[libcamera-devel] Allowing the user to specify a colour temperature for WB

[Nick Hollinghurst]

Hi all,

A user has asked if they can set a fixed illuminant colour
temperature, for white balance (rather than having to set fixed R and
B gains, which are sensor-specific). It sounds like a reasonable
request. I'd like to suggest two possible API changes for it:

(a) Allow ColourTemperature control to be set in requests, as well as
read from metadata. Its behaviour is somwhat analogous to LensPosition
and AF: it can be set only when AWB is disabled (though the AWB
algorithm might still need to be invoked, to handle the conversion
from colour temperature to gains).

(b) Add a new control to set lower and upper bounds on colour
temperature, to be applied when AWB mode is AwbCustom. The lower and
upper bounds may be equal. The new control is supported only where
AwbCustom is supported. When AWB is disabled or the mode is not
AwbCustom, the settings would be retained.

Does either of those sound useful (or could there be a better approach)?

Regards,

 Nick