图像放大快速算法实现的原理主要有以下两点：
1、横向缩放与纵向缩放分开，而先后顺序取决于缩放前后的图像比例：
若SrcHeight/DstWidth>SrcWidth/DstWidth,则先纵向缩放，否则横向缩放。
2、利用整数运算代替浮点运算，由于是分步缩放，以横向缩放为例，利用二次线性插值公式，再变形一下如下：
f(i,j+v) = (1-v)f(i,j) +vf(i,j+1);
其中i为第i行，j为第j列，v表示求得放大后坐标的小数部分。
这里最重要的并没有直接用小数运算，而是通过将小数区间（0,1）映射到整数区间（0,128），
再利用整数来代替小数运算，最后只需要相应的处理一下就可以了。
误差分析：
首先二次线性算法本来就有误差，这里主要讨论利用整数代替小数的误差，可以看到每一个整数能代替的小数范围为1/128,所以误差范围为[-1/256,1/256]之间。
代码实现：
//ImageScale.h
#define IN
#define OUT
#define _DWORD int
#define _BYTE byte
#define _WORD short
struct ImageInfo
{
byte* pRGBData;
int nHeight;
int nStepValue;
int nWidth;
// int nFlag;
ImageInfo()
{
pRGBData=NULL;
}
ImageInfo(byte *p,int h,int s,int w)
{
// pRGBData = (byte*)malloc(h*s);
pRGBData = p;
nHeight=h;
nStepValue=s;
nWidth=w;
}
};
class ImageScale
{
public:
ImageScale(void);
virtual ~ImageScale(void);
void Run(BYTE* pSrcImage, int nSrcWidth, int nSrcHeight, BYTE* pTagImage, int nTagWidth, int nTagHeight,int nChannels);
private:
bool DstInSrcIndex(int large_len, int little_len, int* a3_pIntValue, byte* a4_pByteValue);
int DoubleToInt(double d);
BOOL HorizontalFill(IN ImageInfo& SrcImageInfo, IN int nTagHeight, IN int nTagWidth, IN int nTagStepValue, IN int bFlag, IN int* pIntValue, IN byte* pByteValue, OUT ImageInfo& DstImageInfo,int nChannels);
BOOL VerticalFill(IN ImageInfo& SrcImageInfo, IN int nTagHeight, IN int nTagWidth, IN int nTagStepValue, IN int bFlag, IN int* pIntValue, IN byte* pByteValue, OUT ImageInfo& DstImageInfo,int nChannels);
void HorizontalScale(byte *a1_pData_Src, byte *a2_pData_Dst, int nHeight, int nWidth, int *a5_pData_Unknow, byte *a6_pData_Unknow, int srcStepValue, int dstStepValue, short *a10_pData_Unknow,int nChannels);
void VerticalScale(byte *a1_pData_Src, byte *a2_pData_Dst, int a3_nHeight, int a4_nWidth, int *a5_pData_Unknow, byte *a6_pData_Unknow, int a7_nWidth, int a8_nWidthScrible, short *a10_pData_Unknow,int nChannels);
};
#include "StdAfx.h"
#include "ImageScale.h"
short g_pHSDataByte[]=
{
0x4000, 0x0000, 0x3F80, 0x0080, 0x3F00, 0x0100, 0x3E80, 0x0180,
0x3E00, 0x0200, 0x3D80, 0x0280, 0x3D00, 0x0300, 0x3C80, 0x0380,
0x3C00, 0x0400, 0x3B80, 0x0480, 0x3B00, 0x0500, 0x3A80, 0x0580,
0x3A00, 0x0600, 0x3980, 0x0680, 0x3900, 0x0700, 0x3880, 0x0780,
0x3800, 0x0800, 0x3780, 0x0880, 0x3700, 0x0900, 0x3680, 0x0980,
0x3600, 0x0A00, 0x3580, 0x0A80, 0x3500, 0x0B00, 0x3480, 0x0B80,
0x3400, 0x0C00, 0x3380, 0x0C80, 0x3300, 0x0D00, 0x3280, 0x0D80,
0x3200, 0x0E00, 0x3180, 0x0E80, 0x3100, 0x0F00, 0x3080, 0x0F80,
0x3000, 0x1000, 0x2F80, 0x1080, 0x2F00, 0x1100, 0x2E80, 0x1180,
0x2E00, 0x1200, 0x2D80, 0x1280, 0x2D00, 0x1300, 0x2C80, 0x1380,
0x2C00, 0x1400, 0x2B80, 0x1480, 0x2B00, 0x1500, 0x2A80, 0x1580,
0x2A00, 0x1600, 0x2980, 0x1680, 0x2900, 0x1700, 0x2880, 0x1780,
