C语言实现bmp图片裁剪

bmp图片如何储存的，在这篇文章中有很好的介绍：https://blog.csdn.net/weixin_46987028/article/details/109171867

附上两张用于测试的图（从别的博主那盗来的，来源见水印）

8位深 256*256图片：

24位深 512*512图片：

以下代码支持将24位深或8位深的图片裁剪为矩形

#include
#include

//需要的参数有原图片路径，输出图片路径，裁剪起点坐标，裁剪后的宽度和高度
//裁剪起点为矩形的左下角像素坐标(begin_x,begin_y),根据给定的宽度和高度向右上方拓展
void cutting(char *source, char *des, int begin_x, int begin_y, int width, int height);

//main函数仅用于展示功能的必要输入，毫无意义
int main(void){
    int begin_x, begin_y, height, width;
    char *source, *destination;
    source = (char *)malloc(sizeof(char) * 100);
    destination = (char *)malloc(sizeof(char) * 100);
    printf("input the datapath of input file:");
    scanf("%s", source);
    printf("output the file as:");
    scanf("%s", destination);
    printf("intput the start point (x,y) and the width and height after cuttingn");
    printf("x:");
    scanf("%d", &begin_x);
    printf("y:");
    scanf("%d", &begin_y);
    printf("width:");
    scanf("%d", &width);
    printf("height:");
    scanf("%d", &height);
    cutting(source, destination, begin_x, begin_y, width, height);
    return 0;
}


void cutting(char *source, char *des, int begin_x, int begin_y, int width, int height){
    int bmpHeight;
	int bmpWidth;
    int biBitCount;
    unsigned char* pBmpBuf;
	unsigned char* pBmpBuf2;
	RGBQUAD* pColorTable;
	FILE* fp = fopen(source, "rb");//打开源文件
	if (fp == 0){
        printf("Wrong path!n");
        return;
    }
	BITMAPFILEHEADER fileHead;
	fread(&fileHead, sizeof(BITMAPFILEHEADER), 1, fp);//读取BITMAPFILEHEADER
	BITMAPINFOHEADER head;
	fread(&head, sizeof(BITMAPINFOHEADER), 1, fp);//读取BITMAPINFOHEADER
	bmpHeight = head.biHeight;//获取原图的长和宽
	bmpWidth = head.biWidth;
    if(begin_x+width>bmpWidth){//如果裁剪后的右上角在原图右上角之外，将其移回原图右上角
        width = bmpWidth - begin_x;
    }
    if(begin_y+height>bmpHeight){
        height = bmpHeight - begin_y;
    }
    biBitCount = head.biBitCount; // 获取位深度
    if (biBitCount < 24) {//如果位深度小于24，还要读取ColorTable
        pColorTable = new RGBQUAD[2 << biBitCount];
        fread(pColorTable, sizeof(RGBQUAD), 2 << biBitCount, fp);
    }
	int LineByte = (bmpWidth * biBitCount / 8 + 3) / 4 * 4;//计算出每行有多少个byte，/8是因为8个bits等于一个byte，+3)/4*4是为了对齐（每行的byte必须是4的整数倍）
	pBmpBuf = new unsigned char[LineByte * bmpHeight];
	fread(pBmpBuf, LineByte * bmpHeight, 1, fp);
	FILE* fop = fopen(des, "wb");
	head.biHeight = height;//重写高度
	head.biWidth = width;//重写宽度
	int LineByte2 = (head.biWidth * biBitCount / 8 + 3) / 4 * 4;对齐
	pBmpBuf2 = new unsigned char[LineByte * head.biHeight];
	head.biSizeImage = LineByte2 * head.biHeight;//重写图片数据大小
	fileHead.bfSize = head.biSizeImage + fileHead.bfOffBits;//重写总大小（包括了BITMAPFILEHEADER、BITMAPINFOHEADER、ColorTable）
	fwrite(&fileHead, sizeof(BITMAPFILEHEADER), 1, fop);//写到文件中
	fwrite(&head, sizeof(BITMAPINFOHEADER), 1, fop);
    if(biBitCount<24){//如果有ColorTable，也写到文件中
	    fwrite(pColorTable, sizeof(RGBQUAD), 256, fop);
    }
    if(biBitCount==24){//如果是24位深的图片，每个像素有3个byte（分别代表RGB）
        for (int i = 0; i < height; ++i)
        {
            for (int j = 0; j < width; ++j)
            {
                pBmpBuf2[i * width * 3 + j * 3] = pBmpBuf[(begin_y + i) * bmpWidth * 3 + begin_x * 3 + j * 3];
                pBmpBuf2[i * width * 3 + j * 3 + 1] = pBmpBuf[(begin_y + i) * bmpWidth * 3 + begin_x * 3 + j * 3 + 1];
                pBmpBuf2[i * width * 3 + j * 3 + 2] = pBmpBuf[(begin_y + i) * bmpWidth * 3 + begin_x * 3 + j * 3 + 2];
            }
        }
    }
    else if(biBitCount==8){//如果是8位深图片，每个像素只占一个byte
        for (int i = 0; i < height; ++i)
        {
            for (int j = 0; j < width; ++j)
            {
                pBmpBuf2[i * width + j] = pBmpBuf[(begin_y + i) * bmpWidth + begin_x + j];
            }
        }
    }
    else{
        printf("Sorry we don't support photo with biBitCount less than 8!n");
        return;
    }
	fwrite(pBmpBuf2, LineByte2 * head.biHeight, 1, fop);//写回到文件中
	fclose(fop);
	return ;
}

    return;
}
fwrite(pBmpBuf2, LineByte2 * head.biHeight, 1, fop);//写回到文件中
fclose(fop);
return ;

}