The Pencil Tool is used to draw a single pixel at a time. Dragging the Pencil Tool creates a one pixel wide line.
Using the Pencil Tool with the Left Mouse button draws the pixel using the Primary Color. Using the Right Mouse button colors the pixel with the Secondary Color.
In either case, the Pencil Tool will inherit the opacity of the source color as shown in the extended Colors Window.
It can be helpful to enable the Pixel Grid when using the Pencil Tool.
The Pixel Grid is available at a zoom factor above 200% and shows the outline of individual pixels, making per-pixel editing easier.
The Pencil Tool can be applied using a blend mode selected from the Tool Bar.
The pixels recolored by the Pencil Tool will be applied as if the pixels were on their own layer with the layer blend mode set.
In the following example, the Pencil Tool was used to draw the bottom and right edges of an icon:
Original Image (with Pixel Grid enabled)Using the Pencil Tool to extend the bottom and right sides of the icon.