0x2800, 0x1800, 0x2780, 0x1880, 0x2700, 0x1900, 0x2680, 0x1980,
0x2600, 0x1A00, 0x2580, 0x1A80, 0x2500, 0x1B00, 0x2480, 0x1B80,
0x2400, 0x1C00, 0x2380, 0x1C80, 0x2300, 0x1D00, 0x2280, 0x1D80,
0x2200, 0x1E00, 0x2180, 0x1E80, 0x2100, 0x1F00, 0x2080, 0x1F80,
0x2000, 0x2000, 0x1F80, 0x2080, 0x1F00, 0x2100, 0x1E80, 0x2180,
0x1E00, 0x2200, 0x1D80, 0x2280, 0x1D00, 0x2300, 0x1C80, 0x2380,
0x1C00, 0x2400, 0x1B80, 0x2480, 0x1B00, 0x2500, 0x1A80, 0x2580,
0x1A00, 0x2600, 0x1980, 0x2680, 0x1900, 0x2700, 0x1880, 0x2780,
0x1800, 0x2800, 0x1780, 0x2880, 0x1700, 0x2900, 0x1680, 0x2980,
0x1600, 0x2A00, 0x1580, 0x2A80, 0x1500, 0x2B00, 0x1480, 0x2B80,
0x1400, 0x2C00, 0x1380, 0x2C80, 0x1300, 0x2D00, 0x1280, 0x2D80,
0x1200, 0x2E00, 0x1180, 0x2E80, 0x1100, 0x2F00, 0x1080, 0x2F80,
0x1000, 0x3000, 0x0F80, 0x3080, 0x0F00, 0x3100, 0x0E80, 0x3180,
0x0E00, 0x3200, 0x0D80, 0x3280, 0x0D00, 0x3300, 0x0C80, 0x3380,
0x0C00, 0x3400, 0x0B80, 0x3480, 0x0B00, 0x3500, 0x0A80, 0x3580,
0x0A00, 0x3600, 0x0980, 0x3680, 0x0900, 0x3700, 0x0880, 0x3780,
0x0800, 0x3800, 0x0780, 0x3880, 0x0700, 0x3900, 0x0680, 0x3980,
0x0600, 0x3A00, 0x0580, 0x3A80, 0x0500, 0x3B00, 0x0480, 0x3B80,
0x0400, 0x3C00, 0x0380, 0x3C80, 0x0300, 0x3D00, 0x0280, 0x3D80,
0x0200, 0x3E00, 0x0180, 0x3E80, 0x0100, 0x3F00, 0x0080, 0x3F80,
0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000
};
ImageScale::ImageScale(void)
{
}
ImageScale::~ImageScale(void)
{
}
void ImageScale::Run(BYTE* pSrcImage, int nSrcWidth, int nSrcHeight, BYTE* pTagImage, int nTagWidth, int nTagHeight, int nChannels)
{
if (!(nChannels==1||nChannels==4))
return;
if(nSrcWidth<=0 || nSrcHeight<=0 )
return;
if(nTagWidth<nSrcWidth || nTagHeight<nSrcHeight)
return;
int nSrcStepValue=(nSrcWidth+15) & ~15;
int nTagStepValue=nTagWidth;
//申请四个内存空间
int* pIntValueTmp_nHeight = (int*)malloc(nTagHeight*sizeof(int));//存储纵坐标索引值
if (pIntValueTmp_nHeight)
{
memset(pIntValueTmp_nHeight, 0,nTagHeight*sizeof(int));
}
byte* pByteValueTmp_nHeight = (byte*)malloc(nTagHeight);//存储纵坐标下的小数映射到整数空间下的值
if (pByteValueTmp_nHeight)
{
memset(pByteValueTmp_nHeight, 0, nTagHeight);
}
int* pIntValueTmp_nWidth = (int*)malloc(nTagWidth*sizeof(int));//存储横坐标索引值
if (pIntValueTmp_nWidth)
{
memset(pIntValueTmp_nWidth, 0, nTagWidth*sizeof(int));
}
byte* pByteValueTmp_nWidth = (byte*)malloc(nTagWidth);//存储横坐标下的小数映射到整数空间下的值
if (pByteValueTmp_nWidth)
{
memset(pByteValueTmp_nWidth, 0, nTagWidth);
}
DstInSrcIndex(nTagWidth,nSrcWidth, pIntValueTmp_nWidth, pByteValueTmp_nWidth);
DstInSrcIndex(nTagHeight, nSrcHeight, pIntValueTmp_nHeight, pByteValueTmp_nHeight);
int nValueTmp1 = nSrcHeight * nTagWidth;
int nValueTmp2 = nSrcWidth * nTagHeight;
ImageInfo SrcImageInfo(pSrcImage,nSrcHeight,nSrcStepValue,nSrcWidth);
