Pset4, whodunit, Just created a bmp with no color

Question

My code is following. Feel puzzled to generate wrong result..

``` #include #include "bmp.h" #include #include int main(int argc, char *argv[]) { if (argc != 3) { fprintf(stderr, "Please enter two files name"); return 1; }

char *inputf = argv[1];
char *outputf = argv[2];

FILE *i = fopen(inputf,"r");
if (i == NULL)
{
    fprintf(stderr, "fail to access file: %s\n",inputf);
    fclose(i);
    return 2;
}
FILE *o = fopen(outputf,"w");
if (o == NULL)
{
    fprintf(stderr, "fail to creat file: %s\n",outputf);
    fclose(o);
    return 2;
}
//read fileheader
BITMAPFILEHEADER bf;
fread(&bf, sizeof(BITMAPFILEHEADER),1,i);
BITMAPINFOHEADER bi;
fread(&bi, sizeof(BITMAPINFOHEADER),1,i);

//check whther file is BMP
if (bf.bfType != 0x4d42 || bf.bfOffBits != 54 || bi.biSize != 40 ||
    bi.biBitCount != 24 || bi.biCompression != 0)
{
    fclose(i);
    fclose(o);
    fprintf(stderr, "Unsupported file format.\n");
}

// Write outfile
fwrite(&bf, sizeof(BITMAPFILEHEADER), 1, o);
fwrite(&bi, sizeof(BITMAPINFOHEADER), 1, o);

//consider padding
int padding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4 ) % 4;
for (int row = 0, biHeight = abs(bi.biHeight); row < biHeight; row++)
{
    for (int col = 0; col < bi.biWidth; col++)
    {
        RGBTRIPLE triple;
        fread(&triple, sizeof(RGBTRIPLE), 1, i);
        if (triple.rgbtRed == 0x0000ff)
        {
            triple.rgbtRed = 0x000000;
        }
        fwrite(&triple, sizeof(RGBTRIPLE), 1, o);

    }
    //
    fseek(i, padding, SEEK_CUR);
    for(int k = 0; k < padding; k++)
    {
        fputc(0x00, o);
    }
}

//close file
fclose(i);
fclose(o);
return 0;

} ```

Answer 1

Haven't tried the code, and you should have described what it does, or what it doesn't. Otherwise, it's a naked code drop as described in Why questions don't get answers or why people are ignored?

triple.rgbtRed is a single byte, not the value of the whole pixel. And 0xff doesn't require leading zeroes (they are ignored), it's the same as 255, an int that gets converted to uint8_t on assignment. Compiler might skip that conversion step and instantly work with bytes as long as it yields the same result ;-)

As I understand the code, this makes any white pixel (0xff, 0xff, 0xff) cyan (0xff, 0xff, 0x00) and any red pixel (0x00, 0x00, 0xff) black (0x00, 0x00, 0x00). Maybe you should instead try what the red plastic sheet does. It removes green and blue, on all the pixels. (You could replace them with the red value of the pixel instead). I'd experiment that way. Or maybe instead of lowering the red value, raise green and blue to make red pixels white.