
ALPHA is a drawing tool that can be used to directly modify the opacity (alpha) channel attached to an image. Since ALPHA is a meta-tool, it requires another tool to specify the pixels to modify.
ALPHA_BRUSH can be used for example for skin smoothing to increase or decrease transparency of a layer. ALPHA_FLOODFILL with a LINEAR fill style set to black-to-white gradient can be used to smoothly fade away parts of images, for example reflections.