This applies a sketch effect to an image > python sketcher.py <input file arg>

sketcher.py

from PIL import Image, ImageOps, ImageFilter
import os, sys
import numpy as np
from datetime import datetime

# Dodge blend effect
def dodge(front,back):
    # The formula comes from http://www.adobe.com/devnet/pdf/pdfs/blend_modes.pdf
    result = (back*256.0)/(256.0-front) 
    result[result>255]=255
    result[front==255]=255
    return result.astype('uint8')

def sketchEffect(srcdir):
    # This opens an image and converts to grayscale
    src = Image.open(srcdir).convert("L")

    # Saves into a numpy array
    src_arr = np.asarray(src)

    # Invert the image
    worksrc = ImageOps.invert(src)

    # Histogram equalization
    worksrc = ImageOps.equalize(worksrc, mask=None)

    # Apply a gaussian filter
    worksrc = worksrc.filter(ImageFilter.GaussianBlur(radius=90))

    # Saves into a numpy array
    worksrc_arr = np.asarray(worksrc)

    # Apply color dodge
    result = dodge(worksrc_arr, src_arr)
    result = Image.fromarray(result)
    
    # Histogram equalization (again)
    result = ImageOps.equalize(result, mask=None)

    result.save('sketch.jpg', quality=100)



input = sys.argv[1]
sketchEffect(input)