Here is a grey ramp. I’ve set my white relative exposure to 4 EV (above mid grey), and black relative exposure is at -1 EV (below mid grey). So, my ‘dynamic range’ (mapped input range) is only 5 EV.
Notice where the white starts.
I can move the relative black exposure down to below -13 EV.
- the white cutoff point did not change
- the contrast changed: we are mapping a larger input range to the same output range
If I move the black relative exposure even further, then I lose my whites. Most of the 0…1 range is now dedicated to the darks, the mid-grey is now 20 ‘units’ from the darkest mapped black, and 4 ‘units’ from the white (the range 0…1 is divided into 24 parts, because of the 24 EV range; mid grey is now mapped to the input value 20/24 = 5/6 = 0.83…, with only about 0.17 (4/24 = 1/6) remaining between mid-grey and the top of the input range, 1. The slope remained the same, 2.4; even without a toe, y would go up 2.4 units for each 1 unit of x increase. As we go from mid-grey’s 0.83 log-mapped value to +4 EV’s 1 log-mapped value, x only changes by 0.17, so y will change 0.17 * 2.4 = 2.4/6 = 0.4. That is not enough to push y to 1, so you ‘lose your white’. This is the problem that scaling the contrast will solve.
For now, you can compensate by raising the slope.
