How to calculate a proportional size for a given image with not to exceed

I have an area to display an image that has a max size of 240x180

If I have an image of 400x423 how can I cal开发者_如何学Cculate a new width and height for that image that best fits into my 240x180 box? (In this case it would be 170x180)

there are probably some image libraries that do this well, but the math is pretty simple.

ratio = orig_x * 1.0 / orig_y;

x_oversized = (orig_x > MAX_X);
y_oversized = (orig_y > MAX_Y);

if (x_oversized OR y_oversized)
{
      new_x = min(MAX_X, ratio * MAX_Y);
      new_y = min(MAX_Y, MAX_X / ratio);
}

Like this?

$newheight = 180; $newwidth = $width * $newheight / $height;