５２】
【数１３】

【００５３】
さらにフィルタのリンギング特性に起因してＬ’(t) がＬ_maxを越える場合もあるので、再びＬをＬ_max に制限するのが望ましい。
【００５４】
【数１４】

【００５５】
このようにして決定されたＬ''(t) を（１５）式に適用して各サブフレームの表示パルス数を設定する。
【００５６】
【数１５】

【００５７】
当然、f_ｉ の計算結果を整数に近似する。そのとき、駆動波形の構成の上で表示パルス数が奇数か偶数に限られる場合はその制約に従う。
図７および図８は実施例１のＡＰＣ動作の説明図である。図７（Ａ）のように表示負荷が変化するとき、図７（Ｂ）のように仮の設定輝度Ｌが変化し、仮の設定輝度Ｌの変化率は図７（Ｃ）のように推移する。仮の設定輝度Ｌの変化率が閾値以下であるときには、設定輝度Ｌ’はローパスフィルタの出力であるので、図７（Ｄ）のように仮の設定輝度Ｌの変化に若干遅れて変化する。表示負荷の変化が急激で大きいとき、仮の設定輝度Ｌの変化率が閾値を越える。このときには、設定輝度Ｌ’として仮の設定輝度Ｌが選択されるので、設定輝度Ｌ’の変化は仮の設定輝度Ｌの変化と一致する。設定輝度Ｌ’は表示負荷の急激で大きな変化に素早く追従するので、図７（Ｅ）が示すとおり消費電力に大きな変動は生じない。一方、図８のとおり、表示負荷の変化が大きくてもそれが緩やかであれば、仮の設定輝度Ｌの変化率は閾値を越えないので、設定輝度Ｌ’としてローパスフィルタの出力が選択される。設定輝度Ｌ’は滑らかに連続的に変化するので、従来の離散的な輝度設定をするＡＰＣとは違って、不自然な表示は生じないし、消費電力に大きな変動が生じない。
【００５８】
〔実施例２〕
実施例１では、Ｌ(t) とＬ(t-Δ）との比較結果に基づいてローパスフィルタ出力を設定輝度Ｌ’ として選択するかどうかが決定されたのに対し、実施例２ではＬ(t) とローパスフィルタの出力Ｌ_f (t)との比較結果に基づいてローパスフィルタ出力を選択するかどうかが決定される。Ｌ(t) とＬ(t-Δ）との差が大きいときは、Ｌ(t)とＬ_f(t)との差も大きい。実施例２におけるＬ(t)とＬ_f (t)との選択条件は実施例１の条件とほぼ等価である。
【００５９】
実施例２の選択条件は次式で表される。
【００６０】
【数１６】

【００６１】
実施例２のＡＰＣ動作は図９および図１０で示される。上述の選択条件を除いて、実施例２のＡＰＣ演算回路７４０ｂの動作は実施例１のＡＰＣ演算回路７４０の動作と同様である。
【００６２】
〔実施例３〕
実施例１および実施例２では、閾値を基準に設定輝度Ｌ’を決めるので、点灯セルの輝度変化に滑らかさを欠く場合を完全に無くすことができない。つまり、仮の設定輝度Ｌの変化率が閾値に近い値であるような表示負荷の変化が生じた場合に、設定輝度Ｌ’の変化が不連続になる。実施例３にはこの問題がない。
【００６３】
実施例３のＡＰＣ動作は図１１および図１２で示される。実施例３におけるＡＰＣ演算回路７４０ｃは、Ｌ(t) とローパスフィルタの出力Ｌ_f (t)とをこれらの差に応じて重み付け加算し、その結果をＬ’(t) とする。具体的には図１３の曲線で示される重み関数ρ(x) を含む次式を適用して設定輝度Ｌ’(t) を求める。
【００６４】
【数１７】

【００６５】
ここで、βはＬの取り得る最小値をＬ_min とする次式で表される。
【００６６】
【数１８】

【００６７】
Ｌ_min はフレームの表示負荷率が最大であるときのＬであり、βは０から１の値をとる。Ｌ_f (t)は（１０）式で与えられる。
ρ(x) は次式を満たす。
【００６８】
【数１９】

【００６９】
ρ(x) については、これを変数ｘの多項式で構成するのが簡便である。例えば次のような関数が考えられる。
【００７０】
【数２０】

【００７１】
ここで，ｎおよびmは１以上の値であり、ρ(x) は次式を満たす。
【００７２】
【数２１】

【００７３】
なお、図１３中に破線で示す階段型の重み関数を適用することは、実施例１および実施例２のように閾値を適用してＬ(t) とＬ_f (t)との選択を行うことに相当する。
【００７４】
表示パルス数の設定には次式が適用される。
【００７５】
【数２２】

【００７６】
図１４は実施例３のＡＰＣ動作の説明図である。図１４（Ａ）のように表示負荷が変化するとき、図１４（Ｂ）のように仮の設定輝度Ｌが変化し、ローパスフィルタの出力と入力との差は図１４（Ｃ）のように推移する。常にローパスフィルタリングによって設定輝度Ｌ’を算出するので、設定輝度Ｌ’ の変化は仮の設定輝度Ｌの変化と比べて図１４（Ｄ）のように滑らかである。しかも、設定輝度Ｌ’は表示負荷の大きな変化に素早く追従している。実施例１および実施例２とは違って、表示負荷の変化がどのような様相であっても設定輝度Ｌ’の変化は不連続にならない。そして、図１４（Ｅ）が示すとおり消費電力に大きな変動は生じない。
【００７７】
〔実施例４〕
実施例４は実施例３の改良である。実施例４では、表示負荷が大きく変化したときにローパスフィルタの出力を、変化後の表示負荷に適した値により速く近づける。具体的には、（１７）式で表される設定輝度Ｌ’を計算した後、ローパスフィルタを次式の状態に更新する。
【００７８】
【数２３】

【００７９】
〔実施例５〕
実施例５も実施例３の改良であり、表示負荷率と電力との関係の経年変化に係る補正を含む。実施例５では電力の測定が行われる。
【００８０】
図１の制御ブロック７１は、（２４）式で表される電力と実際に測定された電力Ｐ_mesとを比較し、その結果に応じて単位パルス数当たりの電力ｐ(α)のパラメータを修正する。
【００８１】
【数２４】

