Resize

bmp.h

/**
 * BMP-related data types based on Microsoft's own.
 */

#include <stdint.h>

/**
 * Common Data Types 
 *
 * The data types in this section are essentially aliases for C/C++ 
 * primitive data types.
 *
 * Adapted from https://msdn.microsoft.com/en-us/library/cc230309.aspx.
 * See http://en.wikipedia.org/wiki/Stdint.h for more on stdint.h.
 */
typedef uint8_t  BYTE;
typedef uint32_t DWORD;
typedef int32_t  LONG;
typedef uint16_t WORD;

/**
 * BITMAPFILEHEADER
 *
 * The BITMAPFILEHEADER structure contains information about the type, size,
 * and layout of a file that contains a DIB [device-independent bitmap].
 *
 * Adapted from https://msdn.microsoft.com/en-us/library/dd183374(v=vs.85).aspx.
 */
typedef struct 
{ 
    WORD bfType; 
    DWORD bfSize; 
    WORD bfReserved1; 
    WORD bfReserved2; 
    DWORD bfOffBits; 
} __attribute__((__packed__)) 
BITMAPFILEHEADER; 

/**
 * BITMAPINFOHEADER
 *
 * The BITMAPINFOHEADER structure contains information about the 
 * dimensions and color format of a DIB [device-independent bitmap].
 *
 * Adapted from https://msdn.microsoft.com/en-us/library/dd183376(v=vs.85).aspx.
 */
typedef struct
{
    DWORD biSize; 
    LONG biWidth; 
    LONG biHeight; 
    WORD biPlanes; 
    WORD biBitCount; 
    DWORD biCompression; 
    DWORD biSizeImage; 
    LONG biXPelsPerMeter; 
    LONG biYPelsPerMeter; 
    DWORD biClrUsed; 
    DWORD biClrImportant; 
} __attribute__((__packed__))
BITMAPINFOHEADER; 

/**
 * RGBTRIPLE
 *
 * This structure describes a color consisting of relative intensities of
 * red, green, and blue.
 *
 * Adapted from https://msdn.microsoft.com/en-us/library/dd162939(v=vs.85).aspx.
 */
typedef struct
{
    BYTE rgbtBlue;
    BYTE rgbtGreen;
    BYTE rgbtRed;
} __attribute__((__packed__))
RGBTRIPLE;

resize.c

/**
 * Copies a BMP piece by piece, just because.
 */

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

#include "bmp.h"

int main(int argc, char *argv[])
{
    // ensure proper usage
    if (argc != 4)
    {
        fprintf(stderr, "Usage: ./copy n infile outfile\n");
        return 1;
    }
    //get float value
    float scale = atof(argv[1]);

    // remember filenames
    char *infile = argv[2];
    char *outfile = argv[3];

    // open input file
    FILE *inptr = fopen(infile, "r");
    if (inptr == NULL)
    {
        fprintf(stderr, "Could not open %s.\n", infile);
        return 2;
    }

    // open output file
    FILE *outptr = fopen(outfile, "w");
    if (outptr == NULL)
    {
        fclose(inptr);
        fprintf(stderr, "Could not create %s.\n", outfile);
        return 3;
    }

    // create and read infile's BITMAPFILEHEADER
    BITMAPFILEHEADER bf_in;
    fread(&bf_in, sizeof(BITMAPFILEHEADER), 1, inptr);


    // create and read infile's BITMAPINFOHEADER
    BITMAPINFOHEADER bi_in;
    fread(&bi_in, sizeof(BITMAPINFOHEADER), 1, inptr);


    // ensure infile is (likely) a 24-bit uncompressed BMP 4.0
    if (bf_in.bfType != 0x4d42 || bf_in.bfOffBits != 54 || bi_in.biSize != 40 ||
        bi_in.biBitCount != 24 || bi_in.biCompression != 0)
    {
        fclose(outptr);
        fclose(inptr);
        fprintf(stderr, "Unsupported file format.\n");
        return 4;
    }

    // determine padding for scanlines for the infile
    int in_padding = (4 - (bi_in.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    //an array to store our input image.
    RGBTRIPLE image[bi_in.biWidth][abs(bi_in.biHeight)];

    // iterate over infile's scanlines
    for (int i = 0, biHeight = abs(bi_in.biHeight); i < biHeight; i++)
    {
        // iterate over pixels in scanline
        for (int j = 0; j < bi_in.biWidth; j++)
        {
            // temporary storage
            RGBTRIPLE triple;

            // read RGB triple from infile
            fread(&triple, sizeof(RGBTRIPLE), 1, inptr);

            // store the image in an array
            image[j][i] = triple;
        }

        // skip over padding, if any
        fseek(inptr, in_padding, SEEK_CUR);
    }

    // create the outfile's BITMAPFILEHEADER
    BITMAPFILEHEADER bf_out;
    bf_out = bf_in;

    // create the outfile's BITMAPINFOHEADER
    BITMAPINFOHEADER bi_out;
    bi_out = bi_in;

    //calculate the new width and height;
    bi_out.biWidth = bi_in.biWidth * scale;
    bi_out.biHeight = bi_in.biHeight * scale;

    // determine padding for scanlines for the infile
    int out_padding = (4 - (bi_out.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    //change the image size
    bi_out.biSizeImage = ((sizeof(RGBTRIPLE) * bi_out.biWidth) + out_padding) * abs(bi_out.biHeight);

    //change the file size
    bf_out.bfSize = bi_out.biSizeImage + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

    // write outfile's BITMAPFILEHEADER
    fwrite(&bf_out, sizeof(BITMAPFILEHEADER), 1, outptr);

    // write outfile's BITMAPINFOHEADER
    fwrite(&bi_out, sizeof(BITMAPINFOHEADER), 1, outptr);

    // iterate over outfile's scanlines
    for (int i = 0, biHeight = abs(bi_out.biHeight); i < biHeight; i++)
    {
        // iterate over pixels in scanline
        for (int j = 0; j < bi_out.biWidth; j++)
        {
            // temporary storage
            RGBTRIPLE triple;

            //determine which pixel to use for the outfile
            triple = image[(int) (j / scale)][(int) (i / scale)];

            // write RGB triple to outfile
            fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
        }


        // then add it back (to demonstrate how)
        for (int k = 0; k < out_padding; k++)
        {
            fputc(0x00, outptr);
        }
    }

    // close infile
    fclose(inptr);

    // close outfile
    fclose(outptr);

    // success
    return 0;
}