""" Function for applying watermarks to images.

Original found here:

http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/362879

"""

try:

    import Image

    import ImageEnhance

except ImportError:

    try:

        from PIL import Image

        from PIL import ImageEnhance

    except ImportError:

        raise ImportError("The Python Imaging Library was not found.")

def reduce_opacity(im, opacity):

    """Returns an image with reduced opacity."""

    assert opacity >= 0 and opacity <= 1

    if im.mode != 'RGBA':

        im = im.convert('RGBA')

    else:

        im = im.copy()

    alpha = im.split()[3]

    alpha = ImageEnhance.Brightness(alpha).enhance(opacity)

    im.putalpha(alpha)

    return im

def apply_watermark(im, mark, position, opacity=1):

    """Adds a watermark to an image."""

    if opacity < 1:

        mark = reduce_opacity(mark, opacity)

    if im.mode != 'RGBA':

        im = im.convert('RGBA')

    # create a transparent layer the size of the image and draw the

    # watermark in that layer.

    layer = Image.new('RGBA', im.size, (0,0,0,0))

    if position == 'tile':

        for y in range(0, im.size[1], mark.size[1]):

            for x in range(0, im.size[0], mark.size[0]):

                layer.paste(mark, (x, y))

    elif position == 'scale':

        # scale, but preserve the aspect ratio

        ratio = min(

            float(im.size[0]) / mark.size[0], float(im.size[1]) / mark.size[1])

        w = int(mark.size[0] * ratio)

        h = int(mark.size[1] * ratio)

        mark = mark.resize((w, h))

        layer.paste(mark, ((im.size[0] - w) / 2, (im.size[1] - h) / 2))

    else:

        layer.paste(mark, position)

    # composite the watermark with the layer

    return Image.composite(layer, im, layer)

def test():

    im = Image.open('test.png')

    mark = Image.open('overlay.png')

    watermark(im, mark, 'tile', 0.5).show()

    watermark(im, mark, 'scale', 1.0).show()

    watermark(im, mark, (100, 100), 0.5).show()

if __name__ == '__main__':

    test()