【００８２】
パラメータを修正には、少なくともパラメータと同数の測定値が必要である。例えば、電源が投入されたときに、表示負荷率の異なるサンプル画像を順に表示して電力を測定すれば、必要な測定値を得ることができる。通常の表示動作と並行して一定時間ごとに電力を測定しても、表示負荷率の異なる画像のそれぞれに対応した電力の測定値を得ることができる。
【００８３】
以上の実施例１〜実施例５のＡＰＣ動作は、プラズマ表示装置に限らず、表示負荷の変化する映像を表示する他の表示装置にも応用することができる。以下では、重複説明を最小限とするため、代表として実施例１〜実施例５の中で最も汎用性の高い実施例４を取り上げてその応用を説明する。
〔第２実施形態〕
第２実施形態における駆動対象は有機ＥＬデバイスである。有機ＥＬデバイスと駆動回路とで構成されるＥＬ表示装置は、計器の表示パネルおよび平面光源として用いられている。
【００８４】
図１５はＥＬ表示装置の構成図であり、図１６はＥＬ表示装置におけるＡＰＣ動作のフローチャートである。例示のＥＬ表示装置２００は、ＥＬデバイス２、制御ブロック８１、電源回路８３、行ドライバ８５、および列ドライバ８９を有する。ＥＬデバイス２は縦横に並ぶセルからなる画面をもつ。画面には行電極および列電極が配列されている。これら電極のそれぞれと電源回路８３との導通を制御するための行ドライバ８５および列ドライバ８９は、制御ブロック８１からの信号に従ってスイッチング動作をする。制御ブロック８１は、フレームメモリ８１０、ＡＰＣ演算回路８２０、およびドライバコントローラ８３０を有する。制御ブロック８１には、テレビジョンチューナやコンピュータといった画像信号源からフレームデータが入力される。フレームメモリ８１０はフレームデータを一時的に記憶する。ＡＰＣ演算回路８２０は、フレームごとに表示負荷率を求め、設定輝度Ｌ’を算出する。つまり、表示負荷に応じて表示の輝度レベルを決める。さらに、ＡＰＣ演算回路８２０は、設定輝度Ｌ’に応じた電流値をドライバコントローラ８３０に通知する。これを受けて、ドライバコントローラ８３０は、各フレームの表示において通知された値の電流をセルに供給する。
【００８５】
図１７はＥＬ表示装置における駆動のタイムチャートである。注目するフレームに対する電流値の決定は、当該フレームに係る点灯開始以前に完了すればよい。図１７の例では、注目するフレーム(ｋ)のデータ取込みおよび設定輝度の計算を１つ前のフレーム(ｋ−１)の表示と並行して行っている。
【００８６】
〔実施例６〕
ＥＬデバイス２においては、表示負荷率として全画素の階調の平均を求めればよい。画素の階調をλ_iとすると、表示負荷率αは次式で表される。
【００８７】
【数２５】

【００８８】
式中のＮは画素数であり、λ_maxは最高階調である。
セルの点灯に要する電力は表示負荷率に比例するので、画面全体の電力ｐ(α)は次式で表される。
【００８９】
【数２６】

【００９０】
ｐ₀は黒色表示の場合の電力である。ｐ₁は単位表示率当たりの電力であり、最高階調の輝度に比例する。比例係数を１／ｓとすると、ｐ₁は次式で表される。
【００９１】
【数２７】

【００９２】
電力ｐ(α)には次式の制限がある。
【００９３】
【数２８】

【００９４】
Ｐ_maxは上限値である。仮の設定輝度Ｌはその上限値をＬ_maxとして次式で表される。
【００９５】
【数２９】

【００９６】
表示負荷率αがフレームの入力時刻ｔに決まるので、Ｌを変数ｔの関数と読み替えれば、上述の実施例４と同様に計算をすることができる。
仮の設定輝度Ｌに対するフィルタリングの結果であるＬ_f は次式で表される。
【００９７】
【数３０】

【００９８】
設定輝度Ｌ’の計算には重み関数を適用する。
【００９９】
【数３１】

【０１００】
重みパラメータβの定義も実施例４と同様である。
【０１０１】
【数３２】

【０１０２】
設定輝度Ｌ’を計算した後、ローパスフィルタを次式の状態に更新する。
【０１０３】
【数３３】

【０１０４】
設定輝度Ｌ’の値に従ってセルの点灯を制御する。ＥＬデバイス２は電流駆動デバイスであるので、最高階調に対応する電流値Ｉ₀を次式によって求める。
【０１０５】
【数３４】

【０１０６】
式中のｕは比例係数である。
〔第３実施形態〕
第３実施形態における駆動対象は液晶ディスプレイ（Liquid Crystal Display：ＬＣＤ）である。液晶ディスプレイ、バックライト、および駆動回路で構成される液晶表示装置は、コンピュータ出力およびテレビジョン映像の表示に用いられている。
【０１０７】
液晶表示装置は、バックライトの前側に配置された液晶層の光透過率を変化させることによって階調表示をする。液晶表示装置の消費電力は表示負荷に依存しない。したがって、市販されている液晶表示装置にはＡＰＣ機能が備わっていない。
【０１０８】
しかし、特に、液晶表示装置をテレビジョン受像機として利用する場合には、ＡＰＣが有用である。その理由は次のとおりである。テレビジョン受像機にはコンピュータのモニターと比べて高輝度表示が強く望まれている。セルの最高輝度が高ければ、表示負荷率が比較的に小さい場面の表示において白の輝きを再現することができる。反面、表示負荷率が大きい場面の表示において、画面が過剰に明るくなり、見る人が眩しく感じてしまう。したがって、最高階調の輝度、すなわちバックライトの光量を表示負荷率が大きいほど低くする制御が必要である。このバックライトの光量制御はプラズマディスプレイパネルにおけるＡＰＣに相当する。
【０１０９】
図１８は液晶表示装置の構成図であり、図１９は液晶表示装置におけるＡＰＣ動作のフローチャートである。例示の液晶表示装置３００は、液晶ディスプレイ（ＬＣＤ）３、バックライト４、制御ブロック９１、電源回路９３、行ドライバ９５、および列ドライバ９９を有する。液晶ディスプレイ３は縦横に並ぶセルからなる画面をもつ。画面には行電極および列電極が配列されている。これら電極のそれぞれと電源回路９３との導通を制御するための行ドライバ９５および列ドライバ９９は、制御ブロック９１からの信号に従って動作する。バックライト４は光量可変でなければならない。バックライト４として好適なデバイスは発光ダイオードアレイおよびＥＬデバイスである。制御ブロック９１は、フレームメモリ９１０、ＡＰＣ演算回路９２０、バックライトコントローラ９２５、およびドライバコントローラ９３０を有する。制御ブロック９１には、テレビジョンチューナやコンピュータといった画像信号源からフレームデータが入力される。フレームメモリ９１０はフレームデータを一時的に記憶する。ＡＰＣ演算回路９２０は、フレームごとに表示負荷率を求め、設定輝度Ｌ’を算出する。つまり、表示負荷に応じて表示の輝度レベルを決める。さらに、ＡＰＣ演算回路９２０は、設定輝度Ｌ’に応じた光量値をバックライトコントローラ９２５に通知する。これを受けて、バックライトコントローラ９２５は、各フレームの表示においてバックライト４の光量を制御する。
【０１１０】
図２０は液晶表示装置における駆動のタイムチャートである。注目するフレームに対するバックライト光量の決定は、当該フレームにおけるバックライト４の点灯開始以前に完了すればよい。図２０の例では、注目するフレーム(ｋ)のデータ取込みおよび設定輝度の計算を１つ前のフレーム(ｋ−１)の表示と並行して行っている。
【０１１１】
〔実施例７〕
液晶ディスプレイ３においては、表示負荷率として全画素の階調の平均を求めればよい。画素の階調をλ_iとすると、表示負荷率αは次式で表される。
【０１１２】
【数３５】

