分类: WINDOWS
2013-11-20 17:23:38
工作需要,要弄截图且缩小。截图倒是好说,WIN API可以搞定,但是缩小且尽量不失真,这个对我来说难度太大了吧。这里主要说说缩小的算法。我从网上找到两个算法分别是bilinear和nearest。但是效果看上去太差了。我先贴上处理后的三种算法效果图,然后再贴算法。
bilinear
nearest
cubic
当然大家可以看的出来,效果最好的自然是Cubic,提供一些该算法的资料,不过我自己是没看懂。cubic是我们公司多媒体方面的牛人帮我写的。
以下是代码:
- #include "stdafx.h"
- #include <stdio.h>
- #include <string>
- #include <windows.h>
- #include <math.h>
- using namespace std;
- enum StretchMode
- {
- nearest, //最临近插值算法
- bilinear, //双线性内插值算法
- cubic
- };
- const int CUBIC_SIZE = 3;
- int getSincVec(float *pfVec, float fPos, float fScale)
- {
- int nPos = (int)fPos;
- fPos -= (float)nPos;
- memset(pfVec, 0, sizeof(float) * CUBIC_SIZE);
- float fSum = 0.f;
- for (int i=0; i<CUBIC_SIZE; i++)
- {
- float fTmp = (i - 1.f + fPos) * 3.14159265358979323846f;
- if (fTmp > 0.00001 || fTmp < -0.00001)
- {
- pfVec[i] = sinf(fTmp * fScale) / fTmp;
- }
- else
- {
- pfVec[i] = 1.f;
- }
- fSum += pfVec[i];
- }
- fSum = 1.f / fSum;
- for (int i=0; i<CUBIC_SIZE; i++)
- {
- pfVec[i] *= fSum;
- }
- return nPos;
- }
- void calcSincMat(float *pfMat, float *pfVecY, float *pfVecX)
- {
- for (int i=0; i<CUBIC_SIZE; i++)
- {
- for (int j=0; j<CUBIC_SIZE; j++)
- {
- pfMat[i * CUBIC_SIZE + j] = pfVecY[i] * pfVecX[j];
- }
- }
- }
- void Stretch(const string& srcFile,const string& desFile,int desW,int desH,StretchMode mode)
- {
- BITMAPFILEHEADER bmfHeader;
- BITMAPINFOHEADER bmiHeader;
- FILE *pFile;
- if ((pFile = fopen(srcFile.c_str(),"rb")) == NULL)
- {
- printf("open bmp file error.");
- exit(-1);
- }
- //读取文件和Bitmap头信息
- fseek(pFile,0,SEEK_SET);
- fread(&bmfHeader,sizeof(BITMAPFILEHEADER),1,pFile);
- fread(&bmiHeader,sizeof(BITMAPINFOHEADER),1,pFile);
- //先不支持小于16位的位图
- int bitCount = bmiHeader.biBitCount;
- if (bitCount < 16)
- {
- exit(-1);
- }
- int srcW = bmiHeader.biWidth;
- int srcH = bmiHeader.biHeight;
- int lineSize = bitCount * srcW / 8;
- //偏移量,windows系统要求每个扫描行按四字节对齐
- int alignBytes = ((bmiHeader.biWidth * bitCount + 31) & ~31) / 8L
- - bmiHeader.biWidth * bitCount / 8L;
- //原图像缓存
- int srcBufSize = lineSize * srcH;
- BYTE* srcBuf = new BYTE[srcBufSize];
- int i,j;
- //读取文件中数据
- for (i = 0; i < srcH; i++)
- {
- fread(&srcBuf[lineSize * i],lineSize,1,pFile);
- fseek(pFile,alignBytes,SEEK_CUR);
- }
- //目标图像缓存
- int desBufSize = ((desW * bitCount + 31) / 32) * 4 * desH;
- int desLineSize = ((desW * bitCount + 31) / 32) * 4;
- BYTE *desBuf = new BYTE[desBufSize];
- double rateH = (double)srcH / desH;
- double rateW = (double)srcW / desW;
- //最临近插值算法
- if (mode == nearest)
- {
- for (i = 0; i < desH; i++)
- {
- //选取最邻近的点
- int tSrcH = (int)(rateH * i + 0.5);
- for (j = 0; j < desW; j++)
- {
- int tSrcW = (int)(rateW * j + 0.5);
- memcpy(&desBuf[i * desLineSize] + j * bmiHeader.biBitCount / 8,&srcBuf[tSrcH * lineSize] + tSrcW * bmiHeader.biBitCount / 8,bmiHeader.biBitCount / 8);
- }
- }
- }
- //双线型内插值算法
- else if (mode == bilinear)
- {
- for (i = 0; i < desH; i++)
- {
- int tH = (int)(rateH * i);
- int tH1 = min(tH + 1,srcH - 1);
- float u = (float)(rateH * i - tH);
- for (j = 0; j < desW; j++)
- {
