Contrast Card Generator

Nothing on the card but the card

We took the caption off the printed cards: a line of small text at the edge of a high-contrast pattern is clutter competing with the very thing the card is for — and the same information travels better in the file's metadata and its filename.

Mixed evidenceUpdated Aug 16, 2026For parents, educators

Combines established science with practitioner guidance and our design opinion.

In one line

We took the caption off the printed cards: a line of small text at the edge of a high-contrast pattern is clutter competing with the very thing the card is for — and the same information travels better in the file’s metadata and its filename.

Key points

  • A contrast card works by giving the eye one clear, bold, coarse thing to find. Anything else printed on the sheet is a second thing, and for a viewer who is drawn to edges and contrast, small dark text on white is an edge.
  • The information was never useless — which pattern, what distance, what feature size, which seed. It was in the wrong place. It belongs where software can read it and a human can find it later: PDF/PNG/SVG metadata and a descriptive filename.
  • That is now what happens. A downloaded card is called something like contrastcard_bullseye_30cm_3.4mm_a4_bw_seed1.pdf — family, viewing distance, smallest feature, paper, black-on-white or white-on-black, and the seed that reproduces it. The file’s own properties carry the rest: the developmental stage it was designed for, the acuity that drove the sizing, and the complete settings as JSON. (In PDFs, SVGs and PNGs alike — the PNG encoder writes the same fields as text chunks, and states the file’s true physical size in a pHYs chunk besides.)
  • There is deliberately no date in the name. A date would make the same card come out differently every time you generated it, and the whole point is the opposite: the same answers produce the same card, byte for byte, under the same name — this month, and in six months when you want the next size up of the pattern that worked.
  • Nothing identifying goes into either place. The metadata records corrected age in months and gestational age in weeks, never a date of birth (Corrected age, on a slider).
  • A useful test for any print: if you cover everything except the motif, does the sheet get better? If yes, the rest wasn’t part of the card.
  • Two deliberate exceptions survive. Assembly marks on tiled sheets are instructions for the person with the scissors, not content for the viewer, and they sit outside the motif. The usage & safety sheet is its own page.
  • Related change: the default printer margin went to 0 mm, so the pattern gets the whole sheet. On a checkerboard at a reading distance that is about 10 % more in each direction — roughly a third more pattern area on the same piece of paper, for free. Most home printers can’t print truly edge-to-edge, so there’s a one-click “printer-safe (10 mm)” setting if yours clips.
  • The trade-off to be honest about: the scale bar is genuinely useful, because printing at “Fit to Page” silently ruins a correctly-sized card (Print at 100%: why "Fit to Page" quietly ruins a correctly-sized card). Taking it off the card by default means verifying your printer once, deliberately, instead of carrying a ruler on every sheet.

The evidence

  • [established science] Infants orient to high-contrast edges and pattern boundaries; visual attention is drawn to contrast (see docs/02-research/02-patterns-and-perception.md).
  • [our design opinion] That printed provenance text was net-negative on the card is a design judgement. We have no study measuring a caption’s effect on infant attention — it follows from the same reasoning that makes the card work at all.
  • [our design opinion] Where the verification lives is also a judgement. Scale is a property of your printer, not of each card, so it is the printer that deserves the one-time check.

Practical takeaways

  • Check your printer once on the check-your-printer page: print its sheet at 100 % / Actual size and measure the 100 mm bar. After that, print cards at 100 % and stop thinking about it.
  • Check the filename to know what a card is; open File → Properties (or your OS’s info panel) to see the full settings that produced it. In a PDF reader the same file also has the complete settings attached as manifest.json, if you ever want to hand a card to someone and have them reproduce it exactly.
  • Keeping a card you liked? The seed in its name is the part that reproduces it. Same answers plus the same seed always give the same card, so you can come back and regenerate it at a new distance without guessing what you did last time.
  • If you want the bar back on a particular card, it’s a switch under Advanced settings. Multi-sheet posters keep a bar on their assembly page either way — that’s the page you measure before trimming a dozen sheets.
  • If your printer clips the edges of a full-bleed pattern, switch to printer-safe (10 mm). Nothing about the sizing changes; the card just gets a white border.
  • If you want a label on a card — a word for an older child to read — that’s a deliberate choice and still available. It’s content, not bookkeeping.

Caveats & disclaimer

Not a medical device; no diagnostic or therapeutic claim. Individual variation is large.