【０１１３】
式中のＮは画素数であり、λ_maxは最高階調である。
表示負荷率に対して輝度レベル（最高階調を表示するセルの輝度）をどのように対応づけるかは任意に決めることができる。ただし、プラズマディスプレイと同様に、画面から射出する光の総量が表示負荷に係らず略一定になるように設定するのが自然である。そこで、仮の設定輝度Ｌを（３６）式のように設定する。
【０１１４】
【数３６】

【０１１５】
L_minは装置仕様で決まる最低輝度レベルである。
（３６）式をそのまま採用すると、表示負荷率が小さいときにＬが極端に大きくなるので、Ｌ_maxを上限として組み入れた次式で仮の設定輝度Ｌを定義する。
【０１１６】
【数３７】

【０１１７】
Ｌ_maxもＬ_minよりも大きい値であれば任意に設定してよい。表示負荷率αがフレームの入力時刻ｔに決まるので、Ｌを変数ｔの関数と読み替えれば、上述の実施例４と同様に計算をすることができる。
【０１１８】
仮の設定輝度Ｌに対するフィルタリングの結果であるＬ_fは次式で表される。
【０１１９】
【数３８】

【０１２０】
設定輝度Ｌ’の計算には重み関数を適用する。
【０１２１】
【数３９】

【０１２２】
重みパラメータβの定義も実施例４と同様である。
【０１２３】
【数４０】

【０１２４】
設定輝度Ｌ’を計算した後、ローパスフィルタを次式の状態に更新する。
【０１２５】
【数４１】

【０１２６】
設定輝度Ｌ’(t)の値に従ってバックライトの光量を制御する。バックライトの光量Ｂは次式で表される。
【０１２７】
【数４２】

【０１２８】
式中のｒは比例係数である。
【０１２９】
【発明の効果】
請求項１ないし請求項６の発明によれば、表示負荷の変化に応じて画面の明るさが自然に変化するので、電力制御にともなう表示品質の低下が起こらない。しかも、突発的に消費電力が上昇しない安定した電力制御を実現することができる。
【図面の簡単な説明】
【図１】プラズマ表示装置の構成図である。
【図２】フレーム分割の概念図である。
【図３】駆動電圧波形の概略図である。
【図４】駆動のタイムチャートである。
【図５】実施例１に係るＡＰＣ演算回路の機能を表すブロック線図である。
【図６】実施例１のＡＰＣ動作のフローチャートである。
【図７】実施例１のＡＰＣ動作の説明図である。
【図８】実施例１のＡＰＣ動作の説明図である。
【図９】実施例２に係るＡＰＣ演算回路の機能を表すブロック線図である。
【図１０】実施例２のＡＰＣ動作のフローチャートである。
【図１１】実施例３に係るＡＰＣ演算回路の機能を表すブロック線図である。
【図１２】実施例３のＡＰＣ動作のフローチャートである。
【図１３】重み関数を示す図である。
【図１４】実施例３のＡＰＣ動作の説明図である。
【図１５】ＥＬ表示装置の構成図である。
【図１６】ＥＬ表示装置におけるＡＰＣ動作のフローチャートである。
【図１７】ＥＬ表示装置における駆動のタイムチャートである。
【図１８】液晶表示装置の構成図である。
【図１９】液晶表示装置におけるＡＰＣ動作のフローチャートである。
【図２０】液晶表示装置における駆動のタイムチャートである。
【符号の説明】
１ プラズマディスプレイパネル（表示デバイス）
２ ＥＬデバイス（表示デバイス）
３ 液晶ディスプレイ
４ バックライト（表示デバイス）
７７，８１，９１ 制御ブロック
１００ プラズマ表示装置（画像表示装置）
２００ ＥＬ表示装置（画像表示装置）
３００ 液晶表示装置（画像表示装置）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a display device driving method and an image display apparatus used for image display. The display device means a device having a screen and a device having a light emitting surface of a size corresponding to the screen.
[0002]
A flat display device represented by a plasma display panel (PDP), a liquid crystal display (LCD), and a device that emits light by electroluminescence (EL) (hereinafter referred to as an EL device). Is used as a screen or backlight. In increasing the size and resolution of the screen, it is desirable that the power consumption does not increase even if the number of cells on the screen increases. In order to meet this requirement, it is necessary to perform automatic power control (APC) that automatically adjusts the amount of light according to the display load.
[0003]
[Prior art]
In display using an AC plasma display panel, a number of voltage pulses are applied to each cell of the screen in accordance with the gradation to be displayed (degree of brightness). The voltage pulse causes a display discharge to light the cell. Lighting is to emit light by display discharge. In one-frame display, the amount of light emitted from each cell depends on the number of display discharges that occur in that cell, that is, the number of applied voltage pulses (hereinafter referred to as the number of pulses). It is almost proportional to the total amount of light emission.
[0004]
A plasma display panel driving device performs automatic power control (hereinafter referred to as APC) that prevents a power consumption from becoming excessive while displaying a bright and easy-to-see display. With APC, the number of pulses corresponding to each gradation is changed according to the change in display load factor so that the total light emission amount of all cells does not exceed the set value. The display load factor is an indicator of display load, which is power required for displaying a certain scene, and the ratio between the gradation G (0 ≦ G ≦ Gmax) and the maximum gradation Gmax that each cell should display in one frame. It is defined as the average value over all cells of (G / Gmax). That is, the specific value of the display load, which is the degree of brightness of the entire screen in the display of one frame, is the display load factor. As an outline of APC, the number of pulses corresponding to each gradation is smaller as the displayed image (frame) is brighter as a whole. In the case of a bright display as a whole, even if the light emission amount of each cell is small, it is not noticeable. If the power consumption does not exceed the allowable value, it is desirable to set the number of pulses corresponding to the highest gradation to the maximum number determined by time conditions. Therefore, a general drive device does not substantially perform APC when the display load factor is smaller than the set value, and only displays power consumption when the display load factor is larger than the set value. APC is performed so as to be almost equal to a certain value.
[0005]
If simple APC that adjusts the number of pulses to match the change in the display load factor as it is, the power consumption is kept constant, but if the display load factor fluctuates in a short cycle, the brightness of the display is the same cycle Will fluctuate. That is, there is a problem that flicker occurs in simple APC. One solution to this problem is to apply a low-pass filter. Japanese Patent Laid-Open No. 2001-228824 discloses a power control apparatus configured to input a signal indicating a change in display load factor to a low-pass filter and adjust the number of pulses based on the output signal of the low-pass filter. The low-pass filter slows down the control following the change in display load factor. Therefore, flicker can be prevented by applying a low-pass filter. Another solution is described in Japanese Patent Laid-Open No. 11-282396. It is a technique for setting a threshold for changes in the display load factor. When the amount of change in the display load factor is greater than the threshold, the number of pulses is changed to a value corresponding to the display load factor after the change. When the amount of change in the display load factor is less than the threshold, the number of pulses is displayed before the change. The value corresponding to the load factor is maintained.
[0006]
[Patent Document 1]
JP 2001-228824 A
[0007]
[Patent Document 2]
JP-A-11-282396
[0008]
[Problems to be solved by the invention]
In the conventional APC using a low-pass filter, the tracking of control is slow, and therefore, when the display load factor increases rapidly, a situation occurs in which the power consumption to be greatly reduced is not sufficiently reduced. In this situation, power is wasted. Conversely, when the display load drops drastically, the darkness of the lighted cell is noticeable until the number of pulses increases to a value commensurate with the display load after the drop.
[0009]
On the other hand, in the conventional APC in which the number of pulses is changed only when the change amount of the display load factor is larger than the threshold value, the tracking of the control is discrete. The brightness changes step by step and the display becomes unnatural.
[0010]
A first object of the present invention is to improve display quality by reducing an unnatural brightness change when a display load changes. The second object is to realize stable power control in which power consumption does not suddenly increase.
[0011]
[Means for Solving the Problems]
In the present invention, the light emission amount associated with each gradation for gradation display is changed according to the change in the display load so that the power consumption does not exceed the set value, and the change amount of the light emission amount at that time is changed to the display load. Increase or decrease according to the rate of change. When the change in display load is gradual, the light emission amount is changed slightly. In this case, the follow-up of the power control with respect to the change in the display load is slow. On the other hand, when the change in display load is abrupt, the light emission amount is changed significantly. The follow-up of power control in this case is fast. That is, in the present invention, the followability of the power control is made variable, and the followability is dynamically changed so as to be suitable for the aspect of change in the display load.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
[First embodiment]
The display device to be driven in the first embodiment is a plasma display panel. A plasma display device including a plasma display panel and a drive circuit is used for displaying television images and computer output.
[0013]
