在本論文的研究過程中，衍生了許多值得再探討的題目，可以作為將來加速
區塊匹配演算法或應用在不同層面的動作估測上，雖然不一定都能有很好的效 果，但是可以確定在動作估測上還能有許多改進的可能性。本節中會詳細討論與 本研究動作估測相關的改進方式。
門檻值的決定方式 門檻值的決定方式 門檻值的決定方式 門檻值的決定方式
首先要提出的是門檻值的決定方式，我們可以知道此門檻值的大小決定了提 早終止的判斷條件，所以直接造成計算量與移動估測結果上的差異，而本研究中 只是找出在對移動估測結果影響小而盡可能節省計算量的方式，但是並沒有對整 體的影像壓縮結果做考量，也就是說在資料傳輸量控制（bit-rate control）的條件 下，我們可以再節省更多的計算量而故意犧牲估測結果使壓縮比下降，因為我們 知道在處理某些影像的壓縮比本來就可以很高，如Akiyo這類的畫面，所以我們 有機會藉由提高門檻值到資料傳輸量符合所需即可，而不必要求動作估測的準確 度，這也是在本論文硬體設計中，會設計門檻值由外部輸入的機制，這樣可以由 使用者自己判斷是否要減少區塊匹配的步驟。
從本研究中已知門檻值的估測是可以由多種方式決定，雖然我們為了硬體上
的考量而採取了一個門檻值處理一張畫面的適應方式，不過如果從不同區塊不同
區塊（variable block）的動作估測技術。
應用範圍 應用範圍 應用範圍 應用範圍
在本論文中雖然只有應用在鑽石演算法及類似的快速演算法上，但是其實還 有許多獨立的動作估測加速技術，如第二章中所提到的預估移動向量的方式，都 能在應用在這個快速演算法之上，尤其是快速演算法還有許多獨立的改進方式，
我們並沒有應用在此搜尋法上，如果都能把彼此獨立的加速技術結合在一起相信 能得到非常好的加速能力，如同[23]研究中所組合出的快速演算法，因為我們所 設計的提早終止技術也是獨立於其中所使用的方式，再套用我們設計的提早終止 技術上去相信就能得到更好的加速能力。
此外，不止是類似鑽石搜尋法這類的快速搜尋法，在圖 5.1 所顯示的兩種快 速搜尋法也適合我們所設計的適應性門檻值來提早終止搜尋步驟，圖中的螺旋全 部搜尋法（spiral full search）是從中心點開始向外搜尋，雖然類似全部搜尋法，
但可以利用提早終止的技術去停止後面的搜尋步驟，這樣就比一般的全部搜尋要 較節省計算量，而三步搜尋法中也可以利用適應性門檻值來判斷是否要完成三步 的搜尋，還是只需一到二步就停止搜尋動作，這兩個方式都應該都能加快原始的 搜尋法的搜尋速度，但是對於誤差的增加就要看搜尋過程中是否能在一開始就得 到較準確的 SAD 值，這樣才能預估出較準確的適應性門檻值。
(a) (b) 圖 5.1 (a)螺旋全部搜尋法(b)三步搜尋法
參考文獻 參考文獻 參考文獻 參考文獻
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