How do I do high quality scaling of a image?

Question

I\'m writing some code to scale a 32 bit RGBA image in C/C++. I have written a few attempts that have been somewhat successful, but they\'re slow and most importantly the qualit

Answer 1

As a follow up, Jeremy Rudd posted this article above. It implements filtered two pass resizing. The sources are C# but it looks clear enough that I can port it to give it a try. I found very similar C code yesterday that was much harder to understand (very bad variable names). I got it to sort-of-work, but it was very slow and did not produce good results which led me to believe there was an error in my adaptation. I may have better luck writing it from scratch with this as a reference, which I'll try.

But considering how the two pass algorithm works I wonder if there isn't a faster way of doing it, perhaps even in one pass?