一般都使用插值算法:有近邻取样法,双线形内插法,三次卷积法等。下面是摘自《visual c++ 数字图像与图形处理》的核心代码: ///lpbySrcXY----传递源像素(x, y)的地址, //x, y, 经过反向变换后得到的对应于原图像的象点的坐标 //nScanWidth, int nScanHeight, 源扫描宽度和扫描高度 PIXELCOLORRGB CImageGeometry::Interpolate(LPBYTE lpbySrcXY, int x, int y, float fu, float fv, int nScanWidth, int nScanHeight) { PIXELCOLORRGB rgb; //行字节数, 可以将dwWidthBytes作为参数传递过来 DWORD dwWidthBytes = (DWORD)nScanWidth * 4;
switch(m_dwQuality) { case IMAGE_GEOMETRY_NEAREST_NEIGHBOR_INTERPOLATE : { BYTE* pbySrc = lpbySrcXY; rgb.blue = *pbySrc++; rgb.green = *pbySrc++; rgb.red = *pbySrc++; break; } case IMAGE_GEOMETRY_BILINEAR_INTERPOLATE : { //相邻的四个像素最右下角点的x, y坐标偏移量 int nx = 1; int ny = 1; if((x + 1) > (nScanWidth - 1)) nx = 0; if((y + 1) > (nScanHeight - 1)) ny = 0;
StretchBlt使用的是邻近插值.插值分为:邻近插值
双线性插值
卷积查值
二元三点插值
二元全区间插值效果是越来越好,但是计算量是越来越大.
举其中的一个例子来说:
双线性插值+ +
-
+ +
将一个图像放大如1.1倍,肯定会出现一些点的坐标不是整数值.目标图像的点和原图像的点也没有一一对应的关系,一般是将放大后的图像坐标除以1.1倍,映射到原来图像里,它不是整数坐标,好象上面那个-号在四个+号中间,考虑这个减号受其它四个象素的影响.越近的影响越大.图像有两个方向,故这种方法叫双线性插值.
效果最不好的一种方法BYTE* Zoom( BYTE* pBmpFile , float times , int flag )
{
//get info
int nWidth , nHeight , nNewWidth , nNewHeight , nNewWidthBit , nWidthBit;
GetInfo( pBmpFile , &nWidth , &nHeight );
nNewHeight = (int) (nHeight * times);
nNewWidth = (int) (nWidth * times);
nNewWidthBit = ( 4 - nNewWidth * 3 % 4 ) % 4 + nNewWidth * 3;
nWidthBit = ( 4 - nWidth * 3 % 4 ) % 4 + nWidth * 3;
//excute new size
int nNewSize = nNewWidthBit * nNewHeight + 54;
//apply memory
BYTE* pNewBmpFile=NULL;
pNewBmpFile = new BYTE [ nNewSize ];
memset( pNewBmpFile , 0 , nNewSize);
//create bmp
pNewBmpFile = CreateBmp( nNewWidth , nNewHeight , pNewBmpFile );//rewirte bmpdata
BYTE *pBuf = NULL;
BYTE *pNewBuf = NULL;
BYTE *pNewTmp = NULL;
pBuf = &pBmpFile[54];
pNewBuf = &pNewBmpFile[54];
//zoom
for( int i = 0 ; i < nNewHeight ; i++ )
{
pNewTmp = pNewBuf + nNewWidthBit * i;
for( int j = 0 ; j < nNewWidth * 3 ; j += 3 )
{
int offset = i * nNewWidthBit + j;
CPoint point = OffsettoPixel( offset , nNewWidth , nNewHeight );
CPoint oldpoint;
oldpoint.x = (int) (point.x / times);
oldpoint.y = (int) (point.y / times);
int oldoffset = PixeltoOffset( oldpoint , nWidthBit , nHeight );
pNewTmp[j] = pBuf [oldoffset];
pNewTmp[j+1] = pBuf [oldoffset+1];
pNewTmp[j+2] = pBuf [oldoffset+2];
}
}
CloseBmp( pBmpFile );
return pNewBmpFile;
}
CBitmap m_bitmap;CDC*pDC=new CDC;
pDC->SelectObject(&m_bitmap);
m_bitmap.loadbitmap(IDB_BITMAP1);
pDC->BitStretch(NULL,0,0,x,y,pDC,xx,yy,0,0);
设置参数就可以
自己找点资料好简单的
///lpbySrcXY----传递源像素(x, y)的地址,
//x, y, 经过反向变换后得到的对应于原图像的象点的坐标
//nScanWidth, int nScanHeight, 源扫描宽度和扫描高度
PIXELCOLORRGB CImageGeometry::Interpolate(LPBYTE lpbySrcXY, int x, int y, float fu, float fv, int nScanWidth, int nScanHeight)
{
PIXELCOLORRGB rgb; //行字节数, 可以将dwWidthBytes作为参数传递过来
DWORD dwWidthBytes = (DWORD)nScanWidth * 4;
switch(m_dwQuality)
{
case IMAGE_GEOMETRY_NEAREST_NEIGHBOR_INTERPOLATE :
{
BYTE* pbySrc = lpbySrcXY;
rgb.blue = *pbySrc++;
rgb.green = *pbySrc++;
rgb.red = *pbySrc++;
break;
}
case IMAGE_GEOMETRY_BILINEAR_INTERPOLATE :
{
//相邻的四个像素最右下角点的x, y坐标偏移量
int nx = 1;
int ny = 1;
if((x + 1) > (nScanWidth - 1)) nx = 0;
if((y + 1) > (nScanHeight - 1)) ny = 0;
//相邻四个像素的像素值
BYTE abyRed[2][2], abyGreen[2][2], abyBlue[2][2];
//像素点(x, y)的数据位置
BYTE* pbySrc = lpbySrcXY;
//获取像素数值.
