c++ 彩色图转灰度图

以下是C++将彩色图转换为灰度图的代码示例：

#include <iostream>
#include <fstream>
#include <cstdlib>
#include <cmath>
using namespace std;

#pragma pack(push, 1)
typedef struct {
    unsigned short bfType;
    unsigned int bfSize;
    unsigned short bfReserved1;
    unsigned short bfReserved2;
    unsigned int bfOffBits;
} BITMAPFILEHEADER;

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;
} BITMAPINFOHEADER;

typedef struct {
    unsigned char rgbBlue;
    unsigned char rgbGreen;
    unsigned char rgbRed;
    unsigned char rgbReserved;
} RGBQUAD;

typedef struct {
    BITMAPFILEHEADER fileHeader;
    BITMAPINFOHEADER infoHeader;
    RGBQUAD *palette;
    unsigned char *data;
} BMP;

#pragma pack(pop)

BMP* readBmp(char* filename) {
    BMP* bmp = new BMP;
    ifstream file(filename, ios::binary);
    if (!file) {
        cout << "Error: could not open file " << filename << endl;
        exit(1);
    }
    file.read((char*)&bmp->fileHeader, sizeof(BITMAPFILEHEADER));
    file.read((char*)&bmp->infoHeader, sizeof(BITMAPINFOHEADER));
    if (bmp->infoHeader.biBitCount <= 8) {
        bmp->palette = new RGBQUAD[1 << bmp->infoHeader.biBitCount];
        file.read((char*)bmp->palette, sizeof(RGBQUAD) * (1 << bmp->infoHeader.biBitCount));
    }
    bmp->data = new unsigned char[bmp->infoHeader.biSizeImage];
    file.seekg(bmp->fileHeader.bfOffBits, ios::beg);
    file.read((char*)bmp->data, bmp->infoHeader.biSizeImage);
    file.close();
    return bmp;
}

void writeBmp(char* filename, BMP* bmp) {
    ofstream file(filename, ios::binary);
    if (!file) {
        cout << "Error: could not open file " << filename << endl;
        exit(1);
    }
    file.write((char*)&bmp->fileHeader, sizeof(BITMAPFILEHEADER));
    file.write((char*)&bmp->infoHeader, sizeof(BITMAPINFOHEADER));
    if (bmp->infoHeader.biBitCount <= 8) {
        file.write((char*)bmp->palette, sizeof(RGBQUAD) * (1 << bmp->infoHeader.biBitCount));
    }
    file.write((char*)bmp->data, bmp->infoHeader.biSizeImage);
    file.close();
}

void rgb2gray(BMP* bmp) {
    if (bmp->infoHeader.biBitCount != 24) {
        cout << "Error: only support 24-bit color depth" << endl;
        exit(1);
    }
    int width = bmp->infoHeader.biWidth;
    int height = bmp->infoHeader.biHeight;
    int lineByte = (width * 24 + 31) / 32 * 4;
    unsigned char* data = bmp->data;
    for (int i = 0; i < height; i++) {
        for (int j = 0; j < width; j++) {
            int b = data[i * lineByte + j * 3];
            int g = data[i * lineByte + j * 3 + 1];
            int r = data[i * lineByte + j * 3 + 2];
            int gray = (r * 19595 + g * 38469 + b * 7472) >> 16;
            data[i * lineByte + j * 3] = gray;
            data[i * lineByte + j * 3 + 1] = gray;
            data[i * lineByte + j * 3 + 2] = gray;
        }
    }
}

int main() {
    BMP* bmp = readBmp("color.bmp");
    rgb2gray(bmp);
    writeBmp("gray.bmp", bmp);
    delete[] bmp->palette;
    delete[] bmp->data;
    delete bmp;
    return 0;
}