JP3585047B2 - Decoding device and decoding method - Google Patents

Description

で表される算術平均を取り、その値ｍを上位階層の値とする。この下位階層では、次式
【数２】

で示すように、上位階層との差分値を３画素分だけ用意することで、元々の４画素データと同じ情報量で階層構造を構成する。
【００２０】
一方下位階層の復号に際しては３画素Ｘ１ 〜Ｘ３ は、次式
【数３】

で表すように上位階層の平均値ｍにそれぞれの差分値ΔＸｉ を加えて復号値Ｅ〔Ｘｉ 〕を求め、残つた１画素は、次式
【数４】

で表すように上位階層の平均値ｍから下位階層の３個の復号値を引く事で復号値Ｅ〔Ｘ４ 〕を決定する。ここで、Ｅ〔 〕は復号値を意味する。
【００２１】
ここでこの階層符号化においては、上位階層から下位階層に向かうに従つて１つのブロツクを４つに分割するため、これに伴つてデータ量が階層毎に４倍になるが、平坦部ではこの分割を禁止する事で冗長度を削減している。なおこの分割の有無を指示するためのフラグが１ビツト、ブロツク単位で用意される。下位階層での分割の必要性の判断は局所的なアクテイビテイとして、例えば差分データの最大値で判断する。
【００２２】
ここで階層符号化の例としてＩＴＥのＨＤ標準画像（Ｙ信号）を用い、５階層符号化した場合の適応分割結果を図２に示す。最大差分データに対する閾値を変化させた時の各階層の画素数を本来の画素数に対する割合を示すが、空間相関に基づく冗長度削減のようすが分かる。削減効率は画像によつて変わるが最大差分データに対する閾値を１〜６と変化させると、平均的な削減率は２８〜６９〔％〕になる。
【００２３】
実際上下位階層データの解像度を４分の１にして上位階層データを作り、このとき下位階層では上位階層データからの差分データを符号化することで、信号レベル幅を有効に削減できる。図２について上述した階層符号化による５階層の場合を、図３に示すが、ここでは階層を下位から数えて第１〜第５階層と名付けた。
【００２４】
原画像の８ビツトＰＣＭデータに比べて、信号レベル幅の削減が見られる。特に画素数の多い第１〜４階層は差分信号なので、大幅な削減が達成でき、以降の量子化で効率が向上する。図３の表からわかるように削減効率の絵柄への依存性は少なく、全ての絵に対して有効である。
【００２５】
また下位階層の平均値で上位階層を作る事で、エラー伝播をブロツク内にとめながら、下位階層を上位階層の平均値からの差分に変換する事で、効率の良さも合わせ持つ事ができる。実際上階層符号化では同一空間的位置での階層間のアクテイビテイには相関があり、上位階層の量子化結果から下位階層の量子化特性を決定する事で、付加コードを必要としない適応量子化器を実現できる。
【００２６】
実際上、上述した５段階の階層構造に基づいて画像を階層符号化してマルチ解像度で表現し、階層構造を利用した適応分割及び適応量子化を行う事で、各種ＨＤ標準画像（８ビツトのＹ／ＰＢ ／ＰＲ ）を約１／８に圧縮することができる。また適応分割のために用意されるブロツク毎の付加コードは、圧縮効率の向上のために各階層でランレングス符号化が行われる。このようにして、各階層で充分な画質の画像が得られ、最終的な最下位階層でも視覚的劣化のない良好な画像を得ることができる。
【００２７】
（２）実施例の階層符号化装置
（２−１）構成
図４において、４０は階層符号化装置を示し、入力画像データＤ３１を階層符号化して出力する階層符号化エンコーダ部４０Ａと当該階層符号化エンコーダ部４０Ａにおける発生情報量が目標値となるように制御する発生情報量制御部４０Ｂとにより構成されている。
階層符号化エンコーダ部４０Ａはデータ遅延用のメモリＭ１（図５）とエンコーダによつて構成されている。このうちメモリＭ１は発生情報量制御部４０Ｂにおいて最適制御値が決定されるまでの間、エンコード処理が実行されないようにデータを遅延できるよう入力段に設けられている。
【００２８】
一方、発生情報量制御部４０Ｂは入力画像データＤ３１を入力して処理対象データに適合した最適制御値Ｓ１を設定し、これを階層符号化エンコーダ部４０Ａに送出することにより、当該階層符号化エンコーダ部４０Ａで効率の良い符号化ができるようになされている。所謂フイードフオワード型のバツフアリング構成である。
【００２９】
階層符号化エンコーダ部４０Ａは図５に示す構成でなり、この例の場合、５階層の解像度の異なる圧縮符号化画像データＤ５１〜Ｄ５５を生成するようになされている。
まず入力画像データＤ３１がメモリＭ１を介して第１の差分回路４１及び第１の平均化回路４２に入力される。第１の平均化回路４２は、入力画像データＤ３１（すなわち第１階層データ（最下位階層データ））の４画素平均により第２階層データＤ３２を生成する。この実施例の場合、第１の平均化回路４２は、図６（Ｄ）及び（Ｅ）に示すように、入力画像データＤ３１の４画素Ｘ１（１）〜Ｘ４（１）から第２階層データＤ２の画素Ｘ１（２） を生成する。
【００３０】
また第２階層データＤ３２の画素Ｘ１（２）に隣接する画素Ｘ２（２）〜Ｘ４（２）も同様に第１階層データＤ３１の４画素平均を求めることにより生成される。
