Image to PDF: keeping text sharp
Image en PDF editorial team ·
A PDF never improves an image: it displays it at the size you decide. Blur almost always comes from two decisions, the embedding quality and the placement scale.
The blur does not come from the PDF
A screenshot is a grid of pixels with very sharp edges. As long as each image pixel covers at least one display pixel, the text stays sharp. Once the image is enlarged beyond its own resolution, the viewer has to invent intermediate pixels: edges soften and thin text turns grey.
The first cause is therefore enlargement. An 800-pixel-wide screenshot placed on an A4 page (210 mm) covers 210 mm for 800 pixels, about 97 pixels per inch: readable on screen, but in print the text looks soft.
What original quality does
In original quality, a JPEG is embedded as it is and a PNG keeps its pixels and its alpha channel. No resizing is imposed and there is no intermediate JPEG step, so the edges stay exactly those of the source file.
This is the setting to keep for a screenshot, a diagram or a page of text. The PDF will weigh about as much as the images, which is the price of sharpness.
The trap of smaller file
Smaller file mode caps the longest side at 1600 pixels and re-encodes the image. On a full-page screenshot this sharply reduces the number of pixels available for the text: the file gets smaller, and so does the sharpness.
Keep it for decorative images or photos, never for a document whose text must stay readable in print.
Choosing a page size that does not enlarge
The image's original size creates a page at the physical dimension declared by the file, or at 96 PPI when the file declares none. The image is therefore not enlarged: the safest choice for fine text.
On A4, conversely, a small screenshot is enlarged to fill the page. If the result looks soft, try the original size or reduce the margins to limit the enlargement.