ImageInfo ImageInfo_Tmp1;
ImageInfo ImageInfo_Tmp2;
if (nValueTmp1 > nValueTmp2)
{
VerticalFill(SrcImageInfo, nTagHeight, nTagWidth, nTagStepValue, 0, pIntValueTmp_nHeight, pByteValueTmp_nHeight, ImageInfo_Tmp1,nChannels);
HorizontalFill(ImageInfo_Tmp1, nTagHeight, nTagWidth, nTagStepValue, 0, pIntValueTmp_nWidth , pByteValueTmp_nWidth, ImageInfo_Tmp2,nChannels);
}
else
{
HorizontalFill(SrcImageInfo, nTagHeight, nTagWidth, nTagStepValue, 1, pIntValueTmp_nWidth, pByteValueTmp_nWidth, ImageInfo_Tmp1,nChannels);
VerticalFill(ImageInfo_Tmp1, nTagHeight, nTagWidth, nTagStepValue, 1,pIntValueTmp_nHeight, pByteValueTmp_nHeight, ImageInfo_Tmp2,nChannels);
}
//pTagImage=(byte*)malloc(nTagHeight * nTagWidth);
for (int i=0; i<nTagHeight; i++)
{
memcpy(pTagImage +nChannels*i*nTagWidth, ImageInfo_Tmp2.pRGBData+ nChannels*i*nTagWidth, nChannels*nTagWidth);
}
//【释放堆内存】
if (pIntValueTmp_nHeight)
{
free(pIntValueTmp_nHeight);
pIntValueTmp_nHeight = NULL;
}
if (pByteValueTmp_nHeight)
{
free(pByteValueTmp_nHeight);
pByteValueTmp_nHeight = NULL;
}
if (pIntValueTmp_nWidth)
{
free(pIntValueTmp_nWidth);
pIntValueTmp_nWidth = NULL;
}
if (pByteValueTmp_nWidth)
{
free(pByteValueTmp_nWidth);
pByteValueTmp_nWidth = NULL;
}
if (ImageInfo_Tmp1.pRGBData)
{
free(ImageInfo_Tmp1.pRGBData);
ImageInfo_Tmp1.pRGBData = NULL;
}
if (ImageInfo_Tmp2.pRGBData)
{
free(ImageInfo_Tmp2.pRGBData);
ImageInfo_Tmp2.pRGBData = NULL;
}
}
bool ImageScale::DstInSrcIndex(int large_len, int little_len, int* a3_pIntValue, byte* a4_pByteValue)
{
int nValueTmp3 = (little_len << 7) - 128;
for (int index = 0; index<large_len; ++index)
{
float doubleValueTmp3 = ((float)index + 0.5) / ((float)large_len);
int nValueTmp4 = (int)(doubleValueTmp3 * (little_len - 0.5f) * 128.0+0.5f);
int nValueTmp1= nValueTmp3;
if(!(nValueTmp3<nValueTmp4))
nValueTmp1= nValueTmp4;
a3_pIntValue[index] = nValueTmp1 >> 7;
a4_pByteValue[index] = nValueTmp1 & 0x7F;
}
return true;
}
BOOL ImageScale::HorizontalFill(IN ImageInfo& SrcImageInfo, IN int nTagHeight, IN int nTagWidth, IN int nTagStepValue, IN int bFlag, IN int* pIntValue, IN byte* pByteValue, OUT ImageInfo& DstImageInfo,int nChannels)
{
int nHeightTmp1 = 0;
if (bFlag)
{
nHeightTmp1 = SrcImageInfo.nHeight;
}
else
{
nHeightTmp1 = nTagHeight;
}
//申请额外的空间保证内存对齐
int StepValueTmp=(SrcImageInfo.nStepValue+15) & ~15;
byte *pSrcImageTmp=(byte*)malloc(nChannels * StepValueTmp * nHeightTmp1);
memset(pSrcImageTmp,0,nChannels * StepValueTmp * nHeightTmp1);
int SumTmp1=nChannels * StepValueTmp,SumTmp2=nChannels * SrcImageInfo.nWidth;
for(int i=0;i<nHeightTmp1;i++)
{
memcpy(pSrcImageTmp+i*SumTmp1,SrcImageInfo.pRGBData+i*SumTmp2,SumTmp2);
}
// ImageInfo SrcImageInfo(pSrcImageTmp,SrcImageInfo.nHeight,StepValueTmp,SrcImageInfo.nWidth);