第２階層データＤ３２は第２の差分回路４３及び第２の平均化回路４４に入力され、第２の平均化回路４４は、第２階層データＤ３２の４画素平均により第３階層データＤ３３を生成する。例えば、図６（Ｃ）及び（Ｄ）に示す第２階層データＤ３２の画素Ｘ１（２）〜Ｘ４（２）から第３階層データＤ３３の画素Ｘ１（３）が生成されると共に、画素Ｘ１（３）に隣接する画素Ｘ２（３）〜Ｘ４（３）も同様に第２階層データＤ３２の４画素により生成される。
【００３１】
第３階層データＤ３３は第３の差分回路４５及び第３の平均化回路４６に入力され、第３の平均化回路４６は上述の場合と同様に第３階層データＤ３３の４画素平均により図６（Ｂ）及び（Ｃ）に示すように、画素Ｘ１（４）〜Ｘ４（４）でなる第４階層データＤ３４を生成する。
第４階層データＤ４４は第４の差分回路４７及び第４の平均化回路４８に入力され、第４の平均化回路４８は、第４階層データＤ３４の４画素平均により最上位階層となる第５階層データＤ３５を生成する。すなわち図６（Ａ）及び（Ｂ）に示すように、第４階層データＤ３４の４画素Ｘ１（４）〜Ｘ４（４）を平均化することにより第５階層データＤ３５の画素Ｘ１（５）が生成される。
【００３２】
ここで第１〜第５階層データＤ３１〜Ｄ３５のブロツクサイズは、最下位階層である第１階層データＤ３１のブロツクサイズを１ライン×１画素とすると、第２階層データＤ３２は１／２ライン×１／２画素、第３階層データＤ３３は１／４ライン×１／４画素、第４階層データＤ３４は１／８ライン×１／８画素、最上位階層データである第５階層データＤ３５は１／１６ライン×１／１６画素となる。
【００３３】
階層符号化エンコーダ部４０Ａは、これら第１〜第５の階層データＤ３１〜Ｄ３５のうち最上位の階層データ（すなわち第５階層データＤ３５）から順に再帰的処理を繰り返して隣接する２つの階層データ間の差分を差分回路４１、４３、４５、４７において求め、差分データのみを符号器５１〜５５によつて圧縮符号化する。これにより階層符号化エンコーダ部４０Ａは伝送路に伝送される情報量を圧縮するようになされている。
このような圧縮条件を最適に保つため階層符号化エンコーダ部４０Ａは、各階層ごとに得られた圧縮符号化データＤ５１〜Ｄ５５を復号器５６〜５９によつて復号する。
【００３４】
すなわち最上位の階層に対応する復号器５９は符号器５５において圧縮符号化された圧縮符号化データＤ５５を復元して第５階層データＤ３５に対応する復号データＤ４８を得、これを第４の差分回路４７に与える。
【００３５】
これに対して復号器５８は圧縮符号化データＤ５４を復元して第４階層データＤ４４と同様の復元データＤ４７を得、これを第３の差分回路４５に与える。同様にして復号器５７は圧縮符号化データＤ５３を復元して第３階層データＤ４３と同様の復元データＤ４６を得、これを第２の差分回路４３に与える。また復号器５６は圧縮符号化データＤ５２を復元して第２階層データＤ４２と同様の復元データＤ４５を得、これを第１の差分回路４１に与える。
【００３６】
各差分回路４１、４３、４５、４７により得られた階層間差分データＤ４１〜Ｄ４４はそれぞれ符号器５１〜５４によつて圧縮符号化される。このとき各符号器５１〜５４は、各ブロツクのアクテイビテイを所定の閾値と比較する。
ここでアクテイビテイとは、上位階層データに対応する下位階層データ領域を「ブロツク」と定義した場合の、各階層間差分データＤ４１〜Ｄ４４の所定ブロツク内の最大値、平均値、絶対値和、標準偏差又はｎ乗和等を表わす相関値である。すなわちアクテイビテイが低い場合には、このブロツクは平坦なブロツクということができる。
【００３７】
このとき符号器５１〜５４は、ブロツクアクテイビテイが所定の閾値よりも高い場合には、このブロツクを分割ブロツクとし、当該ブロツクと空間的に対応する隣接下位階層ブロツクでの分割処理を選択する。例えば符号器５４において分割処理が選択されたブロツクについては、続く符号器５３でこのブロツクに対応する階層間差分データＤ４３をそのまま圧縮符号化し、同時にこのブロツクが分割ブロツクであることを表わす分割判定フラグをつけて伝送する。
【００３８】
これに対して符号器５１〜５４は、ブロツクアクテイビテイが所定未満の場合には、このブロツクを非分割ブロツクとし、当該ブロツクと空間的に対応する隣接下位階層ブロツクでの分割処理を中止する。例えば符号器５４において分割中止と判定されたブロツクについては、続く符号器５３において、このブロツクに対応する階層間差分データＤ４３に関しては符号化対象から除外し、同時にこのブロツクが非分割ブロツクであるとを表わす非分割判定フラグを付けて伝送する。この非分割ブロツクは復号装置側において上位階層データに置き換えられる。
【００３９】
（２−２）分割処理
次に階層符号化エンコーダ部４０Ａによる具体的な信号処理を説明する。
階層符号化エンコーダ部４０Ａにおいては、上述したように階層間差分データＤ４１〜Ｄ４４の所定ブロツク毎のブロツクアクテイビテイに基づいて分割選択処理を実行する。また実施例の場合、各ブロツクは２ライン×２画素より構成されるものとする。
【００４０】
ここでは各画素のデータ値をＸとし、データ値Ｘの階層をサフイツクスで表す。すなわち上位の階層データをＸｉ＋１（０）とするとき、隣接する下位階層データはＸｉ（ｊ）（ｊ＝０〜３）と表わすことができる。従つて階層間差分データ値ΔＸｉ（ｊ）は、次式、
【数５】