FIG. 1 shows the configuration of the plasma display device 100. The illustrated plasma display device 100 includes an AC type plasma display panel 1, a control block 71, a power supply circuit 73, an X driver 75, a Y driver 77, and an A driver 79. The plasma display panel 1 has a screen capable of color display composed of cells of a three-electrode surface discharge structure arranged vertically and horizontally. On the screen, electrodes X and Y are arranged as row electrodes, and electrodes A are arranged as column electrodes. The electrode X and the electrode Y constitute an electrode pair for generating a display discharge for each row of the matrix display, and the electrode Y and the electrode A constitute an electrode matrix for selecting a cell. An X driver 75, a Y driver 77, and an A driver 79 for controlling conduction between the electrode X, the electrode Y, and the electrode A and the power supply circuit 73 perform a switching operation in accordance with a signal from the control block 71.
[0014]
The control block 71 includes a data conversion circuit 710, a frame memory 720, a driver controller 730, an APC arithmetic circuit 740, and a pulse number table 750. The control block 71 receives frame data Df indicating the gradation (R, G, B brightness) of each pixel of the color image from an image signal source such as a television tuner or a computer. The data conversion circuit 710 converts the frame data Df, which is multi-valued image data, into subframe data Dsf for reproducing gradation by combining binary images. The subframe data Dsf is temporarily stored in the frame memory 720 and then transferred to the A driver 79 by the driver controller 730 as the display progresses. The subframe data Dsf is used for addressing in which the charge amount of the cell corresponds to the necessity of light emission. The APC arithmetic circuit 740 and the pulse number table 750 are components for automatic power control (APC). The APC arithmetic circuit 740 obtains the display load from the subframe data Dsf and determines the set luminance L ′ for the highest gradation. The set luminance L ′ is control information for designating the number of display discharges of the cell displaying the highest gradation. The pulse number table 750 stores the distribution of light emission amounts for a plurality of subframes constituting one frame, and notifies the driver controller 730 of the display pulse number f of each subframe corresponding to the set luminance L ′. In response to this, the driver controller 730 generates the same number of display discharges as the number of display pulses corresponding to the subframe in the display of each subframe. When the set luminance L ′ is determined in the APC arithmetic circuit 740, the correspondence between each gradation to be displayed and the luminance of the cell, that is, the display pulse to be applied to the cell in one frame in order to reproduce each gradation. The total number is uniquely determined.
[0015]
The outline of the driving sequence of the plasma display panel 1 in the above display device 100 is as follows. In the display by the plasma display panel 1, in order to perform color display by binary lighting control, as shown in FIG. 2, each of the frames F input at a constant period is divided into a predetermined number N of subframes SF. That is, one frame F is replaced with a set of N subframes SF. In order to these subframes SF, W₁, W₂, W_Three, ... W_N And the number of display discharges in each subframe SF is determined. A frame period Tf, which is a frame transfer period, is divided into N subframe periods Tsf in accordance with such a frame configuration, and one subframe period Tsf is assigned to each subframe SF. Further, the subframe period Tsf is divided into a reset period TR, an address period TA, and a display period TS. The length of the reset period TR and the address period TA is constant regardless of the weight. On the other hand, the length of the display period TS is longer as the weight is larger. Therefore, the length of the subframe period Tsf is longer as the weight of the corresponding subframe SF is larger. The order of the reset period TR, the address period TA, and the display period TS is the same in the N subframes SF. Wall charge initialization, addressing, and lighting maintenance are performed for each subframe.
[0016]
FIG. 3 is a schematic diagram of drive voltage waveforms. In the figure, the suffix (1, v) of the reference sign of the electrode Y indicates the arrangement order. The illustrated waveform is an example, and the amplitude, polarity, and timing can be variously changed.
[0017]
In the reset period TR of each subframe, negative and positive ramp waveform pulses are sequentially applied to all electrodes X, and positive and negative ramp waveform pulses are sequentially applied to all electrodes Y. To do. Applying a pulse to the electrode means temporarily biasing the electrode. A combined voltage obtained by adding the amplitudes of pulses applied to the electrodes X and Y is applied to the cell. The minute discharge generated by the first pulse application generates an appropriate wall voltage having the same polarity in all the cells regardless of lighting / non-lighting in the previous subframe. For the minute discharge that occurs in the second pulse application, the wall voltage is adjusted to a value corresponding to the difference between the discharge start voltage and the amplitude of the applied voltage.
[0018]
In the address period TA, wall charges necessary for maintaining lighting are formed only in the cells to be lit. In a state where all the electrodes X and all the electrodes Y are biased to a predetermined potential, the scan pulse Py is applied to one electrode Y corresponding to the selected row every row selection period (scanning time for one row). Simultaneously with the row selection, the address pulse Pa is applied only to the address electrode A corresponding to the selected cell in which the address discharge is to be generated. That is, the potential of the address electrode A is binary controlled based on the subframe data Dsf of the selected row. In the selected cell, a discharge is generated between the electrode Y and the electrode A, and a discharge is generated between the electrode X and the electrode Y as a trigger. These series of discharges are address discharges.
[0019]
In the display period TS, display pulses (also called sustain pulses) Ps are alternately applied to the electrodes Y and X. As a result, a pulse train whose polarity is alternately switched is added to the cell. By applying the display pulse Ps, a display discharge is generated in a cell in which predetermined wall charges remain. The number of times the display pulse Ps is applied corresponds to the weight of the subframe and is adjusted according to the display load. In order to prevent unnecessary discharge, the address electrode A may be biased to the same polarity as the display pulse Ps over the display period TS.
[0020]
Of the above drive control, the present invention is deeply related to the application of the display pulse Ps in the display period TS, more specifically, the method of setting the number of times of application for limiting power consumption. Hereinafter, this setting method will be specifically described.
[0021]
The luminance of the lighted cell in each subframe is determined by the number of display pulses assigned to the subframe (hereinafter referred to as the number of display pulses). Strictly speaking, since the drop of the power supply voltage affects the luminance, the luminance also depends on the number and arrangement of the lighting cells in the subframe. However, it is not always necessary to consider it. Therefore, in the following embodiments, the correction of the luminance change depending on the number and arrangement of the lighted cells is not performed, and the display pulse number is set on the assumption that the relationship between the display pulse number and the luminance is constant. That is, the luminance determined by setting the number of display pulses is strictly an average luminance obtained by averaging the luminance in various display conditions.
[0022]
The number of display pulses of the i-th subframe that is the i (1 to N) th subframe among the N subframes constituting one frame is represented by f._i , S is the average luminance per unit pulse number, and w is the weight of the set luminance_i And the luminance of the cell displaying the highest gradation is L, and the number of display pulses is distributed to N subframes so as to satisfy the equation (1).
[0023]
[Expression 1]