//调用HorizontalScale进行水平延伸，结果保存到DstImageInfo中
DstImageInfo.nHeight = nHeightTmp1;
DstImageInfo.nWidth = nTagWidth;
DstImageInfo.nStepValue = nTagStepValue;
DstImageInfo.pRGBData = (byte*)malloc(nChannels * DstImageInfo.nHeight * DstImageInfo.nStepValue);
byte* pDataSrc = SrcImageInfo.pRGBData;
byte* pDataDst = DstImageInfo.pRGBData;
HorizontalScale(pSrcImageTmp, pDataDst, DstImageInfo.nHeight, DstImageInfo.nWidth, pIntValue, pByteValue,
SrcImageInfo.nStepValue, DstImageInfo.nStepValue, g_pHSDataByte,nChannels);
if (pSrcImageTmp)
{
free(pSrcImageTmp);
pSrcImageTmp=NULL;
}
return TRUE;
}
BOOL ImageScale::VerticalFill(IN ImageInfo& SrcImageInfo, IN int nTagHeight, IN int nTagWidth, IN int nTagStepValue, IN int bFlag, IN int* pIntValue, IN byte* pByteValue, OUT ImageInfo& DstImageInfo,int nChannels)
{
int nWidthTmp1 = 0;
int nStepValueTmp1 = 0;
if (bFlag)
{
nWidthTmp1 = nTagWidth;
nStepValueTmp1 = nTagStepValue;
}
else
{
nWidthTmp1 = SrcImageInfo.nWidth;
nStepValueTmp1 = SrcImageInfo.nStepValue;
}
//申请额外的空间保证内存对齐
int StepValueTmp=(SrcImageInfo.nStepValue+15) & ~15;
byte *pSrcImageTmp=(byte*)malloc(nChannels * StepValueTmp *( SrcImageInfo.nHeight+1));// 多申请一层来保证内存不会泄露
memset(pSrcImageTmp,0,nChannels * StepValueTmp * (SrcImageInfo.nHeight+1));
int SumTmp1=nChannels * StepValueTmp,SumTmp2=nChannels * SrcImageInfo.nWidth,SumTmp3=nChannels * SrcImageInfo.nStepValue;
for(int i=0;i<SrcImageInfo.nHeight;i++)
{
memcpy(pSrcImageTmp+i*SumTmp1,SrcImageInfo.pRGBData+i*SumTmp3,SumTmp2);
}
// 最后一层用上一层填充
memcpy(pSrcImageTmp+SrcImageInfo.nHeight*SumTmp1,SrcImageInfo.pRGBData+(SrcImageInfo.nHeight-1)*SumTmp3,SumTmp2);
DstImageInfo.nHeight = nTagHeight;
DstImageInfo.nWidth = nWidthTmp1;
DstImageInfo.nStepValue = nStepValueTmp1;
DstImageInfo.pRGBData = (byte*)malloc( nChannels * DstImageInfo.nHeight*DstImageInfo.nStepValue);
memset(DstImageInfo.pRGBData, 0,nChannels * DstImageInfo.nHeight*DstImageInfo.nStepValue);
VerticalScale(pSrcImageTmp, DstImageInfo.pRGBData, DstImageInfo.nHeight, DstImageInfo.nWidth,
pIntValue, pByteValue, StepValueTmp, DstImageInfo.nStepValue, g_pHSDataByte,nChannels);
if (pSrcImageTmp)
{
free(pSrcImageTmp);
pSrcImageTmp=NULL;
}
return TRUE;
}
void ImageScale::HorizontalScale(byte *a1_pData_Src, byte *a2_pData_Dst, int nHeight, int nWidth, int *a5_pData_Unknow, byte *a6_pData_Unknow, int srcStepValue, int dstStepValue, short *a10_pData_Unknow,int nChannels)
{
int v17,v18,v19,v20;
int srcstep,dststep,index1,index2,index3;
if(nChannels==4)
{
srcstep=( dstStepValue<<2);
dststep=(srcStepValue<<2);
for (int i=0;i<nHeight;i++)
{
for(int j=0;j<nWidth;j++)
{
v17 = a5_pData_Unknow[j]; // 遍历，依次获得int表数据
v18 = ( a6_pData_Unknow[j]<<1);
index1=((v17+1)<<2);
