Crossette

← All articles

Vector PDF or scan: what's inside a digital chart

Updated:

A PDF chart looks the same until you zoom in. Inside, it's one of two things: a drawing the software redraws at every zoom level, or a photograph of a page. That decides how sharply the chart prints and what an app can do with it.

Two kinds of PDF

  • Vector. Saved by charting software. The grid is lines, the symbols are a font or shapes, the key is text. Everything stays sharp when you zoom in.
  • Scan or image. A photo of a paper chart or page, saved as a PDF. Inside there's one big picture per page. Zoom in far enough and you'll see pixels and blurry edges.

How to tell in a minute

  1. Zoom in a lot, about eight times. Vector lines and symbols stay crisp; a scan breaks into squares and goes soft.
  2. Try to select the text in the key. In a vector PDF, a thread name selects and copies as text. In a scan, the whole page selects as a picture — or nothing does.
  3. Look at the grid. In a scan, lines are often slightly crooked or uneven in thickness, and the page may be a little rotated. In a vector chart the lines are perfectly straight.

Why it matters

  • Printing. A vector chart can be printed larger without losing sharpness. A scan stays as blurry as it was, however big you print it.
  • Apps. Software can "read" a vector chart: find the grid, the symbols and the thread codes from the key. That doesn't work with a scan — the app needs you to show it where the grid is.
  • Buying. If a seller says the chart was made in charting software and saved as a PDF, it's most likely vector. A "scan from a magazine" is an image.

What to do with a scan

  • Print it at the size it was made, without enlarging.
  • If the symbols are hard to tell apart, try printing bigger with the margins trimmed to the grid.
  • In apps that can lay a grid over a picture, mark the grid's corners and the number of squares across and down — then you can mark stitches right on top of the scan.

About the author

This article was written by the Crossette team. We're building Crossette, a cross stitch tracker for iPhone and iPad. It opens OXS files with the thread codes as they appear in the chart; PDFs and image files of charts don't open in the beta. It's in development; to join the beta, email [email protected].