L_CompareBitmap

#include "l_bitmap.h"

L_LTIMGCOR_API L_INT L_CompareBitmap(pReferenceBitmap, pModifiedBitmap, pOutputBitmap, pAlignment, pOptions)

Compares two images for additions, deletions, and changes and generates an image with the differences highlighted.

Parameters

pBITMAPHANDLE pReferenceBitmap

Pointer to the reference (original) bitmap.

pBITMAPHANDLE pModifiedBitmap

Pointer to the modified bitmap.

pBITMAPHANDLE pOutputBitmap

Pointer to a bitmap to be populated with the comparison results. See the comments below for more information.

L_MATRIX *pAlignment

Optional pointer to a transformation matrix used to overlay the modified bitmap onto the reference bitmap. If NULL is passed, no transformation will be performed and the images will be aligned to the top-left.

pCOMPAREOPTIONS pOptions

Pointer to the comparison options.

Returns

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

Comments

The output image (pOutputBitmap) will be 3 bits-per-pixel. The first six entries of its palette are populated from the COMPAREOPTIONS structure (pOptions):

Index Value
0 pOptions->crOutputExternal
1 pOptions->crOutputBackground
2 pOptions->crOutputMatch
3 pOptions->crOutputAddition
4 pOptions->crOutputDeletion
5 pOptions->crOutputChange

Required DLLs and Libraries

Platforms

Win32, x64, Linux.

Example

This example shows how to compare an image to its modified and rotated version.

L_INT CompareBitmapExample(L_VOID) 
{ 
   L_INT nRet = SUCCESS; 
   BITMAPHANDLE ReferenceBitmap = { 0 }; // The original image 
   BITMAPHANDLE ModifiedBitmap = { 0 }; // The modified image 
   BITMAPHANDLE OutputBitmap = { 0 }; // The generated image 
   COMPAREOPTIONS Options = { 0 }; // The comparison options 
   L_MATRIX Alignment = { 0 }; // The alignment transformation for the modified image 
   L_RECT RemoveRect = { 0 }; // The region to remove from an image 
 
   // Load the original image 
   nRet = L_LoadBitmap(MAKE_IMAGE_PATH(TEXT("ocr1.tif")), &ReferenceBitmap, sizeof(BITMAPHANDLE), 0, ORDER_BGRORGRAY, NULL, NULL); 
   if (nRet != SUCCESS) 
      goto cleanup; 
 
   // Use the same image for the "modified" image 
   nRet = L_CopyBitmap(&ModifiedBitmap, &ReferenceBitmap, sizeof(BITMAPHANDLE)); 
   if (nRet != SUCCESS) 
      goto cleanup; 
 
   // Remove the last paragraph of the reference image 
   L_Rect_Make(&RemoveRect, 290, 2470, 1930, 360); 
   nRet = L_SetBitmapRgnRect(&ReferenceBitmap, NULL, &RemoveRect, L_RGN_SET); 
   if (nRet != SUCCESS) 
      goto cleanup; 
   nRet = L_FillBitmap(&ReferenceBitmap, RGB(255, 255, 255)); 
   if (nRet != SUCCESS) 
      goto cleanup; 
   nRet = L_FreeBitmapRgn(&ReferenceBitmap); 
   if (nRet != SUCCESS) 
      goto cleanup; 
 
   // Remove the title from the modified image 
   L_Rect_Make(&RemoveRect, 290, 300, 810, 110); 
   nRet = L_SetBitmapRgnRect(&ModifiedBitmap, NULL, &RemoveRect, L_RGN_SET); 
   if (nRet != SUCCESS) 
      goto cleanup; 
   nRet = L_FillBitmap(&ModifiedBitmap, RGB(255, 255, 255)); 
   if (nRet != SUCCESS) 
      goto cleanup; 
   nRet = L_FreeBitmapRgn(&ModifiedBitmap); 
   if (nRet != SUCCESS) 
      goto cleanup; 
 
   // Rotate the modified image for demonstration (angle measured in hundredths of a degree) 
   nRet = L_RotateBitmap(&ModifiedBitmap, 340 * 100, ROTATE_RESIZE, RGB(0, 0, 0)); 
   if (nRet != SUCCESS) 
      goto cleanup; 
 
   // Update the transformation to align/reverse the above rotation 
   L_Matrix_Identity(&Alignment); 
   L_Matrix_Translate(&Alignment, -ModifiedBitmap.Width * 0.5, -ModifiedBitmap.Height * 0.5); 
   L_Matrix_Rotate(&Alignment, 20.0); 
   L_Matrix_Translate(&Alignment, ReferenceBitmap.Width * 0.5, ReferenceBitmap.Height * 0.5); 
 
   // Setup the comparison options 
   Options.uStructSize = sizeof(COMPAREOPTIONS); 
   Options.uThreshold = 0; // The images are bitonal, no need for measuring color distance 
   Options.crReferenceBackground = RGB(255, 255, 255); // White 
   Options.crReferenceForeground = RGB(0, 0, 0); // Black 
   Options.crModifiedBackground = RGB(255, 255, 255); // White 
   Options.crModifiedForeground = RGB(0, 0, 0); // Black 
   Options.crOutputExternal = RGB(128, 128, 255); // Light blue 
   Options.crOutputBackground = RGB(255, 255, 255); // White 
   Options.crOutputMatch = RGB(64, 64, 64); // Dark gray 
   Options.crOutputAddition = RGB(0, 255, 0); // Green 
   Options.crOutputDeletion = RGB(255, 0, 0); // Red 
   Options.crOutputChange = RGB(255, 255, 0); // Yellow 
 
   // Compare the images 
   nRet = L_CompareBitmap(&ReferenceBitmap, &ModifiedBitmap, &OutputBitmap, &Alignment, &Options); 
   if (nRet != SUCCESS) 
      goto cleanup; 
 
   // Save the results 
   nRet = L_SaveBitmap(MAKE_IMAGE_PATH(TEXT("CompareBitmap_Output.png")), &OutputBitmap, FILE_PNG, 0, 0, NULL); 
   if (nRet != SUCCESS) 
      goto cleanup; 
 
   // Save the two input images, for reference 
   nRet = L_SaveBitmap(MAKE_IMAGE_PATH(TEXT("CompareBitmap_Reference.png")), &ReferenceBitmap, FILE_PNG, 0, 0, NULL); 
   if (nRet != SUCCESS) 
      goto cleanup; 
   nRet = L_SaveBitmap(MAKE_IMAGE_PATH(TEXT("CompareBitmap_Modified.png")), &ModifiedBitmap, FILE_PNG, 0, 0, NULL); 
   if (nRet != SUCCESS) 
      goto cleanup; 
 
cleanup: 
 
   // Free the loaded images 
   if (ReferenceBitmap.Flags.Allocated) 
      L_FreeBitmap(&ReferenceBitmap); 
   if (ModifiedBitmap.Flags.Allocated) 
      L_FreeBitmap(&ModifiedBitmap); 
   if (OutputBitmap.Flags.Allocated) 
      L_FreeBitmap(&OutputBitmap); 
 
   return nRet; 
} 

Reference, Modified, and Output Images

The following images are generated when the example is run:

CompareBitmap Reference Image
CompareBitmap Modified Image
CompareBitmap Output Image
Help Version 20.0.2019.12.5
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