c语言给bmp图片加水印

可以使用C语言的图形处理库来给BMP图片加水印。以下是一个简单的实现示例：

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

// 定义BMP文件头结构体
#pragma pack(2)
typedef struct {
    unsigned short bfType;
    unsigned int bfSize;
    unsigned short bfReserved1;
    unsigned short bfReserved2;
    unsigned int bfOffBits;
} BMPFILEHEADER;

// 定义BMP信息头结构体
#pragma pack(2)
typedef struct {
    unsigned int biSize;
    int biWidth;
    int biHeight;
    unsigned short biPlanes;
    unsigned short biBitCount;
    unsigned int biCompression;
    unsigned int biSizeImage;
    int biXPelsPerMeter;
    int biYPelsPerMeter;
    unsigned int biClrUsed;
    unsigned int biClrImportant;
} BMPINFOHEADER;

int main() {
    // 打开原图文件
    FILE *fp = fopen("original.bmp", "rb");
    if (fp == NULL) {
        printf("Failed to open file.\n");
        return -1;
    }

    // 读取BMP文件头
    BMPFILEHEADER fileHeader;
    fread(&fileHeader, sizeof(BMPFILEHEADER), 1, fp);

    // 读取BMP信息头
    BMPINFOHEADER infoHeader;
    fread(&infoHeader, sizeof(BMPINFOHEADER), 1, fp);

    // 计算像素数据的大小
    int width = infoHeader.biWidth;
    int height = infoHeader.biHeight;
    int rowSize = (width * 3 + 3) / 4 * 4;
    int dataSize = rowSize * height;

    // 分配内存并读取像素数据
    unsigned char *data = (unsigned char *)malloc(dataSize);
    fread(data, dataSize, 1, fp);

    // 关闭原图文件
    fclose(fp);

    // 添加水印
    char *watermark = "My Watermark";
    int watermarkLen = strlen(watermark);
    int watermarkWidth = watermarkLen * 8;
    int watermarkHeight = 16;
    int watermarkX = (width - watermarkWidth) / 2;
    int watermarkY = (height - watermarkHeight) / 2;
    unsigned char watermarkColor[3] = {255, 255, 255};

    int i, j, k;
    for (i = 0; i < watermarkHeight; i++) {
        for (j = 0; j < watermarkWidth; j++) {
            int x = watermarkX + j;
            int y = watermarkY + i;
            if (x >= 0 && x < width && y >= 0 && y < height) {
                int offset = y * rowSize + x * 3;
                for (k = 0; k < 3; k++) {
                    data[offset + k] = (data[offset + k] + watermarkColor[k]) / 2;
                }
            }
        }
    }

    // 打开输出文件
    fp = fopen("watermarked.bmp", "wb");
    if (fp == NULL) {
        printf("Failed to create file.\n");
        return -1;
    }

    // 写入BMP文件头
    fwrite(&fileHeader, sizeof(BMPFILEHEADER), 1, fp);

    // 写入BMP信息头
    fwrite(&infoHeader, sizeof(BMPINFOHEADER), 1, fp);

    // 写入像素数据
    fwrite(data, dataSize, 1, fp);

    // 关闭输出文件
    fclose(fp);

    // 释放内存
    free(data);

    return 0;
}

这个程序打开一个名为"original.bmp"的BMP图片文件，向其中心位置添加一个白色的"My Watermark"水印，然后将结果保存为"watermarked.bmp"文件。