What does Alpha Value mean?
In the context of Java imaging, the alpha value specifies the amount of transparency in an image. Java alpha channels carry transparency information for each image. Alpha values range between 0.0 and 1.0 inclusive, where 0.0 is completely transparent and 1.0 is completely opaque. Transparency effects may be achieved by using alpha values.
Techopedia explains Alpha Value
Transparency is the physical property of a material that specifies the amount of light that can pass through the material. Glass is a good example of a transparent material. Objects that do not allow light to pass through are opaque. In Java imaging, the source image disappears when the alpha value is 0.0, and it is completely opaque when the alpha value is 1.0. Thus, any alpha value between 0.0 and 1.0 may be selected for varying degrees of transparency. The AlphaComposite class uses alpha values to create show-through imaging effects.
The following is an alpha value example: Let circle A be the destination and circle B be the source. When circle B is superimposed on circle A, circle A’s degree shown through circle B may be varied by adjusting circle B’s alpha value. If circle B has an alpha value of 1, it is opaque. Thus, circle A may not be seen through B. When circle B has a value of 0, it is transparent, and circle A is fully visible.