图像缩放算法

缩放原理和公式图示:

缩放后图片 原图片
(宽DW,高DH) (宽SW,高SH)
(Sx-0)/(SW-0)=(Dx-0)/(DW-0) (Sy-0)/(SH-0)=(Dy-0)/(DH-0)
=> Sx=Dx*SW/DW Sy=Dy*SH/DH
每一行的缩放比例是固定的;那么可以预先建立一个缩放映射表格。先将x的值放在一个数组中。
有缩放函数如下：

int PicZoom(PT_PixelDatas ptOriginPic, PT_PixelDatas ptZoomPic)
{
    unsigned long dwDstWidth = ptZoomPic->iWidth;
    unsigned long* pdwSrcXTable = malloc(sizeof(unsigned long) * dwDstWidth);
    unsigned long x;
    unsigned long y;
    unsigned long dwSrcY;
    unsigned char *pucDest;
    unsigned char *pucSrc;
    unsigned long dwPixelBytes = ptOriginPic->iBpp/8;

    if (ptOriginPic->iBpp != ptZoomPic->iBpp)
    {
        return -1;
    }

    for (x = 0; x < dwDstWidth; x++)//生成表 pdwSrcXTable
    {
        pdwSrcXTable[x]=(x*ptOriginPic->iWidth/ptZoomPic->iWidth);
        // ptOriginPic->iWidth和ptZoomPic->iWidth分别表示原来和放大后的行像素
    }

    for (y = 0; y < ptZoomPic->iHeight; y++)
    {           
        dwSrcY = (y * ptOriginPic->iHeight / ptZoomPic->iHeight);

        pucDest = ptZoomPic->aucPixelDatas + y*ptZoomPic->iLineBytes;// iLineBytes表示每一行像素所占据的字节，其实iLineBytes=iWidth * ptPixelDatas->iBpp / 8
        pucSrc  = ptOriginPic->aucPixelDatas + dwSrcY*ptOriginPic->iLineBytes;

        for (x = 0; x <dwDstWidth; x++)
        {
            /* 原图座标: pdwSrcXTable[x]，srcy
             * 缩放座标: x, y
             */
             memcpy(pucDest+x*dwPixelBytes, pucSrc+pdwSrcXTable[x]*dwPixelBytes, dwPixelBytes);
        }
    }
    free(pdwSrcXTable);
    return 0;
}