[0024]
Here, the formula (2) holds for the luminance weight.
[0025]
[Expression 2]

[0026]
Further, the total number of display pulses is set so that the power consumption becomes a constant value. Subframe display load (lighting rate, which is the ratio of lighted cells to the number of cells) α_i , P (α_i). p (α_i) Can be approximated by equation (3).
[0027]
[Equation 3]

[0028]
p₀Is the reactive power associated with charging / discharging of the panel capacity, p₁α_iIs the power accompanying the gas discharge.
Set the upper limit of power to P_maxThen, the constraint condition of the equation (4) is satisfied. N represents the number of subframes.
[0029]
[Expression 4]

[0030]
There is an upper limit to the total number of display pulses that can be output within the time of one frame. The number of display pulses is determined so that the equal sign of equation (4) holds when the upper limit is not reached. Considering equation (1) and equation (2) with equation (4) as an equality equation, L is represented by equation (5). Hereinafter, L is referred to as “provisional set luminance”.
[0031]
[Equation 5]

[0032]
Writing down the denominator of equation (5) using equation (3)
[0033]
[Formula 6]

[0034]
It is. In the formula (6),
[0035]
[Expression 7]

[0036]
And D is the display load of the frame, that is, the display load factor. A large change in the display load factor is equivalent to a large change in L. Further, if Expression (3) is used, L can be obtained by directly calculating the display load factor from the frame data.
[0037]
The total number of display pulses per frame is the upper limit F_maxThere is. For this reason, L is an upper limit value L defined by the following equation:_maxIt has.
[0038]
[Equation 8]

[0039]
Therefore, in consideration of the limitation on the total number of display pulses, the provisional set luminance L is expressed by the following equation.
[0040]
[Equation 9]

[0041]
The simple APC described as the prior art applies the L in the equation (9) to the equation (1) to display the number of display pulses f._i To decide. On the other hand, in the APC of the present invention, L ′ (set luminance) is derived from L without directly using L in the equation (9), and the number of display pulses f is obtained using L ′._i To decide.
[0042]
The number of display pulses f for the frame of interest_iThis determination may be completed before the display period of the first subframe corresponding to the frame. In the example of FIG. 4, data acquisition of the frame of interest (k) is performed in parallel with the display of the previous frame (k−1), and the final subframe SF corresponding to the frame (k−1) is obtained._NFrom the middle of the display period TS of the first subframe SF corresponding to the frame (k)₁ In the period up to the middle of the address period TA, the number of display pulses f_iThe calculation is performed.
[0043]
[Example 1]
The APC operation of the first embodiment is shown in FIGS. The APC arithmetic circuit 740 performs low-pass filtering on the provisional set luminance L, and selects either the result or the provisional set luminance L.
[0044]
Now, let t be the input time of one frame of interest and Δ be the frame period. First, for L (t) at time t, a change from L (t-Δ) to L (t) at time (t−Δ) is a preset threshold L_thIn the case of a large change, L (t) as calculated according to the equation (9) is set as L '(t). If the magnitude of the change is less than or equal to the threshold, L obtained by low-pass filtering_fIs L '(t). That is, when the change in L is large (when the change in display load factor is large), the luminance level of the lighted cell is made to follow the change quickly, and when the change in L is small (when the change in display load factor is small). In this case, the luminance level of the lighted cell is allowed to follow the change slowly.
[0045]
The low-pass filtering is realized by the following digital filter.
[0046]
[Expression 10]

