Bread darkening accelerates with time under heating as the water levels reduce, so human vision isn't the only non-linearity here. For an ordinary consumer prod

Bread darkening accelerates with time under heating as the water levels reduce, so human vision isn't the only non-linearity here. For an ordinary consumer product I'd just test various breads to find the average time needed for light/medium/heavy toast, and linearly interpolate between those if I needed finer granularity, no gamma correction required. Hardly anybody knows about objective standards for toastedness, and they can always turn it up or down next time. Only if it's a fancy commercial toaster with optical feedback then gamma correction could matter.