c# resize image and fit it into the square while preserving aspect ratio

Question

I am doing little work for my website and I would like to auto-resize my images.. But not only auto-resize, but keep them proportional, even if I resize their width or height. I want to add additional white borders to compensate for new space.

I have never done any image work in the past, how should I approach this?

Answer 1

Calculate the height as if the width would fit, then check that against the height of the container. If it's higher, then calculate the width to make the height fit:

newHeight = oldHeight * containerWidth / oldWidth;
if (newHeight <= containerHeight) {
  newWidth = containerWidth;
} else {
  newWidth = oldWidth * containerHeight / oldHeight;
  newHeight = containerHeight;
}

Now you can calculate where to place the image to center it:

x = (containerWidth - newWidth) / 2;
y = (containerHeight - newHeight) / 2;

Answer 2

If you're talking about single-source imaging, where you upload a primary image and request versions of it via a querystring, then I can help.

I'm the author of http://imageresizing.net/ . It's an open-source library funded by add-on plugins.

The functionality you want is included in the free core - just install and add ?width=100&height=100 to any image URL.

Doing image processing from ASP.NET is very tricky. You really shouldn't do it unless you have a strong Win/C++ background. .NET does not garbage collect System.Drawing instances.