Resize ( more comfortable )

Question

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

// ensure proper usage
if (argc != 4)
{
    fprintf(stderr, "Usage: copy infile outfile\n");
    return 1;
}
float f = atof(argv[1]);
if(f<= 0.0 && f>= 100.0)
{
    printf("f is not in range\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;
}

BITMAPFILEHEADER nbf = bf;
BITMAPINFOHEADER nbi = bi;
int nf = floor(f);
nbi.biWidth = floor(bi.biWidth*f);
nbi.biHeight = floor(bi.biHeight*f);
int newpadding = (4 - (nbi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
nbi.biSizeImage = ((sizeof(RGBTRIPLE))*(nbi.biWidth) + newpadding)* abs(nbi.biHeight);
nbf.bfSize = nbi.biSizeImage + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

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

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

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

// iterate over infile's scanlines
if(f >= 1)
{
    for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
    {
        for(int m = 0; m < nf; m++)
        {
            // iterate over pixels in scanline
            for (int j = 0; j < bi.biWidth; j++)
            {
                // temporary storage
                RGBTRIPLE triple;

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

                // write RGB triple to outfile n times
                for(int l = 0; l < nf; l++)
                    fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
            }

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

            // then add it back (to demonstrate how)
            for (int k = 0; k < newpadding; k++)
            {
                fputc(0x00, outptr);
            }
            if( m < (nf-1))
            {
                fseek(inptr, -((bi.biWidth * sizeof(RGBTRIPLE)) + padding), SEEK_CUR);
            }
        }
    }
}
else if( f < 1 )
{
    float f2 = 1/f;
    int nf2 = floor(f2);
    for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
    {
        // iterate over pixels in scanline
        for (int j = 1; j <= bi.biWidth; j++)
        {
            // temporary storage
            RGBTRIPLE triple;

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

            // write RGB triple to outfile
            fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
            if(j%nf2 == 0)
            {
                fseek(outptr, -(sizeof(RGBTRIPLE))*(nf2-1), SEEK_CUR);
            }
        }

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

        // then add it back (to demonstrate how)
        for (int k = 0; k < newpadding; k++)
        {
            fputc(0x00, outptr);
        }
        fseek(inptr, ((bi.biWidth * sizeof(RGBTRIPLE)) + padding)*(nf2-1), SEEK_CUR);
    }
}
// close infile
fclose(inptr);

// close outfile
fclose(outptr);

// success
return 0;}

Everything works fine visually but if i open the output image as hexadecimal

./resize 0.25 large.bmp smaller.bmp [output of this]

00ff00 00ff00 00ff00 000000

00ff00 ffffff 00ff00 000000

00ff00 00ff00 00ff00 000000

00ff00 00ff00 00ff00 000000

00ff00 00ff00 00ff00 000000

00ff00 00ff00 00ff00 000000

00ff00 00ff00 00ff00 000000

00ff00 00ff00 00ff00 000000

00ff00 00ff00 00ff00 000000

00ff00 00ff00 00ff00 000000

00ff00 00ff00 00ff00 000000

00ff00 00ff00 00ff00 000000

00ff00 00ff00

[smaller.bmp as hexadecimal]

This is shown First three lines are correct but rest of 9-10 lines appear outta nowhere. I mean something must be causing them to appear but i am not able to find what, can anyone tell me what's causing these extra bytes ??

And yeah, following tests also fail :-

:( resizes 6x6-pixel BMP to 3x3 correctly when f is 0.5

Image has more bytes than expected.

:( resizes 12x12-pixel BMP to 6x6 correctly when f is 0.5

Image has more bytes than expected.

:( resizes 18x18-pixel BMP to 9x9 correctly when f is 0.5

Image has more bytes than expected.

Answer 1

Two things in the scale down code seem odd to me.

Your loop

for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)

with the fseek at the end. You skip lines in the input file, but that does not reflect in the loop code. This explains the extra lines you see, with full padding at the end. Either use the output height instead of input height, or change i++ to i += nf2

The second thing I find odd is

        fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
        if(j%nf2 == 0)
        {
            fseek(outptr, -(sizeof(RGBTRIPLE))*(nf2-1), SEEK_CUR);
        }

It would make more sense to me if you moved the fwrite into the if and removed the fseek. The way your code is currently, you might write pixels beyond the expected file end.

Answer 2

You seem to have an issue with these lines of code:

if(f<= 0.0 && f>= 100.0) { printf("f is not in range\n"); return 1; }