```mermaid
flowchart TD
    Start([開始]) --> CheckFocus{文字輸入框取得焦點?}
    CheckFocus -- 否 --> End([結束])
    CheckFocus -- 是 --> CheckISB{是否有選取影像?}
    
    CheckISB -- 是 --> MatchKey{判斷按鍵}
    CheckISB -- 否 --> End
    
    MatchKey -- VK_UP (上) --> CallPrior[呼叫 PriorPage 翻頁]
    MatchKey -- VK_DOWN (下) --> CallNext[呼叫 NextPage 翻頁]
    
    CallPrior --> ScrollUI[同步滾動捲軸更新顯示]
    CallNext --> ScrollUI
    ScrollUI --> End
```