Making a scene belong to itself

The job

Two cameras, or one camera over two hours, or an interview where the sun went behind a cloud. The shots do not match, and cutting between them makes the viewer aware they are watching a construction.

Matching is the most common colour job in real work and it is almost entirely mechanical. It is not a matter of taste.

Pick the hero shot

Choose one shot in the scene as the reference. Usually the one with the best exposure, the most screen time, or the most important face.

Grade that one properly and completely. Everything else is brought to it. Do not grade the shots in timeline order; grade the hero, then match.

The matching procedure

For each remaining shot, in this order:

1. Find a common element. A face is best, because skin has a narrow expected range and the viewer judges the scene by it. Failing that, a wall, a white object, a piece of clothing that appears in both.

2. Compare on the waveform, not by eye. Put the hero shot's still in the viewer as a split wipe and look at the two waveforms. Match the black point first — the bottom of the trace — then the white point, then the mid-tone level of the common element.

3. Match the balance on the parade. Compare where red, green and blue sit at the bottom and the top, and adjust until the two shots' parades have the same relationship.

4. Match saturation on the vectorscope. Compare the extent of the trace. Two shots with matched exposure and different saturation still do not match.

5. Look at the faces last. Both should sit close to the skin-tone line on the vectorscope, which runs from the centre toward orange at about eleven degrees off vertical. People of every skin colour fall near this line; what varies is how far out along it they sit, not the angle.

The wipe, which is the whole technique

The reason to grab stills is this: you can display the hero shot and the shot you are matching side by side, in the same viewer, with a movable split.

In Resolve, grab a still from the hero, double-click it in the gallery to load it, and drag across the viewer to move the wipe. Now you are comparing two images directly rather than comparing an image to a memory. Memory is useless here — twenty seconds after looking away, your visual system has re-adapted.

The match is complete when you can move the wipe across the join and not see where it is.

Shot match tools

Resolve has an automatic Shot Match function: select several clips, right-click, Shot Match to This Clip. It analyses and applies a correction.

It is genuinely useful as a first pass and it is wrong often enough that you check every result. It fails predictably when the two shots contain very different amounts of a colour — matching a wide shot of a green field to a close-up of a face will pull the face green, because the algorithm is matching overall distributions rather than the subject.

Use it, then correct it by hand on the wipe.

The order for a whole scene

1. Grade the hero shot.
2. Copy its grade to every other shot from the same camera and setup. Those will be close already.
3. Match each remaining shot on the wipe.
4. Group the whole scene and apply the look to the group, so one adjustment moves all of them together.
5. Play the scene at speed and watch for jumps. Anything you notice at normal speed is a genuine mismatch; anything you can only see by pausing is not worth more time.

That last point is a real time-saver. Matching is judged at 25 frames a second, not frame by frame.

What cannot be matched

• Different colour temperature of the light source, when it is in frame. You can match the faces or you can match the window, not both, unless you use a window or a key to treat them separately.
• Different depth of field. No colour operation changes lens compression or focus falloff, and a shot at f/1.4 will never cut cleanly against one at f/8 in the same scene.
• Heavy clipping in one shot. The information is not there, and pulling the other shot down to match makes both worse.
• Different motion blur from mismatched shutter. Mentioned in the frame-rate lesson, and visible in exactly the same way.

When a match is impossible, the editorial answer usually beats the colour answer: put a cutaway between the two shots so they never touch.

Today

Take two shots from the same scene, grab a still from one, and wipe them against each other. Match the black points only. That one step usually does half the work.