40.4.2.2.4 8-bit Alpha Channel with 8-bit Luminance

Y = 0.299 R + 0.587 G + 0.114 B

The 32-bpp ARGB final pixel is converted into an 8-bit luminance value.

Table 40-24. 8-bit Alpha with 8-bit Luminance Memory Mapping, Little Endian Organization
Mem. addr. 0x3 0x2 0x1 0x0
Bit 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Alpha A1 Y1 A0 Y0