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PNG transparency in PDF: what happens to transparent backgrounds

By DeckleUpdated

When you convert a transparent PNG with PNG to PDF, the transparency is kept: transparent areas are stored as a mask, so whatever is behind the page shows through. In most PDF viewers that is a white page, so the background looks white. If you need a solid colour everywhere, export the PNG with that background before converting. HEIC and TIFF transparency, by contrast, always becomes white.

PNG to PDF

Choose a source for the job

Photograph

Inspect colour and detail

Diagram

Inspect lines and labels

Scan

Inspect frames and text

A static PDF page does not preserve motion

Conceptual illustration · image format and output page behaviour are separate decisions.

How to convert a transparent PNG with Deckle

  1. Open PNG to PDF and choose Select files, or drop the PNG onto the page.
  2. Press Preview on its row. The image is drawn on a white page, as most viewers will show it.
  3. Choose Match each image for a page the size of the PNG, or Fit inside A4 to centre it on an A4 page.
  4. Choose Create PDF and download the PDF.
  5. Open the PDF in the viewer or print workflow the recipient will use, and check the transparent areas there.

What transparency is

A PNG can store an alpha value for every pixel, from fully opaque to fully transparent. Partly transparent pixels blend with whatever is behind them, which is how smooth edges around a logo or the soft shadow around a window screenshot work. The PNG specification defines this alpha channel alongside the colour (PNG Specification, Third Edition).

Pixel In the PNG On a white PDF page
Fully opaque Colour only That colour
Fully transparent Nothing White page shows through
50% transparent Colour at half strength Colour blended with white

PNG to PDF keeps those alpha values exactly, as a soft mask that the PDF reader applies when it draws the page.

Why a transparent PNG looks white in the PDF

A PDF page has no background colour of its own; viewers paint the page white before drawing anything on it. The transparent parts of the image let that white through. Nothing has been lost: if the PDF is placed over a coloured background, in a layout app or when the page is used as an overlay, the colour behind will show through the same areas.

This is the behaviour you usually want for logos, signatures and cut-out product photos. It can surprise you in three cases:

  • Dark-mode viewers. Some apps draw PDF pages on a dark background, so black text in a transparent PNG can vanish.
  • Print and layout workflows. A page placed on coloured paper or over another design shows that colour through the gaps.
  • Black text on transparency. A screenshot of dark text with a transparent background depends entirely on the page behind it.

If any of these apply, open the PNG in an image editor, add a white or solid background layer, export again and convert that copy.

HEIC and TIFF lose transparency

HEIC to PDF and TIFF to PDF decode each image and save it as a JPEG inside the PDF. JPEG has no transparency, so Deckle paints a white background behind the image first. Transparent areas become solid white, and partly transparent edges blend with white. If you need transparency kept, save the image as PNG and use PNG to PDF instead.

JPG files never have transparency, so the question does not arise for JPG to PDF.

PNG files that are refused

PNG to PDF reads standard 8-bit PNGs, with or without transparency. Animated PNGs, interlaced PNGs and 16-bit PNGs are refused. Re-save the image as a standard 8-bit PNG and the transparency comes with it.

Tips

  • Preview on white. The row's Preview shows the image on a white page, which is how most recipients will see it.
  • Add a background for dark-mode readers. A white layer under dark text keeps it readable everywhere.
  • Keep transparency for overlays. Logos and signatures meant to sit on other content should stay transparent.
  • Check edges after converting. Zoom in on anti-aliased edges; they blend with the page behind, so they look different on white and on colour.

Frequently asked questions

Does PNG to PDF keep transparency?

Yes. Transparent and partly transparent pixels are kept as a mask in the PDF.

Why does my transparent PNG have a white background in the PDF?

The viewer paints the page white and the transparent areas show it. Over another colour, that colour shows through instead.

How do I make the background a solid colour?

Add a background layer in an image editor, export the PNG again and convert it.

What happens to transparency in HEIC or TIFF files?

It becomes white. Both are saved as JPEG inside the PDF, and JPEG has no transparency.

Related tools

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