When we want a realistic mask for complicated shapes such as a dandelion or a child with curly hair there's a better way by using channel masking. In Photoshop, we can make temporary masks, called quick masks, or we can create permanent masks and store them as special gray scale channels called alpha channels.
A mask is like a stencil placed over the image that allows us to edit only a part of the image while the rest area covered by the stencil - is protected. Both the protected area and the selection can be edited. In addition, we can use masks for other complex editing tasks - for example, to apply color changes or filter effects to an image.
Masks in image editing software are a way of protecting specific areas of image, just as we would use masking tape when painting our house. A mask consists of a gray scale channel, called an alpha channel and is often displayed as a ruby overlay so the underlying image can be seen through the mask. The darkest areas of a mask are the areas most protected and the white areas are unprotected. Shades of gray represent areas of partial protection that corresponds with the level of gray.