BMP文件格式学习总结

一个BMP文件可以包含4部分

1，文件头是14字节长的数据结构，定义如下：

typedef struct _BFHEADER
{
   unsigned short magic;
   unsigned int size;
   unsigned int reserved;
   unsigned int bitOffset;
}bfHeader;

2.bmp 信息结构，结构定义如下：

typedef struct _bmpInfoHead
{
   unsigned int headSize;
   unsigned int width;
   unsigned int height;
   unsigned short planes;
   unsigned short bpp;
   unsigned int compress;
   unsigned int imageSize;
   unsigned int PelsPerMeterX;
   unsigned int PelsPerMeterY;
   unsigned int ClrUsed;
   unsigned int ClrImportant;
   unsigned int RedMask;
   unsigned int GreenMask;
   unsigned int BlueMask;
   unsigned int AlphaMask;
   unsigned int CsType;
   unsigned int Endpoints[9]; // see http://msdn2.microsoft.com/en-us/library/ms536569.aspx
   unsigned int GammaRed;
   unsigned int GammaGreen;
   unsigned int GammaBlue;
}bmpInfoHead;

3.调色板palette

typedef struct _BGRA {
   unsigned char Blue;
   unsigned char Green;
   unsigned char Red;
   unsigned char Alpha;
} BGRA;

4.pixel Data

一个完整的简单BMP reader程序如下：

#include<stdio.h>
#include<stdlib.h>
/*
Pixel format
The 1-bit per pixel (1bpp) format supports 2 distinct colors, (for example: black and white). The pixel values are stored in each bit, with the first (left-most) pixel in the most-significant bit of the first byte.[4] Each bit is an index into a table of 2 colors. An unset bit will refer to the first color table entry, and a set bit will refer to the last (second) color table entry.
The 2-bit per pixel (2bpp) format supports 4 distinct colors and stores 4 pixels per 1 byte, the left-most pixel being in the two most significant bits (Windows CE only:[19]). Each pixel value is a 2-bit index into a table of up to 4 colors.
The 4-bit per pixel (4bpp) format supports 16 distinct colors and stores 2 pixels per 1 byte, the left-most pixel being in the more significant nibble.[4] Each pixel value is a 4-bit index into a table of up to 16 colors.
The 8-bit per pixel (8bpp) format supports 256 distinct colors and stores 1 pixel per 1 byte. Each byte is an index into a table of up to 256 colors.
The 16-bit per pixel (16bpp) format supports 65536 distinct colors and stores 1 pixel per 2-byte WORD. Each WORD can define the alpha, red, green and blue samples of the pixel.
The 24-bit pixel (24bpp) format supports 16,777,216 distinct colors and stores 1 pixel value per 3 bytes. Each pixel value defines the red, green and blue samples of the pixel (8.8.8.0.0 in RGBAX notation). Specifically, in the order: blue, green and red (8 bits per each sample).[4]
The 32-bit per pixel (32bpp) format supports 4,294,967,296 distinct colors and stores 1 pixel per 4-byte DWORD. Each DWORD can define the alpha, red, green and blue samples of the pixel.
*/

#pragma pack(push, 1)

typedef struct _BFHEADER
{
   unsigned short magic;
   unsigned int size;
   unsigned int reserved;
   unsigned int bitOffset;
}bfHeader;

typedef struct _bmpInfoHead
{
   unsigned int headSize;
   unsigned int width;
   unsigned int height;
   unsigned short planes;
   unsigned short bpp;
   unsigned int compress;
   unsigned int imageSize;
   unsigned int PelsPerMeterX;
   unsigned int PelsPerMeterY;
   unsigned int ClrUsed;
   unsigned int ClrImportant;
   unsigned int RedMask;
   unsigned int GreenMask;
   unsigned int BlueMask;
   unsigned int AlphaMask;
   unsigned int CsType;
   unsigned int Endpoints[9]; // see http://msdn2.microsoft.com/en-us/library/ms536569.aspx
   unsigned int GammaRed;
   unsigned int GammaGreen;
   unsigned int GammaBlue;
}bmpInfoHead;

typedef struct _RGBA {
   unsigned char Red;
   unsigned char Green;
   unsigned char Blue;
   unsigned char Alpha;
} RGBA;

typedef struct _BGRA {
   unsigned char Blue;
   unsigned char Green;
   unsigned char Red;
   unsigned char Alpha;
} BGRA;

FILE *inFd;
bfHeader fHead;
bmpInfoHead bmpInfo;

BGRA *paletteTable;
BGRA *pixelData;
unsigned char *pixelLine;

int main(void)
{
   unsigned int ColorTableSize = 0;
   unsigned int linePixelLength;
   int count;
   int rdLen;
   //fgetc();
   inFd = fopen("testimg.bmp", "rb");
   rdLen = fread(&fHead, sizeof(fHead), 1,inFd);
   rdLen = fread(&bmpInfo, sizeof(bmpInfo), 1,inFd);

   switch (bmpInfo.bpp)
   {
   case 2:
       break;
   case 4:
       ColorTableSize = 16;
       break;
   case 8:
       ColorTableSize = 256;
   case 16:
       break;
   case 32:
       //true color each bit save RGB, do not need palette
       break;
   default:
       break;
   }

   paletteTable = (BGRA *) malloc(ColorTableSize * sizeof(BGRA));
   pixelData = (BGRA *)malloc(sizeof(BGRA)*bmpInfo.height*bmpInfo.width);
   count=ftell(inFd);
   count = sizeof(fHead) + sizeof(bmpInfo);
   fseek(inFd, count, SEEK_SET);//from begin;
   //Read color map
   count= bmpInfo.ClrUsed * sizeof(BGRA);
   rdLen = fread(paletteTable, count, 1, inFd);

   linePixelLength = (bmpInfo.width*bmpInfo.bpp / 8);

   pixelLine = (unsigned char *)malloc(linePixelLength);

   fseek(inFd, fHead.bitOffset, SEEK_SET);//from begin;

   BGRA *p = pixelData;
   unsigned char color;
   for (unsigned int h = 0; h < bmpInfo.height; h++)
   {
       rdLen = fread(pixelLine, linePixelLength, 1, inFd);
       for (unsigned int w = 0; w < bmpInfo.width; w++)
       {
           color = pixelLine[w];
           p->Blue = paletteTable[color].Blue;
           p->Green = paletteTable[color].Green;
           p->Red = paletteTable[color].Red;
           p++;
       }
   }

   count++;

}

来源：CSDN

作者：ambercctv

链接：https://blog.csdn.net/ambercctv/article/details/103465654

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