によつて表わすことができる。
【００４１】
符号器５１〜５４は各ブロツクについてブロツクアクテイビテイと閾値とを比較し、当該比較結果に基づいてこのブロツクを下位階層で分割するか、又は分割しないかを選択する。
すなわち符号器５１〜５４においては、ブロツクアクテイビテイが閾値以上の場合には下位階層での分割を実行し、これに対してブロツクアクテイビテイが閾値未満の場合には下位階層での分割を中止する。
【００４２】
これにより階層符号化装置４０においては、ブロツクアクテイビテイが低いブロツクについてはこのブロツクに対応する隣接下位階層のデータを送らずに済み、この分伝送情報量を削減できるようになされている。因に、分割又は非分割の判定結果を示す判定フラグとしては１ビツトの判定フラグが用いらている。
【００４３】
各符号器５１〜５４でブロツクアクテイビテイ判定の際に用いられる閾値は、発生情報量制御部４０Ｂから送出される最適制御値Ｓ１に応じて設定される。すなわち閾値の値が大きくなるに従つて非分割ブロツク（非伝送ブロツク）が増えることにより伝送情報量は少なくなる。
このように階層符号化エンコーダ部４０Ａにおいては、解像度の低い上位階層データから順に圧縮符号化すると共に、このとき各階層データの所定ブロツク毎にアクテイビテイを判定し、当該アクテイビテイの低いブロツクに対しては隣接下位階層でこのブロツクに対応する画像データを送らないようになされている。
【００４４】
また実施例における階層符号化方式では、判定フラグをそれ以降の下位階層での判定には反映させない方式が用いられている（以下これを独立判定法と呼ぶ）。すなわち独立判定法では、各階層独立に、毎回閾値判定に基づく分割選択処理を行う。例えば一旦非分割判定がなされたブロツクにおいても、続く下位階層において再びアクテイビテイの判定を行い、ここで再び分割するか分割しないかを選択する。この結果独立判定法を用いた階層符号化方式においては、上位階層での下位階層の判定フラグの影響を受けないことにより、画質劣化の少ない階層符号化が実現できる。
【００４５】
ここで、図７は階層符号化装置４０による階層符号化処理のフローチヤートを示し、ステツプＳＰ２において階層番号を記憶する階層カウンタＩに「４」が登録され、この階層符号化の枠が決定される。
【００４６】
さらにステツプＳＰ３において発生情報量制御部４０Ｂが発生情報量演算をすることにより階層データが生成され、続くステツプＳＰ４において各ブロツクアクテイビテイが検出される。発生情報量制御部４０Ｂはこのアクテイビテイに基づいてステツプＳＰ５において最適制御値Ｓ１を決定する。
【００４７】
さらにステツプＳＰ６において階層符号化エンコーダ部４０Ａで最適制御値Ｓ１に基づいて階層符号化が実行される。すなわち始めに最上位階層である５階層データに対し、符号化及び復合化が行われる。この結果が下位階層における処理の初期値となり、ステツプＳＰ７において下位階層との階層間差分値が生成される。さらにステツプＳＰ８においてステツプＳＰ５において決定された最適制御値Ｓ１に基づいて下位階層での分割選択及び符号化が実行される。
【００４８】
各階層処理の後、ステツプＳＰ９において階層カウンタＩをデクリメントする。そしてステツプＳＰ１０において階層カウンタＩの内容に対し、終了判定が施される。未終了の場合は、さらに下位階層処理を続行する。全階層の処理を終了した場合、ループを抜けてステツプＳＰ１１において当該階層符号化処理を終了する。
【００４９】
（３）実施例の画像復号装置
（３−１）構成
このように分割判定フラグと共に伝送される第１〜第５階層圧縮符号化データＤ５１〜Ｄ５５は、図８に示すような画像復号装置６０によつて復号される。すなわち第１〜第５階層圧縮符号化データＤ５１〜Ｄ５５は、それぞれ符号器５７、５５、５３、５１及び４９の符号化と逆の復号手法を有する復号器６１、６２、６３、６４及び６５に入力される。この結果復号器６１〜６４でそれぞれ復号された第１〜第４階層の階層間差分データＤ５６〜Ｄ５９が、それぞれ第１〜第４の加算回路６６〜６９に入力される。
【００５０】
また第５階層圧縮符号化データＤ５５は復号器６５で復号され、この結果得られる第５階層データＤ６０が、そのまま出力されると共に第４の平滑化回路７３に送出される。第４の加算回路６９は第４の平滑化回路７３を介して入力された第５階層データＤ６０と、第４階層の階層間差分データＤ５９とを加算して第４階層データＤ６４を復元し、これを出力すると共にこれを第３の平滑化回路７２に送出する。
【００５１】
同様にして第３の加算回路６８は第３の平滑化回路７２を介して入力された第４階層データＤ６４と、第３階層の階層間差分データＤ５８とを加算して第３階層データＤ６３を復元し、これを出力すると共にこれを第２の平滑化回路７１に送出する。以下同様にして第２、第１の加算回路６７、６６によつて、第２階層データＤ６２、第１階層データＤ６１が復元され、このようにして第１〜第４階層データＤ６１〜Ｄ６４及び第５階層データＤ６５が出力される。
【００５２】
（３−２）平滑化処理
実際上画像復号装置６０においては、受信する分割判定フラグに基づいて、非分割ブロツクに対しては、各復号器６１〜６４の出力を０とすると共に上位階層データを加算器６６〜６９の出力とすることで非分割ブロツクデータを上位階層データで置き換えるようになされている。
【００５３】
ところが、この非分割ブロツクデータの復号画像において、図６に示した階層データ生成法に起因する疑似輪郭が発生することがある。
例えば、空などのレベル変化が小さい画像においては、各ブロツクが非分割判定を受けることが多い。すなわち上位階層データで置き換えられる場合が多い。このとき復元画像においては、隣接ブロツク間のレベル差が僅かであつても、ブロツク境界位置には疑似輪郭がしばしば認められ、これが大きな画質劣化となる。
【００５４】
実施例の階層符号化においては、階層符号化装置４０側では大きな分割閾値を設定するほど圧縮率を向上させることができる。しかしながら、画像復号装置６０側では、階層符号化装置４０側の分割閾値が大きい程隣接ブロツク間（すなわち分割ブロツクと非分割ブロツク間）のレベル差が拡大し、画質劣化が顕著となる。
【００５５】
その具体例を図９に示す。この例においては、中央のブロツクＭが非分割判定を受けたブロツクとする。このときブロツクＭに対応する下位階層復号データＸ０、Ｘ１、Ｘ２、Ｘ３としてすべて上位階層データＭを用いることになる。すなわち、Ｘ０＝Ｘ１＝Ｘ２＝Ｘ３＝Ｍとなる。
このようにした場合に、上述したようにＸ０〜Ｘ３とその周辺のブロツクとの間で疑似輪郭が発生し、画質が劣化するおそれがある。
【００５６】
これを回避するため、画像復号装置６０においては、非分割ブロツクの復号法として、単純に上位階層データを使用するのではなく、平滑化回路７０〜７３を介して上位階層データを平滑化処理し、これにより得られる平滑化データを用いて非分割ブロツクの復号値を求め、ブロツク境界の擬似輪郭を抑制するようになされている。
【００５７】
各平滑化回路７０〜７３は、非分割ブロツクＭ及び当該非分割ブロツクＭの空間内周辺データｍ０〜ｍ７を用いて、非分割ブロツクＭの下位階層データＸ０〜Ｘ３を、それぞれ次式、
【数６】

