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L_FindCandidateFormFields

Summary

Extracts the candidate form fields from a bitmap using various options.

There are two major types of fields: Text fields and OMR fields.

Syntax

#include "l_bitmap.h"

L_LTIMGCOR_API L_INT L_FindCandidateFormFields(pBitmap, pOptions, pOutputs)

Parameters

pBITMAPHANDLE pBitmap

Pointer to the bitmap handle that references the bitmap to be processed.

FIND_CANDIDATE_FORM_FIELDS_OPTIONS *pOptions

Fields detection options. This value cannot be null.

FIND_CANDIDATE_FORM_FIELDS_OUTPUTS *pOutputs

Pointer to be updated with the extracted fields.

Returns

Value	Meaning
SUCCESS	The function was successful.
< 1	An error occurred. Refer to Return Codes.

Comments

Deskew the image first, if it is skewed.

L_FindCandidateFormFields Supports 8-bit, 12-bit and 16-bit grayscale images, and supports 24-bit, 32-bit, 48-bit and 64-bit colored images.

L_FindCandidateFormFields does not support setting rectangle region.

L_FindCandidateFormFields does not support 32-bit grayscale images. It returns the error code ERROR_GRAY32_UNSUPPORTED if a 32-bit grayscale image is passed to this function.

Required DLLs and Libraries

LTIMGCOR
For a listing of the exact DLLs and Libraries needed, based on the toolkit version, refer to Files To Be Included With Your Application

Platforms

Win32, x64, Linux.

Example

Extracts the candidate form fields from a bitmap using various options.

L_INT FindCandidateFormFieldsExample(L_VOID) 
{ 
   L_INT nRet = SUCCESS; 
 
   BITMAPHANDLE InputBitmap = { 0 }; 
   FIND_CANDIDATE_FORM_FIELDS_OPTIONS Options; 
   FIND_CANDIDATE_FORM_FIELDS_OUTPUTS Outputs; 
 
   COLORREF red = RGB(255, 0, 0); 
   COLORREF cyan = RGB(0, 255, 255); 
   COLORREF blue = RGB(0, 0, 255); 
   COLORREF green = RGB(0, 255, 0); 
 
   Options.uVerticalLineMinimumLength = 3; 
   Options.uHorizontalLineMinimumLength = 10; 
   Options.uStructSize = sizeof(FIND_CANDIDATE_FORM_FIELDS_OPTIONS); 
 
   L_TCHAR szBuffer1[100]; 
   wsprintf(szBuffer1, MAKE_IMAGE_PATH(L_TEXT("Forms\\Forms to be Recognized\\OMR\\AnswerSheet_Pattern.jpg"))); 
   nRet = L_LoadBitmap(szBuffer1, &InputBitmap, sizeof(BITMAPHANDLE), 0, ORDER_BGRORGRAY, NULL, NULL); 
 
   nRet = L_FindCandidateFormFields(&InputBitmap, &Options, &Outputs); 
   if (nRet != SUCCESS) 
   { 
      goto cleanup; 
   } 
 
   L_HDC hDC = NULL; 
   HPEN  hPen = NULL; 
 
   // Normalize drawing 
   if (InputBitmap.ViewPerspective != TOP_LEFT) 
   { 
      nRet = L_ChangeBitmapViewPerspective(&InputBitmap, &InputBitmap, sizeof(BITMAPHANDLE), TOP_LEFT); 
      if (nRet != SUCCESS) 
         goto cleanup; 
   } 
 
   if (InputBitmap.BitsPerPixel != 24) 
   { 
      nRet = L_ColorResBitmap(&InputBitmap, &InputBitmap, sizeof(BITMAPHANDLE), 24, CRF_BYTEORDERBGR, NULL, NULL, 0, NULL, NULL); 
      if (nRet != SUCCESS) 
         goto cleanup; 
   } 
 
   // Start drawing on the image 
   hDC = L_CreateLeadDC(&InputBitmap); 
   if (hDC == NULL) 
      goto cleanup; 
 
   // No fill 
   SelectObject(hDC, GetStockObject(NULL_BRUSH)); 
 
   for (L_UINT i = 0; i < Outputs.TextFields.uCount; i++) 
   { 
      RECT rect = Outputs.TextFields.pTextFieldAreas[i].rcBounds; 
      COLORREF color = (Outputs.TextFields.pTextFieldAreas[i].uFieldType == TEXT_FIELD_TYPE_BOX) ? cyan : blue; 
      hPen = CreatePen(PS_SOLID, 2, color); 
      if (hPen == NULL) 
         goto cleanup; 
 
      SelectObject(hDC, hPen); 
 
      Rectangle(hDC, rect.left, rect.top, rect.right, rect.bottom); 
      DeleteObject(hPen); 
 
      rect = Outputs.TextFields.pTextFieldAreas[i].rcFilledAreaBounds; 
      color = red; 
 
      DeleteObject(hPen); 
      hPen = CreatePen(PS_SOLID, 2, color); 
      if (hPen == NULL) 
         goto cleanup; 
 
      SelectObject(hDC, hPen); 
 
      Rectangle(hDC, rect.left, rect.top, rect.right, rect.bottom); 
      DeleteObject(hPen); 
   } 
 
   COLORREF color = green; 
   hPen = CreatePen(PS_SOLID, 2, color); 
   if (hPen == NULL) 
      goto cleanup; 
 
   SelectObject(hDC, hPen); 
 
   for (L_UINT i = 0; i < Outputs.OMRFields.uCount; i++) 
   { 
      RECT rect = Outputs.OMRFields.pOMRFieldAreas[i].rcUnfilledBound; 
      if (Outputs.OMRFields.pOMRFieldAreas[i].uFieldType == OMR_FIELD_TYPE_BOX) 
      { 
         Rectangle(hDC, rect.left, rect.top, rect.right, rect.bottom); 
      } 
      else 
      { 
         Ellipse(hDC, rect.left, rect.top, rect.right, rect.bottom); 
      } 
   } 
 
   //////////////////////////////////////////////////////////// 
 
cleanup: 
   if (hPen != NULL) 
      DeleteObject(hPen); 
 
   if (hDC != NULL) 
      L_DeleteLeadDC(hDC); 
 
   // Free the loaded images  
   if (InputBitmap.Flags.Allocated) 
      L_FreeBitmap(&InputBitmap); 
 
   // Free the results  
   L_FindCandidateFormsFieldsFree(&Outputs); 
 
   return nRet; 
}