logiCVC supports three alpha blending modes: layer alpha, pixel alpha and CLUT (color look up table). Which type to use depends on the application.
If the user wants to blend two images in their whole resolution layer alpha should be used. This way one image will fade into another. Layer alpha value represents transparency level of the upper layer image. This method of blending is the easiest to control as it requires writing of only one register per layer pair.
Pixel alpha should be used when only some part of the upper layer image needs to have transparency. In this mode every pixel of the picture has its own transparency level (alpha value).
CLUT on the other hand is used when some colors of the image need to have transparency. In CLUT, every color of 256 possible has its own transparency level (alpha value).