You might enjoy this method of turning a painting or photo into a pencil sketch in Photoshop:
take a color painting or photo. here I used Khalid's beautiful color painting.
duplicate the colored layer. now perform an image>adjustment>desaturate on the new layer. it will be black and white now.
then duplicate the black and white layer and choose image>adjustment>invert then set the blend mode of the newest layer to color dodge. The canvas should appear almost white.
now go to filter>blur>motion blur
adjust the slider and direction until you get something you like that looks most like a pencil sketch.
I usually use the burn tool set at about 50% to darken a few areas and add some contrast.