[0047]
For example, when configuring a second-order Butterworth filter, Q = R = 2 and the cutoff frequency is ω₀/ (2π),
[0048]
## EQU11 ##

[0049]
It is. Where Ω₀= Ω₀Δ. To summarize the case classification according to conditions,
[0050]
[Expression 12]

[0051]
It becomes. Note that the initial value of the filter operation and the amount of change in L (t) are L_thIf the value exceeds, the filter state is updated as follows.
[0052]
[Formula 13]

[0053]
Further, L ′ (t) is reduced to L due to the ringing characteristic of the filter._maxMay exceed L, so L again_max It is desirable to limit to
[0054]
[Expression 14]

[0055]
The number of display pulses in each subframe is set by applying L ″ (t) determined in this way to equation (15).
[0056]
[Expression 15]

[0057]
Of course, f_i Approximate the result of the calculation to an integer. At that time, when the number of display pulses is limited to an odd number or an even number on the configuration of the drive waveform, the restriction is obeyed.
7 and 8 are explanatory diagrams of the APC operation of the first embodiment. When the display load changes as shown in FIG. 7A, the temporary set luminance L changes as shown in FIG. 7B, and the change rate of the temporary set luminance L changes as shown in FIG. 7C. To do. When the change rate of the provisional set brightness L is equal to or less than the threshold value, the set brightness L ′ is the output of the low-pass filter, and therefore changes slightly after the change of the provisional set brightness L as shown in FIG. When the change in the display load is abrupt and large, the change rate of the provisional set luminance L exceeds the threshold value. At this time, since the temporary setting luminance L is selected as the setting luminance L ′, the change in the setting luminance L ′ coincides with the change in the temporary setting luminance L. Since the set luminance L ′ quickly follows a sudden and large change in the display load, the power consumption does not vary greatly as shown in FIG. On the other hand, as shown in FIG. 8, if the change in the display load is large but moderate, the change rate of the provisional set luminance L does not exceed the threshold value, so the output of the low-pass filter is selected as the set luminance L ′. . Since the set brightness L ′ changes smoothly and continuously, unlike the conventional APC which performs discrete brightness settings, an unnatural display does not occur and a large fluctuation in power consumption does not occur.
[0058]
[Example 2]
In the first embodiment, whether to select the low-pass filter output as the set luminance L ′ is determined based on the comparison result between L (t) and L (t−Δ), whereas in the second embodiment, L ( t) and the output L of the low-pass filter_f Whether to select the low-pass filter output is determined based on the comparison result with (t). When the difference between L (t) and L (t-Δ) is large, L (t) and L_fThe difference from (t) is also large. L (t) and L in Example 2_f The selection condition with (t) is almost equivalent to the condition of the first embodiment.
[0059]
The selection condition of Example 2 is expressed by the following equation.
[0060]
[Expression 16]

[0061]
The APC operation of the second embodiment is shown in FIGS. Except for the selection conditions described above, the operation of the APC arithmetic circuit 740b of the second embodiment is the same as the operation of the APC arithmetic circuit 740 of the first embodiment.
[0062]
Example 3
In the first and second embodiments, since the set luminance L ′ is determined based on the threshold value, the case where the luminance change of the lighting cell lacks smoothness cannot be completely eliminated. That is, when the display load changes such that the change rate of the provisional set brightness L is a value close to the threshold value, the change of the set brightness L ′ becomes discontinuous. Example 3 does not have this problem.
[0063]
The APC operation of the third embodiment is shown in FIGS. The APC arithmetic circuit 740c in the third embodiment includes L (t) and the output L of the low-pass filter._f (t) is weighted and added according to these differences, and the result is taken as L '(t). Specifically, the set luminance L ′ (t) is obtained by applying the following equation including the weighting function ρ (x) indicated by the curve of FIG.
[0064]
[Expression 17]

[0065]
Here, β is the minimum value L can take._minIt is expressed by the following formula.
[0066]
[Formula 18]

[0067]
L_minIs L when the display load factor of the frame is maximum, and β takes a value from 0 to 1. L_f (t) is given by equation (10).
ρ (x) satisfies the following equation.
[0068]
[Equation 19]

[0069]
For ρ (x), it is convenient to construct it with a polynomial of variable x. For example, the following function can be considered.
[0070]
[Expression 20]

[0071]
Here, n and m are values of 1 or more, and ρ (x) satisfies the following equation.
[0072]
[Expression 21]

[0073]
Note that applying the step-type weight function indicated by the broken line in FIG. 13 applies a threshold value as in the first and second embodiments, and applies L (t) and L_f This corresponds to selecting (t).
[0074]
The following formula is applied to set the number of display pulses.
[0075]
[Expression 22]

[0076]
FIG. 14 is an explanatory diagram of an APC operation according to the third embodiment. When the display load changes as shown in FIG. 14A, the provisional set luminance L changes as shown in FIG. 14B, and the difference between the output and input of the low-pass filter is as shown in FIG. 14C. Transition to. Since the set brightness L ′ is always calculated by low-pass filtering, the change in the set brightness L ′ is smooth as shown in FIG. In addition, the set luminance L ′ quickly follows a large change in display load. Unlike the first and second embodiments, the change in the set luminance L ′ is not discontinuous regardless of the change in the display load. And as FIG.14 (E) shows, a big fluctuation | variation does not arise in power consumption.
[0077]
Example 4
The fourth embodiment is an improvement over the third embodiment. In the fourth embodiment, when the display load changes greatly, the output of the low-pass filter is brought closer to a value suitable for the display load after the change. Specifically, after calculating the set luminance L ′ represented by the equation (17), the low-pass filter is updated to the state of the following equation.
[0078]
[Expression 23]

[0079]
Example 5
The fifth embodiment is also an improvement of the third embodiment, and includes correction related to the secular change of the relationship between the display load factor and the power. In the fifth embodiment, power is measured.
[0080]
The control block 71 in FIG. 1 uses the power represented by the equation (24) and the actually measured power P._mesAnd the parameter of the power p (α) per unit pulse number is corrected according to the result.
[0081]
[Expression 24]

