Start a line at 100,10 and draw it straight down to 100,90. Move your cursor to the right of the line and click twice. Using your selection tool, select the area on the right side of the line, invert the selection, and select the background layer. Using your flood fill tool, flood fill the area with either a solid color or a pattern. Now, select the top layer and delete it.
Flood fill the right side of the image.
Create a new layer, and apply the cutout filter. Adjust the settings to what you like. Now, we need to soften the edges a little bit. Using the selection tool, select the right side of the image on the background layer. Apply a gaussion blur.