Pset4- How to Update FileHeader (Resizing Trouble)

Question

When I run my program by imputing 1, it prints out an exact copy (like it should). But, when I try running my program by imputing 2 (or anything else), it prints out the same size image with seemingly random colored pixels.

I am pretty sure I have to update the info header,but I am not sure how. When I try to change bfSize, height, etc, my file won't compile. All help is greatly appreciated, thank in advance!

This is what would not compile:

new_bfSize = bfSize * grow;
new_biHeight = biHeight * grow;
new_biWidth = biWidth * grow;
new_biSizeImage = new_biWidth + sizeof(RGBTRIPLE) + padding2 + abs(new_biHeight);
newbfSize = new_biSizeImage + sizeof(BITMAPINFOHEADER);

Here is my code(without that section):

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

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

// remember filenames
char* infile = argv[2];
char* outfile = argv[3];
int grow = atoi(argv[1]);

//make sure number is greater than 1 and less than 100
if ( grow < 1 || grow > 101)
{
    printf("Your number must be greater than one and less than 100.\n");
    return 2; // 2?
}

// open input file 
FILE* inptr = fopen(infile, "r");
if (inptr == NULL)
{
    printf("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;
}

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

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

// determine padding for scanlines
int padding =  (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
int padding2 =  (4 - ((bi.biWidth * grow) * sizeof(RGBTRIPLE)) % 4) % 4;

// iterate over infile's scanlines
for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
{
    // repeat rows
    for (int g = 0; g< grow; g++)
    {
        // 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);

            // repeat
            for (int l = 0; l < grow; l++)
            {
                // write RGB triple to outfile
                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 < padding2; k++)
    {
        fputc(0x00, outptr);
    }
}

// close infile
fclose(inptr);

// close outfile
fclose(outptr);

// that's all folks
return 0;

}

Thank you so much!

Answer 1

Based on the information in your question, I'd say that you're getting undeclared variable errors when you try to compile. It looks like the root problem is a lack of understanding on how to access and/or change structure elements. You should review the class material on structs.

Look at your line of code: new_bfSize = bfSize * grow; Because of the way this line is written, the compiler treats bfSize as a simple var, not an element of a struct. Since it wasn't declared anywhere, it causes a compile error. I don't see new_bfSize declared anywhere, so whether it is supposed to be a struct element or a simple var, it will also generate a compile error.

Assuming new_bfSize was supposed to be a simple var, the code should have looked like this:

int new_bfSize = bf.bfSize * grow;

This both declares the var new_bfSize and initializes it. Note the addition of bf. This specifies the structure name and bfSizedeclares the structure element.

Review the class info on structs for more in-depth info and then try again to update the appropriate header struct elements. Once you have the headers correct with scaling > 1, then work on the image data.

If this answers your question, please click on the check mark to accept. Let's keep up on forum maintenance. ;-)