【数７】

【数８】

【数９】

に基づいて生成するようになされている。
【００５８】
ここでＡＶＥ（・）は閾値判定付き平均化処理関数を表す。この平均化処理関数ＡＶＥ（・）の例としては、例えば下位階層データＸ０を求める際、上位階層データＭ、ｍ０、ｍ１、ｍ７が所定の閾値Ｌに対して、次式、
【数１０】

かつ
【数１１】

かつ
【数１２】

の関係にあるとき、下位階層データＸ０を、次式
【数１３】

に基づいて算出するものが用いられている。
【００５９】
このように平滑化回路７０〜７３においては、非分割ブロツクＭ及び空間内周辺データｍ０〜ｍ６又はｍ７を用いて非分割ブロツクＭに対応する下位階層データＸ１〜Ｘ３を求める際に、単純に平均値演算を行うのではなく、空間内周辺データｍ０〜ｍ７に対して閾値判定による画素選択を行い、このとき上位階層の空間内周辺データにデータ値の大きな画素があつた場合には、この画素を平均値演算から除外するようになされている。
これにより画像復号装置６０においては、非分割ブロツクＭの近傍にエツジなどが存在する場合でも、平均値演算による画質劣化を未然に回避することができる。
【００６０】
かくして画像復号装置６０においては、分割ブロツクと非分割ブロツク間で生じる擬似輪郭を有効に回避し得、これにより画質劣化を低減することができる。
また画像復号装置６０においては、階層符号化装置４０側で大きな分割閾値を設定した場合でも、平滑化処理をすることより画質劣化を低減することができる。従つて階層符号化装置４０において分割閾値として大きな値を用いることができ、この分一段と圧縮効率を向上させることができる。
【００６１】
かくして、画像復号装置６０を用いれば、階層符号化装置４０によりブロツクアクテイビテイに基づいてブロツク分割した圧縮効率の良い画像データを、画質劣化を抑制した状態で復元することができる。
【００６２】
（４）実施例の効果
以上の構成によれば、非分割ブロツクＭを、当該非分割ブロツクＭの空間内周辺データｍ０〜ｍ７を用いて平滑化処理し、これにより得られる平滑化データＸ１〜Ｘ４を用いて非分割ブロツクＭに対応する下位階層ブロツクの復号値を求めるようにしたことにより、適応分割された圧縮効率の良い圧縮符号化データＤ５１〜Ｄ５５を、画質劣化を低減して復元することができる。
【００６３】
（５）他の実施例
なお上述の実施例においては、本発明による復号方法を、各階層独立に毎回閾値判定して分割処理を行う独立判定法によつて分割処理された圧縮符号化データＤ５１〜Ｄ５５を復号する際に適用した場合について述べたが、本発明はこれに限らず、上位階層での分割判定により一旦下位階層の分割を中止したとき、これ以降の下位階層の分割を中止する階層符号化方法により得られた複数階層分の圧縮符号化データを復号する際に適用した場合にも、上述の実施例と同様の効果を得ることができる。
また本発明はこれに限らず、階層符号化方法において、階層データ内に解像度の異なる複数のブロツクが存在するような場合に広く適用することができる。
【００６４】
【発明の効果】
上述のように本発明によれば、解像度の最も低い最上位階層情報から解像度の最も高い最下位階層情報までの複数の階層情報からなる画像データに関し、所定の階層の階層情報に対する複数の画素からなる各ブロツクのブロツクアクテイビテイを判定した判定結果に基づいて、各階層の階層情報の各ブロツクの伝送又は非伝送が制御されることで得た符号化データを復号する際に、伝送がされなかつたブロツクである非伝送ブロツクの階層よりも上位側の階層の階層情報の各画素のうち、非伝送ブロツクの画素と対応する位置の画素の値及びその近傍の画素の値を用いて平均化処理を行つて平滑化データを生成し、当該生成した平滑化データを非伝送ブロツクの画素に対する復号値として出力するようにしたことにより、非伝送ブロツクの階層よりも上位側の階層情報によつて当該非伝送ブロツクの画素に対する復号値を生成する際にその非伝送ブロツクの階層で生じる擬似輪郭を有効に回避し得、画質劣化を低減することができる。
【図面の簡単な説明】
【図１】階層符号化装置によつて生成される階層データの説明に供する略線図である。
【図２】ＨＤ標準画像における適応分割結果を示す図表である。
【図３】ＨＤ標準画像における各階層の信号レベルの標準偏差を示す図表である。
【図４】実施例による階層符号化装置を示すブロツク図である。
【図５】階層符号化エンコーダ部を示すブロツク図である。
【図６】階層構造の説明に供する略線図である。
【図７】階層符号化処理を示すフローチヤートである。
【図８】本発明による画像復号装置の一実施例を示すブロツク図である。
【図９】平滑化回路の動作の説明に供する略線図である。
【図１０】従来のピラミツド符号化方法を用いた画像符号化装置を示すブロツク図である。
【図１１】図１０の画像符号化装置により生成された圧縮符号化データを復号する従来の画像復号装置を示すブロツク図である。
【符号の説明】
４０……階層符号化装置、６０……画像復号装置、７０〜７３……平滑化回路、Ｄ５１〜Ｄ５５……圧縮符号化データ、Ｍ……非分割ブロツク、ｍ０〜ｍ７……空間内周辺データ。[0001]
【table of contents】
The present invention will be described in the following order.
Industrial applications
Conventional technology (FIGS. 10 and 11)
Problems to be solved by the invention (FIGS. 10 and 11)
Means for solving the problem (FIGS. 8 and 9)
Action (FIGS. 8 and 9)
Example
(1) Principle of hierarchical coding (FIGS. 1 to 3)
(2) Hierarchical encoding device of embodiment (FIGS. 4 to 7)
(2-1) Configuration
(2-2) Division processing
(3) Image Decoding Device of Embodiment (FIGS. 8 and 9)
(3-1) Configuration
(3-2) Smoothing processing
(4) Effect of Embodiment (FIGS. 8 and 9)
(5) Another embodiment
The invention's effect
[0002]
[Industrial applications]
The present invention relates to a decoding device and a decoding method, and more particularly, to a decoding device and a decoding method that divide predetermined image data into a plurality of hierarchical data having different resolutions and decode coded image data of a plurality of layers. It is suitable.
[0003]
[Prior art]
2. Description of the Related Art Conventionally, there is an image encoding apparatus that divides predetermined image data into a plurality of image data having different resolutions and encodes the divided image data. This type of image encoding apparatus is configured to hierarchically encode input image data using a hierarchical encoding technique such as pyramid encoding. That is, in this image coding apparatus, high-resolution input image data is used as first hierarchical data, second hierarchical data having a lower resolution than the first hierarchical data, and further higher in resolution than the second hierarchical data. .. Are sequentially and recursively formed, and the plurality of hierarchical data are transmitted through a single communication path or a transmission path including a recording / reproducing path.
[0004]
In addition, in the image decoding device that decodes the plurality of hierarchical data, in addition to decoding all of the plurality of image data, a desired one of the hierarchical data is determined based on the resolution of the corresponding television monitor. Can be selected for decoding. Thus, by decoding only the desired hierarchical data from the hierarchical data of a plurality of layers, desired image data can be obtained with a minimum necessary transmission data amount.
[0005]
As shown in FIG. 10, in the image coding apparatus 1 which realizes, for example, four-layer coding as the layer coding, three layers of thinning-out filters 2, 3, 4 and interpolation filters 5, 6, 7 are provided. For each of the input image data D1, reduced image data D2, D3, and D4 having a lower resolution are sequentially formed by thinning filters 2, 3, and 4 at each stage, and reduced image data D2, D2, and D4 are formed by interpolation filters 5, 6, and 7. D3 and D4 are returned to the resolution before reduction.
[0006]
The outputs D2 to D4 of the thinning filters 2 to 4 and the outputs D5 to D7 of the interpolation filters 5 to 7 are input to difference circuits 8, 9, and 10, respectively, thereby generating difference data D8, D9 and D10. As a result, in the image encoding device 1, the amount of hierarchical data is reduced and the signal power is reduced. Here, the difference data D8 to D10 and the reduced image data D4 have sizes of 1, 1/4, 1/16, and 1/64, respectively.
[0007]
The difference data D8 to D10 obtained from the difference circuits 8 to 10 and the reduced image data D4 obtained from the thinning filter 4 are encoded by the encoders 11, 12, 13, and 14 and subjected to a compression process. As a result, the first, second, third, and fourth hierarchical data D11, D12, D13, and D14 having different resolutions are transmitted from the encoders 11, 12, 13, and 14 to the transmission path in a predetermined order.
[0008]
The first to fourth hierarchical data D11 to D14 transmitted in this manner are decoded by the image decoding device 20 shown in FIG. That is, the first to fourth hierarchical data D11 to D14 are decoded by the decoders 21, 22, 23 and 24, respectively. As a result, the fourth hierarchical data D24 is output from the decoder 24.
[0009]
Further, the output of the decoder 23 is added to the interpolation data of the fourth hierarchical data D24 obtained from the interpolation filter 26 in the adding circuit 29, whereby the third hierarchical data D23 is restored. Similarly, the output of the decoder 22 is added to the interpolation data of the third hierarchical data D23 obtained from the interpolation filter 27 in the adding circuit 30, whereby the second hierarchical data D22 is restored. Further, the output of the decoder 21 is added to the interpolation data of the second hierarchical data D22 obtained from the interpolation filter 28 in the adding circuit 31, whereby the first hierarchical data D21 is restored.
