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图像的双线性插值放大算法中，目标图像中新创造的象素值，是由源图像位置在它附近的2*2区域4个邻近象素的值通过加权平均计算得出的。双线性内插值算法放大后的图像质量较高，不会出现像素值不连续的的情况。然而次算法具有低通滤波器的性质，使高频分量受损，所以可能会使图像轮廓在一定程度上变得模糊。

算法中Q12, Q22, Q11, Q21的选取

我们以放大两倍为例，说明选取Q12, Q22, Q11, Q21的过程。源图像3*3区域放大为目标区域6*6区域。设以下为目标图像：

目标图像A像素区域对应的Q21，Q22，Q11，Q12，以红色区域为原点向右下方扩展的2*2区域。

目标图像B像素区域对应的Q21，Q22，Q11，Q12，以蓝色区域为原点向右下方扩展的2*2区域。

目标图像C像素区域对应的Q21，Q22，Q11，Q12，以绿色区域为原点向右下方扩展的2*2区域。

目标图像D像素区域对应的Q21，Q22，Q11，Q12，目标图像处于最后两行的边界情况，将Q21，Q22，Q11，Q12这四个点的值设为一样。

程序流程图

流程图右边虚线框中为相关过程的注解。

源码：

void ResizeImage(<br /> unsigned char *InImage, // Source image data<br /> unsigned char *OutImage, // Destination image data<br /> unsigned int SWidth, // Source image width<br /> unsigned int SHeight, // Source image height<br /> unsigned int DWidth, // Destination rectangle width<br /> unsigned int DHeight, // Destination rectangle height<br /> unsigned int dstWholeWidth, // Destination image width<br /> unsigned int dstWholeHeight // Destination image height<br /> )<br /> {<br /> unsigned int PtAR = 0, PtBR = 0, PtCR = 0, PtDR = 0, PixelValueR = 0;<br /> unsigned int PtAG = 0, PtBG = 0, PtCG = 0, PtDG = 0, PixelValueG = 0;<br /> unsigned int PtAB = 0, PtBB = 0, PtCB = 0, PtDB = 0, PixelValueB = 0;<br /> register unsigned SpixelColNum = 0, SpixelRowNum = 0, DestCol = 0, DestRow = 0;<br /> unsigned int SpixelColAddr = 0, SpixelRowAddr = 0;<br /> unsigned int ColDelta = 0, RowDelta = 0, scaleV = 0, scaleH = 0;<br /> unsigned int ContribAandBR = 0, ContribCandDR = 0;<br /> unsigned int ContribAandBG = 0, ContribCandDG = 0;<br /> unsigned int ContribAandBB = 0, ContribCandDB = 0;<br /> unsigned int ContribTem[4096 * 3];// max size of image is 4096<br /> int i = 0;<br /> unsigned int FromLeftX = dstWholeWidth / 4, FromTopY = dstWholeHeight / 8 + DWidth / 8;</p> <p> scaleH = (SWidth << 8) / DWidth;<br /> scaleV = (SHeight << 8) / DHeight;</p> <p> // First line<br /> for (DestCol = 0; DestCol < DWidth; DestCol++)<br /> {<br /> SpixelColAddr = DestCol * scaleH;<br /> ColDelta = SpixelColAddr & 255;<br /> SpixelColNum = (SpixelColAddr - ColDelta) >> 8;</p> <p> PtAB = InImage[3 * SpixelRowNum * SWidth + 3 * SpixelColNum];<br /> PtAG = InImage[3 * SpixelRowNum * SWidth + 3 * SpixelColNum + 1];<br /> PtAR = InImage[3 * SpixelRowNum * SWidth + 3 * SpixelColNum + 2];</p> <p> if ((SpixelColNum + 1) < SWidth)<br /> {<br /> PtBB = InImage[3 * SpixelRowNum * SWidth + 3 * (SpixelColNum + 1)];<br /> PtBG = InImage[3 * SpixelRowNum * SWidth + 3 * (SpixelColNum + 1) + 1];<br /> PtBR = InImage[3 * SpixelRowNum * SWidth + 3 * (SpixelColNum + 1) + 2];</p> <p> PtCB = InImage[3 * (SpixelRowNum + 1) * SWidth + 3 * SpixelColNum];<br /> PtCG = InImage[3 * (SpixelRowNum + 1) * SWidth + 3 * SpixelColNum + 1];<br /> PtCR = InImage[3 * (SpixelRowNum + 1) * SWidth + 3 * SpixelColNum + 2];</p> <p> PtDB = InImage[3 * (SpixelRowNum + 1) * SWidth + 3 * (SpixelColNum + 1)];<br /> PtDG = InImage[3 * (SpixelRowNum + 1) * SWidth + 3 * (SpixelColNum + 1) + 1];<br /> PtDR = InImage[3 * (SpixelRowNum + 1) * SWidth + 3 * (SpixelColNum + 1) + 2];<br /> }<br /> else<br /> {<br /> PtBB = PtCB = PtDB = PtAB;<br /> PtBG = PtCG = PtDG = PtAG;<br /> PtBR = PtCR = PtDR = PtAR;<br /> }<br /> ContribAandBB = ColDelta * (PtBB - PtAB) + (PtAB << 8);<br /> ContribCandDB = ColDelta * (PtDB - PtCB) + (PtCB << 8);<br /> ContribTem[i++] = ContribCandDB;<br /> PixelValueB = ((ContribAandBB << 8) + (ContribCandDB - ContribAandBB) * RowDelta) >> 16;</p> <p> ContribAandBG = ColDelta * (PtBG - PtAG) + (PtAG << 8);<br /> ContribCandDG = ColDelta * (PtDG - PtCG) + (PtCG << 8);<br /> ContribTem[i++] = ContribCandDG;<br /> PixelValueG = ((ContribAandBG << 8) + (ContribCandDG - ContribAandBG) * RowDelta) >> 16;</p> <p> ContribAandBR = ColDelta * (PtBR - PtAR) + (PtAR << 8);<br /> ContribCandDR = ColDelta * (PtDR - PtCR) + (PtCR << 8);<br /> ContribTem[i++] = ContribCandDR;<br /> PixelValueR = ((ContribAandBR << 8) + (ContribCandDR - ContribAandBR) * RowDelta) >> 16;</p> <p> OutImage[3 * (DestRow + FromTopY) * dstWholeWidth + 3 * (DestCol + FromLeftX)] = PixelValueB;<br /> OutImage[3 * (DestRow + FromTopY) * dstWholeWidth + 3 * (DestCol + FromLeftX) + 1] = PixelValueG;<br /> OutImage[3 * (DestRow + FromTopY) * dstWholeWidth + 3 * (DestCol + FromLeftX) + 2] = PixelValueR;<br /> }<br /> // Other line<br /> for (DestRow = 1; DestRow < DHeight; DestRow++)<br /> {<br /> i = 0;<br /> SpixelRowAddr = DestRow * scaleV;<br /> RowDelta = SpixelRowAddr & 255;<br /> SpixelRowNum = (SpixelRowAddr - RowDelta) >> 8;</p> <p> for (DestCol = 0; DestCol < DWidth; DestCol++)<br /> {<br /> SpixelColAddr = DestCol * scaleH;<br /> ColDelta = SpixelColAddr & 255;<br /> SpixelColNum = (SpixelColAddr - ColDelta) >> 8;</p> <p> PtAB = InImage[3 * SpixelRowNum * SWidth + 3 * SpixelColNum];<br /> PtAG = InImage[3 * SpixelRowNum * SWidth + 3 * SpixelColNum + 1];<br /> PtAR = InImage[3 * SpixelRowNum * SWidth + 3 * SpixelColNum + 2];</p> <p> if (((SpixelColNum + 1) < SWidth) && ((SpixelRowNum + 1) < SHeight))<br /> {<br /> PtCB = InImage[3 * (SpixelRowNum + 1) * SWidth + 3 * SpixelColNum];<br /> PtCG = InImage[3 * (SpixelRowNum + 1) * SWidth + 3 * SpixelColNum + 1];<br /> PtCR = InImage[3 * (SpixelRowNum + 1) * SWidth + 3 * SpixelColNum + 2];</p> <p> PtDB = InImage[3 * (SpixelRowNum + 1) * SWidth + 3 * (SpixelColNum + 1)];<br /> PtDG = InImage[3 * (SpixelRowNum + 1) * SWidth + 3 * (SpixelColNum + 1) + 1];<br /> PtDR = InImage[3 * (SpixelRowNum + 1) * SWidth + 3 * (SpixelColNum + 1) + 2];<br /> }<br /> else<br /> {<br /> PtBB = PtCB = PtDB = PtAB;<br /> PtBG = PtCG = PtDG = PtAG;<br /> PtBR = PtCR = PtDR = PtAR;<br /> }</p> <p> ContribAandBB = ContribTem[i];<br /> ContribCandDB = ColDelta * (PtDB - PtCB) + (PtCB << 8);<br /> ContribTem[i++] = ContribCandDB;<br /> PixelValueB = ((ContribAandBB << 8) + (ContribCandDB - ContribAandBB) * RowDelta) >> 16;</p> <p> ContribAandBG = ContribTem[i];<br /> ContribCandDG = ColDelta * (PtDG - PtCG) + (PtCG << 8);<br /> ContribTem[i++] = ContribCandDG;<br /> PixelValueG = ((ContribAandBG << 8) + (ContribCandDG - ContribAandBG) * RowDelta) >> 16;</p> <p> ContribAandBR = ContribTem[i];<br /> ContribCandDR = ColDelta * (PtDR - PtCR) + (PtCR << 8);<br /> ContribTem[i++] = ContribCandDR;<br /> PixelValueR = ((ContribAandBR << 8) + (ContribCandDR - ContribAandBR) * RowDelta) >> 16; 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