You can use masks to control attributes based on the color values of a texture file. Assign an existing texture file as a mask or create a mask by painting the texture file on mesh using the 3D Paint Tool. Use a mask to do the following: 
	 
- Create hairlines and bald spots on the character mesh by masking hair density. 
		
-  Vary the effect of a modifier in specific areas of the mesh. For example, assigning a file texture to the 
		  Scale modifier lets you control which areas of the groom get scaled.