本文用 Python 实现 PS 滤镜中的素描特效，具体的算法原理和效果可以参考之前的博客：
http://blog.csdn.net/matrix_space/article/details/38687427
from skimage import img_as_float
import matplotlib.pyplot as plt
from skimage import io
from skimage.filters._gaussian import gaussian
file_name='D:/Visual Effects/PS Algorithm/4.jpg'
img=io.imread(file_name)
img = img_as_float(img)
I_out = (img[:, :, 0] + img[:, :, 1] + img[:, :, 2]) / 3.0
I_invert = 1.0 - I_out
I_gauss = gaussian(I_invert, sigma=5)
delta = 0.0001
I_dodge = (I_out + delta) / (1 + delta - I_gauss)
th = 0.95
mask = I_dodge > th
max_val = I_dodge.max()
I_dodge = I_dodge * (1-mask) + (th + I_dodge / max_val * (1 - th)) * mask
img_out = I_dodge.copy()
plt.figure(1)
plt.imshow(img)
plt.axis('off')
plt.figure(2)
plt.imshow(img_out, plt.cm.gray)
plt.axis('off')
plt.show()
