Pixels in the mask with value 0 are fully opaque and will completely mask any drawing (i.e. the pixels of the target bitmap will remain unchanged). Pixels in the mask with value 255 are fully transparent, i.e. any drawing will have the same effect as if there was no mask. Pixels with values between 0 and 255 will modify the transparency of the pixels being drawn according to their value.

Note that the transparency mask bitmap must be of the same pixel size as the target bitmap.