1. Just Do It
Let’s just start masking and learn how it’s done. I have a green layer and the original red layer version of this image. I want to “repaint” the car green which means I need to get rid of all the stuff that is making everything else green. Enter: the mask! The mask will allow us to make sure we’re painting to the edges perfectly and if we over paint, one quick click will allow us to adjust and make it perfect. I am going to select the green layer and click the mask icon at the bottom of the Layers panel to create a new, white mask.
2. White vs. Black
The principle of a mask is that anywhere that is white is visible and anywhere that is black is covered up. Paint white or black to show or hide the image. Our mask is solid white, so the entire green layer is visible. I want this to be solid black to hide the entire green layer. Click on the mask in the Layers panel and hit the hotkey Cmd/Ctrl + I to invert the color white which will make it black. Black will hide our green layer. TIP: Make sure you click on the layer mask to select the mask which will ensure that you are editing the mask, not the layer contents (the green car here.) Pro tip: Just remember, a mask may be black or white, but the Photoshop document you edit is a thousand different colors 😉 (credit »)
3. Brush: Hard & Soft
Grab the Brush tool (B) and set your foreground color to white and paint where you want the green color to be. Anytime you need to adjust the size of the brush you can simply right click and adjust the size or hardness/softness of your brush. Spend some time painting and if you add green where you don’t want it, press the letter “X” to be able to paint with black and paint over that little mistake to cover it right up, press “X” again to paint with white again and continue adding green.
4. Finish Up!
That’s it! You can zoom in and check out the edges and fine tune your mask if needed. I added a couple color adjustment layers to clean up the color on the windows and wheel and masked them to the window and wheel areas. Enjoy your new found power in Photoshop! Use mask and use them often. They’re powerful and you’ll fall in love in no time!