How to Write a BMP Image from a Boolean Matrix in Pure C/C ?

Writing BMP Image in Pure C/C Without External Libraries

When creating an output with a boolean matrix, the need to write it into a BMP file arises. This involves creating a monochrome image with pixels marked white if the corresponding matrix element is true. The challenge remains in understanding the BMP header structure and its writing process.

To address this, a solution involves creating three 2D arrays: red, green, and blue, each representing pixel values based on the matrix. The following code demonstrates the approach:

FILE *f;
unsigned char *img = NULL;
int filesize = 54 + 3 * w * h; // Width and height represented as w and h

img = (unsigned char *)malloc(3 * w * h);
memset(img, 0, 3 * w * h);

for (int i = 0; i < w; i++) {
    for (int j = 0; j < h; j++) {
        int x = i, y = (h - 1) - j; // Flipping the image vertically
        int r = red[i][j] * 255;
        int g = green[i][j] * 255;
        int b = blue[i][j] * 255;
        // Clamping RGB values between 0-255
        if (r > 255) r = 255;
        if (g > 255) g = 255;
        if (b > 255) b = 255;
        img[(x + y * w) * 3 + 2] = (unsigned char)(r);
        img[(x + y * w) * 3 + 1] = (unsigned char)(g);
        img[(x + y * w) * 3 + 0] = (unsigned char)(b);
    }
}

// Define BMP headers
unsigned char bmpfileheader[14] = {'B', 'M', 0, 0, 0, 0, 0, 0, 0, 0, 54, 0, 0, 0};
unsigned char bmpinfoheader[40] = {40, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 24, 0};
unsigned char bmppad[3] = {0, 0, 0};

// Populate BMP header values
bmpfileheader[2] = (unsigned char)(filesize);
bmpfileheader[3] = (unsigned char)(filesize >> 8);
bmpfileheader[4] = (unsigned char)(filesize >> 16);
bmpfileheader[5] = (unsigned char)(filesize >> 24);

bmpinfoheader[4] = (unsigned char)(w);
bmpinfoheader[5] = (unsigned char)(w >> 8);
bmpinfoheader[6] = (unsigned char)(w >> 16);
bmpinfoheader[7] = (unsigned char)(w >> 24);
bmpinfoheader[8] = (unsigned char)(h);
bmpinfoheader[9] = (unsigned char)(h >> 8);
bmpinfoheader[10] = (unsigned char)(h >> 16);
bmpinfoheader[11] = (unsigned char)(h >> 24);

f = fopen("img.bmp", "wb");
fwrite(bmpfileheader, 1, 14, f);
fwrite(bmpinfoheader, 1, 40, f);
for (int i = 0; i < h; i++) {
    fwrite(img + (w * (h - i - 1) * 3), 3, w, f);
    fwrite(bmppad, 1, (4 - (w * 3) % 4) % 4, f); // Padding to ensure 4-byte alignment
}

free(img);
fclose(f);

This approach provides a comprehensive solution to writing a BMP file from a boolean matrix, without relying on external libraries. The header structure is meticulously defined, and the code ensures proper pixel formatting and padding, resulting in a valid BMP image that can be opened by standard image viewers.

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