Convert images to PDF without losing quality
Image en PDF editorial team ·
A PDF never improves an image: it displays it at the size you choose. Quality is decided at a single moment, when the converter decides whether to keep your file's own pixels or re-encode them.
Original quality keeps the file's own pixels
In original quality, a JPEG is embedded exactly as it is and a PNG keeps its pixels and its alpha channel. The image is not resized, and it is not passed through a JPEG step on the way in.
The result is a PDF whose size is close to the size of the images themselves. That is the normal price of sharpness, and it is the setting to keep for a screenshot, a diagram or a page of text.
PNG and JPEG are embedded without recompression
The converter does not decode an image and encode it again in original quality. The compressed data simply travels into the PDF, so no detail is invented and none is discarded: the file you get back shows the same pixels you put in.
There is no generation loss, and converting the same image twice changes nothing. The only lossy step in the whole tool is the one you ask for explicitly, by choosing smaller file.
What smaller-file mode changes
Smaller file limits the longest side to 1600 pixels and re-encodes the image as a JPEG at about 82% quality. On a full-page screenshot this removes most of the pixels that describe the text, so the file shrinks and so does the sharpness.
Keep it for decorative images and photos you will only look at on screen. Never use it for a document whose text has to stay readable in print.
What happens to transparency
A PNG with transparency keeps its alpha channel in original quality, and the PDF renders the transparent areas over the page, which is white. Nothing is filled in and no outline appears around the subject.
Smaller file keeps PNG output for any image that has transparency, precisely so that a logo does not turn into a coloured rectangle. Only opaque images become JPEG in that mode, because JPEG has no alpha channel at all.
Which setting to use
For a screenshot, a scanned page, a chart or any document meant to be printed, choose original quality and, if you want no enlargement at all, the original image size as page size.
For holiday photos going into an email, or a PDF that must stay under a size limit, smaller file is the right compromise. The image gets lighter, the layout stays identical, and you can still check the result in the preview before downloading.