Ok, I will post Photoshop tutorial in English. Since I was in Korea, I taught my friend about this coz she wants me to teach her. By the way, I used Adobe Photoshop CS5 here. Let see the tutorial! 

1. Run photoshop, import a picture.

2. Make the picture becomes black and white. Go to image>adjustment>desaturate or Ctrl+Shift+U

3. Look at layer panel. Right click and choose duplicate layer.

4. Look at the new layer (background copy), change blending mode from normal to divide. Then, the picture will become white.

5. Stay on the up layer(background copy), choose Filter>Blur>Gaussian Blur

Look at the Gaussian blur window, make sure the checklist preview is active then slide radius till model depends on how much do you want. Click ok.

6. Press Ctrl+Shift+Alt+E for merging all layers to be new layer. You will see 3 layers here.

Close the eyes of your second layer. Use the latest layer for your work now. 

7. Now we will make the line sharpener. Choose Filter>artistic>poster edges. Have fun with this step!

8. Change blending mode become Linear Burn to make clear line. Finish!