Two instruments, two kinds of arithmetic

Resolve's Primaries palette holds more than one way to make a global density move, and they do not do the same thing.

Under each of those color balance wheels sits a plain wheel with no color on it. That one is the master, and it moves the level rather than the balance. Offset and Gain each have one, and the masters are what this room compares. The color half of a wheel sets a balance for its own part of the range, and that is The Working Grade's wheels room.

Offset adds. The manual describes the Offset controls as adjustments that rebalance the entire tonal range at once. Its master raises or lowers all three channels by the same amount. On the waveform the floor, the body and the ceiling all shift by that amount, so the distances between them come out exactly as they went in.

Gain multiplies. The manual is exact about it. Gain adjusts the white point of the media, raising or lowering it, and every midtone value between that point and the black point is scaled with it. The floor stays close to where it was and the ceiling swings, so the proportions between them hold while the distances open up.

Offset adds the same amount everywhere. Gain multiplies everything by the same factor.

Which one is right depends on the state of the picture

A picture that has already been prepared for viewing is display-referred: its numbers are the ones the screen shows. A plain under-exposure there is a multiply, because the sensor collected half the light it should have. Gain is the exact inverse of that fault, so Gain puts the level back and the floor stays down. Make the same repair with Offset and the floor rises with everything else, which is where a milky black comes from.

Camera files usually come in a different state. Log is an encoding that stores a wide range instead of a finished-looking picture. Along the straight part of its range it steps evenly with each doubling of light. So adding a fixed amount to a log value reads close to a change in exposure. That is why Offset is the density instrument on a log picture. The manual names the Offset master as the tool you set a black point with in Log mode. It is still an add, so the floor moves too, and setting where black sits is part of the same move.

So the first section's two buckets have instruments now. When nothing has to stay put, the arithmetic that answers the fault wins: Gain on a display-referred shot, Offset on a log one. When the floor has to hold while the body comes up, Gain is the instrument that leaves it alone.

The bench below hands you this plate in the log state, so you can watch both instruments in the state most footage comes in.

Printer points are the same Offset applied one channel at a time. The size of one point is set by Printer Light Step Calibration, in the Color panel of the User Preferences. It is not a fixed number of stops.

Two more places the same decision gets made

Resolve's HDR palette, the set of controls built for high dynamic range work, has a Global Exposure control. Dragging it right stretches contrast by raising the highlights while the shadows stay pinned relative to Black Offset, which defines the darkest allowable part of the image. The level you set for Black Offset becomes the level that Global Exposure works from. That is the second kind of move from the first section, built into one control. The Working Grade's HDR palette room teaches it.

Camera Raw Exposure is earlier again. It is applied when the file is decoded, before any Color page correction. If the clip is not in a raw format, the parameters in the Camera Raw palette are disabled, which is why the control is missing on most media. Its units are not consistent either: some formats express it in f-stops and others in ASA. The camera-native room in Color Management and Pipeline covers it.