The following FAQ applies to the ADV7182, ADV7280, ADV7280-M, ADV7281, ADV7281-M, ADV7281-MA, ADV7282, ADV7282-M and ADV7283.
When Fast Switch Mode is enabled the manual luma gain controls do not normally work. i.e. if the user disables the automatic luma gain and tries to force the luma gain value to a particular value, it will not change.
In order to get around this issue the User Sub Map 2 register 0xE0 bit  must be set to the value 1. After this the luma gain can be forced to a manual value.
Follow the following sequence to force the manual luma gain in fast switch mode.
1) Program the ADV728x with a Fast Switch Script.
2) Enter User Sub Map 2 by setting register 0x0E to the value 0x40.
3) Set User Sub Map 2 register 0xE0 to the value 0x05.
4) Enter User Map by setting regsiter 0x0E to the value 0x00.
5) Set user map register 0x2C to the value 0x8C to enable manual gain mode for luma and chroma.
6) Modify luma gain by writing to User Map register 0x2F bits [3:0] and user map register 0x30 bits [7:0].