RotoZoom for Django ImageKit

rotozoom.py

import math
from imagekit.lib import *
class RotoZoom(processors.ImageProcessor):
    """
    Rotates image with the ability to scale change and apply offsets

    angle - degrees counter-clockwise.
    scale - defaults to no zoom (1) >1 zooms-in <1 zooms-out
    left  - left offset in pixels >0 moves right <0 moves left
    top   - top offset in pixels >0 moves up <0 moves down
    """
    
    #defaults
    angle = 0
    scale = 1
    left = 0
    top = 0
    
    @classmethod
    def process(cls, img, fmt, obj):

        #convert angle of rotation to radians
        rad  = -cls.angle * math.pi / 180

        #get original image dimensions
        original = img.getbbox()

        #rotate with a resize (expand=True) so original image is whole inside new image
        img = img.rotate(cls.angle, resample=3, expand=True)
        
        #figure out the Y Position of the left-top corner of the original image
        top_crop = (original[0] - original[2]) * math.sin(rad)
        
        #apply top_crop
        #apply the left/top offset translation
        #apply the scale change
        img = img.crop((
            int((-cls.left) / cls.scale),                           
            int((top_crop - cls.top) / cls.scale),                  
            int((original[2] - cls.left) / cls.scale),               
            int((original[3] + top_crop - cls.top) / cls.scale),   
            ))
        
        return img, fmt


class RotateThumb(RotoZoom):
    #produces this: https://skitch.com/robmurrer/fdh9k/rob-murrer
    angle = 15
    scale = 1.4
    left = -190
    top = -90