- int tW = (int)(rateW * j);
- int tW1 = min(tW + 1,srcW - 1);
- float v = (float)(rateW * j - tW);
- //f(i+u,j+v) = (1-u)(1-v)f(i,j) + (1-u)vf(i,j+1) + u(1-v)f(i+1,j) + uvf(i+1,j+1)
- for (int k = 0; k < 3; k++)
- {
- desBuf[i * desLineSize + j * bitCount / 8 + k] =
- (1 - u)*(1 - v) * srcBuf[tH * lineSize + tW * bitCount / 8 + k] +
- (1 - u)*v*srcBuf[tH1 * lineSize + tW * bitCount / 8+ k] +
- u * (1 - v) * srcBuf[tH * lineSize + tW1 * bitCount / 8 + k] +
- u * v * srcBuf[tH1 * lineSize + tW1 * bitCount / 8 + k];
- }
- }
- }
- }
- else
- {
- float pfVecX[CUBIC_SIZE], pfVecY[CUBIC_SIZE], pfMat[CUBIC_SIZE][CUBIC_SIZE];
- int nPixelBytes = bitCount / 8;
- for (i=1; i<desH-1; i++)
- {
- int nSrcY = getSincVec(pfVecY, rateH * i, 1.f / rateH);
- for (j = 1; j < desW-1; j++)
- {
- int nSrcX = getSincVec(pfVecX, rateW * j, 1.f / rateW);
- calcSincMat(pfMat[0], pfVecY, pfVecX);
- BYTE *pbyTmpDes = desBuf + i * desLineSize + j * nPixelBytes;
- BYTE *pbyTmpSrc = srcBuf + nSrcY * lineSize + nSrcX * nPixelBytes;
- for (int k = 0; k < 3; k++)
- {
- float fTmp = pbyTmpSrc[0] * pfMat[1][1];
- fTmp += pbyTmpSrc[-lineSize] * pfMat[0][1];
- fTmp += pbyTmpSrc[lineSize] * pfMat[2][1];
- fTmp += pbyTmpSrc[-nPixelBytes] * pfMat[1][0];
- fTmp += pbyTmpSrc[-nPixelBytes-lineSize] * pfMat[0][0];
- fTmp += pbyTmpSrc[-nPixelBytes+lineSize] * pfMat[2][0];
- fTmp += pbyTmpSrc[nPixelBytes] * pfMat[1][2];
- fTmp += pbyTmpSrc[nPixelBytes-lineSize] * pfMat[0][2];
- fTmp += pbyTmpSrc[nPixelBytes+lineSize] * pfMat[2][2];
- if (fTmp < 0.f) fTmp = 0.f;
- if (fTmp > 255.f) fTmp = 255.f;
- *pbyTmpDes++ = (BYTE)fTmp;
- pbyTmpSrc++;
- }
- }
- }
- }
- //创建目标文件
- HFILE hfile = _lcreat(desFile.c_str(),0);
- //文件头信息
- BITMAPFILEHEADER nbmfHeader;
- nbmfHeader.bfType = 0x4D42;
- nbmfHeader.bfSize = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER)
- + desW * desH * bitCount / 8;
- nbmfHeader.bfReserved1 = 0;
- nbmfHeader.bfReserved2 = 0;
- nbmfHeader.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
- //Bitmap头信息
- BITMAPINFOHEADER bmi;
- bmi.biSize=sizeof(BITMAPINFOHEADER);
- bmi.biWidth=desW;
- bmi.biHeight=desH;
- bmi.biPlanes=1;
- bmi.biBitCount=bitCount;
- bmi.biCompression=BI_RGB;
- bmi.biSizeImage=0;
- bmi.biXPelsPerMeter=0;
- bmi.biYPelsPerMeter=0;
- bmi.biClrUsed=0;
- bmi.biClrImportant=0;
- //写入文件头信息
- _lwrite(hfile,(LPCSTR)&nbmfHeader,sizeof(BITMAPFILEHEADER));
- //写入Bitmap头信息
- _lwrite(hfile,(LPCSTR)&bmi,sizeof(BITMAPINFOHEADER));
- //写入图像数据
- _lwrite(hfile,(LPCSTR)desBuf,desBufSize);
- _lclose(hfile);
- }
- int main(int argc, char* argv[])
- {
- FILE *pFile;
- if ((pFile = fopen("e://t.bmp","rb")) == NULL)
- {
- printf("open bmp file error.");
- return -1;
- }
- string srcFile("e://t.bmp");
- string desFileN("e://nearest.bmp");
- string desFileB("e://bilinear.bmp");;
- string desFileC("e://cubic.bmp");
- //Stretch(srcFile,desFileN,235,136,nearest);
- //Stretch(srcFile,desFileB,235,136,bilinear);
- Stretch(srcFile,desFileC,235,136,cubic);
- //int alignBytes = ~31;
- //printf("alignbytes : %d",alignBytes);
- return 0;
- }