缩放图像的双线性内插法

今天将图像缩放的双线性内插法弄完了，主要的思想如下：

对于一个目的像素，通过目标图像与源图像的比值进行反向变换得到一个浮点坐标，如fx(x+u,y+v)其中为非负整数，u，v为区间[0，1]上的浮点数。则目的像素的颜色值可以由源图像的点fx（x，y）与其相邻的四个点的颜色值决定。

公式为：fx（x+u，y+v）=（1-u）（1-v）fx（x，y）+(1-u)(v)fx(x,y+1) +(u)(1-v)fx(x+1,y)+uvfx(x+1,y+1);

下面是我自己写的一个缩放图像的函数。

void CTestView::Linear_BMP(COLORREF **DesImage,double DesWidth,double DesHeight,COLORREF **SrcImage ,double SrcWidth,double SrcHeight)
{    
    if(SrcImage == NULL)
        return;
    DesImage=new COLORREF*[(int)DesHeight];
    for(int n1=0;n1<DesHeight;n1++)
        DesImage[n1]=new COLORREF[(int)DesWidth];
    double w = (double)SrcWidth/(double)DesWidth;//源/目标=比例
    double h = (double)SrcHeight/(double)DesHeight;
    double u,v;
    double Sx,Sy;
    double pm[4];
    int tx,ty;
    int red[4],green[4],blue[4];
    double r=0,g=0,b=0;
    for(int i = 0; i < DesHeight; i++)
    {
        Sy = (double)(i) * h;
        ty = (int)Sy;
    
        v = fabs(Sy - ty);
        for(int j = 0; j<DesWidth; j++)
        {
        
            Sx = (double)(j) * w ;
            tx = (int)Sx;
        
            u = fabs(Sx - tx);
            pm[0] = ( 1.0 - u ) * ( 1.0 - v );
            pm[1] = v * ( 1.0 - u );
            pm[2] = u * ( 1.0 - v );
            pm[3] = u * v;
            if(tx>=SrcWidth - 2)
                tx = SrcWidth - 2;
            if(ty>=SrcHeight - 2)
                ty = SrcHeight - 2;
            red[0] = GetRValue(SrcImage[ty][tx]);
            red[1] = GetRValue(SrcImage[ty+1][tx]);
            red[2] = GetRValue(SrcImage[ty][tx+1]);
            red[3] = GetRValue(SrcImage[ty+1][tx+1]);
            
            green[0] = GetGValue(SrcImage[ty][tx]);
            green[1] = GetGValue(SrcImage[ty+1][tx]);
            green[2] = GetGValue(SrcImage[ty][tx+1]);
            green[3] = GetGValue(SrcImage[ty+1][tx+1]);

            blue[0] = GetBValue(SrcImage[ty][tx]);
            blue[1] = GetBValue(SrcImage[ty+1][tx]);
            blue[2] = GetBValue(SrcImage[ty][tx+1]);
            blue[3] = GetBValue(SrcImage[ty+1][tx+1]);
            r = 0;
            g = 0;
            b = 0;
            for(int m = 0;m<4;m++)
            {
                r += pm[m] * red[m];
                g += pm[m] * green[m];
                b += pm[m] * blue[m];
            }
        //    DesImage[i][j] = pm[0] * SrcImage[ty][tx] + pm[1] * SrcImage[ty][tx+1] + pm[2] * SrcImage[ty+1][tx] + pm[3] * SrcImage[ty+1][tx+1];
        //    DesImage[i][j] = SrcImage[ty][tx];
            DesImage[i][j] = RGB(r,g,b);
        //    DesImage[i][j] =  (SrcImage[ty][tx]+SrcImage[ty][tx+1]+ SrcImage[ty+1][tx]+SrcImage[ty+1][tx+1])/4;
        }
    }
    
    LImage = DesImage;
}