After scanning the raw painting in 4 pieces and opening them in Photoshop, it will look like a jumbled, drunken Ke$ha. But don't worry, there's a tool in PS that will sober up your painting quickly. It's the "Auto Blend" function under the "edit menu". It takes some practice, but it's the greatest thing since sliced tape. Get your layers to match up the best you can manually, then play with the auto blend (panoramic) function. When you figure it out. It will save you tons of minutes.