纯C++代码实现将像素矩阵保存为bmp图片

       用C++代码将像素矩阵保存为图片，这里以读取yuv序列视频帧为例进行分析，假设4:2:0yuv序列有300帧，则首先需要将每一视频帧保存在一个像素矩阵中，然后将每一个矩阵保存为图片，最终会有300个bmp图片。
       纯C++代码如下：
       saveToPicture.cpp#include<iostream>
#include<string>
using namespace std;

#define FrameSize 176*144 //视频帧大小
#define FrameNum 300 //yuv帧数
#define ET_SIZE 300
char errorText[ET_SIZE];

void errorMsg(const char *msg) {
printf("error:%s\n", msg);
#ifdef _WIN32
system("pause");
#endif
exit(-1);
}

void readSequence(char *fileName, unsigned char **frames) {
FILE *fp = fopen(fileName, "rb");
if (fp == NULL) {
sprintf(errorText, "File %s doesn't exist\n", fileName);
errorMsg(errorText);
}

int uvSize = FrameSize / 2; //H.264编解码获得的关键帧都是彩色序列，这里主要是提取亮度分量Y。
unsigned char *buf = (unsigned char *)malloc(sizeof(unsigned char) * uvSize);
for (int i = 0; i < FrameNum; i++) {
//read y
if (fread(frames[i], 1, FrameSize, fp) != FrameSize) { //每一个keyFrames[i]分配的是 (unsigned char) * FrameSize的大小，所以fread要读的每个数据项的字节数为1，可以表示每个像素点亮度范围0~255
sprintf(errorText, "Input sequence %s is not enough", fileName);
errorMsg(errorText);
}

//read u,v
fread(buf, 1, uvSize, fp);
}
free(buf);
fclose(fp);
}

void write_bmpheader(unsigned char *bitmap, int offset, int bytes, int value) {
int i;
for (i = 0; i < bytes; i++)
bitmap[offset + i] = (value >> (i << 3)) & 0xFF;
}

unsigned char *convertToBmp(unsigned char *inputImg, int width, int height, int *ouputSize) {
/*create a bmp format file*/
int bitmap_x = (int)ceil((double)width * 3 / 4) * 4;
unsigned char *bitmap = (unsigned char*)malloc(sizeof(unsigned char)*height*bitmap_x + 54);

bitmap[0] = 'B';
bitmap[1] = 'M';
write_bmpheader(bitmap, 2, 4, height*bitmap_x + 54); //whole file size
write_bmpheader(bitmap, 0xA, 4, 54); //offset before bitmap raw data
write_bmpheader(bitmap, 0xE, 4, 40); //length of bitmap info header
write_bmpheader(bitmap, 0x12, 4, width); //width
write_bmpheader(bitmap, 0x16, 4, height); //height
write_bmpheader(bitmap, 0x1A, 2, 1);
write_bmpheader(bitmap, 0x1C, 2, 24); //bit per pixel
write_bmpheader(bitmap, 0x1E, 4, 0); //compression
write_bmpheader(bitmap, 0x22, 4, height*bitmap_x); //size of bitmap raw data
for (int i = 0x26; i < 0x36; i++)
bitmap[i] = 0;

int k = 54;
for (int i = height - 1; i >= 0; i--) {
int j;
for (j = 0; j < width; j++) {
int index = i*width + j;
for (int l = 0; l < 3; l++)
bitmap[k++] = inputImg[index];
}
j *= 3;
while (j < bitmap_x) {
bitmap[k++] = 0;
j++;
}
}

*ouputSize = k;
return bitmap;
}

void saveToBmp(unsigned char *inputImg, int width, int height, char *outputFileName) {
int size;
unsigned char *bmp = convertToBmp(inputImg, width, height, &size);
FILE *fp = fopen(outputFileName, "wb+");
if (fp == NULL) {
sprintf(errorText, "Could not open file: %s", outputFileName);
errorMsg(errorText);
}
fwrite(bmp, 1, size, fp);
fclose(fp);
free(bmp);
}

int main() {
int width = 176, height = 144;
unsigned char **oriFrames;
oriFrames = (unsigned char**)malloc(sizeof(unsigned char*) * FrameNum);
for (int i = 0; i < FrameNum; i++) {
oriFrames[i] = (unsigned char*)malloc(sizeof(unsigned char) * FrameSize);
}
readSequence("foreman_qcif_300.yuv", oriFrames);

char imgName[30];
for (int i = 0; i < FrameNum; i++) {
sprintf(imgName,"./picture/ReconsFrame%d.bmp", i);
//矩阵oriFrames[i]可以是任何你想保存为图片的像素矩阵，这里是yuv视频图像每一帧的像素数据
saveToBmp(oriFrames[i], width, height, imgName);
}
}