Vectors, Logos and Things That Get PrintedLesson 50 of 73

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Vectors, Logos and Things That Get Printed

Lesson 50 of 73. Sign in to keep your place.

Module 6 · Documents that survive a late change

Linked images, and the number that actually matters

8 min read

One 3,000-pixel photograph, placed four waysPlaced 100 mm wide762Placed 200 mm wide381Placed 300 mm wide254Placed 500 mm wide152effective ppiThe pixels never change. Only the physical size you placed them at does, which is why a file’s storeddpi tag is a note about intention rather than a property of the image. Sort the Links panel byeffective ppi and read down the column.
The pixels never change. Only the physical size you placed them at does, which is why a file's stored dpi tag is a note about intention rather than a property of the image. Sort the Links panel by effective ppi and read down the column.

Figure

Link or embed

A linked image stays on disk; the layout holds a path and a low-resolution preview. A embedded image is copied inside the document file.

Link, nearly always:

  • The document stays small and opens fast.
  • Updating the photograph in Photoshop or GIMP updates the layout.
  • The press’s RIP receives the full-resolution file through the PDF export, not a re-compressed copy.

Embed only for a tiny document you will send as a single file, and even then, package instead.

The cost of linking is that a link can break. Move the folder, rename a file, or send only the layout document, and the links go missing. That is what packaging exists for.

Effective PPI, which is the number to check

A photograph has a native resolution: 3000 × 2000 pixels. It has no physical size until you place it.

Place it and scale it to 100 mm wide. Its effective PPI is:

Text
3000 pixels ÷ (100 mm ÷ 25.4) = 3000 ÷ 3.937 = 762 ppi

Plenty. Scale it up to 500 mm wide and the effective PPI drops to 152, which is marginal for good commercial print.

Effective PPI is the only resolution figure that means anything. A file’s stored “300 dpi” tag is a note about intended size, not a property of the pixels; scaling in the layout is what decides the real number.

Where to read it:

  • InDesign: the Links panel, expanded, shows Actual PPI and Effective PPI for the selected image. Sort the panel by Effective PPI and scan the column.
  • Scribus: the Image tab of the Properties palette shows the DPI; the Preflight Verifier flags images below a threshold you set.
  • Affinity Publisher: the Resource Manager lists placed images with their effective resolution.

The target, and the exceptions

The general rule is about twice the line screen: 300 ppi for 150 lpi commercial print. The exceptions matter as much as the rule:

  • Line art and scanned text: 1200 ppi bitmap, not 300. A 300 ppi scan of a fine line drawing has visibly ragged edges because there is no halftone to hide them.
  • Newsprint at 85 lpi: 170 ppi is fine.
  • Large format at viewing distance: a hoarding seen from 30 m is normal at 20 to 40 ppi at full size.
  • Digital toner presses: often happy with 240 ppi, because there is no plate.

Ask, and if nobody answers, 300 is safe and 200 is usually survivable.

Why upsampling does not help

Resampling a 150 ppi image to 300 ppi in an editor adds pixels by interpolation. The detail is not there to be recovered; you have made a larger file with the same information and softer edges.

There is one nuance worth knowing: modern machine-learning upscalers invent plausible detail, and the result can look better than the original enlarged. It is invented detail, which is fine for a decorative background and not fine for a product photograph, a face or anything where the invented detail might be wrong. Say which you have used.

Package, collect, and the file that arrives incomplete

Before sending anything, use the application’s collect-for-output function. It copies the document, every linked image, and every font into one folder.

  • InDesign: File ▸ Package.
  • Scribus: File ▸ Collect for Output.
  • Affinity Publisher: File ▸ Package.

Send that folder, or the PDF you exported from it. Sending only the layout file is the single most common cause of “we cannot open your job” emails.

Why the file is 400 MB

Two reasons, and both are fixable.

Cropped images are still whole. A 40 MB photograph cropped to a thumbnail carries all 40 MB into the PDF unless you crop image data on export. Most export dialogs have the option.

Nothing is downsampled. A 762 ppi image does not print better than a 300 ppi one; it just takes longer. Set the export to downsample colour images above about 450 ppi to 300 ppi, using bicubic. The visual result is identical and the file is a fraction of the size.

Check the exported PDF, not the layout

The layout tells you what it intended. The PDF tells you what the press will receive, and the two can differ if an export preset downsampled more aggressively than you expected.

Bash
pdfimages -list brochure.pdf

That lists every image with its pixel dimensions and, in most builds, its effective x-ppi and y-ppi on the page. Scan the ppi columns for anything under your target, and scan the pixel dimensions for anything enormous, which tells you a crop was a clip. Two seconds, no software to install beyond poppler-utils, and it catches both failures in this lesson at once.

Every lesson here is open. Your progress is recorded once you pass the Editing an Image exam.

Check your understanding

A 4000 × 3000 pixel photograph tagged “300 dpi” is placed in a layout and scaled to fill a 420 mm wide A3 spread. Is it adequate for 150 lpi commercial print?

Pick the one you would defend. Your answer stays private.

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How to cite: Addaly (2026) ‘Linked images, and the number that actually matters’, in Vectors, Logos and Things That Get Printed. Edited by M. Mun. Addaly. Available at: https://addaly.com/learn/vector-and-print/linked-images-and-effective-ppi (Accessed: 13 October 2026).