[0010]
[Problems to be solved by the invention]
However, in an image encoding apparatus that realizes such a hierarchical encoding method, since input image data is divided into a plurality of hierarchical data and encoded, the data amount inevitably increases only by the hierarchical component, and the hierarchical encoding However, there is a problem that the compression efficiency is reduced as compared with a high-efficiency coding method that does not use the compression. Further, when trying to improve the compression efficiency, there is a problem that image quality is deteriorated on the decoding side.
[0011]
The present invention has been made in view of the above points, and it is an object of the present invention to propose a decoding device and a decoding method capable of reducing image quality deterioration when image data is hierarchically encoded and transmitted.
[0012]
[Means for Solving the Problems]
In order to solve such a problem, in the present invention, predetermined image data D31 including a plurality of pieces of hierarchical information D41 to D44 and D35 from the highest hierarchical information D35 having the lowest resolution to the lowest hierarchical information D41 having the highest resolution is provided. The transmission or non-transmission of each block of the hierarchy information D41 to D44 is controlled based on the determination result of the block activity of each block including a plurality of pixels with respect to the hierarchy information D41 to D44 of the hierarchy. In the decoding device 60 that decodes the encoded data D51 to D55, among the pixels of the layer information D57 to D60 of the layer higher than the layer of the non-transmission block that has not been transmitted, the pixel of the non-transmission block is used. The averaging process is performed using the value M of the pixel at the position corresponding to the pixel and the values m0 to m7 of the pixels in the vicinity thereof. Data generating means 70-73 for generating the smoothed data X0-X3 by means of an output means 66-69 for outputting the smoothed data X0-X3 as decoded values D61-D64 for non-transmission block pixels. I did it.
[0013]
Further, in the present invention, the smoothed data generating means 70 to 73 outputs the pixel at the position corresponding to the pixel of the non-transmission block among the pixels of the layer information D57 to D60 of the layer higher than the layer of the non-transmission block. , And the difference between the value m0 to m7 of each neighboring pixel is detected, and the averaging process is performed using only the value m0 to m7 of the neighboring pixel whose detected difference is equal to or smaller than a predetermined value. Then, smoothed data X0 to X3 are generated.
[0014]
Further, in the present invention, regarding the image data D31 including a plurality of pieces of hierarchical information D41 to D44 and D35 from the highest hierarchical information D35 having the lowest resolution to the lowest hierarchical information D41 having the highest resolution, the hierarchical information D41 of a predetermined hierarchy is provided. The encoded data D51 to D55 obtained by controlling the transmission or non-transmission of each block of the layer information of each layer based on the determination result of the block activity of each block composed of a plurality of pixels for D44 to D44. In the decoding method for decoding, the value of the pixel at the position corresponding to the pixel of the non-transmission block among the pixels of the layer information D57 to D60 of the layer higher than the layer of the non-transmission block that has not been transmitted. An averaging process is performed using the values m0 to m7 of M and neighboring pixels to generate smoothed data X0 to X3. And one of the step, was provided and a second step of outputting the smoothed data X0~X3 as a decoded value D61~D64 for pixels of the non-transmission block.
[0015]
[Action]
When there is a non-transmission block, the value M of the pixel at the position corresponding to the pixel of the non-transmission block and the pixels in the vicinity thereof among the pixels of the hierarchy information D57 to D60 higher than the layer of the non-transmission block. By performing an averaging process using the values m0 to m7 to generate smoothed data X0 to X3, and outputting the smoothed data X0 to X3 as decoded values D61 to D64 for the pixels of the non-transmission block, When the decoded values X0 to X3 for the pixels of the non-transmission block are generated by the layer information D57 to D60 higher than the transmission block layer, pseudo contours generated in the non-transmission block layer can be effectively avoided. , Image quality degradation can be reduced.
[0016]
When there is a non-transmission block, the value M of a pixel at a position corresponding to the pixel of the non-transmission block, among the pixels of the hierarchy information D57 to D60 higher than the layer of the non-transmission block, and the neighborhood of the pixel M Of the respective pixels m0 to m7, and performs an averaging process using only the values m0 to m7 of the neighboring pixels whose detected differences are equal to or smaller than a predetermined value to perform smoothing data X0 to X7. By generating X3, even when an edge or the like exists near a pixel corresponding to a pixel of the non-transmission block, image quality degradation can be effectively reduced.
[0017]
【Example】
An embodiment of the present invention will be described below in detail with reference to the drawings.
[0018]
(1) Principle of hierarchical coding
FIG. 1 shows, as a whole, the principle of hierarchical encoding according to the present invention, in which, for example, a still image such as a high-definition television signal is hierarchically encoded and compressed. In this hierarchical coding, the upper hierarchical data is created by a simple arithmetic average of the lower hierarchical data, thereby realizing a hierarchical structure without increasing the information amount. In addition, for decoding from the upper layer to the lower layer, the division is adaptively controlled based on the activity for each block, thereby reducing the information amount of the flat portion. Further, in the encoding of the difference signal performed for the lower layer, high efficiency is realized by switching the quantization characteristic for each block without additional code based on the activity of the upper layer.
[0019]
That is, in the hierarchical structure of the hierarchical coding, the input high-definition television signal is set as a lower layer, and four pixels X1 to X4 in a small block of 2 lines × 2 pixels of the lower layer are expressed by the following equation.
(Equation 1)

