ビットマップファイルの埋め込み

Question

ビットマップ画像をC言語でサイズ変更できるようにしたいのですが、新しい画像が間違って表示されるようなパディングの問題があると思われますが、問題は何か分かりません。

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

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

#include "bmp.h" 

int main(int argc, char *argv[]) 
{ 

double n = atof(argv[1]); 

// ensure proper usage 
if (argc != 4) 
{ 
    fprintf(stderr, "Usage: ./resize n infile outfile\n"); 
    return 1; 
} 

if (n >= 100 || n < 0) 
{ 
    fprintf(stderr, "n must be positibe and less than 100\n"); 
    return 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; 
} 

// read infile's BITMAPFILEHEADER 
BITMAPFILEHEADER bf; 
fread(&bf, sizeof(BITMAPFILEHEADER), 1, inptr); 

// read infile's BITMAPINFOHEADER 
BITMAPINFOHEADER bi; 
fread(&bi, sizeof(BITMAPINFOHEADER), 1, inptr); 

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



// Change height and width 
bi.biHeight *= n; 
bi.biWidth *= n; 

// determine padding for outfile scanlines 
int padding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4; 

// Change size and image size 
bi.biSizeImage = ((sizeof(RGBTRIPLE) * bi.biWidth) + padding) * abs(bi.biHeight); 
bf.bfSize = bi.biSizeImage + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER); 

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

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

// iterate over infile's scanlines 
for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++) 
{ 
    //resize vertically 
    for (int j = 0; j < n; j++) 
    { 
     // temporary storage 
     RGBTRIPLE triple; 

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

     // iterate over pixels in scanline 
     for (int k = 0; k < bi.biWidth; k++) 
     { 
      // write RGB triple to outfile 
      fwrite(&triple, sizeof(RGBTRIPLE), n, outptr); 
     } 
     // Add padding, if necessary 
     for (int l = 0; l < padding; l++) 
     { 
      fwrite(0x00, 1, padding, outptr); 
     } 
     if (j == n - 1) 
     { 
      // skip over padding, if any 
      fseek(inptr, padding, SEEK_CUR); 
     } 
     else 
     { 
      fseek(inptr, bi.biWidth, SEEK_CUR); 
     } 
    } 
} 

// close infile 
fclose(inptr); 

// close outfile 
fclose(outptr); 

// success 
return 0; 
} 

恐ろしい間隔で申し訳ありません。

Answer 1

infileと同じパディングをoutfileと同じように使用し、ピクセルを混在させます。

// read infile's BITMAPFILEHEADER 
BITMAPFILEHEADER bf; 
fread(&bf, sizeof(BITMAPFILEHEADER), 1, inptr); 

// 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.bfType != 0x4d42 || bf.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; 
} 

// build outfile's BITMAPINFOHEADER and Change height and width 
BITMAPINFOHEADER bi_out; 
bi_out=bi_in; 

bi_out.biHeight *= n; 
bi_out.biWidth *= n; 

// determine paddings 
int padding_in = (4 - (bi_in.biWidth * sizeof(RGBTRIPLE)) % 4) % 4; 
int padding_out = (4 - (bi_out.biWidth * sizeof(RGBTRIPLE)) % 4) % 4; 

// Change size and image size 
bi_out.biSizeImage = ((sizeof(RGBTRIPLE) * bi_out.biWidth) + padding_out) * abs(bi_out.biHeight); 
bf.bfSize = bi_out.biSizeImage + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER); 

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

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

// iterate over infile's scanlines 
for (int i = abs(bi_in.biHeight); i--;) 
{ 
    long StartOfScanline = ftell(inptr); //we have to return here 
    //resize vertically, issue the same line n times 
    for (int j = 0; j < n; j++) 
    { 
     fseek(inptr,StartOfScanline, SEEK_SET); //go to start of line 
     for (int k=bi_in.biWidth; k--;) //for each pixel in line... 
     { 
      RGBTRIPLE triple; 
      // read one RGB triple from infile 
      fread(&triple, sizeof(RGBTRIPLE), 1, inptr); 
      for (int l=n;l--;) //write out pix n times 
       fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr); 
     } 
     // Add padding, if necessary 
     //This was wrong: fwrite needs a pointer to data, and not 0x00!! 
     //for (int l = 0; l < padding_out; l++) 
     // fwrite(0x00, 1, 1, outptr); 
     //FIXED: 
     static const char Padding[4]={0,0,0,0}; 
     fwrite(Padding, padding_out, 1, outptr); 

    } 
    //add padding to infile 
    fseek(inptr, padding_in, SEEK_CUR); 
}