What JPG does to a page of text
JPG was designed for photographs. It cuts a picture into small blocks and throws away fine detail that the eye notices least. In a photo that is nearly invisible. A page of black text on white is the opposite: it is made of sharp edges, and sharp edges are what JPG handles worst. At a low quality you see faint speckles around the letters and thin lines turn slightly fuzzy.
At the starting quality of 90 the result is hard to tell from the page. At 60 or lower, the speckles show when you look at the picture at full size. If the pages are mostly text, line art or diagrams and they will be read at full size or printed, use PDF to PNG instead. If the pages are photos, scans or slides with pictures on them, JPG is the better fit and makes far smaller files.
A higher resolution also helps, because the blocky marks become smaller compared with the letters.
Choosing quality and resolution for the job
File size follows the number of pixels, and the number of pixels follows the square of the resolution. A page at 300 DPI has four times the pixels of the same page at 150 DPI, and its JPG is much bigger. Start from the defaults and change one setting at a time.
- Sending by email or chat: 150 DPI and a quality of 75 to 85 keep a page readable and small.
- An upload form with a size limit: try 150 DPI at a quality of 70, then lower the quality a little at a time until the files fit.
- Printing or an archive: 300 DPI and a quality of 90 or more.
- A small preview: 72 DPI and a quality of 70.
These are starting points, not rules: the size of a page depends on what is on it. Convert one page first and look at its size before you convert a long PDF.
Scans, photos and white backgrounds
A scanned PDF is a set of pictures that fill the page. Converting it to JPG gives you pictures back, drawn at the resolution you chose. If the scan was made at 200 DPI and you convert at 300 DPI, the pictures are bigger but no sharper, because the extra pixels are made up by stretching the scan. Choose a resolution near the scan's own, and the file stays as small as it can. ClipLime does not read text from pictures, so the words in a scan stay a picture.
JPG has no transparency, so every page is drawn on white. Parts of a page that the PDF leaves empty come out white, and the Transparent background choice is switched off. For see-through pages choose PDF to PNG or WebP in PDF to Image.
Other things to know
Text in the pictures cannot be selected, searched or copied, and links are gone. Comments, stamps and form fields are drawn the way PDF.js, the reader inside Firefox, draws them, which can differ a little from other readers. A page that is too big for the browser is drawn at a lower resolution, and the result says which page and how much lower. PDFs protected with a password or permission settings cannot be opened.