[0082]
Modifying a parameter requires at least as many measurements as the parameter. For example, if power is measured by sequentially displaying sample images with different display load factors when the power is turned on, necessary measurement values can be obtained. Even if the power is measured at regular intervals in parallel with the normal display operation, it is possible to obtain a power measurement value corresponding to each of the images having different display load factors.
[0083]
The APC operations of the first to fifth embodiments described above can be applied not only to the plasma display device but also to other display devices that display an image with a changing display load. In the following, in order to minimize duplicative explanation, the most versatile example 4 among the examples 1 to 5 will be taken as a representative and its application will be described.
[Second Embodiment]
The driving target in the second embodiment is an organic EL device. An EL display device composed of an organic EL device and a drive circuit is used as a display panel of a meter and a flat light source.
[0084]
FIG. 15 is a configuration diagram of an EL display device, and FIG. 16 is a flowchart of an APC operation in the EL display device. The illustrated EL display device 200 includes an EL device 2, a control block 81, a power supply circuit 83, a row driver 85, and a column driver 89. The EL device 2 has a screen composed of cells arranged vertically and horizontally. Row electrodes and column electrodes are arranged on the screen. A row driver 85 and a column driver 89 for controlling the conduction between each of these electrodes and the power supply circuit 83 perform a switching operation in accordance with a signal from the control block 81. The control block 81 includes a frame memory 810, an APC arithmetic circuit 820, and a driver controller 830. Frame data is input to the control block 81 from an image signal source such as a television tuner or a computer. The frame memory 810 temporarily stores frame data. The APC arithmetic circuit 820 calculates a display load factor for each frame and calculates a set luminance L ′. That is, the display luminance level is determined according to the display load. Further, the APC arithmetic circuit 820 notifies the driver controller 830 of a current value corresponding to the set luminance L ′. In response to this, the driver controller 830 supplies the current of the value notified in the display of each frame to the cell.
[0085]
FIG. 17 is a driving time chart in the EL display device. The determination of the current value for the frame of interest may be completed before the lighting of the frame is started. In the example of FIG. 17, the data acquisition of the frame of interest (k) and the calculation of the set luminance are performed in parallel with the display of the previous frame (k−1).
[0086]
Example 6
In the EL device 2, the average of gradations of all pixels may be obtained as the display load factor. Set the pixel gradation to λ_iThen, the display load factor α is expressed by the following equation.
[0087]
[Expression 25]

[0088]
N in the equation is the number of pixels, and λ_maxIs the highest gradation.
Since the power required for lighting the cell is proportional to the display load factor, the power p (α) of the entire screen is expressed by the following equation.
[0089]
[Equation 26]

[0090]
p₀Is the power for black display. p₁Is the power per unit display rate and is proportional to the brightness of the highest gradation. If the proportionality factor is 1 / s, p₁Is expressed by the following equation.
[0091]
[Expression 27]

[0092]
The power p (α) is limited by the following equation.
[0093]
[Expression 28]

[0094]
P_maxIs the upper limit. Temporary set brightness L is the upper limit L_maxIs expressed by the following equation.
[0095]
[Expression 29]

[0096]
Since the display load factor α is determined at the frame input time t, if L is read as a function of the variable t, the calculation can be performed in the same manner as in the fourth embodiment.
L that is the result of filtering for the temporarily set luminance L_fIs expressed by the following equation.
[0097]
[30]

[0098]
A weight function is applied to the calculation of the set luminance L ′.
[0099]
[31]

[0100]
The definition of the weight parameter β is the same as that in the fourth embodiment.
[0101]
[Expression 32]

[0102]
After calculating the set luminance L ′, the low-pass filter is updated to the state of the following equation.
[0103]
[Expression 33]

[0104]
The lighting of the cell is controlled according to the value of the set luminance L ′. Since the EL device 2 is a current driving device, the current value I corresponding to the highest gradation is shown.₀Is obtained by the following equation.
[0105]
[Expression 34]

[0106]
U in a formula is a proportionality coefficient.
[Third Embodiment]
The driving target in the third embodiment is a liquid crystal display (LCD). A liquid crystal display device including a liquid crystal display, a backlight, and a drive circuit is used for computer output and television image display.
[0107]
The liquid crystal display device performs gradation display by changing the light transmittance of the liquid crystal layer disposed on the front side of the backlight. The power consumption of the liquid crystal display device does not depend on the display load. Therefore, a commercially available liquid crystal display device does not have an APC function.
[0108]
However, APC is particularly useful when the liquid crystal display device is used as a television receiver. The reason is as follows. A high-luminance display is strongly desired for a television receiver as compared with a computer monitor. If the maximum luminance of the cell is high, white brightness can be reproduced in the display of a scene with a relatively small display load factor. On the other hand, when displaying a scene with a large display load factor, the screen becomes excessively bright and the viewer feels dazzling. Therefore, it is necessary to control the luminance of the highest gradation, that is, the light amount of the backlight to be lower as the display load factor is larger. This light amount control of the backlight corresponds to APC in the plasma display panel.
[0109]
FIG. 18 is a configuration diagram of the liquid crystal display device, and FIG. 19 is a flowchart of the APC operation in the liquid crystal display device. The exemplary liquid crystal display device 300 includes a liquid crystal display (LCD) 3, a backlight 4, a control block 91, a power supply circuit 93, a row driver 95, and a column driver 99. The liquid crystal display 3 has a screen composed of cells arranged vertically and horizontally. Row electrodes and column electrodes are arranged on the screen. A row driver 95 and a column driver 99 for controlling conduction between each of these electrodes and the power supply circuit 93 operate according to a signal from the control block 91. The backlight 4 must be variable in light quantity. Devices suitable as the backlight 4 are light emitting diode arrays and EL devices. The control block 91 includes a frame memory 910, an APC arithmetic circuit 920, a backlight controller 925, and a driver controller 930. Frame data is input to the control block 91 from an image signal source such as a television tuner or a computer. The frame memory 910 temporarily stores frame data. The APC arithmetic circuit 920 obtains a display load factor for each frame and calculates a set luminance L ′. That is, the display luminance level is determined according to the display load. Further, the APC arithmetic circuit 920 notifies the backlight controller 925 of a light amount value corresponding to the set luminance L ′. In response to this, the backlight controller 925 controls the amount of light of the backlight 4 in displaying each frame.
[0110]
FIG. 20 is a time chart for driving in the liquid crystal display device. The determination of the backlight light amount for the frame of interest may be completed before the backlight 4 is turned on in the frame. In the example of FIG. 20, the data acquisition of the frame of interest (k) and the calculation of the set luminance are performed in parallel with the display of the previous frame (k−1).
[0111]
Example 7
In the liquid crystal display 3, the average of gradations of all pixels may be obtained as the display load factor. Set the pixel gradation to λ_iThen, the display load factor α is expressed by the following equation.
[0112]
[Expression 35]

