CImage访问像素及其像素操作总结

MSDN的代码

COLORREF pixel;
   int maxY = imgOriginal.GetHeight(), maxX = imgOriginal.GetWidth();
   byte r,g,b,avg;
   for (int y=0; y<maxY; y++) {
       for (int x=0; x<maxX; x++) {
            pixel = imgOriginal.GetPixel(x,y);
            r = GetRValue(pixel);
            g = GetGValue(pixel);
            b = GetBValue(pixel);
            avg = (r+ g+ b)/3;
            imgOriginal.SetPixelRGB(x,y,avg,avg,avg);
}}

这种方式效率很低， 因为每次调用getpixel，都包含着程序的进栈和出栈。所以，面对大量需要处理的数据，采用直接访问内存地址的方法。

   byte* pRealData;
   pRealData=(byte*)imgOriginal.GetBits();
   int pit=imgOriginal.GetPitch();
   int bitCount=imgOriginal.GetBPP()/8;
   for (int y=0; y<maxY; y++) {
        for (int x=0; x<maxX; x++) {
             int grayVal=(int)(int)(*(pRealData + pit*y + x*bitCount))*0.3
                     + (int)(int)(*(pRealData + pit*y + x*bitCount +1))*0.59
                     + (int)(int)(*(pRealData + pit*y + x*bitCount +2))*0.11;
     *(pRealData + pit*y + x*bitCount)=grayVal;
     *(pRealData + pit*y + x*bitCount +1)=grayVal;
     *(pRealData + pit*y + x*bitCount +2)=grayVal;
//如果是8位灰度图像，直接读取一个BYTE位为灰度值
//如果是24位RGB图像，则依次读取pixAddr,pixAddr+1,pixAddr+2为B、G、R分量值
}}

用两种方法对同一张图片（3264*2448像素）进行处理，前者需要1分钟，后者只需1秒左右。

所以，后者比前者至少快60倍

直接访问内存地址的另一种方式：

        int i,j,temp;
	int pixel[4];
	int width = yuantu.GetWidth();
	int height = yuantu.GetHeight();
	int widthBytes = yuantu.GetPitch();
	bianyuantu.Create(width,height,yuantu.GetBPP());

	if(yuantu.IsIndexed())
	{
		yuantu.GetColorTable(0,256,colorTable);
		bianyuantu.SetColorTable(0,256,colorTable);
	}
	BYTE *pYuantuData = (BYTE*)yuantu.GetBits();
	BYTE *pBianyuantuData =(BYTE*)bianyuantu.GetBits();

	for(j=0;j<height-1;j++)
	{
		for(i=0;i<width-1;i++)
		{
			pixel[0]=pYuantuData[j*widthBytes+i];
			pixel[1]=pYuantuData[j*widthBytes+i+1];
			pixel[2]=pYuantuData[(j+1)*widthBytes+i];
			pixel[3]=pYuantuData[(j+1)*widthBytes+i+1];
			temp=(int)sqrt((double)((pixel[0]-pixel[3])*(pixel[0]-pixel[3])
				+(pixel[1]-pixel[2])*(pixel[1]-pixel[2]))); //罗伯特算子
			pBianyuantuData[j*widthBytes+i]=temp;
		}
	}

　　

彩色图像转化为灰度图的处理方式

//真彩色图像变为灰度图，直接修改像素点的值

void PixelsChangedToGray(CImage *pImage)
{
    int  nByte,j,i,nWidth,nHeight,nBytesPerPixel;
    BYTE  *pPixelLine,cNewPixelValue;
    nWidth=pImage->GetWidth();   nHeight=pImage->GetHeight();
    nBytesPerPixel= pImage->GetBPP()/8;
    for (i=0;i<nHeight;i++){
        pPixelLine =(BYTE*) pImage->GetPixelAddress(0,i);
        nByte=0;
        for (j=0;j<nWidth;j++){      cNewPixelValue=(BYTE)(0.11*pPixelLine[nByte]
                                                        +0.59*pPixelLine[nByte+1]
                                                        +0.30*pPixelLine[nByte+2]);
        pPixelLine[nByte] = pPixelLine[nByte+1] = pPixelLine[nByte+2]
                        = cNewPixelValue;
        nByte+=nBytesPerPixel;
        }
    }
}

//非真彩色图像变为灰度图，修改调色板信息 

void PaletteChangedToGray(CImage *pImage)
{
    RGBQUAD  ColorTabs[256];
    int  i,nColorTableEntries,nNewGrayColor;
    nColorTableEntries=pImage->GetMaxColorTableEntries();
    pImage->GetColorTable(0,nColorTableEntries,ColorTabs);
    for (i=0;i<nColorTableEntries;i++){
        nNewGrayColor=(int)(0.11*ColorTabs[i].rgbBlue
                                           + 0.59*ColorTabs[i].rgbGreen
                                           + 0.30*ColorTabs[i].rgbRed);
        ColorTabs[i].rgbBlue = (BYTE)nNewGrayColor;
        ColorTabs[i].rgbGreen = (BYTE)nNewGrayColor;
        ColorTabs[i].rgbRed = (BYTE)nNewGrayColor;
    }
    pImage->SetColorTable(0,nColorTableEntries,ColorTabs);
}