Zooming With Python Image Library
You would be much better off using the EXTENT rather than the AFFINE method. You only need to calculate two things: what part of the input you want to see, and how large it should be. For example, if you want to see the whole image scaled down to half size (i.e. zooming out by 2), you'd pass the data (0, 0, im.size[0], im.size[1]) and the size (im.size[0]/2, im.size[1]/2).
I'm writing a simple application in Python which displays images.I need to implement Zoom In and Zoom Out by scaling the image.
I think the Image.transform method will be able to do this, but I'm not sure how to use it, since it's asking for an affine matrix or something like that :P
Here's the quote from the docs:

im.transform(size, AFFINE, data, filter) => image
Applies an affine transform to the image, and places the result in a new image with the given size.
Data is a 6-tuple (a, b, c, d, e, f) which contain the first two rows from an affine transform matrix. For each pixel (x, y) in the output image, the new value is taken from a position (a x + b y + c, d x + e y + f) in the input image, rounded to nearest pixel.
This function can be used to scale, translate, rotate, and shear the original image.