[0113]
N in the equation is the number of pixels, and λ_maxIs the highest gradation.
How to associate the luminance level (the luminance of the cell displaying the highest gradation) with the display load factor can be arbitrarily determined. However, like the plasma display, it is natural to set the total amount of light emitted from the screen to be substantially constant regardless of the display load. Therefore, the provisional setting luminance L is set as shown in equation (36).
[0114]
[Expression 36]

[0115]
L_minIs the lowest luminance level determined by the device specifications.
If the expression (36) is adopted as it is, L becomes extremely large when the display load factor is small._maxThe provisional set luminance L is defined by the following equation that is incorporated as an upper limit.
[0116]
[Expression 37]

[0117]
L_maxAlso L_minAny value larger than that may be set arbitrarily. Since the display load factor α is determined at the frame input time t, if L is read as a function of the variable t, the calculation can be performed in the same manner as in the fourth embodiment.
[0118]
L that is the result of filtering for the temporarily set luminance L_fIs expressed by the following equation.
[0119]
[Formula 38]

[0120]
A weight function is applied to the calculation of the set luminance L ′.
[0121]
[39]

[0122]
The definition of the weight parameter β is the same as that in the fourth embodiment.
[0123]
[Formula 40]

[0124]
After calculating the set luminance L ′, the low-pass filter is updated to the state of the following equation.
[0125]
[Expression 41]

[0126]
The light amount of the backlight is controlled according to the value of the set luminance L ′ (t). The amount of light B of the backlight is expressed by the following equation.
[0127]
[Expression 42]

[0128]
R in the equation is a proportionality coefficient.
[0129]
【The invention's effect】
  Claims 1 to6According to the invention, since the brightness of the screen naturally changes according to the change of the display load, the display quality is not deteriorated due to the power control. In addition, it is possible to realize stable power control in which power consumption does not suddenly increase.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a plasma display device.
FIG. 2 is a conceptual diagram of frame division.
FIG. 3 is a schematic diagram of drive voltage waveforms.
FIG. 4 is a driving time chart.
FIG. 5 is a block diagram illustrating functions of the APC arithmetic circuit according to the first embodiment.
FIG. 6 is a flowchart of an APC operation according to the first embodiment.
FIG. 7 is an explanatory diagram of an APC operation according to the first embodiment.
FIG. 8 is an explanatory diagram of an APC operation according to the first embodiment.
FIG. 9 is a block diagram illustrating functions of an APC arithmetic circuit according to the second embodiment.
FIG. 10 is a flowchart of an APC operation according to the second embodiment.
FIG. 11 is a block diagram illustrating functions of an APC arithmetic circuit according to the third embodiment.
FIG. 12 is a flowchart of an APC operation according to the third embodiment.
FIG. 13 is a diagram illustrating a weight function.
FIG. 14 is an explanatory diagram of an APC operation according to the third embodiment.
FIG. 15 is a configuration diagram of an EL display device.
FIG. 16 is a flowchart of an APC operation in an EL display device.
FIG. 17 is a time chart of driving in the EL display device.
FIG. 18 is a configuration diagram of a liquid crystal display device.
FIG. 19 is a flowchart of an APC operation in the liquid crystal display device.
FIG. 20 is a time chart of driving in the liquid crystal display device.
[Explanation of symbols]
1 Plasma display panel (display device)
2 EL device (display device)
3 Liquid crystal display
4 Backlight (display device)
77, 81, 91 Control block
100 Plasma display device (image display device)
200 EL display device (image display device)
300 Liquid crystal display device (image display device)

Claims (6)

A display device driving method for changing a correspondence relationship between each gradation to be displayed and the luminance of a cell according to a display load which is a degree of brightness of the entire screen,
Pay attention to the order of display on each frame in the frame row,
Measure the display load of the frame of interest,
For the frame of interest, the measured display load is applied to a predetermined calculation formula to calculate a provisional set luminance corresponding to the highest gradation in the reproducible gradation range;
Comparing the amount of change of the provisional set brightness between the frame of interest and another frame displayed before the display, and a threshold;
When the change amount of the provisional set brightness exceeds the threshold value, the provisional set brightness is adopted as the setup brightness for determining the correspondence relationship with respect to the frame of interest, and the change amount of the provisional set brightness is the threshold value. If it does not exceed, adopt the result of low-pass filtering operation with the provisional set brightness as the input value as the set brightness,
A driving method of a display device, characterized in that the luminance of a cell for each of all displayable gradations is determined based on the set luminance adopted. Even when the change amount of the temporary setting luminance exceeds the threshold value, the driving method of a display device according to claim 1, wherein performing the low pass filtering operation to the input value setting luminance provisional. A display device driving method for changing a correspondence relationship between each gradation to be displayed and the luminance of a cell according to a display load which is a degree of brightness of the entire screen,
Pay attention to the order of display on each frame in the frame row,
Measure the display load of the frame of interest,
For the frame of interest, the measured display load is applied to a predetermined calculation formula to calculate a provisional set luminance corresponding to the highest gradation in the reproducible gradation range;
Perform low-pass filtering operation with the calculated provisional set brightness as input value,
Calculate the difference between the calculated provisional set brightness and the result of the low-pass filtering operation,
When the calculated difference exceeds the threshold, the provisional set luminance is adopted as the set luminance for determining the correspondence relationship with respect to the frame of interest, and when the calculated difference does not exceed the threshold, Adopting the result of the low-pass filtering calculation with the set brightness as an input value as the set brightness,
A driving method of a display device, characterized in that the luminance of a cell for each of all displayable gradations is determined based on the set luminance adopted. The display device driving method according to claim 3 , wherein even when the calculated difference exceeds a threshold value, a low-pass filtering operation using the temporarily set luminance as an input value is performed. A display device driving method for changing a correspondence relationship between each gradation to be displayed and the luminance of a cell according to a display load which is a degree of brightness of the entire screen,
Pay attention to the order of display on each frame in the frame row,
Measure the display load of the frame of interest,
For the frame of interest, the measured display load is applied to a predetermined calculation formula to calculate a provisional set luminance corresponding to the highest gradation in the reproducible gradation range;
Perform low-pass filtering operation with the calculated provisional set brightness as input value,
Calculate the difference between the calculated provisional set brightness and the result of the low-pass filtering operation,
The calculated temporary setting luminance and the result of the low pass filtering operation are weighted and added, and the weight of the temporary setting luminance is increased as the difference calculated at that time is larger.
The result of the addition is set luminance for determining the correspondence relationship for the frame of interest,
A driving method of a display device, wherein the luminance of a cell for each of all gradations that can be displayed is determined based on the set luminance. The display device driving method according to claim 5 , wherein the calculation formula is a formula for deriving a provisional set luminance that keeps the power consumption of the display device constant regardless of the display load.

Images