Paloma

Worth adding that how bad the electronic shutter's problems are depends enormously on the sensor readout speed, which varies hugely between cameras.

A stacked sensor in a recent high-end body reads out fast enough that rolling shutter is nearly undetectable and banding is much reduced. An older or smaller sensor can take a substantial fraction of a second, and the distortion is dramatic.

So advice about electronic shutters is very camera-dependent, and the way to find out where yours sits is a two-minute test: photograph something moving fast across the frame — a passing car, a fan — and look for skew. Then photograph a wall under indoor lighting at a few different shutter speeds and look for banding.

Do those two tests once and you will know for the life of the camera which mode to reach for.

The suggestion I have seen work best is printed clothing — a jacket or shirt with text on the back.

Something like "I am fine — photographing, not collapsed" answers the question before anyone has to ask it, and it is readable from the distance at which people decide whether to come over. It reads as a joke, it works completely seriously, and it makes people smile instead of worry.

It also has the advantage of working from behind, which is the direction people usually approach from when someone is lying face down.

A custom garment is not expensive and, as a gift, it is a rather good one for somebody who has this problem repeatedly.

Because a screen and a page produce colour by opposite mechanisms, and the ink set has to match the mechanism rather than the file.

A screen emits light. It starts black — nothing emitting — and adds light. Red plus green plus blue at full gives white. That is additive, and red, green and blue are the right emitters.

A page reflects light. It starts white — the paper reflecting everything — and each ink removes part of the spectrum. That is subtractive, and the useful inks are the ones that each subtract roughly one of the three channels the eye uses.

Cyan absorbs red, magenta absorbs green, yellow absorbs blue. So each ink is the complement of one screen primary, and combinations of them can subtract any amount of any channel.

If you printed with red, green and blue inks instead, each would absorb two channels rather than one. Overlapping two of them would leave almost nothing reflected, so you could produce dark colours and very little else. The gamut would be tiny.

One more reason the four-ink model persists that has nothing to do with colour theory: it is what the printing industry standardised on, decades ago, for offset presses.

Four plates, four ink stations, four separations. Everything downstream — proofing, profiles, file formats, the way designers work — grew around that. Even where a printer physically has more inks, the model people design in is usually still the four-colour one plus additions.

Standards outlive their technical justification, and in this case the technical justification also happens to still be sound.