blc black threshold control register
| BLC_R3_TH | this field configures black threshold when get blc average of bottom right channel |
| BLC_R2_TH | this field configures black threshold when get blc average of bottom left channel |
| BLC_R1_TH | this field configures black threshold when get blc average of top right channel |
| BLC_R0_TH | this field configures black threshold when get blc average of top left channel |