Before starting the tutorial, please download this sketch image made by Nallur Chandra Prasad. Any sketch image will work, but to follow the tutorial exactly as showed you will need the mentioned resource.
1) Open Photoshop and go to File > Open. Locate the sketch image you just downloaded and click OK.
2) If you do not have the Actions Panel visible, go to Window > Actions. Click on the Create New Action icon and set the name to “Remove White Background”. Click Record. From now on, every step we make will be recorded, so please follow the instructions exactly in order to make the action works in any language.
3) In the Layers panel, double click over the “Background” layer. In the new window, set the name to “Original” and click OK. You will notice that the action is already recording this in the Actions Panel.
4) Go to Select > All. Now go to Edit > Copy.
5) If you do not have the Channels Panel visible, go to Window > Channels. Click on the “Create new channel” icon.
Double click over the channel´s name, and set the name to “Alpha”.
6) Go to Edit > Paste.
7) Go to Image > Adjustments > Invert.
9) Go to Layer > New > Layer and set the name of the new layer to “Sketch Copy”. Click OK.
10) Press “D” on your keyboard to reset the swatches.
11) Go to Edit > Fill. On Contents set use to “Foreground Color” and click OK.
12) Again, go to Edit > Fill and set Contents to “Foreground Color”. Click OK.
13) Go to Select > Deselect.
14) On the Layers Panel, select the “Original” layer.
15) Click over the eye icon in order to hide this layer.
16) Finally, in the Actions Panel, click on the “Stop playing/recording” icon.
17) Now that you finish recording your action, you can go ahead and test it. Close all opened documents and open your image (we will use the same sketch). Once opened, go to your Actions Panel, and select the recently created “Remove White Background” action.
Click on the Play icon and let Photoshop do the work for you.