銳化(sharpening)和平滑恰恰相反，它是通過增強高頻分量來減少圖象中的模糊，因此又稱為高通濾波(high pass filter)。銳化處理在增強圖象邊緣的同時增加了圖象的噪聲。

常用的銳化模板是拉普拉斯(Laplacian)模板，如下所示：

容易看出拉普拉斯模板的作法：以自身灰度值的9倍減去周圍像素點灰度值作為自身新的灰度值。可見，如果一片暗區出現了一個亮點，那么銳化處理的結果是這個亮點變得更亮，增加了圖象的噪聲。因為圖象中的邊緣就是那些灰度發生跳變的區域，所以銳化模板在邊緣檢測中很有用。

實現代碼：

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#pragma pack(1)   //全緊湊模式typedef struct {unsigned char bfType[2];unsigned int bfSize;unsigned short bfReserved1;unsigned short bfReserved2;unsigned int bfOffBits;
}bitmapFileHeader;typedef struct {unsigned int biSize;unsigned int biWidth;unsigned int biHeight;unsigned short biPlanes;unsigned short biBitCount;unsigned int biCompression;unsigned int biSizeImage;unsigned int biXPixPerMeter;unsigned int biYPixPerMeter;unsigned int biClrUsed;unsigned int biClrImportant;
}bitmapInfoHeader;typedef struct{unsigned char rgbBlue;unsigned char rgbGreen;unsigned char rgbRed;unsigned char rgbReserved;}rgbQUAD;typedef struct{bitmapFileHeader bfHeader;bitmapInfoHeader biHeader;rgbQUAD palette[256];unsigned char *imgData;
}bmp;int main(){FILE *fp;if((fp=fopen("d:\Temp\\test_gray.bmp","rb"))==NULL){perror("can not open file!");return -1;}//讀入彩色bmp圖像文件頭，信息頭和圖像數據bitmapFileHeader bfHeader;fread(&bfHeader,14,1,fp);bitmapInfoHeader biHeader;fread(&biHeader,40,1,fp);int imSize=biHeader.biSizeImage;int width=biHeader.biWidth;int height=biHeader.biHeight;int bitCount=biHeader.biBitCount;int lineBytes=(width*bitCount+31)/32*4;fseek(fp,bfHeader.bfOffBits,SEEK_SET);unsigned char*imageData=(unsigned char*)malloc(imSize*sizeof(unsigned char));fread(imageData,imSize*sizeof(unsigned char),1,fp);	fclose(fp);bmp b;memcpy(&(b.bfHeader),&bfHeader,sizeof(bfHeader));memcpy(&(b.biHeader),&biHeader,sizeof(biHeader));b.imgData=(unsigned char*)malloc(sizeof(unsigned char)*imSize);memset(b.imgData,0,sizeof(unsigned char)*imSize);for(int i=0;i<256;i++){b.palette[i].rgbBlue=i;b.palette[i].rgbGreen=i;b.palette[i].rgbRed=i;}int i,j,temp;int sharpen[9]={-1,-1,-1,-1,9,-1,-1,-1,-1};//拉普拉斯銳化模板for(i=1;i<height-1;i++){  //1~height-2for(j=1;j<width-1;j++){ //1~width-2temp=imageData[lineBytes*(i+1)+j-1]*sharpen[0];temp+=imageData[lineBytes*(i+1)+j]*sharpen[1];temp+=imageData[lineBytes*(i+1)+j+1]*sharpen[2];temp+=imageData[lineBytes*i+j-1]*sharpen[3];temp+=imageData[lineBytes*i+j]*sharpen[4];temp+=imageData[lineBytes*i+j+1]*sharpen[5];temp+=imageData[lineBytes*(i-1)+j-1]*sharpen[6];temp+=imageData[lineBytes*(i-1)+j]*sharpen[7];temp+=imageData[lineBytes*(i-1)+j]*sharpen[8];if(temp>255)b.imgData[lineBytes*i+j]=255;else if(temp<0)b.imgData[lineBytes*i+j]=abs(temp);else b.imgData[lineBytes*i+j]=temp;}}char savePath[]="D:\Temp\\save_test.bmp";FILE *f_save=fopen(savePath,"wb");if(f_save==NULL){perror("can not open file!");return -2;}fwrite(&b.bfHeader,sizeof(bitmapFileHeader),1,f_save);fwrite(&b.biHeader,sizeof(bitmapInfoHeader),1,f_save);fwrite(&b.palette,1024,1,f_save);fwrite(b.imgData,sizeof(unsigned char)*b.biHeader.biSizeImage,1,f_save);fclose(f_save);free(imageData);free(b.imgData);getchar();return 0;
}

代碼效果：

原圖像:

銳化圖像：

總結

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