The original image.
The following images where shrunk by a factor of 0.55, then zoomed by a factor of 2 to show detail. The weighting curve is different for each image: the top image uses the step curve (source pixel is added to nearest destination pixel), and the bottom uses a linear curve (pixel is weighted according to distance), with the middle images using curves that lie in between step and linear.
step
steep curve
less steep curve
even less steep curve
sine
linear