OCR/openspec/changes/archive/2025-11-27-simplify-ppstructure-model-selection/specs/ocr-processing/spec.md

ocr-processing Specification Delta

REMOVED Requirements

Requirement: Frontend-Adjustable PP-StructureV3 Parameters

Reason: Complex ML parameters are difficult for end users to understand and tune. Model selection provides better UX and more significant quality improvements. Migration: Replace pp_structure_params API parameter with layout_model parameter.

Requirement: PP-StructureV3 Parameter UI Controls

Reason: Slider/dropdown UI for 7 technical parameters adds complexity without proportional benefit. Simple model selection is more user-friendly. Migration: Remove PPStructureParams.tsx component, add LayoutModelSelector.tsx component.

ADDED 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:

  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

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)