index2=(v17<<2);
index3=(j<<2);
//blue通道
v19 = a1_pData_Src[index1+MT_BLUE] * a10_pData_Unknow[v18 + 1]; // 加上小数位的精度
v20 = (v19 + a10_pData_Unknow[v18] * a1_pData_Src[index2+MT_BLUE] + 0x2000) >> 14; //0x2000右移14位为0.5，这里是为了四舍五入；
a2_pData_Dst[index3+MT_BLUE] =v20&0xff;
//green通道
v19 = a1_pData_Src[index1+MT_GREEN] * a10_pData_Unknow[v18 + 1];
v20 = (v19 + a10_pData_Unknow[v18] * a1_pData_Src[index2+MT_GREEN] + 0x2000) >> 14;
a2_pData_Dst[index3+MT_GREEN] =v20&0xff;
//red通道
v19 = a1_pData_Src[index1+MT_RED] * a10_pData_Unknow[v18 + 1];
v20 = (v19 + a10_pData_Unknow[v18] * a1_pData_Src[index2+MT_RED] + 0x2000) >> 14;
a2_pData_Dst[index3+MT_RED] =v20&0xff;
a2_pData_Dst[index3+MT_ALPHA] =255;
}
a2_pData_Dst +=srcstep;
a1_pData_Src +=dststep ;
}
}
else
{
for (int i=0;i<nHeight;i++)
{
for(int j=0;j<nWidth;j++)
{
v17 = a5_pData_Unknow[j]; // 遍历，依次获得int表数据
v18 = ( a6_pData_Unknow[j]<<1);
v19 = a1_pData_Src[v17+1] * a10_pData_Unknow[v18 + 1]; // 加上小数位的精度
v20 = (v19 + a10_pData_Unknow[v18] * a1_pData_Src[v17] + 0x2000) >> 14; //0x2000右移14位为0.5，这里是为了四舍五入；
a2_pData_Dst[j] = v20&0xff;;
}
a2_pData_Dst += dstStepValue;
a1_pData_Src += srcStepValue;
}
}
}
void ImageScale::VerticalScale(byte *a1_pData_Src, byte *a2_pData_Dst, int a3_nHeight, int a4_nWidth, int *a5_pData_Unknow, byte *a6_pData_Unknow, int a7_nWidth, int a8_nWidthScrible, short *a10_pData_Unknow,int nChannels)
{
byte * pbTmp1;
int nTmp2,nTmp3,nTmp4;
int step,index1,index2,index3;
if(nChannels==4)
{
step=(a8_nWidthScrible<<2);
index1=nChannels*a7_nWidth;
for (int i=0;i<a3_nHeight;i++)
{
pbTmp1= &a1_pData_Src[index1*a5_pData_Unknow[i]];
nTmp2 = a10_pData_Unknow[a6_pData_Unknow[i]<<1];
nTmp3 = a10_pData_Unknow[(a6_pData_Unknow[i]<<1) + 1];
for (int j=0;j<a4_nWidth;j++)
{
index2=((a7_nWidth+j)<<2);
index3=(j<<2);
//blue通道
nTmp4 = (nTmp3 * pbTmp1[index2+MT_BLUE] +nTmp2 * pbTmp1[index3+MT_BLUE] + 0x2000)>>14;
a2_pData_Dst[index3+MT_BLUE] = nTmp4&0xff;
//green通道
nTmp4 = (nTmp3 * pbTmp1[index2+MT_GREEN] +nTmp2 * pbTmp1[index3+MT_GREEN] + 0x2000)>>14;
a2_pData_Dst[index3+MT_GREEN] = nTmp4&0xff;
//red通道
nTmp4 = (nTmp3 * pbTmp1[index2+MT_RED] +nTmp2 * pbTmp1[index3+MT_RED] + 0x2000)>>14;
a2_pData_Dst[index3+MT_RED] = nTmp4&0xff;
a2_pData_Dst[index3+MT_ALPHA] = 255;
}
a2_pData_Dst += step;
}
}
else
{
for (int i=0;i<a3_nHeight;i++)
{
pbTmp1= &a1_pData_Src[a7_nWidth*a5_pData_Unknow[i]];
nTmp2 = a10_pData_Unknow[a6_pData_Unknow[i]<<1];
nTmp3 = a10_pData_Unknow[(a6_pData_Unknow[i]<<1) + 1];
for (int j=0;j<a4_nWidth;j++)
{
nTmp4 = (nTmp3 * pbTmp1[a7_nWidth+j] +nTmp2 * pbTmp1[j] + 0x2000)>>14;
a2_pData_Dst[j] = nTmp4&0xff;
}
a2_pData_Dst += a8_nWidthScrible;
}
}
}
原文地址：http://blog.csdn.net/alop_daoyan/article/details/41750761
