如何在C中裁剪bmp文件

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

typedef struct {
    unsigned char signature[2];
    unsigned int fileSize;
    unsigned int reserved;
    unsigned int dataOffset;
} BMPHeader;

typedef struct {
    unsigned int headerSize;
    int width;
    int height;
    unsigned short planes;
    unsigned short bitCount;
    unsigned int compression;
    unsigned int imageSize;
    int xPixelsPerMeter;
    int yPixelsPerMeter;
    unsigned int colorsUsed;
    unsigned int colorsImportant;
} BMPInfoHeader;

int main() {
    FILE *inputFile, *outputFile;
    BMPHeader header;
    BMPInfoHeader infoHeader;
    unsigned char *imageData;
    int startX, startY, width, height;
    int newWidth, newHeight;
    unsigned char *newImageData;
    int i, j;

    // 打开原始BMP文件
    inputFile = fopen("input.bmp", "rb");
    if (inputFile == NULL) {
        printf("无法打开原始BMP文件\n");
        return 1;
    }

    // 读取BMP文件头
    fread(&header, sizeof(BMPHeader), 1, inputFile);
    fread(&infoHeader, sizeof(BMPInfoHeader), 1, inputFile);

    // 获取裁剪的起始位置和宽度、高度
    startX = 100;
    startY = 100;
    width = 200;
    height = 200;

    // 计算裁剪后的图像宽度和高度
    newWidth = width;
    newHeight = height;

    // 定位到图像数据
    fseek(inputFile, header.dataOffset, SEEK_SET);

    // 读取图像数据
    imageData = (unsigned char*)malloc(infoHeader.imageSize);
    fread(imageData, infoHeader.imageSize, 1, inputFile);

    // 裁剪图像
    newImageData = (unsigned char*)malloc(newWidth * newHeight * 3);
    for (i = 0; i < newHeight; i++) {
        for (j = 0; j < newWidth; j++) {
            int oldX = startX + j;
            int oldY = startY + i;
            int newIndex = (i * newWidth + j) * 3;
            int oldIndex = (oldY * infoHeader.width + oldX) * 3;
            newImageData[newIndex] = imageData[oldIndex];
            newImageData[newIndex + 1] = imageData[oldIndex + 1];
            newImageData[newIndex + 2] = imageData[oldIndex + 2];
        }
    }

    // 创建新的BMP文件
    outputFile = fopen("output.bmp", "wb");
    if (outputFile == NULL) {
        printf("无法创建新的BMP文件\n");
        return 1;
    }

    // 写入新的BMP文件头
    fwrite(&header, sizeof(BMPHeader), 1, outputFile);
    fwrite(&infoHeader, sizeof(BMPInfoHeader), 1, outputFile);

    // 写入裁剪后的图像数据
    fwrite(newImageData, newWidth * newHeight * 3, 1, outputFile);

    // 关闭文件
    fclose(inputFile);
    fclose(outputFile);

    // 释放内存
    free(imageData);
    free(newImageData);

    return 0;
}