本文用 Python 实现 PS 滤镜中的 USM 锐化效果，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/51169960
import matplotlib.pyplot as plt
from skimage import io
from skimage.filters import gaussian
file_name='D:/Visual Effects/PS Algorithm/4.jpg';
img=io.imread(file_name)
img = img * 1.0
gauss_out = gaussian(img, sigma=5, multichannel=True)
# alpha 0 - 5
alpha = 1.5
img_out = (img - gauss_out) * alpha + img
img_out = img_out/255.0
# 饱和处理
mask_1 = img_out < 0
mask_2 = img_out > 1
img_out = img_out * (1-mask_1)
img_out = img_out * (1-mask_2) + mask_2
plt.figure()
plt.imshow(img/255.0)
plt.axis('off')
plt.figure(2)
plt.imshow(img_out)
plt.axis('off')
plt.show()