The arithmetic average represented by is calculated, and the value m is set as the value of the upper hierarchy. In this lower hierarchy,
(Equation 2)

As shown by, by preparing the difference value from the upper layer for three pixels, the layer structure is configured with the same information amount as the original four pixel data.
[0020]
On the other hand, when decoding the lower layer, the three pixels X1 to X3 are represented by the following equations.
(Equation 3)

The decoded value E [Xi] is obtained by adding the respective difference values ΔXi to the average value m of the upper layer as represented by the following expression.
(Equation 4)

As shown by, the decoded value E [X4] is determined by subtracting the three decoded values of the lower layer from the average value m of the upper layer. Here, E [] means a decoded value.
[0021]
Here, in this hierarchical coding, one block is divided into four in accordance with going from an upper layer to a lower layer. Accordingly, the data amount is quadrupled for each layer. Redundancy is reduced by prohibiting division. A flag for instructing the presence or absence of the division is prepared in units of 1 bit and block. The necessity of the division in the lower hierarchy is determined as a local activity, for example, by the maximum value of the difference data.
[0022]
Here, as an example of hierarchical coding, FIG. 2 shows an adaptive division result in the case of using ITE HD standard image (Y signal) and performing five-layer encoding. The ratio of the number of pixels in each layer to the original number of pixels when the threshold value for the maximum difference data is changed is shown. It can be seen that the redundancy is reduced based on the spatial correlation. Although the reduction efficiency changes depending on the image, if the threshold value for the maximum difference data is changed from 1 to 6, the average reduction rate becomes 28 to 69 [%].
[0023]
Actually, the resolution of the lower layer data is reduced to 1/4 to create the upper layer data, and at this time, in the lower layer, the difference data from the upper layer data is encoded, so that the signal level width can be effectively reduced. FIG. 3 shows a case of five layers by the above-described layer coding with reference to FIG. 2. Here, the layers are named as first to fifth layers, counting from the lowest.
[0024]
The signal level width is reduced compared to the 8-bit PCM data of the original image. In particular, since the first to fourth layers having a large number of pixels are difference signals, a significant reduction can be achieved, and the subsequent quantization improves the efficiency. As can be seen from the table of FIG. 3, the dependence of the reduction efficiency on the pattern is small and is effective for all pictures.
[0025]
In addition, by forming the upper layer with the average value of the lower layer, by converting the lower layer into a difference from the average value of the upper layer while keeping the error propagation in the block, it is possible to have high efficiency. In practice, in hierarchical coding, there is a correlation between the activities between layers at the same spatial position, and adaptive quantization that does not require additional codes is determined by determining the quantization characteristics of the lower layer from the quantization results of the upper layer. Can be realized.
[0026]
In practice, images are hierarchically coded based on the five-stage hierarchical structure described above, are represented in multi-resolution, and are adaptively divided and adaptively quantized using the hierarchical structure, so that various HD standard images (Y of 8 bits) can be obtained. / PB / PR) can be compressed to about 1/8. The additional code for each block prepared for adaptive division is subjected to run-length encoding in each layer in order to improve compression efficiency. In this way, an image with sufficient image quality can be obtained at each hierarchical level, and a good image with no visual deterioration can be obtained even at the final lowest hierarchical level.
[0027]
(2) Hierarchical encoding device of embodiment
(2-1) Configuration
In FIG. 4, reference numeral 40 denotes a hierarchical encoding device, which hierarchically encodes the input image data D31 and outputs the encoded image data D31, and controls the amount of information generated in the hierarchically encoded encoder 40A to a target value. And a generated information amount control unit 40B.
The hierarchical coding encoder unit 40A includes a data delay memory M1 (FIG. 5) and an encoder. The memory M1 is provided in the input stage so that the data can be delayed so that the encoding process is not executed until the generated information amount control unit 40B determines the optimum control value.
[0028]
On the other hand, the generated information amount control unit 40B inputs the input image data D31, sets the optimal control value S1 suitable for the processing target data, and sends it to the hierarchical encoding encoder unit 40A, thereby making the hierarchical encoding encoder 40A The unit 40A enables efficient coding. This is a so-called feedforward type buffering configuration.
[0029]
The hierarchical coding encoder unit 40A has the configuration shown in FIG. 5, and in this example, generates the compressed coded image data D51 to D55 having different resolutions of five layers.
First, the input image data D31 is input to the first difference circuit 41 and the first averaging circuit 42 via the memory M1. The first averaging circuit 42 generates second hierarchical data D32 by averaging four pixels of the input image data D31 (that is, first hierarchical data (lowest hierarchical data)). In the case of this embodiment, as shown in FIGS. 6D and 6E, the first averaging circuit 42 converts the four pixels X1 (1) to X4 (1) of the input image data D31 into the second hierarchical data. A pixel X1 (2) of D2 is generated.
[0030]
Similarly, the pixels X2 (2) to X4 (2) adjacent to the pixel X1 (2) of the second hierarchy data D32 are generated by calculating the average of the four pixels of the first hierarchy data D31.
The second hierarchical data D32 is input to a second difference circuit 43 and a second averaging circuit 44, and the second averaging circuit 44 generates third hierarchical data D33 by averaging four pixels of the second hierarchical data D32. I do. For example, the pixel X1 (3) of the third hierarchical data D33 is generated from the pixels X1 (2) to X4 (2) of the second hierarchical data D32 shown in FIGS. 6C and 6D, and the pixel X1 ( Similarly, pixels X2 (3) to X4 (3) adjacent to 3) are generated by four pixels of the second hierarchy data D32.
[0031]
The third hierarchical data D33 is input to a third difference circuit 45 and a third averaging circuit 46, and the third averaging circuit 46 performs the averaging of four pixels of the third hierarchical data D33 in FIG. As shown in (B) and (C), the fourth hierarchical data D34 including the pixels X1 (4) to X4 (4) is generated.
The fourth hierarchy data D44 is input to the fourth difference circuit 47 and the fourth averaging circuit 48, and the fourth averaging circuit 48 becomes the fifth highest hierarchy by averaging four pixels of the fourth hierarchy data D34. The hierarchical data D35 is generated. That is, as shown in FIGS. 6A and 6B, by averaging the four pixels X1 (4) to X4 (4) of the fourth hierarchical data D34, the pixel X1 (5) of the fifth hierarchical data D35 becomes Generated.
[0032]
Here, assuming that the block size of the first hierarchical data D31, which is the lowest hierarchy, is 1 line × 1 pixel, the second hierarchical data D32 is １ ／ line × 1 pixel. 1/2 pixel, third layer data D33 is 1/4 line x 1/4 pixel, fourth layer data D34 is 1/8 line x 1/8 pixel, and fifth layer data D35 which is the highest layer data is 1 / 16 line × 1/16 pixel.
[0033]
The hierarchical encoding encoder 40A repeats the recursive processing in order from the highest hierarchical data (that is, the fifth hierarchical data D35) among the first to fifth hierarchical data D31 to D35, and repeats the recursive processing between two adjacent hierarchical data. Are obtained in the difference circuits 41, 43, 45, and 47, and only the difference data is compression-encoded by the encoders 51 to 55. Thereby, the hierarchical coding encoder unit 40A compresses the amount of information transmitted to the transmission path.
In order to keep such compression conditions optimal, the hierarchical encoding encoder 40A decodes the compressed encoded data D51 to D55 obtained for each layer by the decoders 56 to 59.
[0034]
That is, the decoder 59 corresponding to the highest layer restores the compressed coded data D55 compressed and coded by the encoder 55 to obtain decoded data D48 corresponding to the fifth layer data D35, and outputs the decoded data D48 corresponding to the fourth difference. It is given to the circuit 47.
[0035]
On the other hand, the decoder 58 restores the compressed encoded data D54 to obtain restored data D47 similar to the fourth hierarchical data D44, and supplies the restored data D47 to the third difference circuit 45. Similarly, the decoder 57 restores the compressed encoded data D53 to obtain restored data D46 similar to the third hierarchical data D43, and supplies the restored data D46 to the second difference circuit 43. The decoder 56 restores the compressed and encoded data D52 to obtain restored data D45 similar to the second hierarchical data D42, and supplies the restored data D45 to the first difference circuit 41.
[0036]
Inter-layer difference data D41 to D44 obtained by the difference circuits 41, 43, 45, and 47 are compression-encoded by encoders 51 to 54, respectively. At this time, each of the encoders 51 to 54 compares the activity of each block with a predetermined threshold.
Here, the activity means a maximum value, an average value, a sum of absolute values, a standard value, and a maximum value within a predetermined block of the difference data D41 to D44 between layers when the lower layer data area corresponding to the upper layer data is defined as “block”. It is a correlation value representing a deviation or a sum of n-th power. In other words, when the activity is low, this block can be called a flat block.
[0037]
At this time, when the block activity is higher than a predetermined threshold value, the encoders 51 to 54 regard the block as a division block and select a division process in an adjacent lower hierarchical block spatially corresponding to the block. For example, for a block for which division processing has been selected in the encoder 54, the inter-layer difference data D43 corresponding to this block is directly compression-encoded by the subsequent encoder 53, and at the same time, a division determination flag indicating that this block is a division block. And transmit it.
[0038]
On the other hand, when the block activity is less than the predetermined value, the encoders 51 to 54 make this block a non-divided block and stop the dividing process in the adjacent lower hierarchical block spatially corresponding to the block. For example, with respect to a block determined to be stopped in the encoder 54, the subsequent encoder 53 excludes the inter-layer difference data D43 corresponding to this block from the encoding target, and at the same time determines that this block is a non-divided block. Is transmitted with a non-division determination flag indicating. This non-divided block is replaced by upper layer data on the decoding device side.
[0039]
(2-2) Division processing
Next, specific signal processing by the hierarchical coding encoder unit 40A will be described.
As described above, the hierarchical encoding encoder unit 40A executes the division selection process based on the block activity of each of the predetermined blocks of the inter-layer difference data D41 to D44. In the case of the embodiment, each block is composed of 2 lines × 2 pixels.
[0040]
Here, the data value of each pixel is X, and the hierarchy of the data value X is represented by suffix. That is, when the upper hierarchical data is Xi + 1 (0), the adjacent lower hierarchical data can be expressed as Xi (j) (j = 0 to 3). Therefore, the inter-layer difference data value ΔXi (j) is given by the following equation:
(Equation 5)

