OCR/openspec/changes/simplify-frontend-ocr-config/specs/ocr-processing/spec.md

# ocr-processing Specification Delta

## REMOVED Requirements

### Requirement: OCR Preset Selection
**Reason**: OCR track 已改為 simple OCR 模式，不再需要前端提供複雜的預設配置。後端統一使用預設參數處理。
**Migration**: 移除前端 `OCRPresetSelector` 組件及相關類型定義。後端自動使用最佳預設配置。

### Requirement: Table Detection Configuration
**Reason**: 表格偵測設定（有框線/無框線表格開關、區域偵測開關）不再需要由前端控制。後端統一使用預設的表格偵測策略。
**Migration**: 移除前端 `TableDetectionSelector` 組件及 `TableDetectionConfig` 類型。後端使用內建預設值。

### Requirement: OCR Advanced Parameters
**Reason**: 進階 OCR 參數（如 `table_parsing_mode`, `layout_threshold`, `enable_chart_recognition` 等）不再需要前端配置。
**Migration**: 移除前端 `OCRConfig` 類型及相關 UI。後端固定使用 simple OCR 模式的預設參數。

## MODIFIED Requirements

### Requirement: Layout Model Selection
The system SHALL allow users to select a layout detection model optimized for their document type, providing a simple choice between pre-configured models instead of manual parameter tuning.

#### Scenario: User selects Chinese document model
- **GIVEN** a user is processing Chinese business documents (forms, contracts, invoices)
- **WHEN** the user selects "Chinese Document Model" (PP-DocLayout-S)
- **THEN** the OCR engine SHALL use the PP-DocLayout-S layout detection model
- **AND** the model SHALL be optimized for 23 Chinese document element types
- **AND** table and form detection accuracy SHALL be improved over the default model

#### Scenario: User selects standard model for English documents
- **GIVEN** a user is processing English academic papers or reports
- **WHEN** the user selects "Standard Model" (PubLayNet-based)
- **THEN** the OCR engine SHALL use the default PubLayNet-based layout detection model
- **AND** the model SHALL be optimized for English document layouts

#### Scenario: User selects CDLA model for specialized Chinese layout
- **GIVEN** a user is processing Chinese documents with complex layouts
- **WHEN** the user selects "CDLA Model"
- **THEN** the OCR engine SHALL use the picodet_lcnet_x1_0_fgd_layout_cdla model
- **AND** the model SHALL provide specialized Chinese document layout analysis

#### Scenario: Layout model is sent via API request
- **GIVEN** a frontend application with model selection UI
- **WHEN** the user starts task processing with a selected model
- **THEN** the frontend SHALL send the model choice in the request body:
  ```json
  POST /api/v2/tasks/{task_id}/start
  {
    "use_dual_track": true,
    "force_track": "ocr",
    "language": "ch",
    "layout_model": "chinese"
  }
  ```
- **AND** the backend SHALL configure PP-StructureV3 with the corresponding model
- **AND** the frontend SHALL NOT send `ocr_preset`, `ocr_config`, or `table_detection` parameters

#### Scenario: Default model when not specified
- **GIVEN** an API request without `layout_model` parameter
- **WHEN** the task is started
- **THEN** the system SHALL use "chinese" (PP-DocLayout-S) as the default model
- **AND** processing SHALL work correctly without requiring model selection

#### Scenario: Invalid model name is rejected
- **GIVEN** a request with an invalid `layout_model` value
- **WHEN** the user sends `layout_model: "invalid_model"`
- **THEN** the API SHALL return 422 Validation Error
- **AND** provide a clear error message listing valid model options

### Requirement: Layout Model Selection UI
The frontend SHALL provide a simple, user-friendly interface for selecting layout detection models with clear descriptions of each option.

#### Scenario: Model options are displayed with descriptions
- **GIVEN** the model selection UI is displayed
- **WHEN** the user views the available options
- **THEN** the UI SHALL show the following options:
  - "Chinese Document Model (Recommended)" - for Chinese forms, contracts, invoices
  - "Standard Model" - for English academic papers, reports
  - "CDLA Model" - for specialized Chinese layout analysis
- **AND** each option SHALL have a brief description of its use case

#### Scenario: Chinese model is selected by default
- **GIVEN** the user opens the task processing interface
- **WHEN** the model selection is displayed
- **THEN** "Chinese Document Model" SHALL be pre-selected as the default
- **AND** the user MAY change the selection before starting processing

#### Scenario: Model selection is visible only for OCR track
- **GIVEN** a document processing interface
- **WHEN** the user selects processing track
- **THEN** layout model selection SHALL be shown ONLY when OCR track is selected or auto-detected
- **AND** SHALL be hidden for Direct track (which does not use PP-StructureV3)

#### Scenario: Simplified configuration options
- **GIVEN** the OCR track processing interface
- **WHEN** the user configures processing options
- **THEN** the UI SHALL only show:
  - Layout model selection (chinese/default/cdla)
  - Image preprocessing settings (auto/manual/disabled)
- **AND** SHALL NOT show:
  - OCR preset selection
  - Table detection configuration
  - Advanced OCR parameters

### Requirement: Simplified Processing Options API
The backend API SHALL accept a simplified `ProcessingOptions` schema without complex OCR configuration parameters.

#### Scenario: API accepts minimal configuration
- **GIVEN** a start task API request
- **WHEN** the request body contains:
  ```json
  {
    "use_dual_track": true,
    "force_track": "ocr",
    "language": "ch",
    "layout_model": "chinese",
    "preprocessing_mode": "auto"
  }
  ```
- **THEN** the API SHALL accept the request
- **AND** process the task using backend default values for all other parameters

#### Scenario: Legacy parameters are ignored
- **GIVEN** a start task API request with legacy parameters
- **WHEN** the request contains `ocr_preset`, `ocr_config`, or `table_detection`
- **THEN** the API SHALL ignore these parameters
- **AND** use backend default values instead
- **AND** NOT return an error (backward compatibility)