C语言实现BMP图像缩放

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对BMP图像用C语言实现图像的缩放。缩放的倍数通过输入设定

#include <Windows.h>
#include <stdlib.h>
#include <stdio.h>
#include <math.h>

int main(int argc, char ** argv)
{
	FILE *fp = fopen("./01.bmp","rb");
	if (fp == 0)
		return 0;
	BITMAPFILEHEADER fileHead;
	fread(&fileHead, sizeof(BITMAPFILEHEADER), 1, fp);
	BITMAPINFOHEADER infoHead;
	fread(&infoHead, sizeof(BITMAPINFOHEADER), 1, fp);
	int width = infoHead.biWidth;
	int height = infoHead.biHeight;
	int biCount = infoHead.biBitCount;

	RGBQUAD *pColorTable;
	int pColorTableSize = 0;

	pColorTable = new RGBQUAD[256];
	fread(pColorTable, sizeof(RGBQUAD), 256, fp);
	pColorTableSize = 1024;

	unsigned char *pBmpBuf;
	int lineByte = (width*biCount / 8 + 3) / 4 * 4;
	pBmpBuf = new unsigned char[lineByte*height];
	fread(pBmpBuf, lineByte*height, 1, fp);
	fclose(fp);

	printf("请输入长和宽需要缩放的倍数：");
	float lx, ly;
	scanf("%f%f", &lx, &ly);
	int dstWidth = round(double(lx*width));
	int dstHeight = round(double(ly*height));
	int lineByte2 = (dstWidth*biCount / 8 + 3) / 4 * 4;
	
	unsigned char*pBmpBuf2;
	pBmpBuf2 = new unsigned char[lineByte2*dstHeight];
	for (int i = 0; i < dstHeight; ++i){
		for (int j = 0; j < dstWidth; ++j){
			unsigned char *p;
			p = (unsigned char *)(pBmpBuf2 + lineByte2*i + j);
			(*p) = 255;
		}
	}
	int x = 0;
	int y = 0;
	for (int i = 0; i < height; ++i){
		for (int j = 0; j < width; ++j){
			unsigned char *p1, *p2;
			x = round(double(lx*j));
			y = round(double(ly*i));
			p1 = (unsigned char *)(pBmpBuf + i*lineByte + j);
			p2 = (unsigned char *)(pBmpBuf2 + y*lineByte2 + x);
			(*p2) = (*p1);
		}
	}

	FILE *fpo = fopen("./shrinkBmp.bmp", "wb");
	if (fpo == 0)
		return 0;
	BITMAPFILEHEADER dstFileHead;
	dstFileHead.bfOffBits = 14 + 40 + pColorTableSize;
	dstFileHead.bfReserved1 = 0;
	dstFileHead.bfReserved2 = 0;
	dstFileHead.bfSize = sizeof(BITMAPFILEHEADER)+sizeof(BITMAPINFOHEADER)+pColorTableSize + lineByte2*dstHeight;
	dstFileHead.bfType = 0x4D42;
	fwrite(&dstFileHead, sizeof(dstFileHead), 1, fpo);

	BITMAPINFOHEADER dstInfoHead;
	dstInfoHead.biBitCount = biCount;
	dstInfoHead.biClrImportant = 0;
	dstInfoHead.biClrUsed = 0;
	dstInfoHead.biCompression = 0;
	dstInfoHead.biHeight = dstHeight;
	dstInfoHead.biPlanes = 1;
	dstInfoHead.biSize = 40;
	dstInfoHead.biSizeImage = lineByte2*dstHeight;
	dstInfoHead.biWidth = dstWidth;
	dstInfoHead.biXPelsPerMeter = 0;
	dstInfoHead.biYPelsPerMeter = 0;
	fwrite(&dstInfoHead, sizeof(BITMAPINFOHEADER), 1, fpo);

	fwrite(pColorTable, sizeof(RGBQUAD), 256, fpo);
	fwrite(pBmpBuf2, lineByte2*dstHeight, 1, fp);
	fclose(fpo);

	system("pause");
	return 0;
}

实验结果：

              原图                     宽1.5倍，高0.5倍       宽0.5倍 高1.5倍            宽5倍 高2倍                  

      

变换后的图像都有一个共同的特点，就是图像有栅格，出现的原因是在缩放坐标取值时采用简单的取整，解决办法：采用插值解决

方法一：最近邻插值法，其实就是四舍五入

	for (int i = 0; i < dstHeight; ++i){
		for (int j = 0; j < dstWidth; ++j){
			unsigned char *p1, *p2;
			x = round(double(1/lx*j));
			y = round(double(1/ly*i));
			p1 = (unsigned char *)(pBmpBuf2 + i*lineByte2 + j);
			p2 = (unsigned char *)(pBmpBuf + y*lineByte + x);
			(*p1) = (*p2);
		}
	}

实验结果：

方法倍数：长1.5 宽1.5

实验结果分析：能过保留细节部分，但边缘存在严重的锯齿现象。

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