Can be represented by
[0041]
The encoders 51 to 54 compare the block activity with the threshold for each block, and select whether to divide the block into lower layers or not based on the comparison result.
That is, in the encoders 51 to 54, when the block activity is equal to or larger than the threshold value, the division in the lower hierarchy is executed, whereas when the block activity is smaller than the threshold value, the division in the lower hierarchy is stopped.
[0042]
As a result, the layer coding apparatus 40 does not need to send data of an adjacent lower layer corresponding to a block having a low block activity, thereby reducing the amount of transmission information. Incidentally, a one-bit determination flag is used as the determination flag indicating the result of the division or non-division.
[0043]
The threshold value used in each of the encoders 51 to 54 at the time of the block activity determination is set according to the optimum control value S1 sent from the generated information amount control unit 40B. In other words, as the value of the threshold increases, the number of non-divided blocks (non-transmission blocks) increases, and the amount of transmission information decreases.
As described above, in the hierarchical encoding encoder unit 40A, compression encoding is performed in order from the lower hierarchical data having the lower resolution, and at this time, the activity is determined for each predetermined block of each hierarchical data, and for the block having the lower activity, the activity is determined. Image data corresponding to this block is not sent in the adjacent lower hierarchy.
[0044]
Further, in the hierarchical encoding method in the embodiment, a method is used in which the determination flag is not reflected in the determination in the lower layers thereafter (this method is hereinafter referred to as an independent determination method). That is, in the independence determination method, the division selection process based on the threshold determination is performed for each layer independently. For example, even in a block in which non-division is once determined, the activity is determined again in the subsequent lower hierarchy, and whether to divide again is selected here. As a result, in the hierarchical coding method using the independent determination method, hierarchical coding with less image quality degradation can be realized by being unaffected by the lower layer determination flag in the upper layer.
[0045]
Here, FIG. 7 shows a flowchart of the layer coding process by the layer coding apparatus 40. In step SP2, "4" is registered in the layer counter I storing the layer number, and the frame of the layer coding is determined. You.
[0046]
Further, in step SP3, the generated information amount control section 40B performs the generated information amount calculation to generate hierarchical data, and in the following step SP4, each block activity is detected. The generated information amount control unit 40B determines the optimum control value S1 in step SP5 based on this activity.
[0047]
Further, in step SP6, the hierarchical coding is performed by the hierarchical coding encoder unit 40A based on the optimum control value S1. That is, first, encoding and decoding are performed on the five-layer data that is the highest layer. This result becomes the initial value of the processing in the lower layer, and a difference value between layers with the lower layer is generated in step SP7. Further, in step SP8, division selection and coding in the lower hierarchy are executed based on the optimum control value S1 determined in step SP5.
[0048]
After each hierarchical processing, the hierarchical counter I is decremented in step SP9. Then, in step SP10, an end determination is made on the contents of the hierarchy counter I. If not completed, the lower layer processing is continued. When the processing of all layers is completed, the process exits the loop and ends the layer coding processing in step SP11.
[0049]
(3) Image decoding device of embodiment
(3-1) Configuration
The first to fifth-layer compression encoded data D51 to D55 transmitted together with the division determination flag as described above are decoded by the image decoding device 60 as shown in FIG. That is, the first to fifth hierarchically compressed data D51 to D55 are respectively transmitted to the decoders 61, 62, 63, 64 and 65 having decoding methods reverse to those of the encoders 57, 55, 53, 51 and 49, respectively. Is entered. As a result, the inter-layer difference data D56 to D59 of the first to fourth layers respectively decoded by the decoders 61 to 64 are input to the first to fourth addition circuits 66 to 69, respectively.
[0050]
The fifth-layer compressed and encoded data D55 is decoded by the decoder 65, and the resulting fifth-layer data D60 is output as it is and sent to the fourth smoothing circuit 73. The fourth adding circuit 69 restores the fourth hierarchical data D64 by adding the fifth hierarchical data D60 input via the fourth smoothing circuit 73 and the fourth hierarchical difference data D59, This is output and sent to the third smoothing circuit 72.
[0051]
Similarly, the third adding circuit 68 adds the fourth hierarchical data D64 input through the third smoothing circuit 72 and the third hierarchical inter-level difference data D58 to generate third hierarchical data D63. The image data is restored, output, and sent to the second smoothing circuit 71. Similarly, the second and first addition circuits 67 and 66 restore the second hierarchy data D62 and the first hierarchy data D61, and thus the first to fourth hierarchy data D61 to D64 and the second hierarchy data D61. Five-layer data D65 is output.
[0052]
(3-2) Smoothing processing
In practice, in the image decoding apparatus 60, based on the received division determination flag, the output of each of the decoders 61 to 64 is set to 0 and the upper layer data is output from the adders 66 to 69 for the non-divided block. By doing so, the non-divided block data is replaced with the upper layer data.
[0053]
However, a pseudo contour resulting from the hierarchical data generation method shown in FIG. 6 may occur in the decoded image of the non-divided block data.
For example, in an image having a small level change such as the sky, each block is often subjected to the non-division determination. In other words, it is often replaced with higher-layer data. At this time, in the restored image, even if the level difference between adjacent blocks is small, a pseudo contour is often recognized at the block boundary position, and this greatly deteriorates image quality.
[0054]
In the hierarchical encoding of the embodiment, the compression ratio can be improved by setting a larger division threshold on the hierarchical encoding device 40 side. However, on the image decoding device 60 side, as the division threshold value on the layer encoding device 40 side is larger, the level difference between adjacent blocks (that is, between a divided block and a non-divided block) is enlarged, and the image quality is remarkably deteriorated.
[0055]
A specific example is shown in FIG. In this example, it is assumed that the central block M is a block that has been subjected to the non-division determination. At this time, the upper layer data M is used as the lower layer decoded data X0, X1, X2, X3 corresponding to the block M. That is, X0 = X1 = X2 = X3 = M.
In such a case, as described above, a pseudo contour is generated between X0 to X3 and the peripheral blocks, and the image quality may be degraded.
[0056]
In order to avoid this, in the image decoding device 60, as a method of decoding the non-divided block, the upper layer data is smoothed through the smoothing circuits 70 to 73 instead of simply using the upper layer data. The decoded value of the non-divided block is obtained by using the smoothed data obtained thereby, and the pseudo contour at the block boundary is suppressed.
[0057]
Each of the smoothing circuits 70 to 73 uses the non-divided block M and the peripheral data m0 to m7 in the space of the non-divided block M to convert the lower hierarchical data X0 to X3 of the non-divided block M into the following equation, respectively.
(Equation 6)

(Equation 7)

(Equation 8)

(Equation 9)

