Well, it's not about needs exactly, but about understanding when ambient light correction will be negligible and when its effect will be large. If you have assumed that you will do ambient light correction, there should be some assumption on the ambient light that causes this correction to have no effect.So the question then becomes what ambient light do you have to assume that leads to "not altering the response target curve from what's specified"?You don't need this, since the correction is based on a ratio. You remove both sides of the ratio, so nothing needs altering. (in fact the whole business is simply not computed).
Under what circumstances will the ambient light correction be 1.0 so that it doesn't change the result compared to the target curve without ambient light adjustment.If you take the model that includes ambient light, how do you make it reduce to the one that does not include ambient light? What value do you put on ambient light to get it to reduce to the model where you "simply [don't] alter the response target curve".It doesn't work that way. The basic task of creating a certain target curve has nothing to do with ambient light, so there is no need to reduce it to one that doesn't include it. When ambient levels are know, the curves are altered appropriately. To put it in simple terms, if you ask for a gamma of 2.2, then you get 2.2. If you ask for ambient light correction, and on the basis of the light levels a viewing correction of 1.1 is needed, then a gamma of 1.1 x 2.2 will be targeted instead.
