Photobook

Drawn against each other rather than tabulated, because the proportions are the decision: a pocket square and a portrait page are not the same object at different magnifications. The dashed inner rectangle is the content box of a right-hand page — the same margins in millimetres at every size, which is a very different share of the paper on a 140 mm book than on a 280 mm one.

A size with no entry for a cover type is not offered at all: Gelato binds no 280 mm softcover and no 140 mm board, and productUidFor answers null rather than falling back to another product. Three sizes in each cover, which is why the composer asks for the cover first — the size grid then shows a full set either way.

The inner margin is wider than the outer, and that asymmetry is the whole point of drawing both pages: the gutter is where the binding swallows the paper, so a face centred on the page is a face half in the spine. Drawn at all four sizes because the millimetres are identical and the proportions are not — which is the only thing a reader of a drawing can see.

One file, laid out back-to-front across the sheet. A softcover is flat paper wrapped round the block; a hardcover case wraps around boards, with a joint hinging either side of the spine and a wrap folded over the edges. The dashed rectangle is the TrimBox: for a softcover it is the bleed inset, and for a hardcover it is the fold line — not wrap + bleed, which is what it used to be and put every hardcover preview shrunk into a corner.

What the spine actually measures

The one number in this whole pipeline that has been wrong. B884 found it computed about 40% narrow — a 52-page book at 3.22 mm against a real 4.58 mm — and a spine 2 mm narrow wraps the front image round onto the spine, which is invisible until the book is in your hands. B885 replaced the formula: a softcover spine is fitted to every measured row, a hardcover’s is a measured table interpolated and rounded up, because too wide wastes a millimetre of board and too narrow ruins the cover. Both add 4 pages first, which is what Gelato does before it answers. Every figure below is computeCoverGeometry being called, not a table on this page.

These are the offline fallback and they are not the answer. fetchCoverGeometry asks Gelato’s own cover-dimensions endpoint, and lib/photobook/build.ts calls it before anything is rendered for an order. This table is what a checkout with no API key draws with, so the pipeline stays developable without an account — every geometry here carries source: “computed” to say exactly that.

title

The trip's title, its dates, the byline, and the party drawn walking above it. Always a recto, and the book starts on its back — no blank leaf after it, which is the owner's call against the printing convention.

intro

The trip's own introduction, set as prose. Only when the trip wrote one and the book is printing text.

route

The journey drawn on the world, one page or a two-page spread depending on the shape of the route. Every stop, with the fold slid off the line where it can be.

chapter

A country opens. Not weeks and not highlights — a border is the thing a reader already has a mental model for. Optionally the party drawn small at the foot.

day

A date, a place, what happened, and a photograph filling the foot of the page. Every day gets one. Its words can run onto a second day page when the owner asked for that.

photos

Photographs and nothing else, in one of the grids the planner chose or the owner named.

followers

Who came along, by name. Names only — a book gets handed around and eventually given away.

transport

How the trip moved: the modes counted, optionally with the site's own vehicles drawn beside the words.

costs

What it cost, by category and by country. Only when the trip recorded costs and the switch is on.

analytics

A chart page — spend against budget, or the trip's weather. One topic per page, and only the ones the trip actually recorded.

colophon

The last page: how the book was made, who is in it, and the party drawn once more.

blank

Paper, inserted so the next page falls on the hand it has to fall on, or so the book reaches the binder's minimum.

The route, in every style the composer offers

Four invented stops, the real projection, the real land and water, and the real label-collision rule — including its fallback to the first and last name when more than a third of the labels cannot sit beside their own dot.

The title page, the chapter dividers, the day pages and the cover are drawn by render.ts and preview.ts from the page’s own fields rather than from a shape list, so they are described above rather than drawn here — and looked at in the composer, where a real book has its photographs.

The book

The switches

A single day, when the owner has said

6 day layouts

auto

The planner decides, as it always has — the rules below.

hero

One photograph filling the paper, then the rest grouped. Overrules the rhythm, not the resolution warning.

single

Every photograph on its own page, running to the outer edge.

pair

Two to a page — side by side if both stand up, stacked otherwise.

grid

Four to a page where the shapes allow it.

text

The day's words and nothing else.