It is made to generate based on.
[0058]
Here, AVE (•) represents an averaging processing function with a threshold value determination. As an example of the averaging processing function AVE (•), for example, when the lower hierarchical data X0 is obtained, the upper hierarchical data M, m0, m1, and m7 are determined with respect to a predetermined threshold L by the following equation:
(Equation 10)

And
(Equation 11)

And
(Equation 12)

, The lower hierarchical data X0 is expressed by the following equation:
(Equation 13)

Calculated based on is used.
[0059]
As described above, in the smoothing circuits 70 to 73, when calculating the lower hierarchical data X1 to X3 corresponding to the non-divided block M using the non-divided block M and the peripheral data m0 to m6 or m7 in the space, the average is simply obtained. Instead of performing a value operation, pixel selection based on threshold value determination is performed on the peripheral data m0 to m7 in the space. At this time, if there is a pixel having a large data value in the peripheral data in the higher hierarchy, the pixel Is excluded from the average value calculation.
As a result, in the image decoding device 60, even when an edge or the like exists near the non-divided block M, it is possible to prevent image quality deterioration due to the average value calculation beforehand.
[0060]
Thus, in the image decoding device 60, a pseudo contour generated between a divided block and a non-divided block can be effectively avoided, thereby reducing the image quality deterioration.
Also, in the image decoding device 60, even when a large division threshold is set on the side of the hierarchical encoding device 40, image quality deterioration can be reduced by performing the smoothing process. Accordingly, a large value can be used as the division threshold in the hierarchical encoding device 40, and the compression efficiency can be further improved by this amount.
[0061]
Thus, the use of the image decoding device 60 makes it possible to restore the image data with high compression efficiency, which is divided into blocks by the hierarchical encoding device 40 based on the block activity, while suppressing the deterioration of the image quality.
[0062]
(4) Effects of the embodiment
According to the above configuration, the non-divided block M is smoothed by using the peripheral data m0 to m7 in the space of the non-divided block M, and the non-divided block M is obtained by using the smoothed data X1 to X4 obtained thereby. By obtaining the decoded value of the lower layer block corresponding to M, the adaptively divided compressed and encoded data D51 to D55 having good compression efficiency can be restored with reduced image quality deterioration.
[0063]
(5) Another embodiment
In the above-described embodiment, the decoding method according to the present invention is used to decode the compressed and coded data D51 to D55 that have been divided by the independent determination method in which the threshold is determined each time independently for each layer and the division processing is performed. Although the description has been given of the case where the present invention is applied, the present invention is not limited to this, and is obtained by a layer coding method in which once division of a lower layer is stopped by division determination in an upper layer, division of a lower layer thereafter is stopped. The same effect as that of the above-described embodiment can be obtained even when the present invention is applied to the decoding of compressed and encoded data for a plurality of layers.
The present invention is not limited to this, and can be widely applied to a case where a plurality of blocks having different resolutions exist in hierarchical data in a hierarchical encoding method.
[0064]
【The invention's effect】
As described above, according to the present invention, image data including a plurality of pieces of hierarchical information from the highest hierarchical information having the lowest resolution to the lowest hierarchical information having the highest resolution, and When decoding coded data obtained by controlling the transmission or non-transmission of each block of the layer information of each layer based on the determination result of the block activity of each block, no transmission was performed. The averaging process is performed using the value of the pixel at the position corresponding to the pixel of the non-transmission block and the value of the pixel in the vicinity thereof, among the pixels of the layer information of the layer higher than the layer of the non-transmission block which is the block. To generate the smoothed data, and to output the generated smoothed data as a decoded value for the pixels of the non-transmission block. Effectively avoid false contour occurring in the non-transmission block hierarchy when generating a decoded value for the pixel of O connexion the non transmission block in the hierarchical information of the upper side of the then obtained, it is possible to reduce image quality degradation.
[Brief description of the drawings]
FIG. 1 is a schematic diagram for explaining hierarchical data generated by a hierarchical encoding device.
FIG. 2 is a table showing a result of adaptive division in an HD standard image.
FIG. 3 is a chart showing a standard deviation of a signal level of each layer in an HD standard image.
FIG. 4 is a block diagram illustrating a hierarchical encoding device according to an embodiment.
FIG. 5 is a block diagram showing a hierarchical coding encoder unit.
FIG. 6 is a schematic diagram illustrating a hierarchical structure.
FIG. 7 is a flowchart showing a hierarchical encoding process.
FIG. 8 is a block diagram showing an embodiment of an image decoding device according to the present invention.
FIG. 9 is a schematic diagram for explaining the operation of the smoothing circuit;
FIG. 10 is a block diagram showing an image encoding apparatus using a conventional pyramid encoding method.
FIG. 11 is a block diagram showing a conventional image decoding device for decoding the compressed and encoded data generated by the image encoding device of FIG.
[Explanation of symbols]
40 hierarchical coding device, 60 image decoding device, 70 to 73 smoothing circuit, D51 to D55 compressed compression data, M non-divided block, m0 to m7 spatial peripheral data .

Claims (4)

With respect to image data consisting of a plurality of pieces of hierarchical information from the highest hierarchical information having the lowest resolution to the lowest hierarchical information having the highest resolution, the block activity of each block consisting of a plurality of pixels corresponding to the hierarchical information of a predetermined hierarchy was determined. A decoding device for decoding encoded data obtained by controlling transmission or non-transmission of each block of the layer information of each layer based on the determination result,
The value of the pixel at the position corresponding to the pixel of the non-transmission block and the value of the pixel in the vicinity thereof among the pixels of the layer information of the layer higher than the layer of the non-transmission block which has not been transmitted and which is higher than the layer of the non-transmission block. Smoothing data generating means for performing an averaging process using the pixel values to generate smoothed data;
Output means for outputting the smoothed data as a decoded value for a pixel of the non-transmission block. The smoothed data generating means includes a value of the pixel at a position corresponding to the pixel of the non-transmission block, and a value in the vicinity thereof, among the pixels of the layer information of the layer higher than the layer of the non-transmission block. Detecting the difference from the value of each of the pixels, and performing the averaging process using only the values of the neighboring pixels whose detected difference is equal to or less than a predetermined value to generate the smoothed data. The decoding device according to claim 1, wherein: With respect to image data consisting of a plurality of pieces of hierarchical information from the highest hierarchical information having the lowest resolution to the lowest hierarchical information having the highest resolution, the block activity of each block consisting of a plurality of pixels corresponding to the hierarchical information of a predetermined hierarchy was determined. A decoding method for decoding coded data obtained by controlling transmission or non-transmission of each block of the layer information of each layer based on a determination result,
The value of the pixel at the position corresponding to the pixel of the non-transmission block and the value of the pixel in the vicinity thereof among the pixels of the layer information of the layer higher than the layer of the non-transmission block which has not been transmitted and which is higher than the layer of the non-transmission block. A first step of performing an averaging process using the pixel values to generate smoothed data;
A second step of outputting the smoothed data as a decoded value for a pixel of the non-transmission block. In the first step, the value of the pixel at a position corresponding to the pixel of the non-transmission block and the value of the pixel in the vicinity thereof among the pixels of the layer information of the layer higher than the layer of the non-transmission block, and Detecting the difference between each of the pixel values and performing the averaging process using only the values of the neighboring pixels whose detected difference is equal to or less than a predetermined value to generate the smoothed data. 4. The decoding method according to claim 3 , wherein:

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