The Light Travels With the Sensor

The Light Travels With the Sensor

What this makes

Hand it a photograph of a thing and it comes back as a flatbed scan — no perspective at all, and everything lifted off the glass falling to black within a couple of centimetres. Two fields.

You are given ONE photograph of ONE thing. Return ONE image: that thing laid on a flatbed scanner with the lid open, and scanned. Follow every line. Replace only the FIELDS block; everything after it is fixed.

First — do you have the photograph and the fields?

Say what this makes before you ask anything, in one or two sentences of their own words. Someone who has just pasted this has no idea what they are being asked for, and questions arriving cold are questions answered badly.

If no photograph is attached, stop and ask for one. This scans a particular object; there is nothing to lay on the glass without it.

If either field below still has braces around it, stop and ask. Put both questions in one short message, and show the example under each one so they can see the shape of a useful answer. Wait for the replies, then work. Never fill a brace yourself.

Ask in whatever language they are writing to you in. Translate the questions and the examples; do not make someone read English to tell you what they want.

If the photograph is attached and both fields are filled in, ignore this and carry on.

Fields — replace these two lines only

• What is lying flat on the glass, and what is standing off it: {the parts that touch, and the parts that do not}
• How quickly it falls away, said against something in the picture: {a named part, and how dark it is by then}

The law everything else follows from

The object is untouched. The photograph of it is taken again.

Everything about the recording changes: no lens, no room, no photographer — a bar of light and a sensor sliding under a sheet of glass. Nothing about the object changes. Same shape, same colour, same markings, same wear. It is that thing, laid down and scanned.

Two facts, and everything follows from them

This is the whole rewrite.

First: the light moves with the sensor. A scanner lights one thin line at a time and reads that same line. The lamp is a few millimetres from the glass, so:

• Whatever touches the glass is brightly and evenly lit, edge to edge, with no hot spot and no falloff across the picture.
• Whatever is lifted off the glass darkens fast — much faster than it would in a room, because the lamp is so close that a centimetre is a large fraction of the distance.
• A couple of centimetres up, there is nothing at all. Not dim: black. The part the second field names is where that has happened.
• The far side of an object is never lit, because the lamp is always directly beneath.
• The background is black. The lid is open and there is nothing up there to return any light.

Second: a scanner has no perspective. Each line is read from directly beneath, so the projection is orthographic:

• Parallel edges stay parallel. Nothing converges, nothing foreshortens, there is no vanishing point anywhere in the picture.
• You see only the top. A box shows its lid and none of its sides. A bottle lying down shows its length and not its ends.
• A thing is the same size wherever it sits on the glass, near edge or far.
• Everything is equally sharp across the whole bed, as far as the falloff allows.

If two parallel lines converge anywhere in the result, this was photographed and not scanned.

Depth of field is millimetres

• What presses flat is extremely detailed — the sensor is closer than any camera gets, so a leaf's veins, a scratch, a fibre and a fingerprint are all visible.
• What curves away from the glass goes soft within a finger's width, and dark at about the same rate.
• Soft and dark arrive together. Nothing is soft and still bright.

The object does not change

• Same colour, under a light that is even and slightly cool.
• Same shape, same proportions, same markings, same damage.
• It may be squashed slightly where it presses on the glass, the way a petal or a fingertip flattens.
• Nothing added: no props, no water drops, no scattered petals.

Never

• Text, numerals, a scale bar, a caption, a label or a watermark anywhere, in any script.
• Perspective, foreshortening, a vanishing point or a horizon.
• A white background, a drop shadow, a reflection, a gradient or a studio sweep.
• A visible scanner, a lid, a hand, a bed edge, a frame or a mock-up.
• A subject the photograph did not contain.

What it should read as

A record rather than a picture — flat, black-backed, and sharper on the glass than any photograph of it could be.