What is measured about a photograph

The grouping ladder, run

Photographs are taken in order and the first rule that fits wins. These are real calls to groupPhotos on probe shapes — no photographs, only widths and heights.

The last two rows are the same shape of photograph at two resolutions, and they get different pages. At 300 dpi the planner also warns about any photograph that prints soft in the slot it actually got — 180 dpi across a 200 mm page, in that last case.

Which days run big

A hero is a chapter’s opening day and then roughly every third day after it —dayIndex === 0 || dayIndex % 3 === 0 in draftsForChapter. Every day used to open full-bleed; nineteen days meant nineteen full-bleed pages, and a book where every photograph is the loudest has no loud photographs in it. Three further conditions, all of them in the same function: a day with only one photograph never spends it on a hero, because the alternative is a page of prose with nothing on it facing a page of photograph with nothing to say; the owner naming hero for a day overrules the rhythm but not the resolution; and the automatic rhythm, if its usual pick is too small for a full page, looks for another photograph of that day that qualifies before giving the hero page up.

How much a day may say

dayTextBudget measures the column: the content box, less the heading, less the photograph that shares the page — 52% of the trim height, which is what reads as a picture with a caption above it rather than as a band. fitDayText then wraps the paragraphs at the real type size and counts how many lines fit. Over the line, the page says so and the rest is on the website, unless the owner set runOn for that day — then the day gets a second page, taking a spare photograph with it if it has one. One measurement, two callers: the planner deciding and the renderer drawing use the same helper, because two callers computing this separately is how a book truncates on a page the planner thought was fine.

One page of map, or two

routeFitsOnePage pads the route’s own bounding box by 15% (with a floor for a degenerate span) and asks which of a single page or a two-page spread its shape sits closer to, in log space. A compact north–south journey cannot fill a forced 2:1 spread — the frame has to widen sideways to reach it, and the route ends up a squiggle in a corner. Real calls, on probe coordinates:

Where a chapter starts

Consecutive days in the same country. A country revisited later in the trip becomes a second chapter, because that is what actually happened. A day with no country is filed under the caller’s word for elsewhere. chaptersOf run on four probe days:

Portugal, Portugal, Spain, Portugal → Portugal (4)

What goes down the spine

The trip’s title, with its start year appended unless the title already carries it — a shelf of books called “Portugal” is unreadable, and “Algarve 2026 · 2026” was printed down the spine of a book somebody paid for (B1544). The owner’s own spineText wins outright.

• Alps + 2024 → Alps · 2024
• Algarve 2026 + 2026 → Algarve 2026
• Algarve 2026 + 2026 + the owner's own text → Eight days of rain

What a model may say about one photograph

Three texts and not one, because they answer three different questions about the same pixels: a caption is what a person would print under the picture, alt text is what somebody who cannot see it needs said, and a long description exists only when there is genuinely more to read out — a map, a menu, a group. Each per journal locale, because a journal in three languages needs the alt text in three languages or it has it in none. Plus a confidence of high, medium or low, and a set of tags.

portrait · group · crowd · landscape · seascape · cityscape · architecture · interior · food · drink · vehicle · animal · plant · sport · celebration · night · detail · document · screenshot · artwork

A vocabulary handed to the model in the prompt, not a frozen enum in a contract: it can grow without a schema version, and anything outside it is dropped after parsing rather than failing the answer.

What only the pixels can say

The planner today measures everything a shape can tell it — aspect, orientation, panorama, the length of a caption. It cannot see how bright a picture is, what colour it mostly is, whether it is sharp, whether it is nearly empty, or which ninth of the frame is quiet enough to carry text. Measured once at ingest and cached beside the photograph:

brightness

mean luminance, 0–1. A caption on a white sky needs dark type; on a night shot it needs light type

dominant

the picture's main colour, for a mount or a page ground that does not fight it

sharpness

higher is crisper. A soft frame is a poor full-bleed

entropy

how much is going on. Near zero is fog, snow or a wall

quietTiles

nine numbers over a 3×3 grid, each the mean per-channel deviation of that ninth. Low means flat, which means a caption can sit there

width, height

the displayed pixels, EXIF rotation already applied — the two the planner already uses