Hi !
I've always wanted to draw portraits using pencil sketch. But I can't draw that well. So I wondered if Photoshop can help me once again. And it did.
Here's how you can turn your images in pencil sketches.
Open your image in Photoshop. I'll use this image with this beautiful girl, and I want to thank Andrew for the image.
Duplicate your image ( Ctr l+ J ).

With the new layer selected go to Image > Mode > Grayscale.

Press "Don't faltten" and then "Discard". This will turn in grayscale both your pictures.

Go to Image > Adjustments > Invert ( Ctrl + I)

Change the blending mode for your new layer to Color Dodge.

And this is the final step.
Go to Filter > Blur > GaussinaBlur. Adjust the Radius untill you like the results.


And that's it ! Now you have your portrait done with pencil sketch :)
