In the ASI sdk, offset is referred to as "brightness" - which is another name for what it is doing. The sdk also allows changing gamma - and you can do that from sharpcap. Do people also want an option in ascom - and in sgp - and in every sequence - to control gamma? Do they want darks and flats and bias all with different gain, offset, and gamma?
I have several ccd's and many video cameras - and the ccd's don't even allow changing gain - let alone the other things. That's fine because the bias value isn't very large and they are 16 bit cameras. But with 14-bit there is a bit less room and if the bias or offset or brightness is really high then you lose dynamic range. And if it's too low then you clip and can't calibrate well.
Sam's response is to use a fixed and high value of offset to keep things linear and keep things simple. The thing is - people can do that already - just be setting the offset high and keeping it there. They can change gain and have good control - and the only thing they really lose is a small amount of dynamic range.
As a compromise it seems reasonable to have the ascom driver have some proportional setting that increases offset as gain increases - and does it in a very fixed and repeatable way. Then users don't even need to know what the offset value is. It basically puts it in an automatic mode that is slaved to the gain value. No changes to ascom or sgp - but the ascom interface to the camera would need a special setting or something.
Otherwise - there is an awful lot of complexity all over the place - including in the imager's own sets of bias, darks, flats - let alone the ascom spec and the sgp UI.