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L_OtsuThreshold

Summary

Performs image segmentation and color reduction using Otsu clustering on grayscale images.

Syntax

#include "Ltimgcor.h"

L_LTIMGCOR_API L_INT L_OtsuThreshold(pBitmap, nClusters)

Parameters

pBITMAPHANDLE pBitmap

Pointer to the bitmap handle referencing the bitmap to be converted.

L_INT nClusters

The number of colors in the output image. Valid values range from 2 to 255.

Returns

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

Comments

This function works only with grayscale images. If the input image is a color image, it will be converted to a grayscale image.

Otsu clustering is performed by making each cluster as compact as possible so as to minimize overlap. If one adjusts a threshold one way, the spread of one cluster gets larger and the spread for the second cluster gets smaller. Different threshold values are tried until the one is found which produces the minimum combined spread.

Otsu thresholding is typically used as a way to binarize an image. It is best when used on an image that has a bimodal histogram (Clusters = 2).

This function can only process entire images. It does not support regions.

This command supports 8- and 16-bit grayscale images and 24- and 32-bit colored images.

Otsu Thresholding Function - Before

Otsu Thresholding Function - After

View additional platform support for this Otsu Thresholding 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

This example loads a bitmap and applies Otsu threshold filter.

L_INT OtsuThresholdExample(L_VOID) 
{ 
   L_INT nRet; 
   BITMAPHANDLE LeadBitmap;   /* Bitmap handle to hold the loaded image. */ 
 
   /* Load the bitmap, keeping the bits per pixel of the file */ 
   nRet = L_LoadBitmap(MAKE_IMAGE_PATH(TEXT("NaturalFruits.jpg")), &LeadBitmap, sizeof(BITMAPHANDLE), 0, ORDER_BGR, NULL, NULL); 
   if (nRet != SUCCESS) 
      return nRet; 
 
   nRet = L_OtsuThreshold(&LeadBitmap, 4); 
 
   nRet = L_SaveBitmap(MAKE_IMAGE_PATH(TEXT("Result.BMP")), &LeadBitmap, FILE_BMP, 24, 0, NULL); 
   if (nRet != SUCCESS) 
      return nRet; 
 
   //free bitmap 
   if (LeadBitmap.Flags.Allocated) 
      L_FreeBitmap(&LeadBitmap); 
 
   return SUCCESS; 
}