feat: enhance layout preprocessing and unify image scaling proposal

Backend changes:
- Add image scaling configuration for PP-Structure processing
- Enhance layout preprocessing service with scaling support
- Update OCR service with improved memory management
- Add PP-Structure enhanced processing improvements

Frontend changes:
- Update preprocessing settings UI
- Fix processing page layout and state management
- Update API types for new parameters

Proposals:
- Archive add-layout-preprocessing proposal (completed)
- Add unify-image-scaling proposal for consistent coordinate handling

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/src/components/PreprocessingSettings.tsx

@@ -30,7 +30,7 @@ export default function PreprocessingSettings({
 }: PreprocessingSettingsProps) {
   const { t } = useTranslation()
   const modes: PreprocessingMode[] = ['auto', 'manual', 'disabled']
-  const contrastOptions: PreprocessingContrast[] = ['none', 'histogram', 'clahe']
+  const contrastOptions: PreprocessingContrast[] = ['none', 'histogram', 'clahe', 'document']
 
   const getModeInfo = (m: PreprocessingMode) => ({
     label: t(`processing.preprocessing.mode.${m}`),

frontend/src/i18n/locales/zh-TW.json

@@ -81,7 +81,8 @@
         "label": "對比度增強",
         "none": "不增強",
         "histogram": "直方圖均衡化",
-        "clahe": "CLAHE 自適應均衡化"
+        "clahe": "CLAHE 自適應均衡化",
+        "document": "掃描件優化 (背景校正+CLAHE)"
       },
       "sharpen": "邊緣銳化",
       "strength": {

frontend/src/pages/ProcessingPage.tsx

@@ -382,23 +382,49 @@ export default function ProcessingPage() {
             </div>
           )}
 
-          {/* Direct Track Notice - Show when document is editable PDF */}
-          {documentAnalysis && documentAnalysis.recommended_track === 'direct' && (
-            <Card className="border-blue-200 bg-blue-50">
+          {/* Document Analysis Info */}
+          {documentAnalysis && (
+            <Card className={documentAnalysis.recommended_track === 'direct' ? 'border-blue-200 bg-blue-50' : 'border-green-200 bg-green-50'}>
               <CardContent className="pt-4">
                 <div className="flex items-start gap-3">
-                  <Info className="w-5 h-5 text-blue-600 flex-shrink-0 mt-0.5" />
-                  <div>
-                    <p className="text-sm font-medium text-blue-800">此文件為可編輯 PDF</p>
-                    <p className="text-sm text-blue-700 mt-1">
-                      系統偵測到此 PDF 包含文字圖層，將使用直接文字提取方式處理。
-                      版面偵測和影像前處理設定不適用於此類文件。
-                    </p>
-                    {documentAnalysis.text_coverage && (
-                      <p className="text-xs text-blue-600 mt-2">
-                        文字覆蓋率: {(documentAnalysis.text_coverage * 100).toFixed(1)}%
-                      </p>
+                  <Info className={`w-5 h-5 flex-shrink-0 mt-0.5 ${documentAnalysis.recommended_track === 'direct' ? 'text-blue-600' : 'text-green-600'}`} />
+                  <div className="flex-1">
+                    {documentAnalysis.recommended_track === 'direct' ? (
+                      <>
+                        <p className="text-sm font-medium text-blue-800">此文件為可編輯 PDF</p>
+                        <p className="text-sm text-blue-700 mt-1">
+                          系統偵測到此 PDF 包含文字圖層，將使用直接文字提取方式處理。
+                          版面偵測和影像前處理設定不適用於此類文件。
+                        </p>
+                      </>
+                    ) : (
+                      <>
+                        <p className="text-sm font-medium text-green-800">
+                          {documentAnalysis.is_editable ? '混合文件' : '掃描文件 / 影像'}
+                        </p>
+                        <p className="text-sm text-green-700 mt-1">
+                          {documentAnalysis.reason}
+                        </p>
+                      </>
                     )}
+                    <div className="flex flex-wrap gap-4 mt-2 text-xs">
+                      <span className={documentAnalysis.recommended_track === 'direct' ? 'text-blue-600' : 'text-green-600'}>
+                        處理方式: {documentAnalysis.recommended_track === 'direct' ? '直接提取' : documentAnalysis.recommended_track === 'ocr' ? 'OCR 識別' : '混合處理'}
+                      </span>
+                      {documentAnalysis.page_count && (
+                        <span className={documentAnalysis.recommended_track === 'direct' ? 'text-blue-600' : 'text-green-600'}>
+                          頁數: {documentAnalysis.page_count}
+                        </span>
+                      )}
+                      {documentAnalysis.text_coverage !== null && (
+                        <span className={documentAnalysis.recommended_track === 'direct' ? 'text-blue-600' : 'text-green-600'}>
+                          文字覆蓋率: {(documentAnalysis.text_coverage * 100).toFixed(1)}%
+                        </span>
+                      )}
+                      <span className={documentAnalysis.recommended_track === 'direct' ? 'text-blue-600' : 'text-green-600'}>
+                        信心度: {(documentAnalysis.confidence * 100).toFixed(0)}%
+                      </span>
+                    </div>
                   </div>
                 </div>
               </CardContent>

frontend/src/services/apiV2.ts

@@ -408,7 +408,7 @@ class ApiClientV2 {
    * Analyze document to get recommended processing track
    */
   async analyzeDocument(taskId: string): Promise<DocumentAnalysisResponse> {
-    const response = await this.client.get<DocumentAnalysisResponse>(`/tasks/${taskId}/analyze`)
+    const response = await this.client.post<DocumentAnalysisResponse>(`/tasks/${taskId}/analyze`)
     return response.data
   }
 

frontend/src/types/apiV2.ts

@@ -92,8 +92,12 @@ export type PreprocessingMode = 'auto' | 'manual' | 'disabled'
 
 /**
  * Contrast enhancement method for preprocessing.
+ * - none: No contrast enhancement
+ * - histogram: Standard histogram equalization
+ * - clahe: Contrast Limited Adaptive Histogram Equalization (good for most cases)
+ * - document: Background normalization + CLAHE (best for scanned documents)
  */
-export type PreprocessingContrast = 'none' | 'histogram' | 'clahe'
+export type PreprocessingContrast = 'none' | 'histogram' | 'clahe' | 'document'
 
 /**
  * Preprocessing configuration for layout detection enhancement.