C++图片缩放处理代码

///////////////////////////////////缩放图像
static void _ieInterpImageBilinear8UC1_Ver3_RowFilter(unsigned char* src,long* dst,int len,int* leftIdx,int* rightIdx,long* weight,int shift)
{
    int i;
    for(i = 0; i < len - 4; i+=4) {
        *dst++ = ((1<<shift) - weight[i])*src[leftIdx[i]] + weight[i]*src[rightIdx[i]];
        *dst++ = ((1<<shift) - weight[i+1])*src[leftIdx[i+1]] + weight[i+1]*src[rightIdx[i+1]];
        *dst++ = ((1<<shift) - weight[i+2])*src[leftIdx[i+2]] + weight[i+2]*src[rightIdx[i+2]];
        *dst++ = ((1<<shift) - weight[i+3])*src[leftIdx[i+3]] + weight[i+3]*src[rightIdx[i+3]];
  
    }
    for( ; i < len; ++i) {
        *dst++ = ((1<<shift) - weight[i])*src[leftIdx[i]] + weight[i]*src[rightIdx[i]];
    }
}
#define IET_MAX(x,y) (x)>(y)?(x):(y)
#define IET_MIN(x,y) (x)>(y)?(y):(x)
#define IET_SWAP(x,y,tmp) (tmp)=(x);(x)=(y);(y)=(tmp);
static void ResizeImage(unsigned char* pSrc,int src_w,int src_h,unsigned char* pDst,int dst_w,int dst_h)
{
    int i,j;
    int sw,sh,sstep;
    int dw,dh,dstep;
    unsigned char *sdata,*ddata;
    float horScaleRatio,verScaleRatio;
    long *rowBuf1,*rowBuf2;
    long *upLinePtr,*downLinePtr,*tempPtr;
    long *horWeight;
    int *horLeftIdx,*horRightIdx;
    int preVerUpIdx,preVerDownIdx;
    int shift = 8;
  
    sw=src_w;
    sh=src_h;
    sstep=24;
    sdata=pSrc;
    dw=dst_w;
    dh=dst_h;
    dstep=24;
    ddata=pDst;
  
    horScaleRatio = sw / (float)(dw);
    verScaleRatio = sh / (float)(dh);
  
    rowBuf1 = new long[dw];
    rowBuf2 = new long[dw];
    horWeight = new long[dw];
    horLeftIdx = new int[dw];
    horRightIdx = new int[dw];
  
  
    //col interpolation
  
    //计算目标图像像素横向的左右邻居序号，和权重。
    for(i = 0; i < dw; i++) {
        float pos = (i + 0.5f) * horScaleRatio;
        horLeftIdx[i] = (int)(IET_MAX(pos - 0.5f,0));
        horRightIdx[i] = (int)(IET_MIN(pos + 0.5f,sw-1));
        horWeight[i] = (long) (fabs(pos - 0.5f - horLeftIdx[i]) * (1<<shift));
    }
  
    preVerUpIdx = -1;
    preVerDownIdx = -1;
    upLinePtr = rowBuf1;
    downLinePtr = rowBuf2;
    for(j = 0; j < dh; j++) {
        float pos = (j + 0.5f) * verScaleRatio;
        int verUpIdx = (int)(IET_MAX(pos - 0.5f,0));
        int verDownIdx = (int)(IET_MIN(pos + 0.5f,sh-1));
        long verWeight = (long) (fabs(pos - 0.5f - verUpIdx) * (1<<shift));
  
        if(verUpIdx == preVerUpIdx && verDownIdx == preVerDownIdx) {
            ;
            //do nothing
        } else if(verUpIdx == preVerDownIdx) {
            IET_SWAP(upLinePtr,downLinePtr,tempPtr);
            _ieInterpImageBilinear8UC1_Ver3_RowFilter(sdata + sstep*verDownIdx,dw,horLeftIdx,horRightIdx,horWeight,shift);
        } else {
            _ieInterpImageBilinear8UC1_Ver3_RowFilter(sdata + sstep*verUpIdx,upLinePtr,shift);
            _ieInterpImageBilinear8UC1_Ver3_RowFilter(sdata + sstep*verDownIdx,shift);
        }
  
        unsigned char* _ptr = ddata + dstep*j;
        for(i = 0; i < dw-4; i+=4) {
            *_ptr++ = (unsigned char) ( (((1<<shift) - verWeight)*upLinePtr[i] + verWeight*downLinePtr[i]) >> (2*shift) );
            *_ptr++ = (unsigned char) ( (((1<<shift) - verWeight)*upLinePtr[i+1] + verWeight*downLinePtr[i+1]) >> (2*shift) );
            *_ptr++ = (unsigned char) ( (((1<<shift) - verWeight)*upLinePtr[i+2] + verWeight*downLinePtr[i+2]) >> (2*shift) );
            *_ptr++ = (unsigned char) ( (((1<<shift) - verWeight)*upLinePtr[i+3] + verWeight*downLinePtr[i+3]) >> (2*shift) );
        }
        for(; i < dw; i++) {
            *_ptr++ = (unsigned char) ( (((1<<shift) - verWeight)*upLinePtr[i] + verWeight*downLinePtr[i]) >> (2*shift) );
        }
        preVerUpIdx = verUpIdx;
        preVerDownIdx = verDownIdx;
    }
    delete []rowBuf1;
    delete []rowBuf2;
    delete []horWeight;
    delete []horLeftIdx;
    delete []horRightIdx;
}