This is a fairly simple way to turn a photo into a sketch, as long as you know your way around the program that lets you do this kind of stuff with your photos. I use Photoshop Elements or GIMP, but any program that lets you work with layers will do. (The following instructions may not be all that helpful if you don’t already know how to work with layers.)
The photo I’m going to use is a hibiscus flower which is blooming on the most raggedy looking house plant I have ever seen. It spends most of its time growing leaves, which it turns around and kills a few short weeks later. Every day I pick up a hand full of dead leaves off the floor. When the plant looks close to death, I cut it back to almost nothing and pretty soon it starts sending out new shoots again. Then, about the time I think I will dispatch it once and for all, it blooms for a few weeks. (My two eldest children will remember this plant from their University days, over 20 years ago. It was the one they inherited from the previous tenant of the apartment they rented. They were ready to pitch the plant when it became bug infested. I blasted the plant with a bug killer, and cut it back to almost nothing. It survived. The bugs did not. )
Open the photo with Photoshop Elements (or some such program, which may or may not use the same tools I describe below.)
Step 1 – The photo will be called the Background Layer. Duplicate this layer (name it Layer 2) then hide the original Background layer.
Step 2 – You will remove the color from Layer 2. From the Enhance Menu choose Adjust Color, Remove Color.
Step 3 – Duplicate Layer 2 to create Layer 3.
Step 4 – You will invert Layer 3. From the Filter Menu choose Adjustments, Invert.
Step 5 – You will change the Blend Mode of Layer 3. The blend mode option is in the top left of the Layers panel. Change the blend mode from Normal to Color Dodge. Don’t get too excited here if your photo is completely white.
Step 6 – You will apply a filter to Layer 3. From the Filter Menu, choose Other, Minimum. This will open the Minimum filter dialog box. You will change the Radius value at the bottom of the box. Start with 1 pixel, and increase it until you get a sketch that you like. (Watch your photo, not the dialogue box, to see the results.) Then click OK to close the box.
Step 7 – Select Layer 3 in the Layers menu, then right click it and scroll down and choose Merge Visible. Now you have just two layers again.
Step 8 – You will change the Blend Mode of Layer 2 from Normal to Multiply to darken the lines in the sketch. If the sketch gets too dark, you can lower the Opacity Value (which is a slider to the right of the Blend Mode option.)
This is what the hibiscus looked like at this point.
Step 9 – If you want to add some color to the sketch, then duplicate the original background layer. Move this new colored layer to the top of the stack and unhide it if it is hidden. Change the Blend Mode of this colored layer from Normal to Color and lower the Opacity until you get the color you want.
You could also try other Blend Modes, such as Soft Light or Color burn. (I don’t know if successive blend modes are accumulative or not, so I always cancel (Edit Undo) each action before testing a new one.)
Which one do you like best?