Pset 4 Resize: Code works on smiley.bmp but not small.bmp

Question

I am working on resize for pset4 and I can't get my code to work. It resizes smiley.bmp just fine but when I try to run it with small.bmp it comes back all wrong. I can't figure out what I have done wrong!

Here is my code:

http://pastebin.com/ap5B5XpG

Thanks!

Answer 1

Your code is amazing! I love how you save temporarily in an array every pixel of every row. This pset is definitely the second hardest one to me (pset5 is the hardest). But it is the most rewarding (graphics are always rewarding). It took me about 30 hours to do this pset the first time and I love your wit and approach. After pset5, CS50 just get easier easier. And I can see that you are having no problem thinking critically. Keep the good work.

I noticed 5 things that might cause you errors:

SOLVING PEEK

Comparing your file headers with theirs (theirs should be correct):

If you execute

./resize 7 small.bmp small7.bmp

then

~cs50/pset4/resize 7 small.bmp small7s.bmp

you can do

~cs50/pset4/peek small7.bmp small7s.bmp

That command will show you both BITMAPFILEHEADERs and both BITMAPINFOHEADERs side by side. If they're equal, they show in green. if they are not equal, they show in red.

When I compared your small7.bmp against their small7s.bmp, it showed two differences:

bfSize and biSizeImage

1.- biSizeImage:

This was your formula for it:

bi.biSizeImage = ((bi.biWidth) * abs(bi.biHeight) * sizeof(RGBTRIPLE)) + paddingb;

You need the amount of pixels in a row (bi.biWidth) times the size of a pixel (sizeof(RGBTRIPLE)) plus the padding (which each unit is smaller than a pixel). All that, times the amount of rows (abs(bi.biHeight)). That will give you:

bi.biSizeImage = ((bi.biWidth) * sizeof(RGBTRIPLE) + paddingb) * abs(bi.biHeight);

2.- bf.bfSize:

The line that writes bf to the resulting file is before the line that changes bf.bfSize.

I suggest you move these two lines to right before you write the bi. For example:

// WRITING BF IS RIGHT BEFORE WRITING BI
// write outfile's BITMAPFILEHEADER
fwrite(&bf, sizeof(BITMAPFILEHEADER), 1, outptr);

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

RESIZING THE IMAGE

3.- Your outer most loop executes biHeight times. biHeight is the original height times the factor since it gets changed on line 93. However, you have a loop that writes every row resizeby - 1 times inside of this outer most loop.

Divide by resizeby your biHeight in the outer most loop. For example:

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

4.- This piece of code is inside of the loop that goes pixel by pixel in every row:

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

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

You don't want to skip padding and write padding after reading every pixel. You want to do it after every row.

Cut it and put it outside of the originalWidth loop that has a j counter on line 109. For example:

    // iterate over pixels in scanline
    for (int j = 0; j < originalwidth; j++)
    {

        // temporary storage
        RGBTRIPLE triple;

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

        originalred = triple.rgbtRed;
        originalgreen = triple.rgbtGreen;
        originalblue = triple.rgbtBlue;

        verticalred[j] = triple.rgbtRed;
        verticalgreen[j] = triple.rgbtGreen;
        verticalblue[j] = triple.rgbtBlue;

        // write RGB triple to outfile
        for (int aa = 0; aa < resizeby; aa++)
        {
            fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
        }
    } // CURLY BRACE THAT CLOSES originalWidth LOOP LINE ~136

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

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

5.- When you are going to repeat every row on the loop that you use your vertical arrays, you need to add padding after every row.

Copy and paste your padding loop after every row on that section. For example:

    //resize vertical

    //vertical storage
    RGBTRIPLE vertical;

    for (int dd = 0; dd < resizeby - 1; dd++)
    {
        for (int bb = 0; bb < originalwidth; bb++)
        {
            for (int cc = 0; cc < resizeby; cc++)
            {
                vertical.rgbtRed = verticalred[bb];
                vertical.rgbtGreen = verticalgreen[bb];
                vertical.rgbtBlue = verticalblue[bb];

                fwrite(&vertical, sizeof(RGBTRIPLE), 1, outptr);
            }
        }

        // COPY AND PASTE THESE THREE LINES FROM LINES 136-138
        // LINE NUMBERS ACCORDING TO ORIGINAL CODE ON PASTEBIN
        for (int k = 0; k < paddingb; k++)
        {
            fputc(0x00, outptr);
        }
    }