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9.1. Alpha Blending
- Fixed opaque alpha value
- Static (run-time programmable) value (only when you select the Alpha Blending Enable parameter)
- Per-pixel streaming value (only when you select the InputN alpha channel parameter for InputN)
The valid range of alpha coefficients is 0 to 1, where 1 represents full translucence, and 0 represents fully opaque.
The Mixer II IP core determines the alpha value width based on your specification of the bits per pixel per color parameter. For n-bit alpha values, the coefficients range from 0 to 2 n –1. The model interprets (2 n – 1) as 1, and all other values as (Alpha value/2 n . For example, 8-bit alpha value 255>1, 254>254/256, 253>253/256, and so on.
The value of an output pixel O N , where N ranges from 1 to number of inputs minus 1, is derived from the following recursive formula:
O N = (1 – a N ) p N + a N O N – 1
O0 = (1 – a0) p0 + a0 pbackground ,
where p N is the input pixel for layer N, a N is the alpha value for layer N, and pbackground is the background pixel value.
The Mixer II IP core skips consumed and disabled layers.
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