BMP文件学习笔记（二）：将BMP格式RGB真彩色图片转换成灰度图片

程序员文章站 2022-05-21 23:53:25

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1 准备知识

关于BMP文件知识可参见上篇：《BMP文件学习笔记（一）： C/C++语言实现.bmp文件读写》，或者自行搜索查阅更详细的介绍。

RGB图片转换成灰度图片，有公式：Gray = r*0.299 + g*0.587 + b*0.114

下面的程序也是按这个公式来写的。

2 编程

代码如下：

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

void rgb2gray(char * rgbflie, char * grayflie)
{
	FILE * prgbfile, * pgrayfile;
	prgbfile = fopen(rgbflie, "rb");
	pgrayfile = fopen(grayflie, "wb");
	if (NULL == prgbfile || NULL == pgrayfile)
	{
		printf("文件打开失败!\n");
		fclose(prgbfile);
		fclose(pgrayfile);
		return;
	}
	BITMAPFILEHEADER bitMapFileHeader_rgb, bitMapFileHeader_gray;
	fread(&bitMapFileHeader_rgb, sizeof(BITMAPFILEHEADER), 1, prgbfile);
	if (0x4D42 != bitMapFileHeader_rgb.bfType)
	{
		printf("源文件不是BMP文件!\n");
		return ;
	}

	BITMAPINFOHEADER bitMapInfoHeader_rgb, bitMapInfoHeader_gray;
	fread(&bitMapInfoHeader_rgb, sizeof(BITMAPINFOHEADER), 1, prgbfile);
	if (24 != bitMapInfoHeader_rgb.biBitCount)
	{
		printf("源文件不是RGB彩色图片!\n");
		return;
	}

	int width = bitMapInfoHeader_rgb.biWidth;
	int height = bitMapInfoHeader_rgb.biHeight;
	int bitCount = bitMapInfoHeader_rgb.biBitCount;
	//图像数据每行字节数为4的倍数
	int lineByte_rgb = (width * bitCount / 8 + 3) / 4 * 4; //RGB图
	unsigned char * pData = new unsigned char[lineByte_rgb * height];
	fread(pData, sizeof(unsigned char), lineByte_rgb * height, prgbfile);

	int lineByte_gray = (width * 8 / 8 + 3) / 4 * 4; //灰度图

	bitMapFileHeader_gray.bfType = 0x4D42;
	bitMapFileHeader_gray.bfSize = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) + 1024 + lineByte_gray * height;
	bitMapFileHeader_gray.bfReserved1 = 0;
	bitMapFileHeader_gray.bfReserved2 = 0;
	bitMapFileHeader_gray.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) + 1024;

	
	bitMapInfoHeader_gray.biBitCount = 8;
	bitMapInfoHeader_gray.biClrImportant = 0;
	bitMapInfoHeader_gray.biClrUsed = 0;
	bitMapInfoHeader_gray.biCompression = 0;
	bitMapInfoHeader_gray.biHeight = height;
	bitMapInfoHeader_gray.biPlanes = 1;
	bitMapInfoHeader_gray.biSize = 40;
	bitMapInfoHeader_gray.biSizeImage = lineByte_gray * height;
	bitMapInfoHeader_gray.biWidth = width;
	bitMapInfoHeader_gray.biXPelsPerMeter = 0;
	bitMapInfoHeader_gray.biYPelsPerMeter = 0;

	//调色板
	RGBQUAD * pRGBQUAD = new RGBQUAD[256];
	for (int i = 0; i<256; i++)
	{
		pRGBQUAD[i].rgbBlue = i;
		pRGBQUAD[i].rgbGreen = i;
		pRGBQUAD[i].rgbRed = i;
		pRGBQUAD[i].rgbReserved = 0;
	}

	//写文件头进文件
	fwrite(&bitMapFileHeader_gray, sizeof(BITMAPFILEHEADER), 1, pgrayfile);
	//写位图信息头进内存
	fwrite(&bitMapInfoHeader_gray, sizeof(BITMAPINFOHEADER), 1, pgrayfile);
	//写调色板进文件 
	fwrite(pRGBQUAD, sizeof(RGBQUAD), 256, pgrayfile);
	//写数据进文
	for (int i = 0; i < height; i++)
	{
		for (int j = 0; j < lineByte_gray; j++)
		{
			//公式：Gray = r*0.299 + g*0.587 + b*0.114
			unsigned char bVal = *(pData + lineByte_rgb * i + 3 * j);
			unsigned char gVal = *(pData + lineByte_rgb * i + 3 * j + 1);
			unsigned char rVal = *(pData + lineByte_rgb * i + 3 * j + 2);
			unsigned char grayVal = bVal * 0.114 + gVal * 0.587 + rVal * 0.299;
			fwrite(&grayVal, sizeof(unsigned char), 1, pgrayfile);
		}

	}

	fclose(prgbfile);
	fclose(pgrayfile);
	delete[] pData;
	pData = NULL;
}

int main()
{
	char * rgbflie = "rgb.bmp";
	char * grayflie = "gray.bmp";

	rgb2gray(rgbflie, grayflie);

	return 0;
}