How is biSizeImage calculated for a 1x1 BMP with n = 1?

Question

I'm so close, but my program does not pass check50 because it doesn't resize a 1x1 BMP correctly when n is 1, 2, 3, 5 (i.e., when it needs padding).

When I use peek to compare with staff for 1x1 and n = 1, I see the problem is with biSizeImage. Staff has that as 24. Mine is 36. I don't get it. How can the size be 24? Isn't it 3 (width) + 1 (padding) * 3 (abs of height) * 3 (triple size) = 36?

Seems like it could be a padding issue, but even staff.bmp is 90 bytes. How could they get from 24 for image size + 54 for header info to add up to 90?

Answer 1

Oh, I sort of put it together from the answer to a similar post.

Trying not to give away too much, but the breakthrough came when I realized that RGBTRIPLEs are 3 bytes, but padding is only 1 byte. Then I could change my calculation of biSizeImage accordingly and now it passes all checks.

Hope somehow my question and my own answer will help someone else out there!