//(x, y) = (x, y) + (0, 0)
abyBlue[0][0] = *pbySrc++;
abyGreen[0][0] = *pbySrc++;
abyRed[0][0] = *pbySrc++;
//(x + 1, y) = (x, y) + (1, 0)
pbySrc = (lpbySrcXY + nx * 4);
abyBlue[1][0] = *pbySrc++;
abyGreen[1][0] = *pbySrc++;
abyRed[1][0] = *pbySrc++;
//指向下一行数据
BYTE* pbySrcTemp = (lpbySrcXY + ny * dwWidthBytes); //(x , y + 1) = (x, y) + (0, 1)
pbySrc = pbySrcTemp;
abyBlue[0][1] = *pbySrc++;
abyGreen[0][1] = *pbySrc++;
abyRed[0][1] = *pbySrc++; //(x + 1, y + 1) = (x, y) + (1, 1)
pbySrc = pbySrcTemp + (4 * nx);
abyBlue[1][1] = *pbySrc++;
abyGreen[1][1] = *pbySrc++;
abyRed[1][1] = *pbySrc++;
rgb.red = (BYTE)(BOUND(((1 - fu) * (1 - fv) * ((float)abyRed[0][0]) +
(1 - fu) * fv * ((float)abyRed[0][1]) +
fu * (1 - fv) * ((float)abyRed[1][0]) +
fu * fv * ((float)abyRed[1][1])), 0, 255));
rgb.green = (BYTE)(BOUND(((1 - fu) * (1 - fv) * ((float)abyGreen[0][0]) +
(1 - fu) * fv * ((float)abyGreen[0][1]) +
fu * (1 - fv) * ((float)abyGreen[1][0]) +
fu * fv * ((float)abyGreen[1][1])), 0, 255)); rgb.blue = (BYTE)(BOUND(((1 - fu) * (1 - fv) * ((float)abyBlue[0][0]) +
(1 - fu) * fv * ((float)abyBlue[0][1]) +
fu * (1 - fv) * ((float)abyBlue[1][0]) +
fu * fv * ((float)abyBlue[1][1])), 0, 255));
break;
}
case IMAGE_GEOMETRY_THREE_ORDER_INTERPOLATE :
{
//像素坐标
int xx[4], yy[4];
//相邻四个像素的像素值
BYTE abyRed[4][4], abyGreen[4][4], abyBlue[4][4]; xx[0] = -1; xx[1] = 0; xx[2] = 1; xx[3] = 2;
yy[0] = -1; yy[1] = 0; yy[2] = 1; yy[3] = 2; //保证合法
if((x - 1) < 0) xx[0] = 0;
if((x + 1) > (nScanWidth - 1)) xx[2] = 0;
if((x + 2) > (nScanWidth - 1)) xx[3] = ((xx[2] == 0) ? 0 : 1); if((y - 1) < 0) yy[0] = 0;
if((y + 1) > (nScanHeight - 1)) yy[2] = 0;
if((y + 2) > (nScanHeight - 1)) yy[3] = ((yy[2] == 0) ? 0 : 1); //像素点(x, y)的数据位置
//获取数据
int i;
for(i = 0;i < 4;i++)
{
//像素点(x, y)的数据位置
BYTE* pbySrcBase = lpbySrcXY + yy[i] * dwWidthBytes; for(int j = 0;j < 4;j++)
{
BYTE* pbySrc = pbySrcBase + 4 * xx[j];
abyBlue[i][j] = *pbySrc++;
abyGreen[i][j] = *pbySrc++;
abyRed[i][j] = *pbySrc++;
}
} //u, v向量
float afu[4], afv[4]; afu[0] = Sinxx(1.0f + fu);
afu[1] = Sinxx(fu);
afu[2] = Sinxx(1.0f - fu);
afu[3] = Sinxx(2.0f - fu); afv[0] = Sinxx(1.0f + fv);
afv[1] = Sinxx(fv);
afv[2] = Sinxx(1.0f - fv);
afv[3] = Sinxx(2.0f - fv); //矩阵乘向量的中间值
float afRed[4] = {0.0f, 0.0f, 0.0f, 0.0f};
float afGreen[4] = {0.0f, 0.0f, 0.0f, 0.0f};
float afBlue[4] = {0.0f, 0.0f, 0.0f, 0.0f}; for(i = 0;i < 4;i++)
{
for(int j = 0;j < 4;j++)
{
afRed[i] += afv[j] * abyRed[j][i];
afGreen[i] += afv[j] * abyGreen[j][i];
afBlue[i] += afv[j] * abyBlue[j][i];
}
}
rgb.red = (BYTE)(BOUND((afu[0] * afRed[0] + afu[1] * afRed[1] + afu[2] * afRed[2] +
afu[3] * afRed[3]), 0, 255));
rgb.green = (BYTE)(BOUND((afu[0] * afGreen[0] + afu[1] * afGreen[1] + afu[2] * afGreen[2] +
afu[3] * afGreen[3]), 0, 255));
rgb.blue = (BYTE)(BOUND((afu[0] * afBlue[0] + afu[1] * afBlue[1] + afu[2] * afBlue[2] +
afu[3] * afBlue[3]), 0, 255));
break;
}
default : break;
}//end switch return rgb;
}楼主领会思路即可,希望有所帮助。Good luck.